Photosynthesis
Photosynthesis--the process through which green plants harvest light energy to make organic compounds from water and carbon dioxide (CO2)--is inhibited by moderate to high temperatures, but the causes of this inhibition are not clear. An increase in temperature is thought to be detrimental to the membranes of chloroplasts--the organelles, akin to mitochondria, where photosynthesis takes place--but this has been difficult to prove at moderate temperatures (about 35ºC) known to inhibit photosynthesis in many plants. The decreased photosynthesis at moderate temperatures could also be due to a corresponding increase in respiration or photorespiration, or a decline in the activation state of the CO2-fixing enzyme rubisco (1). ... (2) now provide the best evidence yet that the number of unsaturated lipids (that is, fatty acids with double bonds) in the thylakoid membrane of chloroplasts--which contain the light-absorbing system, electron transport chain, and ATP synthase--is important in determining a plants ability for growth and photosynthesis at temperatures of 35ºC or more. ... The reduced level of lipid unsaturation improved the rate of photosynthesis at 40ºC and markedly improved plant growth at 36ºC. This provides an unambiguous demonstration of how reducing the unsaturation of thylakoid membrane lipids improves photosynthesis and growth at moderately high temperatures.