CHANGES IN STRUCTURE AND FUNCTION OF PHOTOSYNTHETIC APPARATUS OF BRASSICA PODS DURING SEED MATURATION

Rate of photosynthesis; primary photochemical reactions, viz. whole ch ain electron transport, PSI and PSII activities; polypeptide profiles and lipid composition of thylakoid membranes were determined at differ ent stages of Brassica pod development. Net CO2 exchange rate increase d till 20 days after anthesis (DAA), remained constant till 30 DAA and decreased thereafter. While stomatal conductance followed a similar p attern, transpiration rate and internal CO2 concentration were least a ffected by age. Chlorophyll content decreased from 10 DAA till maturit y, However, Chl a:b ratio increased during the period of active photos ynthesis and was maximum at 30 DAA. Among the photochemical activities , PSII activity was reduced to 30% in mature pods. Qualitatively, the polypeptide composition of PSI, PSII and their light harvesting comple xes were not affected adversely by aging. Total lipids, phospholipids, glycolipids and total free fatty acids decreased with maturity. Howev er, the decrease in glycolipid content was more severe particularly du ring maturity phase. It seems that decrease in glycolipid content of t hylakoids and chlorophyll content of chloroplasts are responsible for the decrease in photochemical activity and hence a reduction in CO2 as similation at later stages of pod development