DYNAMIC ASPECTS OF WATER-RELATIONS IN GERMINATION OF HIRSCHFELDIA INCANA SEEDS

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Seed germination of Hirschfeldia incana was found sensitive to substrate hydration, being progressively inhibited in increasingly high levels of hydration. This phenomenon was analyzed kinetically. Water-sensitivity was unaffected by light conditions, though germination was promoted by a short irradiation and to a lesser extent by continuous irradiation and inhibited by darkness. Water-sensitivity was greatly modified by temperature. Kinetics of the germination process (timing of maximal sensitivity to promotive short irradiation) were unaffected by hydration, but were hastened by temperatures which modified water-sensitivity. The equilibrium level of seed moisture-content was strongly dependent on substrate hydration, which also determined the kinetics of water uptake. The level of water sensitivity was determined by the hydration or temperature during the initial 8-16 hrs of incubation. GA hastened the processes of germination and reduced water-sensitivity, the growth regulators Amo-1618, CCC, and coumarin retarded germination, but only the latter two enhanced water-sensitivity. It was concluded that the level of germination in each condition was determined by its effects on the relative rates of the germination processes and the build-up of an inhibition. It is suggested that the latter is due to effects of hydration on the resistance to diffusion of oxygen into the seed through the enclosing mucilaginous seed coat.
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