CELL DAMAGE, WATER STATUS AND GAS EXCHANGES IN CASTOR BEAN AS AFFECTED BY CATIONIC COMPOSITION OF WATER

Castor bean is an oilseed crop which is able to adapt to various edaphoclimatic conditions and has considerable contents of oil in its seeds, with potential for use in the castor oil industry. In this context, this study aimed to evaluate changes in membrane damage, water status and gas exchanges in castor bean plants (cv. 'BRS Energia') in response to irrigation water salinity and cationic composition. Randomized blocks were used to test six cationic compositions (S-1 - Control; S-2 - Na+; S-3 - Ca2+; S-4 - Na+ + Ca2+; S-5 - K+ and S-6 - Na+ + Ca2+ + Mg2+), in four replicates. Plants in the control treatment were subjected to irrigation using water of low electrical conductivity (S-1 - ECw = 0.6 dS m(-1)), whereas those in the other treatments were irrigated using 4.5 dS m(-1) water prepared with different cations. Higher leaf succulence associated with lower water saturation deficit is an indication of tolerance to salt stress in castor bean plants irrigated with K+-rich water. The presence of Na+ in irrigation water caused the highest water saturation deficit in castor bean leaf blades. The lowest damage in cell membranes was observed in plants irrigated with Ca2+-rich water. The damaging effect of salt stress on castor bean gas exchanges depends on the cationic composition of water and occurred in the following order: Na+>Na++Ca2+>Ca2+>Na++Ca2++Mg2+>K+.