The study examined photosynthetic efficiency of two barley landraces (cvs. Arabi Abiad and Arabi Aswad) through a prompt fluorescence technique under influence of 14 different abiotic stress factors. The difference in the behavior of photosynthetic parameters under the same stress factor in-between cv. Arabi Abiad and cv. Arabi Aswad indicated different mechanisms of tolerance and strategies for the conversion of light energy into chemical energy for both the landraces. This study confirmed the suitability of some chlorophyll fluorescence parameters as reliable biomarkers for screening the plants at the level of photosynthetic apparatus., H. M. Kalaji, A. Rastogi, M. Živčák, M. Brestic, A. Daszkowska-Golec, K. Sitko, K. Y. Alsharafa, R. Lotfi, P. Stypiński, I. A. Samborska, M. D. Cetner., and Obsahuje bibliografii
In this study, the JIP test was used to assess the drought tolerance of two sweet cherry cultivars (Prunus avium L.) (modern and autochthonous). Plants were exposed to progressive drought by withholding water and their fast (< 1 s) chlorophyll fluorescence kinetics was evaluated. JIP test analysis showed that drought stress caused a greater decrease in performance indices (PIABS and PItotal) in a modern cultivar, as compared to an autochthonous one. Our results suggest that limited reoxidation of primary quinone electron acceptor (QA), higher amount of secondary quinone electron acceptor (QB-) nonreducing reaction centres, or inhibition of the electron transport between QA and QB, decreased more seriously the photosynthetic performance of the modern cultivar. Further, higher positive L- and K-bands observed for the modern cultivar also suggest lower energetic connectivity between PSII units and increased inhibition of oxygen-evolving complex over autochthonous cultivar. Our results suggest that the autochthonous cultivar Crveni hrušt had better photosynthetic performance under drought conditions, compared to the modern cultivar New Star.
The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol-1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol-1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m-2 s-1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m-2 s-1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD730) to the photoinactivation of PS2. and I. Kurasová ... [et al.].
The effect of UV-A radiation (365 nm) and the protective effect of preillumination with red light (RL, 664 nm, 10 min) or with a combination of red and far-red light (FRL, 727 nm, 10 min) on the activity of the PSII as well as the expression levels of selected genes, especially those encoding chloroplast proteins (sAPX, tAPX, CAB1, and D1), were studied in leaves of the 26-d-old hy3 mutant of Arabidopsis thaliana, which is deficient in the phytochrome B apoprotein. The effects were compared with corresponding effects observed in the hy2 mutant of A. thaliana, which is deficient in the phytochrome chromophore. Illumination with UV-A decreased the photosynthetic pigment content, the maximum photochemical quantum yield of PSII (Fv/Fm), and the effective quantum yield of PSII (ΦPSII). The reduction of the Fv/Fm ratio and ΦPSII was more pronounced in the mutants as compared to wild-type plants (WT). The preillumination of the leaves with RL caused a significant reduction in the inhibitory effect of UV-radiation on the PSII activity in the WT plants, but it caused only a small decrease in the hy3 mutant. The preillumination of leaves with RL and FRL combination compensated the protective effect of RL on the UV-induced decrease of the fluorescence parameters in the WT. Such reversibility is typical for involvement of red/far-red reversible phytochromes at low intensity light. The results suggest an important role of red/far-red reversible phytochromes (phytochrome B) in the resistance of PSII to UV-A radiation caused by changes in contents of either carotenoids or other UV-absorbing pigments probably through biosynthesis of these pigments. The data also demonstrated that phytochrome B and other phytochromes can affect the PSII stress resistance by the fast regulation of the expression of genes encoding antioxidant enzymes and transcription factors at the step of gene transcription., V. D. Kreslavski, F.-J. Schmitt, C. Keuer, T. Friedrich, G. N. Shirshikova, S. K. Zharmukhamedov, A. A. Kosobryukhov, S. I. Allakhverdiev., and Seznam literatury
Sensing and classification of drought stress levels are very important to agricultural production. In this work, rice drought stress levels were classified based on the commonly used chlorophyll a fluorescence (ChlF) parameter (Fv/Fm), feature data (induction features), and the whole OJIP induction (induction curve) by using a Support Vector Machine (SVM). The classification accuracies were compared with those obtained by the K-Nearest Neighbors (KNN) and the Ensemble model (Ensemble) correspondingly. The results show that the SVM can be used to classify drought stress levels of rice more accurately compared to the KNN and the Ensemble and the classification accuracy (86.7%) for the induction curve as input is higher than the accuracy (43.9%) with Fv/Fm as input and the accuracy (72.7%) with induction features as input. The results imply that the induction curve carries important information on plant physiology. This work provides a method of determining rice drought stress levels based on ChlF.
Dust deposition on leaf surfaces can impact the growth and physiological traits of plants. We carried out a field experiment to investigate short-term effects of light surface dust on photosynthesis of cotton in the Tarim Basin using chlorophyll fluorescence and gas-exchange techniques. JIP-test analysis of OJIP curves showed that the total performance index for leaves without dust decreased by 32% at noon compared to the morning value. High irradiance at noon reduced actual quantum yield of PSII and increased nonphotochemical quenching for leaves without dust, showing photoinhibition. It suggested that light surface dust alleviated photoinhibition of cotton to high irradiance on a short-term basis. For the leaves without dust, high irradiance induced photoinhibition not only with respect to the photochemistry reactions but the biochemical pathways of CO2 fixation. Mechanisms such as thermal dissipation and enhanced electron flux to PSI protected the photosynthetic apparatus under high irradiance., L. Li, G. Mu., and Obsahuje bibliografii
Primary leaves of young plants of common bean (Phaseolus vulgaris cv. Carioca and Negro Huasteco) and cowpea (Vigna unguiculata Walp cv. Epace 10) were exposed to high irradiance (HI) of 2 000 µmol m-2 s-1 for 10, 20, and 30 min. The initial fluorescence (F0) was nearly constant in response to HI in each genotype except for Carioca. A distinct reduction of maximum fluorescence (Fm) was clearly observed in stressed genotypes of beans after 20 min followed by a slight recovery for the longer stress times. In common bean, the maximum quantum yield (Fv/Fm) was reduced slowly from 10 to 30 min of HI. In cowpea, only a slight reduction of Fv/Fm was observed at 20 min followed by recovery to normal values at 30 min. HI resulted in changes in the photochemical (qP) and non-photochemical (qN) quenching in both species, but to a different extent. In cowpea plants, more efficiency in the use of the absorbed energy under photoinhibitory conditions was related to increase in qP and decrease in qN. In addition, lipid peroxidation changed significantly in common bean genotypes with an evident increase after 20 min of HI. Hence the photosynthetic apparatus of cowpea was more tolerant to HI than that of common bean and the integrity of cowpea cell membranes was apparently maintained under HI. and L. C. S. Ferreira ... [et al.].
Al3+ in combination with kinetin showed more protection against degradation of chlorophyll (Chl) and protein than Al3+ or kinetin alone during dark-induced senescence in wheat primary leaf segments. MV-dependent whole chain electron transport, photosystem (PS) 2 mediated oxygen evolution, and PS1 activities were also delayed to a greater extent. Absorbed excitation energy distribution was more in favour of PS1 in Al3+ plus kinetin-treated leaf thylakoids at 72 h. and D. Subhan, S. D. S. Murthy.
The purpose of the current investigation was to evaluate the influence of antimycin A (AA) as an activator of the alternative respiratory pathway (AP) on photosynthetic pigment composition and functional activity of the photosynthetic apparatus of wheat seedlings (Triticum aestivum L.) under exposure to high temperature as well as their acclimation. Our results indicated that a significant decrease (44-74%) of photosynthetic pigment contents was caused by a long-term exposure to high temperature (42°C), while the short-term exposure resulted in 20-46% decline. However, a combined effect of AA and long-term high temperature reduced the total pigment contents by 28-41%. Our results demonstrated that the reduction of the chlorophyll a/b ratio was less significant under the combined effect of AA and high temperature than that under the stressful condition without AA. We observed that short-term and long-term high temperature modified PSII functionality of the first leaves in wheat seedlings, which was manifested by the low maximal quantum yield of PSII photochemistry, maximum fluorescence yield in the dark-adapted state, and by high minimum fluorescence yield in the dark-adapted state. The quantum yield of PSII photochemistry decreased rapidly by 16-24% under the combination of AA and high temperature. Overall, these results suggest that the activation of the alternative pathway, induced by AA, contributed to the stabilization of the photosynthetic apparatus in wheat seedlings under high temperature., A. Batjuka, N. Škute, A. Petjukevičs., and Obsahuje bibliografii
Chlorophyll a (Chl a) has an asymmetrical molecular organization, which dictates its orientation and the location of the pigment in the mature photosynthetic apparatus. Although Chl a fluorescence (ChlF) is widely accepted as a proxy for plant photosynthetic performance under countless stress conditions and across species, a mechanistic understanding of this causality is missing. Since water plays a much greater role than solvent for the photosynthetic machinery, elucidating its influence on Chl a may explain the reliable reflection of plant stress response in the ChlF signal. We examine the effect of hydration from well-watered to lethal drought on ChlF imagery results across morphologically diverse species to begin testing the impact of molecular scale hydration of Chl a on ChlF. Our results support a conceptual model where water is an integral part of the photosystems' structure and directly influences Chl a behavior leading to changes in the energy partitioning and ultimately in ChlF., C. R. Guadagno, D. P. Beverly, B. E. Ewers., and Obsahuje bibliografické odkazy