[citation needed] Occasional or prolonged high temperatures cause different morpho-anatomical, physiological and biochemical changes in plants.
[1] Heat stress is defined as increased temperature level sufficient to cause irreversible damage to plant growth and development.
[2][3] Global warming is particularly consequence of increased level of green house gases such as CO2, methane, chlorofluorocarbons and nitrous oxides.
The Intergovernmental Panel on Climatic Change (IPCC) has predicted a rise of 0.3 °C per decade (Jones et al., 1999) [4] reaching to approximately 1 and 3 °C above the present value by 2025 and 2100 AD, respectively.
High temperature directly affect injuries such as protein denaturation and aggregation, and increased fluidity of membrane lipids.
Immediately after exposure to high temperature stress-related proteins are expressed as stress defense strategy of the cell.
In many species it has been demonstrated that HSPs results in improved physiological phenomena such as photosynthesis, assimilate partitioning, water and nutrient use efficiency, and membrane stability.
Since an integrated CTD value can be measured almost instantaneously on scores of plants in a small breeding plot (thus reducing error normally associated with traits measured on individual plants), work has been conducted to evaluate its potential as an indirect selection criterion for genetic gains in yield.
However, such differences cannot be detected in high relative humidity environments because the effect of evaporative cooling of leaves is negligible.
Plants can be assessed for leaf conductance using a viscous flow porometer that is available on the market (Thermoline and CSIRO, Australia).
This instrument can give a relative measure of stomatal conductance in a few seconds, making it possible to identify physiologically superior genotypes from within bulks.