Plants differ in how much the response of net photosynthetic rate
(PN) to temperature (T) changes with the T during leaf development, and also in the biochemical basis of such changes in response. The amount of photosynthetic acclimation to T and the components of the photosynthetic system involved were compared in Arabidopsis thaliana and Brassica oleracea to determine how well A. thaliana might serve as a model organism to study the process of photosynthetic acclimation to T. Responses of single-leaf gas exchange and chlorophyll fluorescence to CO2 concentration measured over the range of 10-35 °C for both species grown at 15, 21, and 27 °C were used to determine the T dependencies of maximum rates of carboxylation (VCmax), photosynthetic electron transport (Jmax), triose phosphate utilization rate (TPU), and mesophyll conductance to carbon dioxide (g'm). In A. thaliana, the optimum T of PN at air concentrations of CO2 was unaffected by this range of growth T, and the T dependencies of VCmax, Jmax, and g'm were also unaffected by growth T. There was no evidence of TPU limitation of PN in this species over the range of measurement conditions. In contrast, the optimum T of PN increased with growth T in B. oleracea, and the T dependencies of VCmax, Jmax, and g'm, as well as the T at which TPU limited PN all varied significantly with growth T. Thus B. oleracea had much a larger capacity to acclimate photosynthetically to moderate T than did A. thaliana.
In order to clarify the relationship between chill-induced disturbance in photosynthetic, respiratory electron transport and the metabolism of reactive oxygen species (ROS), leaf gas exchange, chlorophyll fluorescence quenching, respiration, and activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) were investigated in chloroplasts and mitochondria of cucumber (Cucumis sativus) leaves subjected to a chill (8 °C) for 4 d. Chilling decreased net photosynthetic rate (PN) and quantum efficiency of photosystem 2 (ΦPS2), but increased the ratio of ΦPS2 to the quantum efficiency of CO2 fixation (ΦCO2) and non-photochemical quenching (NPQ) in cucumber leaves. While chilling inhibited the activity of cytochrome respiration pathway, it induced an increase of alternative respiration pathway activity and the reduction level of Q-pool. Chilling also significantly increased O2* production rate, H2O2 content, and SOD and APX activities in chloroplasts and mitochondria. There was a more significant increase in SOD and APX activities in chloroplasts than in mitochondria with the increase of membrane-bound Fe-SOD and tAPX in chloroplasts being more significant than other isoenzymes. Taken together, chilling inhibited PN and cytochrome respiratory pathway but enhanced the photosynthetic electron flux to O2 and over-reduction of respiratory electron transport chain, resulting in ROS accumulation in cucumber leaves. Meanwhile, chilling resulted in an enhancement of the protective mechanisms such as thermal dissipation, alternative respiratory pathway, and ROS-scavenging mechanisms (SODs and APXs) in chloroplasts and mitochondria. and W. H. Hu ... [et al.].
Effíciency of the energy transformation for CO2 fixation (E), and kinetics of the initial 02-mediated electron transport of Spimlina platemis (Gom.) Geitl. and Chlorella vulgaris Beijerinck cells were measured after adaptation to various growth irradiances (7) by means of the delayed fluorescence (DF) induction curves. Maxima of the membrane potential expenses during induction period were observed at I half saturating oxygen evolution; they were shifted according to growth 1 remaining higher in Spirulina than in Chlorella. The alterations of absorbance and fluorescence spectra at 25 oC after adaptation to / demonstrated changes in composition of pigments of algae, created to compensate for the imbalance in radiation absorption between the two photosystems. For Spirulina cells, the value of E was higher after growing under low /, or under blue radiation absorbed mainly by photosystem (PS) 1 (400-500 nm) with excitation by yellow (570 nm) radiation. For Chlorella cells, it was also higher after growing under low I. Under such conditions the half-rise time for DP-phase of DF induction curve decreased, which reflected an acceleration of kinetics of the initial electron transport between photosystems. An opposite situation was observed with Spirulina cells grown under high I or yellow radiation, and Chlorella cells from high I. Enhancement of effective PS2/PS1 ratio associated with decrease of reaction centre (RC) 2/RCl stoichiometry may be a cause of the increase of E and high membrane energization under saturating I in algae adapted to low 1.
Photosynthetic responses of potato (Solanum tuberosum L. cv. Chunzao) were examined during potato virus Y (PVYNTN) infection. PVYNTN infection significantly reduced net photosynthetic rate and stomatal conductance, but had little influence on intercellular CO2 concentration. As the disease developed, the maximum carboxylation velocity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the maximum electron transport rate contributing to ribulose-1,5-bisphosphate regeneration gradually decreased, followed by substantial reductions in the relative quantum efficiency of photosystem 2 (PS2) electron transport, the efficiency of excitation energy capture by open PS2 reaction centres, and photochemical quenching, but not in sustained photoinhibition. Thus PVYNTN depressed photosynthesis mainly by interfering with the enzymatic processes in the Calvin cycle which resulted in a down-regulation of electron transport. and Y. H. Zhou ... [et al.].
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.].
We investigated the effect of moderate Cu2+ and Cd2+ stress by applying chlorophyll (Chl) fluorescence and P700 absorbance measurements to monitor the photosynthetic electron transport activity of 3-week-old Pisum sativum L. cv. Petit Provençal plants grown in a modified Hoagland solution containing 50 μM CuSO4 or 5 μM CdCl2. Both heavy metals caused a slight inhibition in PSII photochemistry as indicated by the decrease in the effective quantum efficiency of PSII (ΦPSII), the maximum electron transport capacity (ETRmax), and the maximum quantum yield for electron transport (α). PSI photochemistry was also affected by these heavy metals. Cu2+ and Cd2+ decreased the quantum efficiency of PSI (ΦPSI) as well as the number of electrons in the intersystem chain, and the Cu2+ treatment significantly reduced the number of electrons from stromal donors available for PSI. These results indicate that PSII and PSI photochemistry of pea plants are both sensitive to moderate Cu2+ and Cd2+ stress, which in turn is easily detected and monitored by Chl fluorescence and P700 absorbance measurements. Therefore, monitoring the photochemistry of pea plants with these noninvasive, yet sensitive techniques offers a promising strategy to study heavy metal toxicity in the environment., B. Wodala ... [et al.]., and Obsahuje bibliografii
Using EPR spectroscopy it was found that CdCl2 and HgCl2 interact (1) with the intermediates Z./D., i.e. with the tyrosine radicals on the donor side of photosystem (PS) 2 situated in the 161st position in D1 and D2 proteins; (2) with the primary donor of PS1 (P700) whereby the oxidation of chlorophyll (Chl) a dimer in the reaction centre of PS1 occurs yet in the dark; (3) with the manganese cluster which is situated in the oxygen evolving complex. Due to these interactions of investigated metal chlorides with the photosynthetic apparatus, the interruption of the photosynthetic electron transport through photosynthetic centres occurs. Monitoring of time dependence of EPR signal I of chloroplasts treated with CdCl2 or HgCl2 after switching off the light suggests that all mechanisms, i.e. direct, cyclic, and non-cyclic reductions of P700+ are damaged. The formation of complexes between mercury or cadmium ions and amino acid residues constituting photosynthetic peptides was suggested as possible mechanism of their inhibitory action. The higher HgCl2 efficiency in comparison with that of CdCl2 was explained by higher ability of mercury ions to form complexes with amino acids, what was demonstrated by their apparent binding constants: K = 10 200 M-1 for Hg2+ ions, and K = 3 700 M-1 for Cd2+ ions. and F. Šršeň, K. Kráľová.
The photosynthetic response of three Arachis hypogaea L. cultivars (57-422, 73-30, and GC 8-35) grown for two months was measured under water available conditions, severe water stress, and 24, 72, and 93 h following re-watering. At the end of the drying cycle, all the cultivars reached dehydration, relative water content (RWC) ranging between 40 and 50 %. During dehydration, leaf stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) decreased more in cvs. 57-422 and GC 8-35 than in 73-30. Instantaneous water use efficiency (WUEi) and photosynthetic capacity (Pmax) decreased mostly in cv. GC 8-35. Except in cv. GC 8-35, the activity of photosystem 1 (PS1) was only slightly affected. PS2 and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) were the main targets of water stress. After re-watering, cvs. 73-30 and GC 8-35 rapidly regained gs, E, and PN activities. Twenty-four hours after re-watering, the electron transport rates and RuBPCO activity strongly increased. PN and Pmax fully recovered later. Considering the different photosynthetic responses of the studied genotype, a general characterisation of the interaction between water stress and this metabolism is presented. and J. A. Lauriano ... [et al.].
The distribution of rare earth elements (REEs) in the fern Dicranopteris dichotoma Bernh plants from a light rare earth elements mine (LRM) and a non-mining (NM) area in Longnan county of Jiangxi province, China were investigated by means of inductively coupled plasma-mass spectrometry, transmission electron microscopy, and energy-dispersive X-ray microanalysis. The photosynthetic characteristics of D. dichotoma were studied by chlorophyll (Chl) a fluorescence kinetics. Contents of REEs in the lamina and the root of D. dichotoma were higher than those in soils, and were mainly distributed in lamina. A part of them was found in the chloroplast. By comparing with D. dichotoma from NM area, the efficiency of photosystem 2 photochemistry and electron transport rate were significantly enhanced in lamina of the plant from LRM because most of REEs deposits were distributed along cell wall, in vacuole, and in chloroplast. High contents of REEs in lamina did not decrease the photosynthetic activities in LRM plants of D. dichotoma. Besides, D. dichotoma could change its β-carotene content to avoid the damaging effect of high REEs content. and L. F. Wang ... [et al.].