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It is known that many plants typically die when exposed to temperatures of 40 to 50°C (I believe, these figures relate to exposure times of ~1–2 hours). When a plant is heated, what is the mode of action at the cellular level that results in the death of the plant? What are the main mechanisms involved?

P.S. I have read that at high temperatures plants synthesize heat-shock proteins, so I am not sure if this plays a role in the death of the plant. Another obvious effect following heating is the damage/denaturation of some chlorophylls (but a plant should be able to survive the loss of some photosynthesis; e.g. detaching leaves will not kill a plant).

Any explanation is greatly appreciated.

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  • $\begingroup$ High temperatures cause 'global' damage, i.e. damage to pretty much the entire plant, everywhere, in every cell. One of the most major mechanisms is denaturations of proteins in the cell; proteins misfold, aggregate, lose their structure and function, and cannot sustain the variety of metabolic and other activities in the cell. Heat shock proteins are proteins responsible for stabilizing or re-folding proteins that denature. They are expressed as a last line of defense, which can only partial protect or rescue the plant from accumulating proteinaceous debris and temperature-related damage. $\endgroup$ – S Pr Nov 9 '18 at 11:34
  • $\begingroup$ And perhaps I should add that if you cause such widespread protein dysfunction, you obviously and adversely affect cell signaling, transport of metabolites, the ability of the cell to regulate its own behavior, or multiply, or generate energy, regulate water content, fight off microbial pathogens, let alone sustain the catabolic, long chain of reactions required for photosynthesis and growth. The list is very long if you go into molecular detail. And on the cellular level, plant cells survive by maintaining gradients and compartments which require a positive energy balance to upkeep. $\endgroup$ – S Pr Nov 9 '18 at 11:43
  • $\begingroup$ At roughly 95F/35C the rate of carbon fixation saturates and remains fixed to higher temperatures because of state recovery in RuBisCo. In other words, the rate of photosynthesis is saturated (or maxed out) above 35C or so. However metabolic reaction rates continue to increase with increasing temperature, o the plant consumes more carbon than it fixes when temperatures are above 35C or so. Tissues need oxygen, but the solubility of oxygen in water declines with increasing temperature. Diffusion of oxygen in water increases with temperature which leads to oxygen starvation with increasing temp. $\endgroup$ – Jim Young Nov 9 '18 at 17:27
  • $\begingroup$ Distributed storage and parallel redundancy means it takes a lot. There are pathogens (cankers) that clog the phloem - when it girdles a trunk, roots die once their carbohydrate stores are exhausted (months) and the plant dies quickly afterward. Other pathogens clog the xylem - death follows rapidly because transpiration leads to desiccation. Application of artificial auxins and cytokinins and other phytohormones can affect phytotoxicity and kill plants. Most herbicides are artificial auxins. $\endgroup$ – Jim Young Nov 12 '18 at 0:19

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