Effects of drought stress on pigment, ascorbic acid and free amino acids content in leaves of two apple tree cultivars

Photosynthetic pigments, ascorbic acid and free amino acids content in leav es of Malus domestica Borkh. cv, 'Elstar' and cv. 'Jonagold wilmuta' subjec ted to mild drought or no drought were measured by HPLC in order to detect drought stress. Water deficit (Psi(L) of approximately -1.9 MPa) increased ascorbic acid and zeaxanthin and decreased total chlorophyll (a+b), neoxant hin and beta-carotene in leaves of cv. 'Jonagold wilmuta'. The results indi cate that mild drought induced oxidative stress in leaves of cv. 'Jonagold wilmuta'. Drought (Psi(L) of approximately -2.0 MPa) had no statistically s ignificant effects on oxidative stress indicators measured in leaves of cv. 'Elstar'. The free amino acid content increased in leaves of stressed plan ts in both cultivars. The most pronounced difference was found between cont rol and stressed leaves in Om, Arg and Pro content in cv. 'Elstar' and Pro and Arg content in cv. 'Jonagold wilmuta'. The results indicate that the to lerance to water deficit depends on the apple tree cultivar.