In this historical review we summarize discoveries related to the flowering genes in controlling leaf area index (LAI, the leaf area per unit ground area) in sorghum, soybean, or pea crop stands. We also analyze similar work on Arabidopsis and dwarf and intermediate stem height genes in wheat and rice. and G. B. Begonia, M. T. Begonia.
At the whole plant level, the effect of stress is usually perceived as a decrease in photosynthesis and growth. That is why this review is focused mainly on the effect of drought on photosynthesis, its injury, and mechanisms of adaptation. The analysed literature shows that plants have evolved a number of adaptive mechanisms that allow the photochemical and biochemical systems to cope with negative changes in environment, including increased water deficit. In addition, the acquisition of tolerance to drought includes both phenotypic and genotypic changes. The approaches were made to identify those metabolic steps that are most sensitive to drought. Some studies also examined the mechanisms controlling gene expression and putative regulatory pathways. and I. Yordanov, V. Velikova, T. Tsonev.
Plants of spring wheat (Triticum aestivum L. cv. Saxana) were grown during the autumn. Over the growth phase of three leaves (37 d after sowing), some of the plants were shaded and the plants were grown at 100 (control without shading), 70, and 40 % photosynthetically active radiation. Over 12 d, chlorophyll (Chl) and total protein (TP) contents, rate of CO2 assimilation (PN), maximal efficiency of photosystem 2 photochemistry (FV/FP), level of lipid peroxidation, and activities of antioxidative enzymes ascorbate peroxidase (APX) and glutathione reductase (GR) were followed in the 1st, 2nd, and 3rd leaves (counted according to their emergence). In un-shaded plants, the Chl and TP contents, PN, and FV/FP decreased during plant ageing. Further, lipid peroxidation increased, while the APX and GR activities related to the fresh mass (FM) decreased. The APX activity related to the TP content increased in the 3rd leaves. The plant shading accelerated senescence including the increase in lipid peroxidation especially in the 1st leaves and intensified the changes in APX and GR activities. We suggest that in the 2nd and 3rd leaves a degradation of APX was slowed down, which could reflect a tendency to maintain the antioxidant protection in chloroplasts of these leaves. and M. Špundová ... [et al.].
In a controlled experiment, Salix matsudana cuttings were subjected to three atmospheric temperatures (i.e. control, 0.5 and 1.0 °C above the control, respectively) to explore their short-term plastic responses to simulated atmospheric temperature rise. Warming affected significantly net photosynthetic and transpiration rates, but had no significant impacts on water use efficiency, ratio of sub-stomatal to atmospheric CO2 concentration, maximum quantum yield, water saturation deficit, tissue density, and water loss. Leaf natality and leaf mortality were affected significantly by increasing atmospheric temperature. Total plant biomass, leaf mass ratio, root mass ratio, and canopy productivity index exhibited significant responses to the warming treatments, but obvious differences in the changing details did appear among the four traits. Hence: (1) S. matsudana cuttings were sensitive to small-range atmospheric temperature increases such as 0.5-1.0 °C, which can alter growth and allocation through modifying photosynthetic rate and leaf turnover. (2) Short-term physiological acclimation did not occur in young individuals of S. matsudana. (3) The warming depressed growth of young individuals of S. matsudana to various extents. and W. M. He, M. Dong.
Permanent plastid-nuclear complexes (PNCs) exist in tobacco cells from their mitosis up to programmed cell death (PCD). PNCs in senescing cells of tobacco leaves were typical by enclosure of peroxisomes and mitochondria among chloroplasts which were in contact with nucleus. Such a complex position provides simultaneous interaction of these organelles and direct regulation of metabolism and PCD avoiding the cytosol. and T. Selga, M. Selga, A. Ozoliņa.
Photoacoustic spectra (PAS) were obtained for the cyanobacterium Synechococcus (Anacystis nidulans) cells embedded in isotropic and stretched polyvinyl alcohol films. The polarized radiation with the electric vector changing in 30° intervals with respect to given direction in a sample plane was used. Two cyanobacterium strains, one with very low biliprotein content, second with normal amount of biliproteins were investigated. The polarized absorption and fluorescence spectra were also measured. Conclusions were drawn about the thermal deactivation occurring in differently oriented pools of chromophores and about mutual orientation of their transition moments. Thermal deactivation in carotenoids (Cars) of both strains was different. The ratio of Car thermal deactivation to the thermal deactivation of chlorophyll (Chl) was higher in cyanobacteria with lower content of biliproteins than in the strain with normal amount of these complexes. Hence biliproteins can play the role in excitation energy transfer from Cars to Chls. For complex biological samples, polarized PAS can be a more sensitive method to investigate the directions of the absorption transition moments than the widely used polarized absorption spectra. and A. Planner ... [et al.].
The influence of higher temperatures on the polypeptide composition of thylakoid membranes and pigment-protein complexes, as well as on some parameters of their functional activity, in both acclimated and non-acclimated young pea plants, was studied. Almost the whole set of polypeptides in thylakoid membranes as vvell as in T40 particles was preserved after heat treatment (5 h, 55 °C). During acclimation of the plants to high temperatures a reorganization of the photosynthetic apparatus took plače. In its thylakoids the oligomer/monomer ratio of the photosystem (PS) 2 light- harvesting antenna was more than 50 % higher compared to similar samples of the non-acclimated plants. After both the treatment of 5 h at 55 °C only (non-acclimated plants) and that with step-wise increasing temperatures (acclimated plants), the PSI activity was practically unchanged in all three variants, whereas the PS2 activity decreased more significantly in non-acclimated plants only.
Photon-induced absorbance changes at 830 nm (ΔA830) related to redox transformations of P700, primary electron donor of photosystem 1 (PS1), were examined in barley leaves treated with diuron and methyl viologen. In such leaves, only soluble reductants localized in chloroplast stroma could serve as electron donors for P700+. Δ A830 were induced by 1-min irradiation of leaves with "actinic light" (AL, 700±6 nm) of various irradiances. Two exponentially decaying components with half-times of 2.75 (fast component, relative magnitude of 62 % of ΔA830) and 11.90 s (slow one, 38 % of ΔA830) were distinguished in the kinetics of dark relaxation of ΔA830 after leaf irradiation with saturating AL. The components reflecting P700+ dark reduction in two units of PS1 differed in the rate of electron input from stromal reductants. The decline in AL irradiance reduced steady state δA830 magnitude, which was also accompanied by a decrease in the contribution of fast component to the overall P700+ dark reduction kinetics. The photon-response curves were obtained separately for rapidly and slowly decaying δA830. The values of half-saturating irradiance were 0.106 and 0.035 μmol m-2 s-1 for rapidly and slowly reduced PS1 units, respectively. The ratio of rate constants of P700+ dark reduction for rapidly and slowly reduced PS1 units was 1.4 times higher than the ratio of their half-saturating irradiances thus indicating higher relative antenna size in rapidly reduced PS1 units. The latter finding, taken together with higher relative amount of P700, favours the view that rapidly and slowly reduced PS1 units reflect P700+ reduction by stromal reductants in spatially separated PS1α and PS1β complexes. and E. A. Egorova, N. G. Bukhov.