Catalase transcript accumulation in response to dehydration and osmotic stress in leaves of maize viviparous mutants.

The effect of osmotic stress and dehydration on maize catalase transcript accumulation was examined in leaves of abscisic acid (ABA)-deficient and ABA-insensitive mutants. We have found that the response of Cat1 to osmotic stress and dehydration is not via an ABA-mediated pathway in young leaves, suggesting that there are two different mechanisms by which Cat1 responds to osmotic stress in embryos and in leaves. The Cat2 transcript increased in response to osmotic stress, but was repressed by dehydration. On the other hand, the Cat3 transcript is up-regulated by dehydration and osmotic stress only in ABA-deficient mutant leaves, implying that ABA may act as a repressor for Cat3 expression in response to dehydration and high osmoticum. We also found that the VP1 trans-acting factor is not required for the induction of Cat1 by ABA in leaves, but may play a role in stabilizing the Cat1 transcript after an initial induction. The exact nature of the signals triggering Cat responses to osmotic stress and dehydration is not clear. We speculate that oxygen free radicals may play a role in this response. Osmotic stress and dehydration may indirectly induce production of oxygen free radicals in leaves, thus triggering the antioxidant response.