Effects of Exposures of Seeds to Various Physical Agents. I. Effects of Brief Exposures to Heat and Cold on Germination and Light-Sensitivity

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Abstract
The effect on germination of brief conditioning at various temps. of grains or seeds of several spp. of plants was studied, and the effects of such conditioning on light-sensitivity enzyme activity, and, in two instances, on subsequent growth were observed. Grains or seeds of Digitaria sanguinalis, Sporobolus airoides, Raphanus sativus, and Linum usitatissimum were conditioned at temps. ranging from 10[degree] to 75[degree]C for 1 hr. air-dry, fully-imbibed, or with some intermediate water content. Grains or seeds of Zea mays, Triticum vulgare, Raphanus, and Linum were conditioned at 100[degree]C for 20-60 min. while air-dry. Certain other spp. also were studied. Digitaria and Sporobolus exhibited a 3-fold germination response to light: low temp. conditioning, photo-inhibition; high temp. conditioning, photo-stimulation; intermediate temps., indifference to light. Responses to light were modified by water content as well as temp. treatment. Treatments suppressing germination diminished amylase, oxidase, and autolytic activity. Treatments preventing germination could be partially overcome by addition of glucose, sucrose, hydro-quinone, ascorbic acid, soil extract, or light, depending on treatment and sp. treated. Stunting of seedlings from heat-treated seeds was observed in some instances, while many temp. or light and temp. treatments promoted germination. Induction of light-sensitivity in Raphanus and Linum by 100[degree]C conditioning was observed. The differential tolerances of several seeds to high temps. were considered in relation to oil content, and it is suggested that one injurious effect of heat on seeds is on oxidation-reduction systems; this is in addition to the role of heat in protein denaturation and enzyme inactivation.

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