| Popis: |
Plants in the tropics frequently experience stressful environmental conditions such as excessive sunlight including solar ultraviolet (UV) radiation or high leaf temperatures. In view of progressing climate change, the combination of various stress factors, particularly during extreme drought periods and heat waves, may cause damage to the photosynthetic system followed by cell death in leaves, resulting in reduction of total photosynthetic productivity. The present article reviews a series of investigations on tropical forest species in Panama. Recording of chlorophyll a (Chl a) fluorescence parameters served as a versatile method to assess the degree of damage and acclimation in chloroplasts. Analysis of chloroplast pigments and antioxidative cell constituents provided valuable information on the acclimation state of leaves. The studies indicate that tropical plants are capable of adjusting to potentially harmful conditions in their respective habitats. One important way of protecting photosystem II is the operation of the violaxanthin cycle and, in certain species, the lutein epoxide cycle. Responses to excess solar radiation in young and mature canopy sun leaves, in leaves of plants growing in treefall gaps and understory of the tropical forest are highlighted. The response of photosystem I to excessive visible light, as well as damaging and acclimatory processes induced by solar UV radiation in photosystems I and II, has been investigated. A reassessed method of Chl a fluorescence measurements was used to determine the limits of heat tolerance in sun and shade leaves of C3 species and in sun leaves of species exhibiting crassulacean acid metabolism (CAM). |
