Читать книгу Physiology of Salt Stress in Plants - Группа авторов - Страница 30

The chlorophyll biosynthesis in plants occurs in the plastid involving more than 17 enzymes encoded by the nucleus (Pattanayak and Tripathy 2002). Various environmental stresses, including salt stress, downregulate the chlorophyll biosynthesis. Exposure of young and etiolated rice seedlings with salt stress showed that the decrease in the chlorophyll biosynthesis was the result of the reduced transcript expression and protein abundance of biosynthetic enzymes 5‐aminolevulinic acid (ALA) dehydratase, porphobilinogen deaminase, coproporphyrinogen III oxidase, protoporphyrinogen IX oxidase, Mg‐protoporphyrin IX chelatase, and protochlorophyllideoxidoreductase (Turan and Tripathy 2015). Although ALA synthesis decreased, the gene/protein expression of glutamyl‐tRNA reductase increased, suggesting that it may play a role in acclimation to salt stress. In mature Sunflower plants, the salt‐stress‐induced downregulation of chlorophyll biosynthesis in leaves showed a correlation with the reduced level of glutamate and 5‐ALA accumulation (Santos 2004). Salinity downregulates the expression of chlorophyllide‐a‐oxygenase (CAO), which is involved in Chl b synthesis. The reduced Chl b synthesis contributes to an increased Chl a/b ratio observed in salt stress (Pattanayak and Tripathy 2002). The adaptation of plants to downregulate the chlorophyll biosynthesis is essential for protecting the chloroplast from the photo‐oxidative damage by the ROS generated by light and triplet chlorophylls in the absence of photosynthesis (Turan and Tripathy 2015). Thus, the downregulation of chlorophyll biosynthesis might be part of the stress avoidance and protection mechanism in plants.