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Heat stress can be defined as temperatures hot enough for sufficient time that they cause irreversible damage to plant function or development.
The way in which heat stress occurs in specific climatic zones is a complex issue. Plants can be damaged in different ways by either high day or high night temperatures, by either high air or high soil temperatures, and by the tissue desiccation that accompanies high temperatures in arid or semi-arid environments. Also, crop species and cultivars differ in their sensitivity to high temperatures. Cool-season annual species are more sensitive to hot weather than warm-season annuals.
High day temperatures can have direct damaging effects associated with hot tissue temperatures or indirect effects associated with the plant water deficits that arise from high evaporative demands.
A combination of high temperatures and intense solar radiation is common in many countries.
This makes it difficult to conduct meaningful experiments in controlled environments that realistically reproduce a ‘heat stress’. The use of growth chambers with lighting systems that mainly depend on fluorescent lights can result in serious artifacts. Control of humidity at high temperatures is technically difficult, so plants may suffer more from ‘drought stress’ as the soil dries quickly. To avoid these problems, treatments based on detached leaves that are placed in water and incubated at various temperatures with or without light have been used.
The protocols below address these various considerations.
Heat Stress and its Impact. AE. Hall. Botany and Plant Sciences Department,
University of California, Riverside, CA, USA