The effect of light quality and gibberellic acid (GA3) on photosynthesis and respiration rates of pea seedlings

Abstract

CO2 exchange were measured on pea seedlings (Pisum sativum L. var. Bördi) cultivated from seeds imbibed either in water (C-plants) or in gibberellic acid (GA3) at the concentration of 25 μg/1 (GA-plants), and then grown under 17 W/m(2) blue light (B-plants) or 11 W/m(2) red light (R-plants).When measured under the same light conditions as during growth the net photosynthesis (APS) rate in B-plants was about twice higher than that in R-plants. Dark respiration (DR) rate was 70% higher in B- than in R-plants. Red light retarded the development of photosynthetic activity, but GA3 suppressed this effect. The hormone enhanced net photosynthesis and dark respiration to the same extent.When measured under saturating white light net photosynthesis rate of C-plants was also two times higher in B-plants than in R-plants. Growth conditions had only a slight effect on the APS of GA-plants under white light. APS rates of GA-plants grown under red light were higher under white light than those of C-plants, but lower than those of plants grown under blue light.We assume that blue light induced formation of plants that were adapted to higher light intensity: red light had an opposite effect, whereas gibberellic acid induced formation of plants that were adapted to medium light intensity.

Effect of red light on ribulose 1,5-bisphosphate carboxylase activity in pea leaves

“…Red light conditions during plant growth usually reduce their rate of CO: assimilation (Hernischfeger et al 1974, Romanowska et al 1984, Voskresenskaya et al 1984, Leong et al 1985. This effect of red light has been recently explained as a result of incomplete development of the light harvesting system (Buschmann et al 1978, Leong et al 1986, Eskins and McCarthy 1987.…”

“…The temperature during the 16 h of illumination period was 25 ~ while in the darkness 20 ~ Experiments were carried out on 21 d old seedlings. Measurements of CO2 gas exchange in saturating white light were described previously (Romanowska et al 1984). scintillation vials and evaporated to dryness.…”