Effect of drought on physiological aspects of Crassulacean acid metabolism in Doritaenopsis

Abstract

Drought effects on photosynthesis, stomatal conductance, transpiration, reducing sugar, total sugar, starch, protein, phosphoenolpyruvate carboxylase, superoxide dismutase, and peroxidase activity were studied on Doritaenopsis. Five-month-old in vitro cultured Doritaenopsis orchids were transplanted under ex vitro condition in a greenhouse for 8 months. Four nutrient solutions, i.e. 1/2S, 1S, 3/2S and 2S with the electrical conductivity of 0.9, 1.4, 1.9 and 2.4 dS m −1, respectively, were supplied in ebb and flood irrigation system. Imposition of drought was done by withholding the supply of nutrient solution. Under light and dark condition photosynthesis, stomatal conductance and transpiration decreased with increasing the duration of drought. Rewatering after 15 days of drought resulted in sudden revival from the stress. In drought condition reducing sugar content increased while total sugar and starch content decreased. With the imposition of drought protein content increased at 1/2S nutrient solution while decreased maximally at 3/2S. In control condition peroxidase and superoxide dismutase activity was maximum at 2S and 1/2S, respectively. Imposition of drought increased the phosphoenolpyruvate carboxylase and peroxidase activity while superoxide dismutase activity was decreased at 1S nutrient solution.