Expression pattern and physiological roles of Plastid Terminal Oxidase (PTOX) in wild and cultivated barley genotypes under drought stress

Abstract

Plastid terminal oxidase (PTOX) is a plastid-localized protein that acts as plastoquinol oxidase. The objective of this study was to determine the role of plastid terminal oxidase in response to drought stress and examine the differential response of PTOX pathway in both cultivated (Yousef and Morocco) and tolerant wild barley (spantaneum; HS) genotypes. Plants were subjected to different levels of soil water availability including control, mild and severe drought stress. Decrease in leaf relative water content as a result of progressive drought stressed led to decrease in stomatal conductance and increased enzymatic antioxidant machinery in all genotypes. Drought stress did not affect the PTOX transcript and protein level in cultivated genotypes Yousef and Morocco. However, PTOX gene expression and protein content significantly increased in HS genotype under severe drought. Assessment of PTOX activity via fast fluorescence induction curve in presence of PTOX specific inhibitor revealed that PTOX could efficiently oxidize plastoquinon pool and acts as alternative electron pathway in HS genotype. Results indicated that the role of PTOX in stress response was more significant in the wild barley than the cultivated barley varieties, where the emphasis has been on the desirable agronomic traits.