Search

Photoinhibition is the inhibition of photosynthesis by excessive light resulting in the reduction of plant growth. Exposure to additional stress factors during exposure to light increases the potential for photoinhibitory effects. Reversible photoinhibition is indicative of a protective mechanism aimed at dissipating excess light energy, while irreversible photoinhibition indicates damage to the photosynthetic systems. The present review summarizes the physiological mechanisms of photoinhibition and discusses the interaction between light and other stress factors. In addition, some of the features and strategies that help plants avoid or restrict the occurrence of photoinhibition are analyzed. Most of these defense mechanisms are associated with the dissipation of excessive energy such as heat. Therefore, these mechanisms would regulate the carbon available to the plant by the output ratio of ATP/NADPH to the stressful environmental conditions. Understanding these mechanisms can help avoid plant cell death and increase plant productivity.

Arabidopsis thaliana dynamin-like protein 1E (ADL1E) is known to regulate mitochondrial elongation. The adl1e mutant has no morphological phenotype, and the growth and photosynthetic activity of the mutant are similar to those of the wild type. Leaf O2 uptake, which is supported by mitochondrial activity in the dark, is increased 1.7-fold by mutation in adl1e gene. The ATP content in the dark of guard and mesophyll cell protoplasts (GCPs and MCPs, respectively) was 2.5- to 4-fold higher in GCPs of the mutant and the wild type, and increased upon the addition of glucose in both genotypes. Oligomycin, an inhibitor of mitochondrial ATPase, suppressed ATP synthesis in both GCPs and MCPS isolated from adl1e plants, indicating that mutant had higher mitochondrial activity. The stomatal apertures of mutant and wild-type plants were then analyzed in vitro. In the light, the stomata of both genotypes showed similar patterns of opening. However, in the dark response, the stomata of the adl1e mutant closed faster than did those of the wild type. Oligomycin severely inhibited dark-induced stomatal closure in both cell types. The results suggest that stomatal closure in the dark is governed by cytosolic ATP concentration, which is stimulated by mitochondrial activity.