ECOLOGICAL PHYSIOLOGY OF THE CHLOROPLAST SMALL HEAT-SHOCK PROTEIN

We recently showed that the chloroplast small heat-shock protein (chip smHsp) protects photosynthetic electron transport in vitro during heat stress; however, in vivo evidence of the importance of this Hsp to organismal thermotolerance is lacking. Here we report positive relationships between chip smHsp production and organismal thermotolerance among diverse species and ecotypes of Chenopodium album. Positive relationships were also observed between smHsp production and photosynthetic thermotolerance among tomato genotypes differing in heat tolerance and between heat-tolerant wild-type and heat-sensitive mutant genotypes of Agrostis palustris. These results indicate that genetic variation in production of the chip smHsp is an important determinant of whole-plant thermotolerance. We recently showed that the mitochondrial smHsp protects respiratory electron transport in vitro in plants and humans, suggesting that the mitochondrial smHsp is also an important adaptation to stress.