Biomedical subjects
A N Burdett
Publications and source records attributed to A N Burdett.
Two effects of prolonged far red light on the response of lettuce seeds to exogenous gibberellin.
Prolonged far red irradiation of imbibed lettuce seeds (Lactuca sativa L. cv. Grand Rapids) makes them unresponsive to subsequent treatment with gibberellin. It has been found that this effect is overcome by supplying gibberellin buffered at a low pH. On the basis of this and other evidence it is suggested that an extended far-red exposure causes a loss of gibberellin sensitivity through an effect on the permeability of the endosperm. In seeds treated simultaneously with gibberellin and far red light, the hormone is taken up at the beginning of the irradiation, but its action is suspended until the seeds are placed in the dark.
Antagonistic effects of high and low temperature pretreatments on the germination and pregermination ethylene synthesis of lettuce seeds.
Red light-induced germination of Grand Rapids lettuce seeds (Lactuca sativa L.) incubated at 20 C was inhibited if the seeds were first imbibed at 30 C for 36 hours. This effect was counteracted by exogenous ethylene and associated with a reduction in the rate at which the seeds produced ethylene throughout the pregermination period. A chilling treatment reversed the effect of a prior imbibition at 30 C on both germination and ethylene production. The possibility that the pretreatments influence germination through their effects on ethylene production is discussed.Other evidence presented indicates that the inability of seeds to germinate at supraoptimal temperature is not due either to a rapid loss of far red-absorbing phytochrome or to an inadequate capacity for ethylene synthesis. It was also shown that a chilling treatment potentiated germination at high temperature without affecting the ethylene synthetic capacity of the seeds.
Ethylene synthesis in lettuce seeds: its physiological significance.
The germination and pregermination ethylene production of Grand Rapids lettuce seeds (Lactuca sativa L.) incubated at 20 C after a red light treatment are inhibited if the seeds are first imbibed at 30 C for 36 hours. In this study, low concentrations of ethylene were found to enhance the germination of seeds pretreated at 30 C more than that of untreated controls. In the presence of high concentrations of ethylene, pretreated seeds and controls germinated at a similar rate. These results are consistent with the view that a prolonged imbibition at 30 C inhibits germination at a lower temperature through its effect on the ethylene production of the seeds. As a further test of the hypothesis, estimates were made of the pregermination ethylene content of untreated seeds and pretreated seeds incubated in the presence of sufficient ethylene to make them germinate as rapidly as untreated seeds. The values obtained were 0.65 and 0.74 nanoliter of ethylene per gram (dry weight) of seeds, respectively.
Synergistic action of ethylene with gibberellin or red light in germinating lettuce seeds.
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