In the past decades, it has become clear that superoxide radical (O2 .-) can be generated from photosystem II (PSII) during photosynthesis. Depending on the extent of its accumulation, O2 .- plays an important role in plant physiology and pathology. The photoinhibition/repair cycle is a typical process in PSII which is mainly responsible for the survival of plants under the photoinihibition condition. It is therefore of significant importance to determine O2 .- production in this cycle, and then explore how O2 .- is controlled by PSII within a normal physiological level. With this in mind, we herein investigate the variation of the O2 .- levels in PSII under Mn-depleted and photoactivated conditions mimicking the photoinhibition/repair cycle in vitro. The effect of intrinsic SOD-like component on the O2 .- levels was also studied. Results show that PSII has the ability to regulate the O2 .- levels in these two processes by simultaneously modulating the O2 .- generation activity and intrinsic SOD-like activity. This finding could shed new lights on the photoprotective property of PSII against O2 .- and other reactive oxygen species. and Y. G. Song ... [et al.].
Leaf stomatal conductance (gs), transpiration rate (E), and light-saturated net photosynthetic rate (PNmax) at three developmental stages (tillering stage, jointing-booting stage, and milking stage) and leaf total nitrogen concentration (LTNC) and δ13C value at milking stage were measured for a conventional rice line (Minghui 63) and its corresponding Bacillus thuringiensis (Bt)-gene [cry1A
(b and c)] introduced line (Bt line) under three fertilizer levels. Compared to conventional line, Bt line showed lower gs, which was associated with lower P Nmax and E, but instantaneous water-use efficiency (WUE), measured as the ratio of PNmax to E, was higher in the Bt line than in the conventional line, particularly in the jointing-booting stage. However, δ13C values were not significantly different across treatments, suggesting that intrinsic water-use efficiency (WUEin) might be indistinguishable between Bt and conventional lines. LTNC was higher but PNmax was lower in Bt line compared to conventional line, resulting in significantly lower photosynthetic nitrogen-use efficiency (PNUE). This might result from the additional cost of producing Bt protein in the Bt line due to the effect of competing nitrogen with photosynthetic machinery. Bt-gene introduction and expression does not significantly change WUEin but may significantly decrease leaf PNUE. Thus we suggest that Bt rice should be carefully examined in relation to environmental risks (e.g. water-body pollution) before planting commercially. and R. Q. Guo ... [et al.].
Calligonum caput-medusae is known to grow well when irrigated with water containing NaCl. The aim of this study was to investigate ecophysiological responses of C. caput-medusae to different NaCl concentrations. In our study, we examined the effect of 0, 50, 100, 200, and 400 mM NaCl. Our results demonstrated that maximum seedling growth occurred at 50 mM NaCl. Photosynthetic parameters, such as the photosynthetic pigment content and gas exchange parameters, correlated with growth response. High salinity (≥ 100 mM NaCl) resulted in a significant reduction of the plant growth. Similarly, marked declines in the pigment content, maximal efficiency of PSII photochemistry, net photosynthetic rate, transpiration rate, and stomatal conductance were also detected. However, intercellular CO2 concentration showed a biphasic response, decreasing with water containing less than 200 mM NaCl and increasing with NaCl concentration up to 400 mM. Water-use efficiency and intrinsic water-use efficiency exhibited the opposite response. The reduction of photosynthesis at the high NaCl concentration could be caused by nonstomatal factors. High salinity led also to a decrease in the relative water content and water potential. Correspondingly, an accumulation of soluble sugars and proline was also observed. Na+ and
Cl- concentrations increased in all tissues and K+ concentrations were maintained high during exposure to NaCl compared with the control. High salinity caused oxidative stress, which was evidenced by high malondialdehyde and hydrogen peroxide contents. In order to cope with oxidative stress, the activity of antioxidative enzymes increased to maximum after 50 mM NaCl treatment. The data reported in this study indicate that C. caput-medusae can be utilized in mild salinity-prone environments., Y. Lu, J.-Q. Lei, F.-J. Zeng, B. Zhang, G.-J. Liu, B. Liu, X.-Y. Li., and Obsahuje bibliografii
Primary events in the photoinactivation of photosystem (PS) 2 membrane fragments by low and high "visible light" irradiance (17 to 1 700 W m'2) and UV-B irradiation (90 W m'2) were analyzed by measuiing flash-induced absorption changes at 830 nm that reflect transient formation of P680+ and Pheo*. Following results were obtained: (7) Irradiation with "visible light" under aerobic conditions affects the PS 2 electron transfer at two different sites: {a) within the PS 2 reaction centre by impairment of primary charge separation (P680 Pheo Qa P680+Pheo'QA), and (7>) on tiie PS 2 donor side by inhibition of the electron transfer from to P680+. (2) In PS 2 membrane fragments with intact 02-evolution the primary charge separation is the most sensitive target of the photoinhibition by "visible light". The UV-B irradiation, however, affects predominantly the oxygen-evolving complex or the electron transfer from the oxygen-evolving complex to Yz®’'. (5) Susceptibility of the P680 Yz segment to photoinhibition by "visible light" is drastically increased in the samples with lifetimes of Yz°* and P680+ having been signifícantly prolonged by Tris- treatment. Susceptibility of the primaiy charge separation to photoinhibition, however, is not dependent on the lifetimes of P680+ and Yz®’'.
Pulses of rainfall are particularly pivotal in controlling plant physiological processes in ecosystems controlled by limited water, and the response of desert plants to rainfall is a key to understanding the responses of desert ecosystems to global climatic change. We used a portable photosynthesis system to measure the responses of the diurnal course of photosynthesis, light-response curves, and CO2-response curves of two desert shrubs (Nitraria sphaerocarpa Maxim. and Calligonum mongolicum Turcz) to a rainfall pulse in a desert-oasis ecotone in northwestern China. The photosynthetic parameters, light- and CO2-response curves differed significantly before and after the rainfall pulse. Their maximum net photosynthetic rate (PN) values were 23.27 and 32.92 μmol(CO2) m-2 s-1 for N. sphaerocarpa and C. mongolicum, respectively, with corresponding maximum stomatal conductance (gs) values of 0.47 and 0.39 mol(H2O) m-2 s-1. The PN of N. sphaerocarpa after the rainfall was 1.65 to 1.75 times the value before rainfall, whereas those of C. mongolicum increased to approximately 2 times the prerainfall value, demonstrating the importance of the desert plants response by improving their assimilation rate to precipitation patterns under a future climate., B. Liu, W. Z. Zhao, Z. J. Wen., and Obsahuje bibliografii