Methods for studying the mechanism of water stress effects on photosynthesis

Abstract

It is a triviality to state that any kind of stress will affect virtually all plant reactions, if only it is strong enough. But even mild stress of sufficient duration will induce a sequence of secondary events leading to changes in plant metabolism, structure and growth. These changes are far too complex to provide information on primary mechanisms of stress damage. A now well known phenomenon which illustrates the consequences of secondary stress damage is inhibition of the photosynthetic machinery due to exposure of plants to a combination of water stress and high light intensities. Photoinhibitory damage must not be considered as a primary water stress effect, since it is not observed at low light intensities (Powles 1984). In order to understand the manner in which photosynthetic processes are initially affected, water stress must be imposed experimentally in a well-defined manner and over a relatively short time interval. Unfortunately this means that experimental conditions will deviate considerably from what we call “natural.” Therefore, the results obtained in this way must later be critically examined to establish their relevance under field conditions. In the following chapter, methods and results are described that outline our approach to determining the possible mechanisms by which water stress initially affects photosynthesis and plant metabolism.