Differential Detergent Stability of the Major Light-Harvesting Complex II in Thylakoids Isolated from Monocotyledonous and Dicotyledonous Plants.

A survey of isolated thylakoids from 11 different higher plant species (Spinacia oleracea L., Pisum sativum L., Vicia faba L., Brassica napus L., Vigna sinensis L., Vinca minor L., Secale cereale L., Triticum aestivum L., Triticosecale Wittn., Hordeum vulgare L., Zea mays L.) indicated that the ratio of the oligomeric:monomeric form of the light-harvesting complex II was twofold higher for the dicots (3.16 +/- 0.35) than the monocots (1.64 +/- 0.25) examined under identical separation procedures. Under conditions specifically designed to stabilize the oligomeric form in vitro, we show that the oligomeric form of dicot light-harvesting complex II is twice as stable to solubilization in the presence of sodium dodecyl sulfate (SDS) than that observed for monocots. This decreased stability of monocot light-harvesting complex II is associated with a twofold increase in the trienoic fatty acid level of thylakoid phosphatidylglycerol but with no significant changes in the trienoic fatty acid levels in the major galactolipids. In addition, SDS polyacrylamide gel electrophoresis and western blot analyses with monoclonal antibodies indicated that monocots exhibited greater heterogeneity in the polypeptide complements associated with subfractions of light-harvesting complex II than the dicots examined. The data indicate that the oligomeric form of the light-harvesting complex II is not the result of a simple oligomerization of a common monomeric unit. We suggest that the difference in stability of the oligomeric form of light-harvesting complex II in isolated thylakoids of monocots and dicots is probably due to a differential accessibility to SDS. The differential SDS accessibility may be due to differences in thylakoid protein-protein and/or protein-lipid interactions.