ARSENATE INDUCES WATER STRESS

The effects of arsenate and arsenite on growth and transpiration were investigated in cucumber plants grown in nutrient solution containing 2, 10, and 100 M phosphate, respectively. Root and shoot growth decreased by 48-64% compared to the control in all treatments and there was no significant difference between the effects of arsenic As(V) and As(III) except for the lowest phosphate concentration. At 2 M phosphate As(III) had significantly higher growth inhibition than As(V). The inhibition of transpiration was between 46-68% in all treatments, and As(V) had stronger effect at 10 M phosphate compared to 100 M. Arsenic caused fast wilting 2 hours after the commencement of the treatment. However, the formation of adventitious roots prevented the loss of turgor. The hypothesis that aquaporins might be involved in the action of As(V) has been tested by comparison of the effect of As(V) and Hg, the inhibitor of aquaporins. Both treatments resulted in similar inhibition of growth and transpiration, increase in water saturation deficit and decrease in root exudation. Data imply that (i) phosphate reduces arsenate uptake, (ii) arsenate can be at least partially detoxified in cucumber at higher phosphate concentrations, (iii) arsenate may be reduced to arsenite and (iv) As(V) may interfere with the proper functioning of aquaporins.