The influence of calcium channel blockers and ionophore on Cu2+-induced changes of the photosynthetic activity of runner bean plants (Phaseolus coccineus L.) was investigated. Excess Cu2+ was applied to leaves by injection or via the roots to examine a short/local or a long time/systemic effect of this metal, respectively. The changes in fluorescence parameters indicated that the mechanism of toxic action of Cu2+ ions on the photosynthetic apparatus was only partially connected with Ca2+ or Ca2+ channels. In young plants Ca2+ diminished especially photochemical and nonphotochemical dissipative processes induced by short- and long-term influence of excess Cu2+. Blocking of Ca2+ channels did not change direct Cu2+ action on the photosynthetic activity, however, their opening distinctly intensified the inhibitory effect of the metal. After a longer accumulation peri od the effect of Cu2+ ions did not change significantly due to modified Ca2+ penetration through membranes (except that caused by La3+). Copper directly introduced into older leaves diminished only at its highest concentration the activity both of the donor and acceptor sides of photosystem 2 (PS2) connected with Rfd decrease and increase of LNU. A similar effect was observed also after a long-term Cu2+ action, but disturbances on the acceptor side of PS2 were observed only at a higher Ca2+ content in the nutrient solution. Ca2+ ions, particularly after openning of channels, intensified direct inhibitory Cu2+ action on the photosynthetic activity expressed by decreased values of Fv/F0 and Rfd. Lanthanum and verapamil, at a lower Ca2+ content in the medium, decreased the photosynthetic activity of Cu2+-treated plants. This effect was also seen after additional Ca2+ supply to the leaves. and W. Maksymiec, T. Baszyński.
Previous evidence has demonstrated that vertical leaves of Styrax camporum, a woody shrub from the Brazilian savanna, have a higher net photosynthetic rate (PN) compared with horizontal leaves, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. In the present study, leaf temperature (T leaf), gas exchange and chlorophyll (Chl) a fluorescence with light interception on adaxial and also on abaxial surfaces of vertical and horizontal mature fully-expanded leaves subjected to water deficit (WD) were measured. Similar
gas-exchange and fluorescence values were found when the leaves were measured with light interception on the respective surfaces of horizontal and vertical leaves. WD reduced N values measured with light interception on leaf surfaces of both leaf types, but the effective quantum yield of PSII (ΦPSII) and the apparent electron transport rate (ETR) were reduced only when the leaves were measured with light interception on the adaxial surface. WD did not decrease the maximum quantum yield of PSII (Fv/Fm) or increase T leaf, even at the peak of WD stress. Vertical leaf orientation in S. camporum is not related to leaf heat avoidance. In addition, the similar P N values and the lack of higher values of ΦPSII and ETR in vertical compared with horizontal leaves measured with light interception by each of the leaf surfaces suggests that the vertical leaf position is not related to photoprotection in this species, even when subjected to drought conditions. The exclusion of this photoprotective role could raise the alternative hypothesis that diverse leaf angles sustain whole plant light interception efficiency increased in this species., A. M. Feistler, G. Habermann., and Obsahuje bibliografii
Based on the examination and quantitative comparison of the approaches used to assess the energy partitioning in photosystem II, the unified method was proposed to calculate the contribution of the components of nonphotochemical quenching. and D. Kornyeyev, C. R. Guadagno, N. D’Ambrosio.
Globally, water deficit is one of the major constraints in chickpea (Cicer arietinum L.) production due to substantial reduction in photosynthesis. Photorespiration often enhances under stress thereby protecting the photosynthetic apparatus from photoinhibition. Application of bioregulators is an alternative to counter adverse effects of water stress. Thus, in order to analyze the role of bioregulators in protecting the photosynthetic machinery under water stress, we performed an experiment with two contrasting chickpea varieties, i.e., Pusa 362 (Desi type) and Pusa 1108 (Kabuli type). Water deficit stress was imposed at the vegetative stage by withholding water. Just prior to exposure to water stress, plants were pretreated with thiourea (1,000 mg L-1), benzyladenine (40 mg L-1), and thidiazuron (10 mg L-1). Imposed water deficit decreased relative water content (RWC), photosynthetic rate (P N), quantum efficiency of PSII (Fv/Fm), and enhanced lipid peroxidation (LPO). However, bioregulator application maintained higher RWC, P N, Fv/Fm, and lowered LPO under water stress. Expression of Rubisco large subunit gene (RbcL) was low under water stress both in the Kabuli and Desi type. However, bioregulators strongly induced its expression. Although poor expression of two important photorespiratory genes, i.e., glycolate oxidase and glycine decarboxylase H subunit, was observed in Desi chickpea under imposed stress, bioregulators in general and cytokinins in particular strongly induced their expression. This depicts that the application of bioregulators protected the photosynthetic machinery by inducing the expression of RbcL and photorespiratory genes during water deficit stress., T. V. Vineeth, P. Kumar, G. K. Krishna., and Obsahuje seznam literatury
The seeds of soybean cv. Aldana and spring wheat cv. Torka were soaked for 24 h in solution of zearalenone [ZEN, 2,4-dihydroxy-6-(10-hydroxy-6-oxo-trans-1-undecenyl)-benzonic acid lactone, 4 mg dm-3] and then they were sown in the pot experiment in an open vegetation hall. The after-effects of ZEN on growth of plants, net photosynthetic (PN) and transpiration (E) rates, stomatal conductance (gs), photochemical efficiency of photosystem II (PSII) and on final seeds yield, were determined. A significant increase of seeds yield was revealed in plants of both cultivars i.e. by 22% and 19% of seed (grain) number and by 28 and 24% of seed (grain) mass, in soybean and in wheat, respectively. The photosynthetic rate (PN) was stimulated during the juvenile and final phase by about 13.6% (average) in soybean plants. During other developmental stages, assimilation of CO2 was retarded. The response of CO2 assimilation in wheat plants was less pronounced as compared to that in soybean, but an increase of PN by over 24% near the final stage of development was observed. The quantum yield of PSII electron transport (ΦPSII) in soybean plants was changed after the treatment of seeds by ZEN similarly as for the rate of CO2, whereas in wheat it continued to gradually increase i.e. during the whole growth period. Changes of ΦPSII both in soybean and in wheat plants, as the response to ZEN treatment, were accompanied with an increase in the efficiency of changes occurring within the antenna (Fv'/Fm') as well as within centres of photochemical reactions (qp). The conclusion is that ZEN can affect plant growth and development in many ways, as well as in the status and functioning of the photosynthetical apparatus. Some of the effects can be very longlasting, as e.g. stimulation of production of seed yield in response to treatment of seeds with this substance. and J. Kościelniak ... [et al.].
Seedling performance may determine plant distribution, especially in water-limited environments. Plants of Caragana korshinskii commonly grow in arid and semiarid areas in northwestern China, and endure water shortage in various ways, but little is known about their performance when water shortage occurs at early growth stages. The water relations, photosynthetic activity, chlorophyll (Chl) content and proline accumulation were determined in 1-year-old seedlings growing in a 1:1 mixture of Loess soil and Perlite and subjected to (1) a water deficit for 20 days and (2) kept adequately watered throughout. The water deficit induced low (-6.1 MPa) predawn leaf water potentials (LWP), but did not induce any leaf abscission. Stomatal conductance (gs), leaf transpiration rate (E), and net photosynthetic rate (PN) decreased immediately following the imposition of the water deficit, while the maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm) and the effective quantum yield of PSII (ΦPSII) decreased 15 days later. An early and rapid decrease in gs, reduced E, increased Chl (a+b) loss, increased the apparent rate of photochemical transport of electrons through PSII (ETR)/PN, as well as a gradual increase in non-photochemical quenching of fluorescence (NPQ) and proline may have contributed to preventing ΦPSII from photodamage. C. korshinskii seedlings used a stress-tolerance strategy, with leaf maintenance providing a clear selective advantage, considering the occasional rainfall events during the growing season. and X. W. Fang ... [et al.].
In seedlings of Vigna radiata (L.) R. Wilczek cultivars ADT-1 and CO-5 exposed to acidic showers (H2SO4 : HNO3 : HCl, 4 : 2 : 1, v/v) of different pH (7.0, 5.5, 4.0, and 2.5) for 10 d, net CO2 uptake and stomatal conductance were reduced. The chlorophyll (Chl) a and b contents were reduced but the carotenoid (Car) content increased. In vivo Chl a fluorescence patterns of both the cultivars were altered. No significant change in photosystem (PS) 1 activity was observed except at pH 2.5 where an inhibition was evident. By contrast, PS2 activities declined rapidly with increasing acidity. The room temperature absorption spectra of isolated chloroplasts showed very little changes. SDS-PAGE analysis revealed depletion of 23, 33, and 55 kDa polypeptides. Cultivar CO-5 was more sensitive to acidic rain than cv. ADT-1. and G. Kumaravelu, M. P. Ramanujam.
The effects of growth temperature on changes in net photosynthetic rate (PN) and the chlorophyll fluorescence induction parameter Fv/Fm were investigated after cold stress in inbred maize lines with different degrees of cold tolerance. There was no significant difference between lines grown at optimum temperatures of 25/23 and 20/18 °C as regards PN and Fv/Fm determined at the growth temperature, but these parameters were lower for plants grown at a suboptimum temperature of 15/13 °C. After cold treatment, the decrease in PN was more pronounced in chilling-sensitive lines. The higher the growth temperature was, the more pronounced decrease occurred in PN and Fv/Fm. Thus at low growth temperature both damaging and adaptive processes occur. and T. Janda ... [et al.].
Photosynthesis, chlorophyll (Chl) a fluorescence, and nitrogen metabolism of hawthorn (Crataegus pinnatifida Bge.), subjected to exogenous L-glutamic acid (GLA) (200 mg l-1, 400 mg l-1, and 800 mg l-1) that possibly affect secondary metabolic regulation, were measured. The results indicated that photosynthetic and fluorescence characteristics of hawthorn exhibited positive responses to the application of GLA. Different concentrations of GLA caused an increase in Chl content, net photosynthetic rate
(PN) and stomatal conductance (g s) as well as transpiration rate (E), and improved the carboxylation efficiency (CE), apparent quantum yield (AQY) and maximum carboxylation velocity of Rubisco (Vcmax). Application of GLA could also enhance the maximum ratio of quantum yields of photochemical and concurrent non-photochemical processes in PSII (Fv/F0), the maximal quantum yield of PSII (Fv/Fm), the probability that an absorbed photon will move an electron into the electron transport chain beyond QA (ΦEo) as well as the performance index on absorption basis (PIABS), but decreased the intercellular CO2 concentration
(Ci) and the minimal fluorescence (F0). Application of GLA also induced an increase in nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2) activities, and increased the soluble protein content, leaf nitrogen (N) content and N accumulation in leaves as well as the plant biomass. However, the effects were different among different concentrations of GLA, and 800 mg l-1 GLA was better. This finding suggested that application of GLA is recommended to improve the photosynthetic capacity by increasing the light energy conversion and CO2 transfer as well as the photochemical efficiency of PSII, and enhanced the nitrogen metabolism and growth and development of plants. and C. YU ... [et al.].
Over last decades, several studies have been focused on
short-term high light stress in lichens under laboratory conditions. Such studies reported a strong photoinhibition of photosynthesis accompanied by a partial photodestruction of PSII, involvement of photoprotective mechanisms, and resynthetic processes into gradual recovery. In our paper, we applied medium [800 μmol(photon) m-2 s-1] light stress to induce negative changes in PSII funcioning as well as pigment and glutathione (GSH) content in two Antarctic fruticose lichen species. Chlorophyll (Chl) fluorescence parameters, such as potential and effective quantum yield of photosynthetic processes and fast transients (OJIP) recorded during high light exposition and recovery, revealed that Usnea antarctica was less susceptible to photoinhibition than U. aurantiaco-atra. This might be supported by a more pronounced high light-induced reduction in Chl a and b contents in U. aurantiaco-atra compared with U. antarctica. In both experimental species, total GSH showed an initial increase during the first 30-40 min of high light treatment followed by a decrease (60 min) and an increase during dark recovery. Full GSH recovery, however, was not finished in U. aurantiaco-atra even after 5 h indicating lower capacity of photoprotective mechanisms in the species. OJIP curves showed high light-induced decrease in both species, however, the recovery of the OJIPs shape to pre-photoinhibitory values was faster and more apparent in U. antarctica than in U. aurantiaco-atra. The results are discussed in terms of sensitivity of the two species to photoinhibition and their photosynthetic performance in natural environment., K. Balarinová, M. Barták, J. Hazdrová, J. Hájek, J. Jílková., and Obsahuje bibliografii