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Combined Effect of Water Deficit and Salt Stress on the Structure of Mesophyll Cells in Wheat Seedlings

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Effect of Salt Stress on Plants | Genetics

A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the 'Kautsky effect') in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.

Effect of salt stress on growth andbiochemical parameters of Pisum sativum L.

N2 - A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the 'Kautsky effect') in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.

Effect of salt and water stress on fruit quality, ..

AB - A comparison of the effects of ionic stress and an uncoupler on long-term fluorescence transients (the 'Kautsky effect') in the green alga Dunaliella tertiolecta indicated that the large quenching induced by ionic stress was caused by a pH gradient across the thylakoid membrane. This possiblity was given support by the increase in the slow phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in algae subjected to ionic stress. Low-temperature fluorescence emission spectra indicated that salt stress enhanced photosystem-I emission in the dark, and a comparison of simultaneous emissions at 695 and 720 nm at room temperature indicated a further increase in photosystem-I emission during the fluorescence transients. Taken together with the decrease in the fast phase of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-induced fluorescence relaxation in stressed algae, our results indicate that ionic stress stimulates cyclic electron flow, and that non-cyclic flow is inhibited. The effect of sucrose-induced osmotic stress was similar to, but less marked than, the effects of NaCl and KCl; the effect of decreasing the external salinity was small.

The purpose of the work was to assess the combined effect of drought and salinity (50, 100, 200 mМ NaCl) on the mesoand ultrastructure of mesophyll cells of wheat seedlings. Stress development was estimated by a decrease in the relative water content (RWC) and CO2-dependent O2 evolution (An) in leaves. The decrease in the RWC and in An occurred rapidly in the absence of salt in the substrate and slowly in the presence of salt, especially at a treatment of 100 mM NaCl. The resumption of watering led to the recovery of the both parameters in all variants except one with 200 mM NaCl. Structural studies showed that a weak drought stress (RWC 60%) without salinity led to the destruction of cell membranes and hyaloplasm, which did not occur in all salt treatments. By contrast, the ultrastructure of nuclei in weak drought without salinity remained unchanged, whereas in all salt treatments chromatin changed substantially. Heterochromatin underwent a strong condensation followed by the fusion into a united mass with the simultaneous loss of electron density. A strong water stress (RWC 40%) in all variants led to cell destruction and the hydrolysis of cell compounds. Under the drought without salinity, vacuoles disappeared, whereas in salt-treated samples they were retained and filled with organelles being at different degrees of degradation. Cell nuclei under strong drought stress lost their rounded shape, nuclear envelopes were destroyed, and at the end only a finely dispersed substance remained. Thus, under the combined action of drought and salt, there is some critical level of salt concentration in substrate above which the effect of NaCl changes to the adverse, which enhances the action of drought. Among structural components of mesophyll cells, the most sensitive parts to NaCl are nuclei and their chromatin.

Effects of Stress on Photosynthesis ..

We suppose that the salt concentration in the substrate above a certain critical level increases the effects of drought, and the nucleus and chromatin are most sensitive to NaCl of the structural components of mesophyll cells. The goal of this work was to examine the responses of mesophyll cell structures to water deficit and salt stress in leaves of wheat seedlings.

During the development of drought, the decrease in RWC of leaves to 60% was accompanied by the suppression of the net evolution of O2 (An). The suppression was most rapid in the absence of salt in substrate and slowest in the case of 100 mM NaCl. Further decrease in RWC of leaves to 40% (strong stress) corresponded to the complete termination of An in all treatments (). The resumption of watering led to the recovery of An in all treatments except one with 200 mM NaCl (). The rate of transpiration decreased rapidly in salt treated plants; its increase after resumption of watering was similar to increase in photosynthetic capacities in each treatment (). Increase in Na+ concentration in leaves of salt treated plants was the biggest in 200-mM treatment, up to 2220 mmol Na+ per kg DW. In 100- and 50-mM treated plants it reached 1700 and 750 mmol Na+ per kg DW, respectively. Then Na+ concentration in leaf displayed decrease that continued with resumption of watering and was significant in 100- and 200-mM treated plants but was not significant in 50-mM treated plants ().

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Effects of Stress on Photosynthesis by R

At present it is generally accepted that the main damaging factors at the cellular level in drought and salinity are the osmotic and toxic effects of salt [1] . Our experiments demonstrate that the supply of salt to the substrate leads to a more gradual depletion of substrate water () and a slower decrease in RWC of leaves () and in their photosynthetic capacity (). This effect was more pronounced at 100-mM NaCl treatment compared with 50- and 200-mM NaCl treatment. It was shown earlier [18] and here () that, under the progressing drought in the presence of NaCl, the photosynthetic activity of wheat leaves decreased more slowly than in the absence of salt. However, if 200 mM NaCl was added to the substrate, the photosynthetic activity in leaves was not recovered after the resumption of watering. This salt treatment led to the dramatic increase in Na+ concentration in the leaves (see ) and to plant death.

Effects of Stress on Photosynthesis : ..

The effect of the presence of NaCl in substrate under progressing drought was also shown for plants by structural studies. Namely, the decrease in the RWC of leaves to 60% (weak stress) did not change the leaf mesostructure in all treatments both in the presence and absence of salt in substrate (, , and ). Further decrease in the RWC to 40% (strong stress) led to dramatic changes in the leaf mesostructure in drought without salt in substrate (), whereas structural changes in the salt treatments were less pronounced (, , and ). In weak water stress, the destruction of the plasmalemma, tonoplast, and hyaloplasm of mesophyll cells was not accompanied by the loss of the vacuolar space, while in strong water stress, a dramatic shrinking of cell walls and the complete disappearance of vacuoles occurred (see , and ). In drought with the presence of salt in substrate, the changes in chloroplast structure of mesophyll cells were in agreement with observations of other authors [11] [12] ; cell walls and the vacuolar space changed little. Presumably, the damage of the barrier between the cell wall and the vacuole in water stress causes a rapid efflux of water. In the presence of salt, this efflux is hindered even during the cell membrane destruction (see and ).

Salinity Stress and Salt Tolerance | InTechOpen

In addition to these effects of salt treatments, our data indicate that NaCl adversely affects cell nuclei even in weak stress (, and ). In weak water stress without salt in substrate, the condensation of chromatin did not differ from that in the control plants, though the destruction of cell membranes occurred (see and ). At the same RWC of leaves in salt-exposed seedlings, significant changes in the chromatin struc-

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