Drought-induced changes and recovery of photosynthesis in two bean cultivars (Phaseolus vulgaris L.)

The effects of soil drought on photosynthesis and chlorophyll fluorescence in the leaves of two common bean (Phaseolus vulgaris L.) cultivars – Zarya and Tangra were studied, as well as recovery of photosynthesis after re-watering. Drought was imposed 14 days after the emergency by withholding water for 10 days in which soil water potential reached -0.9 MPa. Water stress led to a noticeable decrease in both the initial slope of the An/Ci curve and Amax in the primary leaf of the studied cultivars. The most marked reduction in leaf gas exchange was observed in cv. Tangra.  was reduced more than three folds and Amax - more than six folds. Exposure of bean plants to soil drought and provoked leaf water deficit resulted in a dramatic reduction (with an 84.17%) of An at normal ambient CO2 concentration (Ca=370 mol mol-1). The lower reduction in leaf gas exchange parameters were observed in cv. Zarya. Drought stress induces an increase of F0 accompanied by a decrease of Fm in the studied cultivars, being cv. Zarya less affected. The Fv/Fm ratio was significantly decreased in cv. Tangra and only showed a slight tendency to a decrease in cv. Zarya. Cv. Tangra presented a decrease of 56% in qP in the primary leaf, while in cv. Zarya qP decreased with 32%. Accordingly, Y strongly decreased in cv. Tangra, while in cv. Zarya Y was less affected. 3 days after re-watering photosynthesis of cv. Zarya was about 87% from the control plants, while in cv. Tangra photosynthesis was only 68% from control. Chlorophyll fluorescence parameters were recovered to the greater extent. On the basis of the data obtained we could arrange photosynthetic apparatus of cv. Zarya as relatively drought tolerant and that of cv. Tangra as drought sensitive.