Expression of selected drought-related genes and physiological response of Greek cotton varieties

Drought-tolerant cotton varieties are very important for Greece and throughout the world. Four Greek cotton varieties (Zeta 2, Zeta 5, Korina and Eva) and an Australian variety (Siokra L23) were subjected to three water-stress levels (0.0, -0.1 and -0.3 MPa). Morphological and physiological parameters studied were plant height, total leaf area, shoot, root and total plant fresh and dry weights, stomatal resistance (SR), water potential (Psi(w)), and relative water content. Siokra L23 was confirmed to be the most drought-tolerant variety based on its high SR and Psi(w), it's having the smallest total leaf area, and expression of drought-tolerance-related genes. The Greek cotton varieties were ranked from most to least drought tolerant as follows: Eva, Korina, Zeta 2, Zeta 5. Molecular responses of the cotton varieties were studied by investigating the expression of five drought-tolerance-related genes, namely, trehalose-6-P synthase, heat-shock protein calmodulin-binding homolog, late embryogenesis abundant (Lea) proteins 14A and 5D, and NAD(P)H oxidase. Reverse transcription-polymerase chain reaction was performed utilizing total RNA samples isolated after a 4-d drought treatment (i.e. at the end of the stress period). Heat-shock protein calmodulin-binding homolog was induced by water stress in drought-tolerant varieties (Eva and Siokra L23) and Zeta 2. This correlation between physiological and molecular data for this gene allows it to be used in cotton breeding programs. Trehalose-6-P synthase and NAD( P) H oxidase genes were not expressed in almost all varieties and treatments. In contrast, the Lea genes showed, with minor exceptions, expression that was independent of variety and treatment. Eva and Korina varieties should be used under conditions of water shortage, whereas Zeta varieties provide a significant advantage to the grower when planted under conditions of high water availability.