Influence of UV-radiation on the photosynthesis and photosynthetic carbon metabolism in high mountainous plants

Abstract

The influence of UV-radiation on the 14 CO 2 assimilation rate of three high mountainous plants (Heracleum lehmannianum Bunge, Prangos pabularia Lind L. and Lathyrus mulkak Lipsky) with different photosynthetic intensity and directivity of photosynthetic carbon metabolism was studied. The investigation was carried out in the Biological Station of The Institute of Plant Physiology and Genetics (Academy of Sciences of Republic of Tajikistan), located on an austral decline (2350 m above sea level) of the Hissar valley (Tajikistan). It is proved, that plants show different responses to dissecting away of UV-rays. Almost tenfold fall in the intensity of 14 CO 2 fixation (during 30 sec) is noted for H. lehmannianum; in P. pabularia there was twofold fall in depression, and in L. mulkak the dissecting away of UV-rays resulted in the minor rising of the photosynthetic rate. Under both film dropping UVrays and in open area, we have not revealed essential differences in the 14 CO 2 assimilation rate in all three plants.The experiments were carried out in three variants:2. The plants were covered with polyethylene film.3. The plants were covered with polyethylene film enriched with 2-oxi-4-alcoxibenzophenol (0.65%), cutting off the UV part of solar spectrum.The study of 14 C incorporation into the products of photosynthesis has manifested essential differences between investigated plants. From the control experiment, using the Heracleum leaves, more than 65% of a label was included into the intermediates of the Calvin cycle (among them about 20% into PGA). The dissecting away of UV-radiation resulted in a depression of 14 C incorporation into PGA and PES. The key products, which, at 30 sec exposure, concentrated the most part of label were sugars, predominantly sucrose. Intermediates of the glycolic pathway concentrated a small part of 14 C (22%). The depressing of CO 2 photosynthetic assimilation in Prangos was accompanied by a sharp slump of 14 C incorporation into intermediates of the Calvin cycle. The label was found out in sugars predominantly and in intermediates of the glycolic pathway. In control plants we detected an increase of 14 C lobe in monosaccharides. The content of label in intermediates of glycolic pathway decreased. In Lathyrus leaves under investigation we revealed intensive label incorporation into intermediates of the Calvin cycle and its decrease in the metabolites of the glycolic pathway. We found minor quantities of 14 C contents in sugars and PEP-products. It is supposed that the UV-rays influence the activity of RUBISCO and other enzymes of the Calvin cycle. The mechanisms of UV-rays influence on carboxylation system and the possibility of their regulatory role in high mountainous plants are under discussion.

Oxidative stress and leaf senescence

“…Kobza and Edwards [ 34 ] as well as Law and Crafts-Brandner [ 17 , 34 ] suggested that Rubisco deactivation might be more important than altered thylakoid function in decreasing CO 2 assimilation under high temperatures. Abdullaev et al [ 35 ] has also reported that the reduction of CO2 photosynthetic assimilation could induce deactivation of Rubisco and other Calvin enzyme in high mountainous plant treated with UV-radiation.…”