With the aim to contribute to the elucidation of the role of phytohormones in response of plants to adverse environmental conditions, seedlings of Phaseolus vulgaris, Nicotiana tabacum, Beta vulgaris, and Zea mays were supplied with water, 100 µM abscisic acid (ABA), or 10 µM N6-benzyladenine (BA) immediately before imposition of water stress (WS). In all four species, contents of chlorophylls (Chls) and carotenoids were markedly decreased during WS and after rehydration only in plants pre-treated with water but not in those pre-treated with ABA or BA. Contents of pigments of xanthophyll cycle increased during WS more in plants pre-treated with ABA or BA than in those pre-treated with water, but the degree of their de-epoxidation was highest in the later. Similarly, the efficiency of photosystem 2, determined as variable to maximal Chl fluorescence ratio, was not markedly decreased in bean plants pre-treated with ABA or BA in contrast to those pre-treated with water. The imposed WS was not severe enough to damage chloroplast ultrastructure. However, different changes in a size of starch inclusions were observed. In bean plants, the amount of starch increased considerably in plants pre-treated with water, while it decreased in BA pre-treated plants and no change was found in ABA pre-treated ones. The starch content declined under WS in sugar beet and tobacco plants but only moderate changes were found in ABA or BA pre-treated plants. Thus the application of BA and especially of ABA reduced the negative effects of subsequent WS. and D. Haisel ... [et al.].
Pigment contents of chloroplasts and net photosynthetic rate were dramatically reduced in maize leaves suffering from iron deficiency. However, the reduction in photosynthesis was probably not caused by decreased contents of chlorophylls and carotenoids and by photon absorption; the primary limiting factor for photosynthesis may rather be the decrease of electron transport activity in photosystem 1. Iron-deficient leaves suffered serious acceptor-side photoinhibition, and more than 60 % of absorbed photons were dissipated, while less than 40 % was used in photochemical reaction. Thermal energy dissipation depending on xanthophyll cycle and D1 protein turnover was enhanced when acceptor-side photoinhibition occurred in iron-deficient maize leaves. and Chuang-Dao Jiang, Hui-Yuan Gao, Qi Zou.
In this study, the effects of lanthanum were investigated on contents of pigments, chlorophyll (Chl) fluorescence, antioxidative enzymes, and biomass of maize seedlings under salt stress. The results showed that salt stress significantly decreased the contents of Chl and carotenoids, maximum photochemical efficiency of PSII (Fv/Fm), photochemical quenching (qP), and quantum efficiency of PSII photochemistry (ΦPSII), net photosynthetic rate (P N), and biomass. Salt stress increased nonphotochemical quenching (qN), the activities of ascorbate peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and the contents of malondialdehyde and hydrogen peroxide compared with control. Pretreatment with lanthanum prior to salt stress significantly enhanced the contents of Chl and carotenoids, Fv/Fm, qP, qN, ΦPSII, P N, biomass, and activities of the above antioxidant enzymes compared with the salt-stressed plants. Pretreatment with lanthanum also significantly reduced the contents of malondialdehyde and hydrogen peroxide induced by salt stress. Our results suggested that lanthanum can improve salt tolerance of maize seedlings by enhancing the function of photosynthetic apparatus and antioxidant capacity., R. Q. Liu, X. J. Xu, S. Wang, C. J. Shan., and Obsahuje seznam literatury
The quantitative changes of chloroplast ultrastructure and dimensions in mesophyll (MC) and bundle sheath (BSC) cells, associated with the onset of leaf senescence, were followed along the developmental leaf blade gradient of the third leaf of maize (Zea mays L.). To ascertain whether the rapidity of structural changes associated with the transition of chloroplasts from mature to senescent state is a heritable trait, the parental and the first filial generations of plants were used. The heterogeneity of leaf blade, associated with the development of maize leaf (with the oldest regions at the apex and the youngest ones at the base) was clearly discernible in the ultrastructure and dimensions of chloroplasts; however, there were differences in the actual pattern of chloroplast development between both genotypes as well as between both cell types examined. While the course of MC chloroplasts' development at the onset of leaf senescence in maize hybrid followed that of its parent rather well, this did not apply for the BSC chloroplasts. In this case, each genotype was characterized by its own distinguishable developmental pattern, particularly as regards the accumulation of starch inclusions and the associated changes of the size and shape of BSC chloroplasts. and A. Vičánková, D. Holá, J. Kutík.
Maize plants of CPB2 and CPB8 hybrids were kept under water deficit for 22 d. In the CPB8 hybrid, leaf rolling initiated at the 9th d of water deficit period, while in CPB2 hybrid it was at the 15th d. Both hybrids showed leaf rolling initiation at the same leaf water potential, ΨW of -0.480±0.095 MPa. At leaf rolling initiation, the leaf osmotic potential, ΨS was -0.730±0.085 MPa in CPB8 and 0.630±0.110 MPa in CPB2. The leaf temperature and stomatal conductance were higher in CPB8 than in CPB2. Values of leaf ΨW, ribulose-1,5-bisphosphate carboxylase activity, chlorophyll content, and specific leaf area were similar in both hybrids. Phosphoenolpyruvate carboxylase activity and protein content were lower in the CPB2 hybrid than in CPB8. In both hybrids leaf rolling initiation was associated with: (1) higher leaf temperature, with leaf rolling effect related to leaf temperature reduction, and (2) lower leaf ΨS, related to osmotic adjustment as an additional component of drought-tolerance strategy. and D. Fernandez, M. Castrillo.
The herbicides diuron, fluridone, or sulcotrione differently reduced chlorophyll (Chl) and carotenoid (Car) contents. Four days after herbicide treatment, application of sulcotrione resulted in a Chl/Car ratio of 5.88, similar as in untreated controls; diuron resulted in ratio of 5.24, while fluridone induced a greater diminution in Car contents and yielded a final ratio of 7.02. Sulcotrione induced a more rapid decrease than fluridone did in the quantum yield of photosystem 2 (PS2) as monitored by Chl fluorescence. Measurements of DPIP reduction with isolated thylakoids indicated that sulcotrione was a more effective inhibitor of the Hill reaction in cucumber, a herbicide sensitive species, than in maize, a herbicide-insensitive species. These results are consistent with the view that inhibition of electron transport via reduction in plastoquinone contents in plants leads to the major herbicidal effect of sulcotrione in mature green tissues. and J.-S. Kim ... [et al.].
Significant differences in net photosynthetic rate (PN) of leaves between two maize (Zea mays L.) strains (Shuang 105 and 40×44) grown in the field were observed. At several growth stages, PN of 40×44 was higher than that of Shuang 105 (from 10.3 to 32.5 %). Moreover, the strain 40×44 had a higher plant height, larger leaf area, lower chlorophyll content, and higher photochemical efficiency of photosystem 2 (PS2) (Fv/Fm and ΔF/Fm') than strain Shuang 105. Shuang 105, which showed lower PN, had lower stomatal conductances (gs) but slightly higher intercellular CO2 concentrations (Ci) than those of 40×44. Hence the differences in
PN between the two strains did not result from the difference in gs, but probably from that in light reaction system. and Hua Jiang, Da-Quan Xu.
F0 fluorescence and thermoluminescence (TL) were recorded simultaneously on various dark-adapted leaf samples. Above 40 °C, a sharp peak of TL coincided with the onset of the heat-induced F0 rise. It results from a back-transfer of an electron from the secondary QB- to the primary acceptor QA of photosystem 2, followed by a luminescence-emitting recombination with Tyr-D1. This demonstrates that the critical temperature at which the F0 starts rising also corresponds to a shift towards the left of the QA↔QB- equilibrium.
We compared responses of maize, tomato, and bean plants to water stress. Maize reached a severe water deficit (leaf water potential -1.90 MPa) in a longer period of time as compared with tomato and bean plants. Maize stomatal conductance (gs) decreased at mild water deficit. gs of tomato and bean decreased gradually and did not reach values as low as in maize. The protein content was maintained in maize and decreased at low water potential (ψw); in tomato it fluctuated and also decreased at low ψw; in bean it gradually decreased. Ribulose-1,5-bisphosphate carboxylase/oxygenase activity remained high at mild and moderate stress in maize and tomato plants; in bean it remained high only at mild stress. and M. Castrillo ... [et al.].
Environmental factors that influence stomatal conductance (gs) interact through a complex network of signal transduction and have therefore highly interdependent effect.
In the present study we examined how plant water status affects stomatal sensitivity to the change of CO2 concentration ([CO2]). We investigated the short-term dynamic of stomatal response to a sudden [CO2] increase (from 400 to 700 µmol(CO2) mol-1) in maize supplied with different amounts of water (resulting ψw = -0.35, -0.52 and -0.75 MPa). Gas exchange measurements were performed in short logging intervals and the response was monitored under two different levels of water vapour pressure deficit (VPD) of 1 and 2 kPa in order to observe the impact of air humidity. Generalized logistic curves were fitted to standardized stomatal response data, which enabled us to objectively estimate the level (relative decrease of g s) and the dynamics of the response.
Soil water stress and high VPD significantly decreased relative stomatal closure in response to [CO2] rise, but simultaneously accelerated stomatal response to [CO2], as revealed by shorter half life (t1/2). VPD significantly affected the response of well-watered plants. In contrast, a fast stomatal reaction of water-deprived plants was predetermined by a low xylem water potential (ψw) of the leaf and the influence of air humidity was minor. and J. Hladnik ... [et al.].