Formation of early-light-inducible-protein complexes and status of xanthophyll levels under high light and cold stress in barley ( Hordeum vulgare L.)

Abstract

In our previous work we found considerable accumulation of early light-inducible proteins (ELIPs) in barley during adaptation to combined high light and cold stress, an accumulation which occurred preferen tially in the apical part of the leaves (M.-H. Montane et al., 1997, Planta 202: 293-302). Here we studied, under the same conditions, the effect of adaptation on the composition of thylakoid membrane proteins and pigments, particularly xanthophylls and chlorophyll, and their distribution within the barley leaf. It was observed that high light fluxes appeared to favour the trimerization of the light-harvesting complex of photo system II (LHC II) whereas cold appeared to favour the monomers of LHC II. High light, cold or the combina tion of both factors had only a small effect on the protein composition of the thylakoid membranes except for the proteins of LHC II which were found to decrease under high light to a greater extent at 25 °C than at 5 °C. The total xanthophyll-cycle carotenoid content increased linearly with cellular development, the highest amount being observed in the apical part of the leaf. Cold and high light acted synergistically to induce less than a doubling in the amount of total xanthophylls, while chlorophylls a and b remained nearly constant. The fraction consisting of antheraxanthin plus zeaxan thin was up to 4- to 5-fold higher at 5 °C than at 25 °C. As determined previously (Montane et al. 1997), the same conditions caused a 15-fold increase in the accu mulation of ELIPs. Consequently, neither the distribu tion of total xanthophylls nor that of antheraxanthin plus zeaxanthin along the leaf followed the same pattern as ELIP. Thus, the accumulation of xanthophylls cannot be stoichiometrically correlated with that of ELIPs. Using electrophoresis in the presence of decylmaltoside, we could demonstrate for the first time that ELIPs of 13.5 kDa are contained in high-molecular-mass com plexes of >100 kDa, which are located in the unstacked stroma lamellar region of the thylakoid membranes.