ABSTRACT
Under field conditions, the performance of a plant in terms of growth, development, biomass accumulation and yield depends on the ability of metabolism and physiology to adapt and acclimate to fluctuating environmental conditions (Boyer, 1982). Numerous biotic (e.g. insects, fungi, and viruses) and abiotic (e.g. temperature, availability of water, and nutrients) factors affect growth and vigour. Deficits in the availability of essential resources (light, water, carbon, and nitrogen) are detrimental to plant performance. Similarly, variations in environmental conditions away from those which are optimal may result in ‘stress’ that also limits vigour. Studies on the responses of plants to a range of adverse environments has led to the concept of a phenomenon called ‘oxidative stress’ that is characterized by the accumulation of potentially harmful active oxygen species (AOS) in plant tissues. Oxidative stress can be caused by perturbations in metabolism such as a loss of coordination between source (energy producing) and sink (energy using) processes. In photosynthesis this can occur when the rate of photon absorption exceeds the rate of photon utilization.
