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

In our previous work we found considerable accumulation of early light-indu cible proteins (ELIPs) in barley during adaptation to combined high light a nd cold stress, an accumulation which occurred preferentially 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 com position of thylakoid membrane proteins and pigments, particularly xanthoph ylls and chlorophyll, and their distribution within the barley leaf. It was observed that high light fluxes appeared to favour the trimerization of th e light-harvesting complex of photosystem II (LHC II) whereas cold appeared to favour the monomers of LHC II. High light, cold or the combination of b oth factors had only a small effect on the protein composition of the thyla koid membranes except for the proteins of LHC II which were found to decrea se under high light to a greater extent at 25 degrees C than at 5 degrees C . The total xanthophyll-cycle carotenoid content increased linearly with ce llular 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 re mained nearly constant. The fraction consisting of antheraxanthin plus zeax anthin was up to 4- to 5-fold higher at 5 degrees C than at 25 degrees C. A s determined previously (Montane et al. 1997), the same conditions caused a 15-fold increase in the accumulation of ELIPs. Consequently, neither the d istribution of total xanthophylls nor that of antheraxanthin plus zeaxanthi n 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 demonstr ate for the first time that ELIPs of 13.5 kDa are contained in high-molecul ar-mass complexes of >100 kDa, which are located in the unstacked stroma la mellar region of the thylakoid membranes.