Studies on the Mechanism of Stem Growth Inhibition by Visible Radiation.

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Abstract
Exposure of a dwarf pea (Morse''s Progress No. 9) to a single brief irradiation with red light results in an inhibition of growth which persists for several days. After 4 or 5 days the plants resume growth at the dark-grown rate. Far-red irradiation will negate the red effect. The effect of a series of gibberellin doses on the growth responses of irradiated or dark-grown peas has been determined. In the absence of applied gibberellin the growth of irradiated plants is inhibited compared to that in darkness. At saturating doses of gibberellin the irradiated and dark-grown plants are the same height. The proportionate responses of irradiated and dark-grown plants are equal at equal doses of gibberellin. It is concluded that visible radiation probably inhibits stem growth in this species through an effect on the level of endogenous gibberellin.