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

Galina Semenova, Irina Fomina, Anatoly Ivanov

Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Russia.
Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Russia; Biosphere Systems International Foundation, Tucson, USA..
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Russia.

DOI: 10.4236/cellbio.2014.31002                

Abstract

The purpose of the work was to assess the combined effect of drought and salinity (50, 100, 200 mМ NaCl) on the meso- and 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 (A_n) in leaves. The decrease in the RWC and in A_n 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.

Keywords

Chromatin; Meso- and Ultrastructure of Mesophyll; Salt and Water Stress; Triticum aestivum

Conflicts of Interest

The authors declare no conflicts of interest.

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