Variations in response of CaPAO and CaATG8c genes, hormone, photosynthesis and antioxidative system in pepper genotypes under salinity stress

Abstract

The present study aimed to explore the effect of salinity on the expression of CaPAO and CaATG8c genes as well as the tolerance mechanism in pepper genotypes (Dolmalik, Carliston, and Maras). Salt-stress resulted in a considerable decrease in plant growth, photosynthetic activity, carboxylation efficiency, and cytokinin, in addition to SOD, APX, GR, GSH and GSH/GSSG in Dolmalik and Carliston genotypes. In this respect, plant growth, carboxylation efficiency and phtosythesis activity markedly were decreased in Carliston and Dolmalik genotypes by salinity stress. In contrast, a slight decreases was found in Maras genotype. Furthermore, the lowest Na+ and Cl− ion concentration was detected in the leaves of Maras genotype as compared to Dolmalik and Carliston genotypes. Therfore, salinity had a slight impact on Maras indicating greater tolerance to salinity, and salt-tolerant genotype neutralized the over-accumulation of sodium by a reduction in Cl- uptake. In peppers, CaPAO and CaATG8c genes are responsible for pheophorbide a oxygenase and autophagy activities, respectively. Based on the results, salinity caused the up-regulation of CaPAO, and this coincided with a marked decrease in chlorophyll, and a significant increase in cytokinin oxidase content in salt-sensitive genotypes. In contrast, in salt-tolerant genotype, CaPAO was down-regulated and accompanied by a reduction in cytokinin oxidase and a slight decrease in chlorophyll content. The CaATG8c expression was upregulated in salt-tolerant genotype, accompanied by the highest soluble protein content. In contrast, a slight increase in CaATG8c expression and a decrease in soluble protein content were detected in salt-sensitive genotypes. These results suggest that the expression of CaATG8c and CaPAO genes in pepper genotypes can be important for their adaption to salinity stress.