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

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