Action of Maleic Hydrazide on Dormancy, Cell Division, and Cell Expansion

Maleic hydrazide (MH) can inhibit cell division in dormant lettuce seeds in which cell division occurs in the absence of growth by cell expansion. Concentrations of MH that inhibit normal growth of wheat seedlings by 85 to 90% have no effect on the growth of wheat from irradiated grain, which grows without any cell division. Thus MH affects mitosis in a system where gibberellic acid (GA) does not, and (MH has no effect on cell expansion in a system where GA is active. When wheat is treated with a combination of MH and GA, the two chemicals apparently act independently on growth, All these findings suggest that the effect of MH on seedling growth can be largely or entirely attributed to an inhibition of cell division and not to any appreciable effont on cell expansion. MH and GA do not appear to give specific interactions on lettuce seed gerraination, thereby providing further evidence against the theory that MH and GA affect growth through common mechanisms. A number of similarities between effects of MH and of ionizing radiation are discussed, including the capacity to permit gerraination and limited seedling growth of wheat without cell division. (auth)