Abstract: Red pine (Pinus resinosa Ait.) and paper birch (Betula papyrifera Marsh.) seedlings exposed to sulfur dioxide produced acetaldehyde and ethanol, and exhibited increased production of ethylene and ethane. Gas chromatographic measurement of head space gas from incubation tubes containing leaves or seedlings was a simple method of simultaneously measuring all four compounds. Increased ethylene production had two phases, a moderate increase from the beginning of the stress period and a large increase just prior to appearance of leaf lesions. Ethane production in SO2-stressed plants did not increase until lesions appeared. Acetaldehyde and ethanol production began within 6 hours at 0.3 microliter per liter SO2 and 24 hours at 0.1 microliter per liter SO2 and continued throughout a 6-day fumigation. Production of acetaldehyde and ethanol continued when plants were removed to clean air for up to 2 days. A higher concentration of SO2 (0.5 microliter per liter) induced acetaldehyde and ethanol production within 2 hours of the start of fumigation of birch and pine seedlings. A number of other stresses, including water deficit, freezing, and ozone exposure induced production of acetaldehyde and ethanol. Production of these compounds was not due to hypoxia, as the O2 partial pressure in the incubation vessels did not decline. Increasing the O2 partial pressure to 300 millimeters Hg did not affect production of these compounds. Production of ethylene, acetaldehyde, and ethanol declined when more than 80% of the leaf area became necrotic, while ethane production was linearly related to the percentage of necrosis. A number of woody and herbaceous plant species produced acetaldehyde and ethanol in response to freezing stress, while others did not. Measurement of these four compounds simultaneously in the gas phase may be a valuable method for monitoring plant stress, particularly air pollution stress.

Abstract: Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the starchy endosperm protein of rice (Oryza sativa L. Japonica cv Koshihikari) during seed development confirmed that storage protein begins to accumulate about 5 days after flowering. Two polypeptide groups, 22 to 23 and 37 to 39 kilodaltons, the components of glutelin, the major storage protein in rice seed, appeared 5 days after flowering. A 26-kilodalton polypeptide, the globulin component, also appeared 5 days after flowering. Smaller polypeptides (10- to 16-kilodaltons) including prolamin components, appeared about 10 days after flowering. In contrast, the levels of the 76- and 57-kilodalton polypeptides were fairly constant throughout seed development. Transmission electron microscopy and fractionation by sucrose density gradient centrifugation of the starchy endosperms at various stages of development showed that protein body type II, the accumulation site of glutelin and globulin, was formed faster than protein body type I, the accumulation site of prolamin.The 57-kilodalton polypeptide but not the glutelin subunits was labeled in a 2-hour treatment with [(14)C]leucine given between 4 and 12 days after flowering to developing ears. In vivo pulse-chase labeling studies showed the 57-kilodalton polypeptide to be a precursor of the 22 to 23 and 37 to 39 kilodalton subunits. The 57-kilodalton polypeptide was salt-soluble, but the mature glutelin subunits were almost salt insoluble.In vitro protein synthesis also showed that the mRNAs directly coding the 22 to 23 and 37 to 39 kilodalton components were absent in developing seeds and that the 57-kilodalton polypeptide was the major product. Thus, it was concluded that the two subunits of rice glutelin are formed through post-translational cleavage of the 57-kilodalton polypeptide.

Abstract: Treatment of suspension-cultured Glycine max cv Harosoy 63 cells with soluble chitosan (20-500 micrograms per milliliter) increased membrane permeability as shown by leakage of electrolytes, protein, and UV absorbing material. Severe damage to the cell membrane by chitosan (100 and 500 μg/ml) was also indicated by reduced staining with fluorescein diacetate and the leakage of fluorescein from preloaded cells. Other basic polymers (poly-l-lysine, histone, DEAE-dextran, protamine sulfate, and glycol chitosan) also increased permeability, whereas the basic monomers l-lysine and d-glucosamine, and acidic or neutral polymers were not active. Chitosan-induced leakage was inhibited by divalent cations, the order of effectiveness being Ba2+ > Ca2+ > Sr2+ > Mg2+. Na polygalacturonate and Na poly-l-aspartate also reduced polycation-induced leakage, probably by formation of polycation-polyanion complexes. A chitosan-polygalacturonate complex precipitated on mixing solutions of the two polymers containing approximately equal numbers of galacturonate and glucosamine residues, but not with either polymer in excess. A similar concentration-dependent precipitation of chitosan by Na poly-l-aspartate was found. Leakage from Phaseolus vulgaris cv Grandessa cells was also induced by chitosan, and was inhibited by Ca2+ and Na polygalacturonate.

Abstract: Nitrogen isotope fractionation by Pearl Millet ( Pennisetum americanum L. and P. mollissimum L.) grown on nitrate was associated with nitrate reductase activity. Fractionation was evidenced at the step of nitrate reduction when the substrate-to-enzyme ratio was high (possibly saturating for the active sites of the nitrate reductase enzyme), for instance in young seedlings having a low nitrate reductase activity or in seedlings grown on high nitrate concentration. When the substrate concentration was low (and, hence, the active sites of the enzyme were possibly not saturated), the isotopic discrimination could only be associated with the uptake of nitrate into the cell. In that case, isotopic fractionation was null. It is concluded that the uptake of nitrate does not discriminate among nitrogen isotopes.

Abstract: Nitrogen nutrition strongly affected the growth rate of young sunflower (Helianthus annuus L.) leaves. When plants were grown from seed on either of two levels of N availability, a 33% decrease in tissue N of expanding leaves was associated with a 75% overall inhibition of leaf growth. Almost all of the growth inhibition resulted from a depression of the daytime growth rate. Measurements of pressure-induced water flux through roots showed that N deficiency decreased root hydraulic conductivity by about half. Thus, N deficiency lowered the steady-state water potential of expanding leaves during the daytime when transpiration was occurring. As a result, N-deficient leaves were unable to maintain adequate turgor for growth in the daytime. N deficiency also decreased the hydraulic conductivity for water movement into expanding leaf cells in the absence of transpiration, but growth inhibition at night was much less than in the daytime. N nutrition had no detectable effects on plastic extensibility or the threshold turgor for growth.

Abstract: The marine cyanobacterium, Synechococcus sp. Nageli (strain RRIMP N1) changes its affinity for external inorganic carbon used in photosynthesis, depending on the concentration of CO(2) provided during growth. The high affinity for CO(2) + HCO(3) (-) of air-grown cells (K((1/2)) < 80 nanomoles [pH 8.2]) would seem to be the result of the presence of an inducible mechanism which concentrates inorganic carbon (and thus CO(2)) within the cells. Silicone-oil centrifugation experiments indicate that the inorganic carbon concentration inside suitably induced cells may be in excess of 1,000-fold greater than that in the surrounding medium, and that this accumulation is dependent upon light energy. The quantum requirements for O(2) evolution appear to be some 2-fold greater for low CO(2)-grown cells, compared with high CO(2)-grown cells. This presumably is due to the diversion of greater amounts of light energy into inorganic carbon transport in these cells.A number of experimental approaches to the question of whether CO(2) or HCO(3) (-) is primarily utilized by the inorganic carbon transport system in these cells show that in fact both species are capable of acting as substrate. CO(2), however, is more readily taken up when provided at an equivalent concentration to HCO(3) (-). This discovery suggests that the mechanistic basis for the inorganic carbon concentrating system may not be a simple HCO(3) (-) pump as has been suggested. It is clear, however, that during steady-state photosynthesis in seawater equilibrated with air, HCO(3) (-) uptake into the cell is the primary source of internal inorganic carbon.

Abstract: The control of photosynthetic starch/sucrose formation in leaves of soybean ( Glycine max L. Merr.) cultivars was studied in relation to stage of plant development, photosynthetic photoperiod, and nitrogen source. At each sampling, leaf tissue was analyzed for starch content, activities of sucrose-metabolizing enzymes, and labeling of starch and sucrose (by 14 CO 2 assimilation) in isolated cells. In three of the four varieties tested, nodulated plants had lower leaf starch levels and higher activities of sucrose phosphate synthetase (SPS), and isolated mesophyll cells incorporated more carbon (percentage of total 14 CO 2 fixed) into sucrose and less into starch as compared to nonnodulated (nitrate-dependent) plants. The variation among cultivars and nitrogen treatments observed in the activity of SPS in leaf extracts was positively correlated with labeling of sucrose in isolated cells (r = 0.81) and negatively correlated with whole leaf starch content (r = −0.66). The results suggested that increased demand for assimilates by nodulated roots may be accommodated by greater partitioning of carbon into sucrose in the mesophyll cells. We have also confirmed the earlier report (Chatterton, Silvius 1979 Plant Physiol 64: 749-753) that photoperiod affects partitioning of fixed carbon into starch. Within two days of transfer of nodulated soybean Ransom plants from a 14-hour to a 7-hour photoperiod, leaf starch accumulation rates doubled, and this effect was associated with increased labeling of starch and decreased labeling of sucrose in isolated cells. Concurrently, activities of SPS, sucrose synthase, and uridine diphosphatase in leaves were decreased. Four nodulated soybean cultivars were grown to maturity in a greenhouse. Fully expanded leaves at the top of the canopy were sampled during vegetative growth (45 days), at flowering (79 days), and at mid-podfill (120 days). In general, activities of SPS and uridine-5′-diphosphatase were highest during vegetative growth, and they decreased during reproductive development, whereas activity of sucrose synthase and leaf starch content tended to increase. Leaf starch was negatively correlated with levels of SPS (r = −0.71). The results support the postulate that sucrose-P synthetase is a key control point regulating the photosynthetic formation of sucrose, and, hence, starch.

Abstract: Suboptimal N nutrition increased the water potential for stomatal closure in water stressed cotton ( Gossypium hirsutum L.) leaves. This increased sensitivity to water stress had two components, increased accumulation of abscisic acid (ABA) and increased apparent stomatal sensitivity to ABA. Low N increased the threshold water potentials for stomatal closure and ABA accumulation by about 4 bars and 2 bars, respectively. Low N also greatly increased stomatal response to low concentrations of exogenous ABA applied to excised leaves through the transpiration stream. In low N leaves, kinetin decreased stomatal response to ABA to the level observed with high N leaves. Kinetin by itself had little effect on stomata, nor did it alter stomatal response to ABA in high N leaves. The results suggest a cytokinin-ABA balance which is altered by suboptimal N nutrition to favor stomatal closure during stress. Ambient temperature and N nutrition interacted to alter stomatal response to water stress. Stress-induced ABA accumulation and apparent stomatal sensitivity to ABA were independently affected. The effects of each treatment, and their interaction, could be explained as the net result of changes in both accumulation and apparent sensitivity. Although the results document environmental control of stomatal response to ABA, either altered partitioning of ABA between active and inactive pools, or altered sensitivity of the guard cells, could account for the data.

Abstract: The flux of radioactivity from 3,4-[14C]methionine into S-adenosyl-l-methionine (SAM), 1-aminocyclopropane-1-carboxylic acid (ACC), spermine, and spermidine while inhibiting conversion of ACC to ethylene by 100 millimolar phosphate and 2 millimolar Co2+ was studied in aged peel discs of orange (Citrus sinensis L. Osbeck) fruit. Inhibition up to 80% of ethylene production by phosphate and cobalt was accompanied by a 3.3 times increase of label in ACC while the radioactivity in SAM was only slightly reduced. Aminoethoxyvinylglycine (AVG) increased the label in SAM by 61% and reduced it in ACC by 47%. Different combinations of standard solution, in which putrescine or spermidine were administered alone or with AVG, demonstrated clearly that inhibition of ethylene biosynthesis—at the conversion of SAM to ACC—by AVG, exogenous putrescine or exogenous spermidine, stimulated the incorporation of 3,4-[14C]methionine into spermidine.

Abstract: Highly purified vacuoles were isolated from protoplasts derived from green barley (Hordeum vulgare var. Numar) leaves, in order to determine their role as a NO3− storage sink. α-Mannosidase and acid phosphatase activities were used as markers to identify vacuoles, α-mannosidase being the more suitable. Nitrate and α-mannosidase, which were released from vacuoles destroyed during lysis of protoplasts, moved at unequal rates in the density gradient used for vacuole isolation. Purified vacuoles retained less NO3− than α-mannosidase during a single washing. Empirically determined corrections were used to account for NO3− movement in estimating the percentage of total cellular nitrate found in the vacuole. Vacuoles from plants grown in the presence of NO3− contained 58% of the total cellular NO3− and therefore represent a major NO3− storage pool.

Abstract: Coniferyl alcohol is the primary substrate for peroxidase-mediated lignification, a process which depends on the generation of H 2 O 2 by NADH oxidation. We measured the concentrations of various phenols (synthetic and natural) at which maximal enhancement of NADH oxidation occurs. Coniferyl alcohol was found to stimulate NADH oxidation at a much lower concentration (0.01 mm) than other natural or synthetic phenols (1-100 mm). In addition, coniferyl alcohol prevented the conversion of active peroxidase into the inactive intermediate compound III—which is usually formed in the presence of NADH—at equally low concentrations. This conversion was found to be a prerequisite for stimulation of NADH-oxidation, but it was not necessarily connected to stimulation. The oxidation of NADH and coniferyl alcohol (or guaiacol) can occur simultaneously, but there is a strong competitive interaction between these two substrates. At pH 5, the presence of NADH at concentrations 30 to 60 times lower than the phenols completely prevents their oxidation. The results are discussed in relation to the role of cell wall peroxidases in conversion of coniferyl alcohol to lignin and in formation of H 2 O 2 .

Abstract: An experimental chemical N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N′-phenylurea (EDU), is an effective protectant against acute and chronic foliar injury due to ozone (03) when sprayed on intact leaves or supplied to the plants through soil application. An 03-sensitive snap bean cultivar (Phaseolus vulgaris L. `Bush Blue Lake 2909) was systemically treated with EDU (0, 25, 50, and 100 milligrams per 15-centimeter diameter pot) to determine if EDU-induced or activated protective oxyradical and peroxyl scavenging enzymes. EDU-enhanced tolerance to O3 injury always correlated with increases in superoxide dismutase (SOD) and catalase activities in the leaves. Peroxidase levels correlated more closely with foliar injury. Greater SOD levels in young leves compared to older leaves were associated with lower ozone sensitivities in these tissues. Polyacrylamide slab gel electrophoresis separations and specific determinations of SOD activity showed that EDU-treated plants possessed markedly greater SOD activity than non-treated plants. Tolerant plant tissues may have enhanced enzyme scavenging capabilities for the protection against toxic oxyradicals. Experimental confirmation for the oxyradical theory for O3 phytotoxicity and SOD involvement in the detoxification process are presented.

Abstract: Corn ( Zea mays , L.), bean ( Phaseolus vulgaris L.), barley ( Hordeum vulgare L.), spinach ( Spinacia oleracea L.), and sugarbeet ( Beta vulgaris L.) grown under iron deficiency, and Potamogeton pectinatus L, and Potamogeton nodosus Poir. grown under oxygen deficiency, contained less chlorophyll than the controls, but accumulated Mg-protoporphyrin IX and/or Mg-protoporphyrin IX monomethyl ester. No significant accumulation of these intermediates was detected in the controls or in the tissue of plants stressed by S, Mg, N deficiency, or by prolonged dark treatment. Treatment of normal plant tissue with δ-aminolevulinic acid in the dark resulted in the accumulation of protochlorophyllide. If this treatment was carried out under conditions of iron or oxygen deficiency, less protochlorophyllide was formed, but a significant amount of Mg-protoporphyrin IX and Mg-protoporphyrin IX monomethyl ester accumulated. These results are consistent with the presence of an O 2 , Fe-requiring step between Mg-protoporphyrin IX monomethyl ester and protochlorophyllide.

Abstract: In apple (Malus domestica Borkh.) sorbitol is the primary product of photosynthesis, the major translocated form of carbon, and a common fruit constituent and storage compound. Previous work on sorbitol metabolism has revealed a NADPH-dependent aldose 6-phosphate reductase (A6PR) in green tissues, and a NAD-dependent sorbitol dehydrogenase in nongreen tissues. Results here show a decrease in sorbitol dehydrogenase activity and an increase in A6PR activity as leaves developing in the spring undergo the transition from sink to source. Sorbitol dehydrogenase activity reached a minimum as A6PR peaked. These changes were related to increases in leaf carbohydrate levels, especially sorbitol, and to increases in rates of net photosynthesis. Studies conducted in the autumn on senescing leaves also showed changes in enzyme activites, leaf carbohydrate levels, and photosynthesis. At this time, however, sorbitol dehydrogenase increased in specific activity, whereas A6PR activity, leaf carbohydrates, and photosynthetic rates all decreased substantially. Other experiments showed differences in the ability of young and mature leaves to metabolize sorbitol and in the distribution of sorbitol enzymes in leaves at transitional developmental stages. The results suggest that sorbitol metabolism in apple is tightly controlled and may be related to mechanisms regulating partitioning or source and sink activity.

Abstract: Leaf discs and detached leaves exposed to l-cysteine emitted a volatile sulfur compound which was proven by gas chromatography to be H(2)S. This phenomenon was demonstrated in all nine species tested (Cucumis sativus, Cucurbita pepo, Nicotiana tabacum, Coleus blumei, Beta vulgaris, Phaseolus vulgaris, Medicago sativa, Hordeum vulgare, and Gossypium hirsutum). The emission of volatile sulfur by cucumber leaves occurred in the dark at a similar rate to that in the light. The emission of leaf discs reached the maximal rate, more than 40 picomoles per minute per square centimeter, 2 to 4 hours after starting exposure to l-cysteine; then it decreased. In the case of detached leaves, the maximum occurred 5 to 10 h after starting exposure. The average emission rate of H(2)S during the first 4 hours from leaf discs of cucurbits in response to 10 millimolar l-cysteine, was usually more than 40 picomoles per minute per square centimeter, i.e. 0.24 micromoles per hour per square decimeter. Leaf discs exposed to 1 millimolar l-cysteine emitted only 2% as much as did the discs exposed to 10 millimolar l-cysteine. The emission from leaf discs and from detached leaves lasted for at least 5 and 15 hours, respectively. However, several hours after the maximal emission, injury of the leaves, manifested as chlorosis, was evident. H(2)S emission was a specific consequence of exposure to l-cysteine; neither d-cysteine nor l-cystine elicited H(2)S emission. Aminooxyacetic acid, an inhibitor of pyridoxal phosphate dependent enzymes, inhibited the emission. In a cell free system from cucumber leaves, H(2)S formation and its release occurred in response to l-cysteine. Feeding experiments with [(35)S]l-cysteine showed that most of the sulfur in H(2)S was derived from sulfur in the l-cysteine supplied and that the H(2)S emitted for 9 hours accounted for 7 to 10% of l-cysteine taken up. (35)S-labeled SO(3) (2-) and SO(4) (2-) were found in the tissue extract in addition to internal soluble S(2-). These findings suggest the existence of a sulfur cycle which converts l-cysteine to SO(4) (2-) through cysteine desulfhydration.

Abstract: Transitions in carbohydrate metabolism and translocation rate were studied for evidence of control of export by the sugar beet ( Beta vulgaris L. Klein E.) source leaf. Steady-state labeling was carried out for two consecutive 14-hour light periods and various quantities related to translocation were measured throughout two 24-hour periods. Starch accumulation following illumination was delayed. Near the end of the light period, starch stopped accumulating, whereas photosynthesis rate and sucrose level remained unchanged. At the beginning of the dark period there was a 75-minute delay before starch was mobilized. The rate of import to the developing sink leaves at night was similar to that during the day, whereas export decreased considerably at night. Starch accumulation and degradation seemed to be initiated in response to the level of illumination. Cessation of starch accumulation before the end of the light period was initiated endogenously. Exogenous control appeared to be mediated by the level of sucrose in the source leaf while endogenous control seemed to be keyed to photoperiod or photosynthetic duration.

Abstract: Endopolygalacturonase isolated from culture filtrates of the fungus Rhizopus stolonifer was shown previously to act as an elicitor of biosynthetic capacity for the antifungal agent, casbene, in castor bean (Ricinus communis L.) seedlings (S.-C. Lee, C.A. West 1981 Plant Physiology 67:633-639). Selective amidation of exposed carboxyl groups of the pure fungal endopolygalacturonase using intermediate activation with a water-soluble carbodiimide under mild conditions leads to inactivation of its enzymic activity. Tests of active and partially inactivated preparations of the enzyme reveal a close correlation between the levels of catalytic and elicitor activities. This suggests that the catalytic activity of the enzyme is necessary for its function as an elicitor. Treatment of the cell-free particulate fraction of homogenates of castor bean seedlings with the active fungal endopolygalacturonase results in the production of a heat-stable, water-soluble component which is highly active as an elicitor of casbene synthetase activity. Several additional lines of evidence, including the susceptibility of the heat-stable elicitor fraction to partial inactivation following prolonged treatment with endopolygalacturonase, indicate that the heat-stable elicitor is most likely a pectic fragment of the plant cell wall and that it is a required intermediate in the process of elicitation of casbene synthetase activity by the fungal endopolygalacturonase.

Abstract: The lipid microviscosity of microsomal membranes from senescing cut carnation (Dianthus caryophyllus L. cv. White Sim) flowers rises with advancing senescence. The increase in membrane microviscosity is initiated within 3 to 4 days of cutting the flowers and coincides temporally with petal-inrolling denoting the climacteric-like rise in ethylene production. Treatment of young cut flowers with aminoethoxyvinylglycine prevented the appearance of petal-inrolling and delayed the rise in membrane microviscosity until day 9 after cutting. When freshly cut flowers or aminoethoxyvinylglycine-treated flowers were exposed to exogenous ethylene (1 microliter per liter), the microviscosity of microsomal membranes rose sharply within 24 hours, and inrolling of petals was clearly evident. Thus, treatment with ethylene accelerates membrane rigidification. Silver thiosulphate, a potent anti-ethylene agent, delayed the rise in microsomal membrane microviscosity even when the flowers were exposed to exogenous ethylene. Membrane rigidification in both naturally senescing and ethylene-treated flowers was accompanied by an increased sterol:phospholipid ratio reflecting the selective loss of membrane phospholipid that accompanies senescence. The results collectively indicate that the climacteric-like surge in ethylene production during senescence of carnation flowers facilitates physical changes in membrane lipids that presumably lead to loss of membrane function.

Abstract: Concentration curves for sugar and amino acid uptake by Beta vulgaris L. leaf tissues contained both a saturable and a linear component. Similarly shaped curves were obtained for influx of sucrose, glucose, and 3- O -methyl glucose by leaf discs, whole petiole slices, petiole segments containing pith tissue only, and petiole segments containing vascular bundles, although the tissues took up the various sugars via different proportions of saturable versus linear uptake. Two millimolar p -chloromercuribenzenesulfonic acid selectively inhibited the saturable component of sucrose uptake, but had almost no effect on the linear component. Uptake of glucose and 3- O -methyl glucose remained unaffected by p -chloromercuribenzenesulfonic acid treatment. Anoxia was found to inhibit the linear component of both sucrose and 3- O -methyl glucose influx, while the saturable component remained unaffected. The linear component of sucrose uptake was also competitively inhibited by maltose, as well as being selectively promoted by certain exposures to 5 millimolar N -ethylmaleimide, 2 micrograms per milliliter cycloheximide, and high levels of mannitol acting as osmoticum. These results support the proposal that the linear component is due to a process more complex than simple, or exchange, diffusion. It would also appear that the linear transport component utilizes a separate energy source than does the saturable component of sucrose influx. Evidence for phloem loading from the apoplast was re-examined with respect to the present findings. Saturable sucrose uptake by minor vein tissues may represent retrieval of solute from the free space, which could explain the `apoplastic loading9 phenomenon.

Abstract: Depodding soybean (Glycine max [L] Merr. cv Wye) plants results in an apparent inhibition of senescence as indicated by leaf chlorophyll and soluble protein retention. However, leaf photosynthesis and ribulose bisphosphate carboxylase (Rubisco) levels begin to decline earlier in depodded than in control, podded plants. The initial decline in photosynthesis is correlated with a decrease in leaf transpiration, while the latter decline is associated with the loss of Rubisco. Total soluble protein remains high in depodded plants because several polypeptides, three in particular, increase in amounts sufficient to offset the loss of Rubisco. Thus, depodding appears to change the function of the leaf rather than simply delaying or preventing the decline in leaf function. Changes in specific leaf weight and starch content following depodding suggest that the leaf may be changing to a storage organ.

Abstract: The potential of measurements of chlorophyll fluorescence in vivo to detect cellular responses to salinity and degrees of salt stress in leaves was investigated for three crop plants. Sugar beet (Beta vulgaris L.) (salt tolerant), sunflower (Helianthus annuus L.) (moderately salt tolerant), and bean (Phaseolus Vulgaris L. cv Canadian Wonder) (salt intolerant) were grown in pots and watered with mineral nutrient solution containing 100 millimolar NaCl. The fast rise in variable chlorophyll fluorescence yield that is correlated with photoreduction of photosystem II acceptors increased in leaves of sugar beet plants treated with salt suggesting stimulation of photosystem II activity relative to photosystem I. In sunflower, this fast rise was depressed by approximately 25% and the subsequent slow rate of quenching of the chlorophyll fluorescence was stimulated. These differences were more marked in the older mature leaves indicating an increasing gradient of salt response down the plant. The salt effect in vivo was reversible since chloroplasts isolated from mature leaves of salt-treated and control sunflower plants gave similar photosystem II activities. Unlike in sugar beet and sunflower, leaves of salt-treated bean progressively lost chlorophyll. The rate of slow quenching of chlorophyll fluorescence decreased indicating development of a partial block after photosystem II and possible initial stimulation of photosystem II activity. With further loss of chlorophyll photosystem II activity declined. It was concluded that measurements of chlorophyll fluorescence in vivo can provide a rapid means of detecting salt stress in leaves, including instances where photosynthesis is reduced in the absence of visible symptoms. The possible application to screening for salt tolerance is discussed.

Abstract: The conversion of l-glutamate to δ-aminolevulinate, in preparations of cucumber etiochloroplasts incubated in vitro , was inhibited by protoheme IX and Mg-protoporphyrin IX. Mg-protoporphyrin IX was destroyed in the presence of air and plastids; this breakdown was accelerated by S -adenosyl methionine. Mg-protoporphyrin IX was also converted to protochlorophyllide in vitro. This conversion exhibited an absolute requirement for atmospheric oxygen and was strongly stimulated by S -adenosyl methionine and by darkness. Based on these results, and on the results of the preceding paper (Spiller, Castelfranco, Castelfranco 1981 Plant Physiol 68: 107-111), a comprehensive hypothesis for the role of O 2 and Fe in chlorophyll biosynthesis is formulated.

Abstract: Stress ethylene production in bean ( Phaseolus vulgaris L., cv. Taylor9s Horticultural) leaf tissue was stimulated by Cd 2+ at concentrations above 1 micromolar. Cd 2+ -induced ethylene biosynthesis was dependent upon synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase. Activity of ACC synthase and ethylene production rate peaked at 8 h of treatment. The subsequent decline in enzyme activity was most likely due to inactivation of the enzyme by Cd 2+ , which inhibited ACC synthase activity in vitro at concentrations as low as 0.1 micromolar. Decrease in ethylene production rate was accompanied by leakage of solutes and increasing inhibition of ACC-dependent ethylene production. Ca 2+ , present during a 2-hour preincubation, reduced the effect of Cd 2+ on leakage and ACC conversion. This suggests that Cd 2+ exerts its toxicity through membrane damage and inactivation of enzymes. The possibility of an indirect stimulation of ethylene biosynthesis through a wound signal from injured cells is discussed.

Abstract: A protein, extracted from Katahdin potato ( Solanum tuberosum L. cv `Katahdin9) tubers and purified by ion exchange chromatography and gel filtration, agglutinates avirulent strains of the bacterial wilt pathogen, Pseudomonas solanacearum, but only weakly agglutinates virulent strains. The agglutinin has very low hemagglutinating activity (in contrast to potato lectin) and is a glycoprotein containing about 61% carbohydrate. The carbohydrate moiety contains 91% (weight%) arabinose, 5% galactose, 3% glucose, and 1% glucosamine. The protein portion is rich in hydroxyproline (42%), lysine (16%), serine (9%), and proline (9%). The entire agglutinin has a molecular weight of 91,000 ± 5,000 and is very basic (pI > 11). Shape estimations based on the concentration dependence of the sedimentation coefficient, the high viscosity ([η] = 92.7), the frictional coefficient ( f / f o = 2.15), and axial ratio ( a / b = 25) indicate that the agglutinin is a prolate ellipsoid.

Abstract: Although intact fruits of unripe cantaloupe (Cucumis melo L.) produce very little ethylene, a massive increase in ethylene production occurred in response to excision. The evidence indicates that this wound ethylene is produced from methionine via 1-aminocyclopropanecarboxylic acid (ACC) as in ripening fruits. Excision induced an increase in both ACC synthase and the enzyme converting ACC to ethylene. Ethylene further increased the activity of the enzyme system converting ACC to ethylene. The induction by ethylene required a minimum exposure of 1 hour; longer exposure had increasingly larger effect. The response was saturated at approximately 3 microliters per liter ethylene and was inhibited by Ag+. Neither ethylene nor ACC had a promotive or inhibitory effect on ACC synthase beyond the effect attributable to wounding.

Abstract: Ethylene at hormonally significant levels inhibited net photosynthesis of the cultivated peanut (Arachis hypogaea L.) as measured by gas analysis. Upon the removal of ethylene, the inhibition was naturally overcome at the concentration-exposure duration combinations tested. Increased length of exposure of 1 microliter of ethylene per liter of air up to 6 hours increased the degree of net photosynthesis inhibition (68% reduction after 6-hour exposure). Significantly greater inhibition of photosynthesis by ethylene was detected on peanut genotypes having higher photosynthetic efficiency. In contrast to peanut, hormonal concentrations of ethylene only moderately inhibited sweet potato, Jerusalem artichoke, and sunflower photosynthesis and was without effect on beans, peas, Irish potato, Mimosa pudica, and white clover. No inhibition could be found by ethylene on ribulose 1,5-biphosphate carboxylase activity in vitro. Photosynthesis was lowered at all CO2 concentrations below ambient at an O2 concentration of 1.5%, indicating that the action of ethylene was not affected by low O2; concomitantly, an increase in the CO2 compensation point occurred. Diffusion resistance measurements of leaf water vapor loss made on ethylene-treated peanut leaves showed a measurable decrease in leaf conductance which correlated with net photosynthesis decrease. Ethylene influenced the conductance of abaxial stomata more so than adaxial.

Abstract: Using a highly sensitive vibrating electrode, the pattern of naturally occurring electric currents around 1-day-old primary roots of Lepidium sativum L. growing vertically downward and the current pattern following gravistimulation of the root has been examined. A more or less symmetrical pattern of current was found around vertically oriented, downward growing roots. Current entered the root at the root cap, the meristem, and the beginning of the elongation zone and left the root along most of the elongation zone and in the root hair zone. After the root was tilted to a horizontal position, we observed current flowing acropetally at the upper side of the root cap and basipetally at the lower side within about 30 seconds in most cases. After a delay of several minutes, acropetally oriented current was also found flowing along the upper side of the meristematic zone. The apparent density of the acropetal current in the root cap region increased and then decreased with time. Gravitropic curvature was first visible approximately 10 minutes after tilting of the root to the horizontal position. Since the change in the pattern of current in the root cap region precedes bending of the root and is different for the upper and lower side, a close connection is suggested between the current and the transduction of information from the root cap to the elongation zone following graviperception in the cap.

Abstract: The apparent association of ornithine decarboxylase (ODC) with rapid cell proliferation in developing tomato (Lycopersicon esculentum Mill. cv. Pearson ms-35) fruits has been previously described. Further evidence is provided by the use of two ODC inhibitors, alpha-difluoromethylornithine (alpha-DFMO) and alpha-methylornithine (alpha-MO). Fruit development was inhibited by these inhibitors if applied during the period of intensive cell division. When applied in vitro, the two inhibitors were shown to inhibit the activity of ODC but not that of arginine decarboxylase (ADC). When applied in vivo, alpha-DFMO, a catalytic irreversible inhibitor, caused 97.1% reduction of ODC activity in the dialyzed extract from the treated ovaries, while it had no effect on ADC. On the other hand, alpha-MO, a reversible inhibitor, did not reduce the activity of these two enzymes in the dialyzed extracts when applied in vivo. The dialysis procedure probably removed alpha-MO from the enzyme fraction. Putrescine, the product of both ODC and ADC, alleviated the inhibition of fruit development but did not restore ODC activity to the control level. These results suggest that in the young developing tomato fruit, ODC is the enzyme responsible for the synthesis of putrescine, which is essential for the early stages of fruit development. The reduced activity of ODC elicited by putrescine suggests a mechanism of feedback regulation by enzyme repression or release of an ODC anti-enzyme.

Abstract: The effects of 1 millimolar glyphosate (N-[phosphonomethyl]glycine) upon the activities of enzymes of aromatic amino acid biosynthesis, partially purified by ion-exchange chromatography from mung bean seedings (Vigna radiata [L.] Wilczek), were examined. Multiple isozyme species of shikimate dehydrogenase, chorismate mutase, and aromatic aminotransferase were separated, and these were all insensitive to inhibition by glyphosate. The activities of prephenate dehydrogenase and arogenate dehydrogenase were also not sensitive to inhibition. Two molecular species of 3-deoxy-d-arabino-heptulosonate 7-phosphate (DAHP) synthase were resolved, one stimulated several-fold by Mn2+ (DAHP synthase-Mn), and the other absolutely dependent upon the presence of Co2+ for activity (DAHP synthase-Co). Whereas DAHP synthase-Mn was invulnerable to glyphosate, greater than 95% inhibition of DAHP synthase-Co was found in the presence of glyphosate. Since Co2+ is a Vmax activator with respect to both substrates, glyphosate cannot act simply by Co2+ chelation because inhibition is competitive with respect to erythrose-4-phosphate. The accumulation of shikimate found in glyphosate-treated seedlings is consistent with in vivo inhibition of both 5-enolpyruvylshikimic acid 3-phosphate synthase and one of the two DAHP synthase isozymes. Aromatic amino acids, singly or in combination, only showed a trend towards reversal of growth inhibition in 7-day seedlings of mung bean. The possibilities are raised that glyphosate may act at multiple enzyme targets in a given organism or that different plants may vary in the identity of the prime enzyme target.