The plant as a metapopulation

In mammals, cadmium is widely considered as a non-genotoxic carcinogen acting through a methylation-dependent epigenetic mechanism. Here, the effects of Cd treatment on the DNA methylation patten are examined together with its effect on chromatin reconfiguration in Posidonia oceanica. DNA methylation level and pattern were analysed in actively growing organs, under short- (6 h) and long- (2 d or 4 d) term and low (10 mM) and high (50 mM) doses of Cd, through a Methylation-Sensitive Amplification Polymorphism technique and an immunocytological approach, respectively. The expression of one member of the CHROMOMETHYLASE (CMT) family, a DNA methyltransferase, was also assessed by qRT-PCR. Nuclear chromatin ultrastructure was investigated by transmission electron microscopy. Cd treatment induced a DNA hypermethylation, as well as an up-regulation of CMT, indicating that de novo methylation did indeed occur. Moreover, a high dose of Cd led to a progressive heterochromatinization of interphase nuclei and apoptotic figures were also observed after long-term treatment. The data demonstrate that Cd perturbs the DNA methylation status through the involvement of a specific methyltransferase. Such changes are linked to nuclear chromatin reconfiguration likely to establish a new balance of expressed/repressed chromatin. Overall, the data show an epigenetic basis to the mechanism underlying Cd toxicity in plants.

/pdf/in-posidonia-oceanica-cadmium-induces-changes-in-dna-3cu7uj83mr.pdf

In Posidonia oceanica cadmium induces changes in DNA methylation and chromatin patterning

Publisher Summary This chapter discusses the phenomenon of lodging in wheat, barley, and oats. Lodging is the state of permanent displacement of the stems from their upright position, which is induced by external forces exerted by wind, rain, or hail. It may culminate in the plants being laid flat on the ground and sometimes involve breakage of the stems. The severity of lodging and the extent of the losses resulting from it depend on the crop's environment and on the growth stage at which lodging occurs. The chapter describes two types of lodging: stem lodging and root lodging and examines various causes of lodging. It discusses the effects of lodging on crop development and yield, including (1) effects on grain yield, (2) effects on grain quality, (3) effects on culm development and tillering, (4) physiological effects of lodging, (5) impact of lodging on grain harvest, and (6) incidence of diseases in lodging crops. Environmental and Agronomic Factors that affecting lodging and the way lodging should be prevented is also discussed in the chapter.

Lodging in Wheat, Barley, and Oats: The Phenomenon, its Causes, and Preventive Measures

Summary

The effects of reducing the plant density of winter wheat (cv. Haven) on canopy formation, radiation absorption and dry matter production and partitioning were investigated in field experiments in 1996/97 and 1997/98. Crop densities established ranged from 19 to 338 plants m−2. Grain yield was maintained with large reductions in plant density. At low plant densities the relative growth rate of the crop increased allowing a maintenance of crop dry matter production. An 18 fold reduction in plant density led only to a six fold reduction in green area index at the beginning of stem extension and by anthesis the difference was less than two fold. Crops grown at low plant densities increased green area per plant through increased duration of tiller production, green area per shoot and shoot survival. Main stem leaf number, phyllochron and tiller production rate were not significantly affected by plant density. Radiation use efficiency was greater at the low plant densities. We propose that better radiation distribution through the canopy and increased canopy nitrogen ratio were the causative mechanisms for this increase in RUE. As a result of increased green area per shoot and a decrease in ear production, more radiation was absorbed per shoot at the low plant densities, allowing an increase in grain number per ear from 32 to 48.

The physiological response of winter wheat to reductions in plant density

A detailed study was made of the tillering of barley plants grown at densities which ranged from 50 to 1600 plants m–2. Throughout the season the initiation of tiller buds and their growth in length and leaf number were followed, and measurements were made of leaf sheath and lamina length and lamina width. A proportion of tillers died and their positions and times of death are given.Three phases of tillering were recognized. The first, tiller bud initiation, was little affected directly by density. During the second phase, buds did not grow or did grow and emerge from the subtending leaf sheath. If they grew, there was no difference in growth rate of tillers at different densities. At the higher densities fewer buds developed, and the morphology of those tillers which did grow was affected by density. This suggests that the growth of the tiller bud may be controlled by levels of endogenous gibberellin, while in the final stage, growth after emergence from the subtending leaf sheath, competition for light appears to be the factor which determines whether a tiller survives to produce an ear. The data are discussed in relation to the practical importance of tillering.

The effect of plant density on tiller growth and morphology in barley

A morphogenetic study, from the first-leaf stage onwards, was made of barley plants grown at a range of plant populations from 50 to 1600 plants m~2. Increasing density reduced leaf number from 10-2 to 8 and caused stem internode elongation to start earlier at a lower node. Final stem length was reduced due to earlier cessation of growth. The lamina and sheath length of the lower leaves was increased with increasing density, and lamina width was de creased. At the highest density the apex reached the double ridge stage 6 days earlier than at the lowest density, and this difference persisted throughout the development of the apex. The rate of primordium production was little affected by density, but the duration was markedly affected. Primordium production stopped abruptly, first at the highest density, and then successively at the lower densities. At this stage changes were seen at the tip of the apex, and eventually the 10 distal primordia died. There were small differences in the length of shoot apex or ear during growth, but earlier cessation of growth in the higher densities led to a shorter ear. Growth of the internodes of the floral apex started first at the high density. These observations suggest that plants grown at high densities had a high concentration of gibberellins (GA) in their tissues. The promotion of apex development by the higher concentra tion of GA gave rise to earlier competition for nutrients diffusing through the apex. This lead to starvation of the tip of the apex and earlier death of this region and, consequently, fewer spikelets. Differences in the light environment of the plants, either intensity or red/far red ratio, most probably brought about the differences in GA.

Plant Population Induced Growth Correlations in the Barley Plant Main Shoot and Possible Hormonal Mechanisms

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Plant Population Induced Growth Correlations in the Barley Plant Main Shoot and Possible Hormonal Mechanisms