Activitatea proceselor FS II şi REDOX la frunzele de cimişir de vârste diferite ca indicatori ai rezistenţei lor la şocul сu temperaturi negative

The resistance of annual and biennial leaves of boxwood to the effects of negative temperatures has been studied. The parameters of PS II activity and the parameters of the redox potential were deter-mined in different periods after exposure to shock at temperatures of -5°C, -10°C , -15°C and -20°C. It was shown that the stability and ability to recover from damage caused by shock at different temperatures, were higher in annual leaves compared to biennial leaves.

Kinetin mitigates Cd-induced damagesto growth, photosynthesis and PS II photochemistry of Trigonella seedlings by up-regulating ascorbate-glutathione cycle

Cytokinins (CKs) plays a key role in plant adaptation over a range of different stress conditions. Here, we analyze the effects of a cytokinin (i.e., kinetin, KN) on the growth, photosynthesis (rate of O2 evolution), PS II photochemistry and AsA–GSH cycle in Trigonella seedlings grown under cadmium (Cd) stress. Trigonella seeds were sown in soil amended with 0, 3 and 9 mg Cd kg-1 soil, and after 15 days resultant seedlings were sprayed with three doses of KN, i.e.,10 μM (low, KNL), 50 μM (medium, KNM) and 100 μM (high, KNH); subsequent experiments were performed after 15 days of KN application, i.e., 30 days after sowing. Cadmium toxicity induced oxidative damage as shown by decreased seedling growth and photosynthetic pigment production (Chl a, Chl b and Car), rates of O2-evolution, and photochemistry of PS II of Trigonella seedlings, all accompanied by an increase in H2O2 accumulation. Supplementation with doses of KN at KNL and KNM significantly improved the growth and photosynthetic activity by reducing H2O2 accumulation through the up-regulation AsA–GSH cycle. Notably, KNL and KNM doses stimulated the rate of enzyme activities of APX, GR and DHAR, involved in the AsA–GSH cycle thereby efficiently regulates the level of AsA and GSH in Trigonella grown under Cd stress. The study concludes that KN can mitigate the damaging effects of Cd stress on plant growth by maintaining the redox status (>ratios: AsA/DHA and GSH/GSSG) of cells through the regulation of AsA-GSH cycle at 10 and 50 μM KN under Cd stress conditions. At 100 μM KN, the down-regulation of AsA-GSH cycle did not support the growth and PS II activity of the test seedlings.

Biochemical Characterization on Photosynthetic Activities during Dark Incubated Senescence of Wheat Primary Leaves by Gibberellic Acid

In annual crop plants like maize, rice and wheat etc. Senescence limits crop yields of annual crops like maize rice and wheat. Delayed leaf senescence is a desirable agronomic trait to improve crop yield. In this study 10 µM GA reduced the loss of wheat primary leaves under incubated dark conditions. GA reduced the loss of pigments, proteins, electron transport activities, spectral properties. The restoration of WCE activity by GA was closely associated with the restoration of PS II activity compared to that of PS I. GA treated leaf thylakoid membranes showed an increase in absorption at 680 nm moderate increase at 480 nm and 440 nm at 72 h during dark incubation. GA protected the degradation of water oxidation complex polypeptides (33, 23, 17 KDa) of PS II and slightly protected the PS I polypeptides.

Physiological Response of Black Gram [Vigna mungo (L.) Hepper] Grown on Fly Ash-Amended Soil: Growth, Photosynthesis, and Antioxidant Defense

The present study deals with the growth, photosynthesis, antioxidant defense along with the metal accumulation in black gram [Vigna mungo (L.) Hepper] grown on various combination of fly ash amended garden soil. Significant improvement of soil quality such as pH, nitrogen and organic carbon was observed in 25% of fly ash amendments. Besides, the bioaccumulation of Fe, Cu, Mn, and Zn was remarkably increased with the increase of fly ash in amended soil. Fly ash (25%) amended with garden soil led to a 62% increase in plant biomass. Photosynthetic rate, stomatal conductance, and chlorophyll content significantly increased under 25% fly ash amendments soil, though photosystem (PS) II activity remained unchanged compared to the plants grown in garden soil. Furthermore, the activity of some antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and guaiacol peroxidase was increased over control under different fly ash amendments. Taken together, garden soil amended with 25% of fly ash not only improved the physicochemical properties of the soil but also contributed to better growth and photosynthesis in black gram.

Dynamics of the photosystem II photochemical activity in the developing Brassica nigra L. seeds

Dynamics of the PS II activity in the pod walls, seed coat and embryo cotyledons at early and middle maturation stages of Brassica nigra L. has been studied using the Junior-PAM fluorometer (Heinz Walz Gmbh, Germany). The maximum quantum yield Fv/Fm, effective quantum yield Y(II) and coefficient of photochemical fluorescence quenching qP have been evaluated. We demonstrated maturation-dependent fluctuation of the PS II activity in the different part of seeds: Fv/Fm, Y(II) and qP decreased in the pod walls and seed coat, but increased in the cotyledons of embryo. During transition from early to middle stage of maturation, the maximal electron transport rate of PS II in the cotyledons increased and reached the maximum at higher level of photosynthetic active radiation. Improving the efficiency of PS II in the developing cotyledons of the embryo can be attributed to adaptation of the chloroplasts to a higher light probably due to the increase of light transmission through the seed coat and pericarp at later stages of seed maturation. Refs 29. Figs. 3.