Influence of Visible and Near Infrared Radiant Energy on Organ Development and Pigment Synthesis in Bean and Corn

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Abstract
The design of a growth chamber and a water-cooled and filtered irradiation system is described for growing plants under controlled conditions of tem. and humidity, irradiation, and nutrition. Seedling growth and pigment synthesis in bean and corn were studied following continuous irradiation for about 6 days with the following spectral regions: 436 m[mu] mercury line, 630-700 m[mu], 700-1150 m[mu], 725-1150 m[mu], and 765-1150 m[mu]. Irradiances of 150 to 450 [mu]w/cm2 in the 725 to 1150 m/[mu] band induced a strong photomorphogenic response in terms of rapid leaf development in corn and bean and of hypocotyl inhibition, accelerated epicotyl development and disappearance of the terminal hook in bean with the synthesis of only traces of chlorophyll. No combination of far red energy was found which induced strong photomorphogenic response with no detectable chlorophyll. The infrared band of 765 to 1150 m[mu] induced a weak photomorphogenic response with no measurable chlorophyll synthesis. Blue irradiances of 2 [mu]w/cm2 induced weak photomorphogenic effects with a chlorophyll concn. about 1000-fold greater than that in plants treated with 725-1150 m[mu] and with an equal degree of development. It is concluded that there is no quantitative relationship between chlorophyll synthesis and photomorphogenesis. In bean and corn, fresh leaf wt. increased with increase in irradiance to 725-1150 m[mu]. The irradiances were 0, 150, 450, and 1500 [mu]w/cm 2. The 2 lowest irradiances induced an increased synthesis of leaf protochlorophyll and carotene over that produced in the dark, calculated on either a fresh wt. or total plant basis. All irradiation treatments caused large increases in antho-cyanin in bean hypocotyls. The maximum synthesis occurred under the conditions producing the maximum photomorphogenic effects. It is concluded that the synthesis of anthocyanin in the hypocotyl of bean is dependent on a photo-process which does not involve photosynthesis, as shown by marked formation of anthocyanin in the far red where photosynthesis could not occur.