ABSTRACT
This chapter develops a more general concept of the effects of stress conditions on the photosynthetic apparatus. It is based on the observation that a variety of stress conditions interfere with the process of assimilate allocation. Stress conditions substantially change assimilate partitioning and lead to an accumulation of carbohydrates in source leaves. The interaction between production and consumption of assimilates requires a tight regulation of the conversion of light energy and photosynthetic electron transport. Photosystem II is composed of the reaction center complex, the inner antennae, the light-harvesting antenna system, and the water oxidizing complex. In higher plants, but not in mosses, ferms, and algae, D1 protein degradation is further controlled by thylakoid protein phosphorylation. Stress conditions substantially affect D1 protein turnover. The changes in D1 protein turnover play an important role in the molecular mechanism of stress-induced chlorosis. It has long been known that stress conditions lead to substantial alterations of chloroplast ultrastructure.
