RESPONSE OF SEEDLINGS TO VARIOUS WAVEBANDS OF LOW INTENSITY IRRADIATION

Abstract

Seedlings of red kidney bean (Phase-olus vulgaris) and pea (Pisum sativum) were grown in gravel culture subirrigated with tap water in the absence of visible and near-visible radiant energy and irradiated with 500 and 100 ergs ner sq. cm. per sec. of 5 bands radiation including blue (4047 and 4358 A Hg lines), yellow-green (5461, 5770 and 5791 A Hg lines), red (6400-9000 A incandescent), far red (6800 A to 12000 A incandescent), and 1500 ergs per sq. cm. per sec. of near infrared (7200 A to 12000 A incandescent). With red kidney bean, the yellow-green and red bands caused the most pronounced morphological differences as compared with plants grown in the complete absence of radiant energy. The far red produced almost as great an effect, but the blue and high intensity infrared were much less effective. The longer wavelengths of the visible spectrum caused a marked increase in leaf size and expansion and a shortening of the hypocotyl and 1st internode. Evidently, in the absence of radiant energy the major portion of the reserve material translocated from the cotyledons remained in those parts of the plant immediately adjacent to the cotyledonary node, i.e., the hypocotyl and the 1st internode. The longer wavelengths of the visible spectrum increased the total amt. of reserves translocated from the cotyledons, and also greatly increased the proportion translocated beyond the hypocotyl and 1st internode, i.e., to the epicotyl above the 1st internode, and to the roots. The accelerated movement was considerably greater toward the apical portions of the stem than to the roots. The process is not directly related to chlorophyll synthesis since a minimum morphological response was produced by the blue region with a strong development of chlorophyll and almost a maximum morph. response occurred in the far red where only a trace of chlorophyll appeared. Pea gave much the same type of response as red kidney bean as to total stem length, leaf expansion and weight and translocation of material from the cotyledons. The far red had essentially the same type of effect on maize, soybean, tomato, cocklebur, and potato as it had on red kidney bean. The far red region caused a disappearance of the plumular hook of the dicotyledonous plants, a shortening of the hypocotyl where present, an increased leaf expansion and an increased size of roots. Only a trace of green color was apparent in the leaves of any of these plants under the far red.