Drought stress increases both cyanogenesis and β-cyanoalanine synthase activity in tobacco

Abstract

Results of relative water content (RWC) detection and morphology observation indicated that tobacco ( Nicotiana tabaccum L. cv. Samsun N/N) plants could resist drought stress for 2 days. Ethylene production rates of the tobacco leaves were increased by 9–12-folds during the 2 days of drought stress. Ethylene production rate of the tobacco roots was also increased by about 10-folds during the first day of drought stress. In the meantime, after 1 day of drought stress the cyanide levels in the tobacco leaves and roots were increased by 6.3 and 3.5-folds, respectively. However, during the second day of drought stress the cyanide levels declined to similar levels as those in the unstressed tobacco. Upon drought stress activity of β-cyanoalanine synthase (CAS, EC 4.4.1.9), the main enzyme for cyanide detoxification in plants, sharply increased in the tobacco leaves and roots, but declined once the tobacco plants were re-watered. Activity detection on gel following non-denaturing polyacrylamide gel electrophoresis (PAGE) showed that activities of the two CAS isozymes in tobacco were both induced by drought stress. Spraying 10 μmol l −1 KCN solution onto the leaves of normally watered tobacco plants could obviously induce the CAS activity in the leaves, showing a close relationship between cyanide detoxification necessity and CAS activity therein. The above results indicate that cyanogenesis may be induced by drought stress in plants and CAS may play an important role during the defense of plants against drought stress by cyanide detoxification.