Updated by John F Angus and Howard M Rawson, CSIRO Plant Industry, Canberra
Plants can be classified in their temperature responses into broad groups. One group is defined by sensitivity to low temperature: ‘chilling-sensitive’ species are unable to grow, and often suffer visible damage, below 10–15°C and ‘chilling-tolerant’ species are able to grow down to 0°C and able to survive below this temperature. Within each group, important temperature-sensitive processes are leaf expansion and stem elongation, both of which depend on cell expansion before the cell walls harden.
Another division is based on differences in the pathway of CO2 fixation during photosynthesis, where species in which initial fixation occurs via Rubisco and the photosynthetic carbon reduction cycle are designated C3 species and species in which initial fixation occurs via phosphoenolpyruvate (PEP) carboxylase and the four-carbon dicarboxylic acid pathway are designated C4 species. C4 species include maize and sorghum and such species have high optimum temperatures (≥30°C) for growth. Most C4 plants are also chilling sensitive (Section 14.4). C3 species, on the other hand, show considerable variation in their optimum growth temperature, which can range from close to 30°C in rice to less than 10°C in some alpine species, and they also include a wide range of both chilling-sensitive and chilling-tolerant plants.