Chlorophyll‐protein levels and degree of thylakoid stacking in radish chloroplasts from high‐light, low‐light and bentazon‐treated plants

Abstract

The level of 7 chlorophyll‐carotenoid‐proteins was determined in chloroplasts from radish seedlings (Raphanus sativusL. var. Saxa Treib) grown in high‐light (HL; 90 W m−2and low‐light (LL; 10 W m−2) growth conditions with and without application of the photosystem 2 herbicide bentazon (10−4M) and compared with the degree of thylakoid stacking.The photosynthetic apparatus of HL‐chloroplasts contains higher proportions of the photosystem 1 chlorophylla‐proteins CPI and CPIa than LL‐chloroplasts or chloroplasts from bentazon‐treated plants.In LL‐chloroplasts and in chloroplasts from bentazon‐treated plants a higher proportion of light‐harvesting chlorophylla/b‐proteins (LHCP1, LHCP2, LHCP3, LHCPy) is found. Bentazon treatment changes the proportion of LHCPs to about the same levels under both HL and LL‐growth conditions. The amounts of free chlorophyll found in bentazon chloroplasts (27–29%) is higher than in the HL or LL‐controls (16–18%).The increase in degree of thylakoid stacking (% proportion of appressed membranes per total chloroplasts membranes) of LL‐chloroplasts as compared to HL‐chloroplasts of 7 to 9% (3rd to 5th day of illumination) is paralleled by a similar increase in the LHCPs of 5% and 8% (3rd and 5th day). The importance of light harvesting chlorophylla/b‐proteins as a prerequisite for thylakoid stacking is discussed.