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Summary

Both endogenous and exogenous factors are involved in modulating and coordinating gene expression during plant development. Among them are light and plant hormones such as ethylene, cytokinins, abscisic acid, gibberellins, and brassinosteroids. Light and brassinosteroids have received particular attention because of their obvious and pronounced effects on early plant development following seed germination. By contrast, much less is known about the terminal stage of plant development referred to as senescence and the factors controlling this cell death program. Plant hormones such as ethylene and jasmonic acid have, however, been implicated in the initiation and progression of leaf senescence.

At all stages of their life cycle, plants are prone to various forms of oxidative stress. Upon illumination, excited tetrapyrroles such as chlorophyll, heme, and their precursors as well as degradation products can transfer their excitation energy onto oxygen, leading to the formation of highly reactive singlet oxygen. Angiosperms being the most highly evolved group of plants must have evolved efficient strategies to prevent the accumulation of such potentially harmful compounds. It is the aim of this chapter to summarize current concepts on the regulation of plant gene expression by light and the plant hormone jasmonic acid, with particular emphasis on the mechanisms by which higher plants prevent photooxidative self-poisoning. Special reference is made to the plastid compartment, which is the major site of tetrapyrrole metabolism and a source of signals that coordinate nuclear gene expression in response to light.