Comparative effect of supplementary red and far-red radiation on the growth of pinto bean seedlings, Phaseolus vulgaris L

Abstract

Photomorphogenesis has been covered thoroughly in a number of reviews, Wassink and Stolwijk (1956), Mohr (1962) and Lockhart (1963) and includes such phenomena as photoperiodism, phototropism, opening or closing of hypocotyl hook, seed germination and leaf expansion. The elongation of the stem as related to various spectral qualities is another aspect of photomorphogenesis. In the early investigations, compartments covered with colored glass or filters were used to determine growth of plants under different portions of the visible spectrum. More recent workers, e.g., Wassink et al. (1951), Stolwijk (1954), Downs et al. (1957) and Meijer (1959), have used radiation of narrower and purer quality and of known energy levels to investigate plant growth. It is generally agreed that both quality and intensity of the radiation are of concern in photomorphogenic responses as demonstrated by a greater inhibition of stem elongation by blue light than by red light under high intensities. However, red light is more inhibitory under low intensities. The approach of the earlier investigations on the effect of light on growth has been anatomical, Brotherton and Bartlett (1918), Priestly (1919), Avery et al. (1937), Jahn (1941), Bindloss (1942) and Thomson (1950, 1951 and 1954). Some of these investigators do not. agree as to which growth parameter, the rates of cell division or cell elongation, is the more affected by light. Furthermore, analyses of stem growth based on the rate of cell division and cell elongation have not been adequately investigated. Obviously the presence of nodes has complicated such analyses of stem growth. Analyses of growth at the cellular level as influenced by red and far-red light have been incomplete and fragmentary. The present investigation is an integrated analysis of the entire stem growth of Phaseolus vulgaris L., cu1tivar Pinto, as influenced by supplementary red and far-red radiation. This investigation will cover the following aspects of the growth of Pinto bean seedlings: 1) Overall growth, 2) stem development and elongation, 3) an analysis of the growth regions of the stem. For this last aspect, the presence of nodes is disregarded except as a means of defining the regions of the stem. This approach is similar to the analysis of the broad bean root growth made by Gray and Scho1e (1951).