Fig. 1.

A simplified scheme of the photosynthetic-related mechanisms that can be affected by cold, drought and salinity. Blue and brown arrows correspond to cold and drought/salinity signals, respectively. Adverse environmental conditions that cause osmotic stress induce stomatal closure, which determines the rate of CO₂ assimilation. Abscisic acid (ABA) is involved in most drought and high salt responses and can mediate some low temperature effects. Arrow thickness represents signal contribution. Dashed lines represent possible interactions. PSI, photosystem I; PSII, photosystem II; ROS, reactive oxygen species; 3PGA, 3-phosphoglycerate; RuBP, ribulose-1,5-biphosphate; PG, phosphoglycolate; CF, coupling factor; C_i, internal CO₂; C_c, CO₂ in the chloroplast.