Acclimation by the Thylakoid Membranes to Growth Irradiance and the Partitioning of Nitrogen Between Soluble and Thylakoid Proteins

Abstract

Three characteristics of shade plants are reviewed. Firstly, they have relatively more chlorophyll b and the associated light-harvesting chlorophyll a/b-protein complex (LHC). Two currently accepted reasons for this are not supported by quantitative analysis. Instead, the reduced protein cost of complexing chlorophyll in LHC and the turnover of the 32 kDa herbicide binding protein are considered. Secondly, shade plants have low electron transport capacities per unit of chlorophyll. This is primarily related to a reduction in the amount of electron transport components such as the cytochrome f complex and the ATPase. The nitrogen cost of the thylakoid membranes per unit of light absorbed is thereby reduced, but the irradiance range over which light is used with high efficiency is also reduced. Thirdly, shade plants have less RuP2 carboxylase and other soluble proteins for a given amount of chlorophyll. However, while the ratio of RuP2 carboxylase protein to thylakoid protein declined, the ratio of the RuP2 carboxylase activity to electron transport activity increased. For several species, the relationship between the rate of CO2 assimilation and leaf nitrogen content depends on the irradiance during growth.