Lethality results from a combination of the cellular changes that the heat invokes and the inability to restore normal function afterwards. High temperatures can have harmful effects on flowering and seed production in many plants, ultimately resulting in reductions in yield. In Saskatchewan, high temperatures during July when canola is flowering, cause reductions in fertility and the number of seeds per pod, which leads to reductions in yield. High temperatures cause changes in protein structure and disable them leading to a disruption of cell function. Heat Shock Proteins Heat stress will also cause changes in which genes are expressed, or switched on.
Heat stress decreases the synthesis of most proteins.
For example, when you increase the temperature of soybean from 25 degrees C to 40 degrees C, the plant stops synthesis of its usual set of proteins, and instead enhances synthesis of 30-50 other proteins. These heat inducible proteins are called heat shock proteins. Heat shock proteins were first discovered in fruit flies but have also been identified in plants, microorganisms and other animals. Some heat shock proteins become localised in the nucleus or the chloroplast to protect functions such as photosynthesis. Others are chaperonins which guide how the proteins fold after they are synthesised.