Effects of salt stress on some physiological and photosynthetic parameters at three different temperatures in six soya bean (Glycine max L. Merr.) cultivars

The effect of NaCl (-0.1, -0.4 and -0.7 MPa) on some physiological parameters in six 23-day-old soya bean cultivars (Glycine max L. Merr. namely A 3935, CX-415, Mitchell, Nazlican, SA 88 and Turksoy) at 25, 30 and 35 degrees C was investigated. Salt stress treatments caused a decline in the K+/Na+ ratio, plant height, fresh and dry biomass of the shoot and an increase in the relative leakage ratio and the contents of proline and Na+ at all temperatures. Effects of salt stress and temperature on Chl content, Chl a/b ratio (antenna size) and qN (heat dissipation in the antenna) varied greatly between cultivars and treatments; however, in all cases approximately the same qP value was observed. It indicates that the plants were able to maintain the balance between excitation pressure and electron transport activity. Pigment content and the quantum efficiency of photosystem II exhibited significant differences that depended on the cultivar, the salt concentration and temperature. The cultivars were relatively insensitive to salt stress at 30 degrees C however they were very sensitive both at 25 and 35 degrees C. Of the cultivars tested CX-415 and SA 88 were the best performers at 25 degrees C compared with SA 88 and Turksoy at 35 degrees C.