Greening under high light or cold temperature affects the level of xanthophyll-cycle pigments, early light-inducible proteins, and light-harvesting polypeptides in wild-type barley and the chlorina f2 mutant

Etiolated seedlings of wild type and the chlorina f2 mutant of barley (Hord eum vulgare) were exposed to greening at either 5 degrees C or 20 degrees C and continuous illumination varying from 50 to 800 mu mol m(-2) s(-1). Exp osure to either moderate temperature and high light or low temperature and moderate light inhibited chlorophyll a and b accumulation in the wild type and in the f2 mutant. Continuous illumination under these greening conditio ns resulted in transient accumulations of zeaxanthin, concomitant transient decreases in violaxanthin, and fluctuations in the epoxidation state of th e xanthophyll pool, Photoinhibition-induced xanthophyll-cycle activity was detectable after only 3 h of greening at 20 degrees C and 250 mu mol m(-2) s(-1). Immunoblot analyses of the accumulation of the 14-kD early light-ind ucible protein but not the major (Lhcb2) or minor (Lhcb5) light-harvesting polypeptides demonstrated transient kinetics similar to those observed for zeaxanthin accumulation during greening at either 5 degrees C or 20 degrees C for both the wild type and the f2 mutant. Furthermore, greening of the f 2 mutant at either 5 degrees C or 20 degrees C indicated that Lhcb2 is not essential for the regulation of the xanthophyll cycle in barley. These resu lts are consistent with the thesis that early light-inducible proteins may bind zeaxanthin as well as other xanthophylls and dissipate excess light en ergy to protect the developing photosynthetic apparatus from excess excitat ion. We discuss the role of energy balance and photosystem II excitation pr essure in the regulation of the xanthophyll cycle during chloroplast biogen esis in wild-type barley and the f2 mutant.