Abstract: Ecotypic differences in the photosynthetic carbon metabolism of Mollugo verticillata were studied. Variations in C3 and C4 cycle activity are apparently due to differences in the activities of enzymes associated with each pathway. Compared to C4 plants, the activities of C4 pathway enzymes were generally lower in M. verticillata, with the exception of the decarboxylase enzyme, NAD malic enzyme. The combined total carboxylase enzyme activity of M. verticillata was greater than that of C3 plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C3 or C4 plants, ribulose bisphosphate carboxylase was present in both mesophyll and bundle sheath cell chloroplasts in M. verticillata. The localization of this enzyme in both cells in this plant, in conjunction with an efficient C4 acid decarboxylation mechanism most likely localized in bundle sheath cell mitochondria, may account for intermediate photorespiration levels previously observed in this species.

Abstract: Severance of the stele of young main roots of pea (Pisum sativum L.) results in formation of a bridge of vascular tissue in the remaining cortex. Cell divisions occur close to the severed vascular tissues on both the proximal and distal sides of the cut within 24 h. Differentiation of new vascular strands subsequently begins in the same locations and progresses from both sides of the wound into the remaining cortex and also back along the original vascular strands. Most of the vascular tissue which forms the bridge through the cortex differentiates in the acropetal direction. Continuous strands composed of single sieve elements bypass the wound somewhat sooner than the first complete xylem strands; the latter in 60–70% of the cases, are present by 3 d. Cambial activity subsequently adds more xylem and phloem. Vascular regeneration is not affected by removal of the epicotyl or the root tip; it is greatly reduced but not prevented by removal of the cotyledons.

Abstract: Nearly a century ago botanists first examined and described an arrangement of green leaf cells known today as Kranz leaf anatomy with its characteristic green mesophyll and bundle sheath cells. In evaluating this pioneering work Haberlandt (1914) states: “— the (bundle) sheath — contains numerous chloroplasts, which are moreover often large and very brightly colored. It is uncertain whether this green inner sheath merely represents an unimportant addition to the chlorophyll-apparatus of the plant, or whether there exists some as yet undiscovered division of labour between the chloroplasts in the sheath and those in the girdle (mesophyll) cells.” Research within the last decade has revealed this “undiscovered division of labor” between mesophyll and bundle sheath cells and chloroplasts. The physical localization of chloroplasts in these adjacent leaf cells initially made direct studies difficult and contributed to some controversy about this division of labor. However to understand C4 photosynthesis one must have a clear picture of Kranz leaf anatomy because two green cell types are present in all plants in which C4 photosynthesis has been well documented.

Abstract: Adventitious roots develop in bean hypocotyl cuttings in four rows parallel to and between the four pairs of vascular bundles, in contrast to their irregular development in petiole and epicotyl cuttings where the distribution pattern of xylem bundles is also irregular. Auxin, applied acropetally or basipetally, increases the number of roots but does not alter the pattern of their emergence. Similarly, [2-l4CJIAA which is translocated mainly via the vascular bundles (but also laterally towards the cortex and pith) accumulates in the root-forming areas

Abstract: The activity of adenosine 5′ triphosphate sulfurylase was determined in crabgrass mesophyll cells, bundle sheath strands, and whole leaf extracts. The enzyme was assayed by following molybdate-dependent pyrophosphate release from ATP, 35SO42− incorporation into adenosine 5′ phosphosulfate, and ATP synthesis dependent upon adenosine 5′ phosphosulfate and inorganic pyrophosphate. With all assays, greater than 90% of the activity was found in extracts from bundle sheath strands. The activities in whole leaf extracts were consistently intermediate between the activities of mesophyll and bundle sheath extracts and extract-mixing experiments gave no indication of enzyme activation or inhibition in vitro. Whole leaf activities were several hundred-fold less than concurrent measurements of ribulose 1,5-bisphosphate and phosphoenolpyruvate carboxylase activities, which is interpreted as being consistent with the relative amounts of elemental carbon and sulfur found in higher plants. A hypothesis is presented for the intercellular compartmentation of sulfur assimilation in relationship to NO3− and CO2 assimilation in leaves of C4 plants.

Abstract: Xylem transfer cells are strongly developed in the departing leaf traces of the mature wheat node. Their differentiation is initiated soon after the appearance of the first tracheary elements in these bundles. and wall ingrowth development reaches its peak just as the leaf to which the bundle belongs becomes fully expanded. It is suggested that the xylem transfer cells play an important role in redirecting solutes travelling in the xylem of the mature leaf to the developing leaves at the shoot apex. It is further suggested that they form an integral part of the normal xylem transpiration pathway, compensating for xylem restrictions and discontinuities in the mature node. Phloem transfer cells also appear very early in the differentiation of the nodal vasculature, although their function remains obscure.

Abstract: In multicellular tissues such as the cortex of roots and the mesophyll cells of leaves, where there are no specialized vascular elements, the pathways for the movement of ions are the symplast and apoplast. Observation of calcium transport in regions where these pathways are physically or physiologically blocked can provide information on the pathways of calcium movement. In roots, calcium movement to the central xylem is heavily reduced in regions where suberization and cellulose thickening of the endodernis constitutes a barrier to apoplastic movement. The implication that calcium moves with difficulty in symplastic pathways in general is supported by the relative immobility of calcium in the phloem, its slow rates of diffusion across layers of cells such as in fruit cortical tissue, and lack of redistribution from aging leaves to other parts of the plant. It is suggested that suberization of bundle sheath cells in many monocotyledons may have a restrictive effect on the transfer of calcium bet...

Abstract: SUMMARY Pollen tubes of maize enter the silk intercellularly via multicellular hairs located on two opposite sides of the silk or epidermis cells of the silk proper. The silk contains two vascular bundles. A strand of “transmitting tissue” is associated with each bundle, separated from xylem elements by one parenchyma layer. The pollen tubes grow intercellularly towards the “transmitting tissue” and then between the cells of this tissue down the silk. The diameter of the pollen tubes ranges between 6–13 μm but increases to 26–55 μm at the enlarged section of the tube.

Abstract: Arundinella hirta L. is a C4 plant having an unusual C4 leaf anatomy. Besides mesophyll and bundle sheath cells, A. hirta leaves have specialized parenchyma cells which look morphologically like bundle sheath cells but which lack vascular connections and are located between veins, running parallel to them. Activities of phosphoenolpyruvate and ribulose-1,5-bisphosphate carboxylases and phosphoenolpyruvate carboxykinase, NADP-and NAD-malic enzymes were determined for whole leaf extracts and isolated mesophyll protoplasts, specialized parenchyma cells, and bundle sheath cells. The data indicate that A. hirta is a NADP-malic enzyme type C4 species. In addition, specialized parenchyma cells and bundle sheath cells are enzymatically alike. Compartmentation of enzymes followed the C4 pattern with phosphoenolpyruvate carboxylase being restricted to mesophyll cells while ribulose-1,5-bisphosphate carboxylase and decarboxylating enzymes were restricted to bundle sheath and specialized parenchyma cells.

Abstract: SummaryDuring the first four or five weeks of fruitlet development, root-absorbed 45 Ca entered the vascular bundles throughout the whole fruit. Subsequently, no uptake could be detected in the outer cortex. When the fruitlets were about six weeks old, 45 Ca applied to the roots two weeks before had diffused through the cells, including the pith, although radioactivity in the vascular bundles associated with the carpels, sepals and petals remained high at this time. There was very little uptake by the fruits of 45 Ca supplied in early August: autoradiographs prepared four weeks later showed activity to be mainly in the fruit stalk, whilst in the fruit, trace amounts were found in the cartilaginous pericarp and ventral carpellary bundles. It is suggested that part of the calcium requirement moves into the fruit skin from the epidermis of the fruit stalk as well as through the vascular system.The significance of the changing pattern in distribution of 45 Ca is discussed in relation to other changes in the f...

Abstract: The potential for glycolate and glycine metabolism and the mechanism of refixation of photorespiratory CO2 in leaves of C4 plants were studied by parallel inhibitor experiments with thin leaf slices, different leaf cell types and isolated mitochondria of C3 and C4Panicum species. CO2 evolution by leaf slices of P. bisulcatum, a C3 species, fed glycolate or glycine was light-independent and O2-sensitive. The C4P. maximum and P. miliaceum leaf slices fed glycolate or glycine evolved CO2 in the dark but not in the light. In C4 species, dark CO2 evolution was abolished by the addition of phosphoenolpyruvate (PEP)4. The addition of maleate, a PEP carboxylase inhibitor, resulted in photorespiratory CO2 efflux by C4 leaf slices in the light also. However, PEP and maleate had no effect on either glycolate-dependent O2 uptake by the C4 leaf slices or on glycolate and glycine metabolism in C3 leaf slices. The rate of photorespiratory CO2 evolution in the C3Panicum species was 3 times higher than that observed with the C4 species. The ratio of glycolate-dependent CO2 evolution to O2 uptake in both groups was 1:2. Isolated C4 mesophyll protoplasts or their mitochondria did not metabolize glycolate or glycine. However, both C3 mesophyll protoplasts and C4 bundle sheath strands readily metabolized glycolate and glycine in a light-independent, O2-sensitive manner, and the addition of PEP or maleate had no effect. C4 bundle sheath- and C3-mitochondria were capable of oxidizing glycine. This oxidation was linked to the mitochondrial electron transport chain, was coupled to three phosphorylation sites and was sensitive to electron transport inhibitors. C4 bundle sheath- and C3-mitochondrial glycine decarboxylation was stimulated by oxaloacetate and NAD had no effect. In marked contrast, mitochondria isolated from C4 mesophyll cells were incapable of oxidizing or decarboxylating added glycine. The results suggest that in leaves of C4 plants bundle sheath cells are the primary site of O2-sensitive photorespiratory CO2 evolution and the PEP carboxylase present in the mesophyll cells has the Potential for efficiently refixing CO2 before it escapes out of the leaf. The relative role of the PEP carboxylase mediated CO2 pump and reassimilation of photorespiratory CO2 are discussed in relation to the apparent lack of photorespiration in leaves of C4 species.

Abstract: Chloroplasts or cells from maize (Zea mays) bundle sheath show a very low intensity of delayed light emission compared with mesophyll protoplasts or chloroplasts. The bundle-sheath chloroplasts retain only the fast (less than 1 ms) component of the emission. They also fail to show fluorescence induction in contrast to the mesophyll, which behaved normally. The mesophyll material could be made to resemble the bundle-sheath chloroplasts in respect of both phenomena by adding to it 1-(3',4'-dichlorophenyl)-3,3-dimethyl-urea and hydroxylamine, together. It is concluded that Photosystem II, that gives rise to both effects, is not active in the bundle sheath but may be present in an inhibited form.

Abstract: The ambiguous location of photosynthetic carboxylases of mesophyll and bundle sheath chloroplasts of sorghum was investigated after successful homogeneous preparation. The phosphoenol pyruvate carboxylase was found as a particulate enzyme in the mesophyll cell chloroplasts and ribulose 1,5-biphosphate carboxylase in the stroma of the bundle sheath cell chloroplasts. Extensive characterization was carried out on these 2 enzymes for better understanding of the enzyme action.

Abstract: Downy mildew infected ragi plants exhibits a wide range of symptoms. Histopathological studies of the diseased plant have revealed that the fungus mycelium is present in root, stem, floral parts and seed causing morphological and anatomical changes. The mycelium develops profusely in the sub-stomatal spaces and from this the sporangiophores emerge through the stomata. In the leaf tissue invaded by the fungus, the chloroplasts and leucoplasts are either few or absent. Cells of the mesophyll in the case of the diseased leaves are distorted. Sometimes, the cells of the invaded tissue dissolve and the mycelium or sex organs occupy the space thus created. In the leaf tissue, the intercellular spaces surrounding the vascular sheaths are the primary centres of mycelial development. The sex organs are mostly confined to the vicinity of the vascular bundles. In the infected leaf, very few epidermal hairs are developed.

Abstract: The activity of adenosine 5' triphosphate sulfurylase was determined in crabgrass mesophyll cells, bundle sheath strands, and whole leaf extracts. The enzyme was assayed by following molybdate-dependent pyrophosphate release from ATP, 35S042- incorporation into adenosine 5' phosphosulfate, and ATP synthesis dependent upon adenosine 5' phosphosulfate and inorganic pyrophosphate. With all assays, greater than 90% of the activity was found in extracts from bundle sheath strands. The activities in whole leaf extracts were consistently intermediate between the activities of mesophyll and bundle sheath extracts and extract-mixing experiments gave no indication of enzyme activation or inhibition in vitro. Whole leaf activities were several hundred-fold less than concurrent measurements of ribulose 1,5-bisphosphate and phosphoenolpyruvate carboxylase activities, which is interpreted as being consistent with the relative amounts of elemental carbon and sulfur found in higher plants. A hypothesis is presented for the intercellular compartmentation of sulfur assimilation in relationship to N03- and CO2 assimilation in leaves of C4 plants.

Abstract: The tissue distributions of dhurrin [p-hydroxy-(S)-mandelonitrile-β-d-glucoside] and of enzymes involved in its metabolism have been investigated in leaf blades of light-grown Sorghum bicolor seedlings. Enzymic digestion of these leaves using cellulase has enabled preparations of epidermal and mesophyll protoplasts and bundle sheath strands to be isolated with only minor cross-contamination. Dhurrin was located entirely in the epidermal layers of the leaf blade, whereas the two enzymes responsible for its catabolism, namely dhurrin β-glucosidase and hydroxynitrile lyase, resided almost exclusively in the mesophyll tissue. The final enzyme of dhurrin biosynthesis, uridine diphosphate glucose:p-hydroxymandelonitrile glucosyltransferase, was found in both mesophyll (32% of the total activity of the leaf blade) and epidermal (68%) tissues. The bundle sheath strands did not contain significant amounts of dhurrin or of these enzymes. It was concluded that the separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions. The well documented production of HCN (cyanogenesis), which occurs rapidly on crushing Sorghum leaves, would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.

Abstract: Nitrogen assimilation in crabgrass Digitaria sanguinalis (L.) Scop., was studied by comparing leaf extracts with isolated mesophyll cell and bundle sheath strand extracts. The results show that both nitrate and nitrate reductase are localized in mesophyll cells; glutamine synthetase is nearly equally distributed in the mesophyll and bundle sheath; approximately 67% of the glutamate synthase activity is in the bundle sheath and 33% is in the mesophyll; and 80% of the glutamate dehydrogenase activity is in the bundle sheath, with the NADH-dependent form exhibiting a 2.5-fold higher activity than the NADPH-dependent form. Isolated crabgrass mesophyll cells reduce NO 2 − coupled to the photochemical production of O 2 but are inactive with NO 3 − . The NO 2 − -dependent O 2 evolution is light-dependent; inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea; stimulated by photophosphorylation uncouplers; and exhibits a stoichiometry of O 2 evolved to NO 2 − reduced of 1.45 and 0.67 in coupled and uncoupled experiments, respectively. Isolated bundle sheath strands are inactive in O 2 evolution with NO 3 − or NO 2 − . Based on these results, plus literature data, two schemes for crabgrass leaf nitrogen assimilation are presented, depending on whether the plant is using ammonium or nitrate as its nitrogen source. It is proposed that the increased nitrogen use efficiency in crabgrass and other C 4 plants is due partially to a “division of labor” between mesophyll and bundle sheath cells, where NO 3 − and NO 2 − reductase in mesophyll cells act as nitrogen reduction traps in an analogous fashion to phosphoenolpyruvate carboxylase acting as a CO 2 trap during C 4 photosynthesis.

Abstract: : The woods of Octomeles and Tetrameles are similar in appearance and gross morphology. The large diameters and thin walls of the vessel elements and libriform fibers are responsible for the light-weight, non-durable quality of the woods; the small amount of wood parenchyma present probably does not contribute appreciably to this condition. The woods are quantitatively different in several respects, for instance in fiber length and vessel element diameter. The cambium is more conspicuously storied in Tetrameles than in Octomeles. The wood of Dad-sea is different from that of the two monotypic tree genera in the family and is similar to that of some other “woody herbs.” The secondary phloem regions of Octomeles and Tetrameles are strikingly similar in the zone of functional sieve tube elements, but the amount and distribution of sclerenchyma in the zone of sieve tube obliteration are different.