THE ROLE OF NITRATE IN THE OSMOTIC AND NUTRITIONAL CONTROL OF PLANT DEVELOPMENT

I postulate that certain of the effects of nitrate on plant developmen t are mediated by the combination of an osmotic effect on water uptake and a nutritional effect on protein synthesis. This hypothesis is dis cussed with reference to effects on seed germination, apical dominance , lateral root initiation flowering and leaf senescence. The postulate d osmotic effect of nitrate is consistent with the well-established ro le of both nitrate and reduced forms of N as major osmotica in plant c ells, and also with the similarity and interaction between development al effects of nitrate and water. Evidence of the nutritional component of developmental effects of nitrate is provided by a comparison of re sponses induced by nitrate and by other osmotica of less nutritional s ignificance. Carbohydrate has also been reported to influence developm ent by a combination of osmotic and nutritional effects. The proposed hypothesis is a unifying concept which provides a similar physiologica l explanation for a wide range of diverse developmental responses that are usually attributed to the effect or interaction of different horm onal factors.