We exploited leaves of tobacco (Nicotiana tabacum L., cv. Wisconsin 38) with introduced chimeric construct consisting of SAG12 promoter fused with ipt gene for cytokinin synthesis and therefore prolonged life-span. As a control we used its wild type. In 12-week-old plants, the first leaves of control plants showed senescence symptoms at the time of sampling. Carotenoid content decreased with increasing leaf age both in control and in transgenic plants. On the other hand, the first leaves of transgenic plants demonstrated better antioxidant capacity represented by carotenoids compared to the leaves of control plants of the same age. They stayed still green at this age. and D. Procházková, D. Haisel, N. Wilhelmová.
The influence of a cytokinin, 6-benzylaminopurine (BAP), on chloroplast structure was studied using biochemical methods and electron microscopy. The average degree of thylakoid stacking was determined by digitonin fractionation and differential centrifugation of chloroplasts from tobacco plantlets after treatment with different concentrations of BAP in agar medium during cultivation in viíro. An elevated concentration of BAP in the medium induced an increase in grana stacking. This was in accordance with the lowering of the chlorophyll a/b ratio in these chloroplasts. The relative amoímt of proteins and carotenoids increased in both stromal and (to a lesser extent) granal chloroplast thylakoid fractions with the BAP concentration. The electron microscopic studies revealed nearly the same volume density of thylakoid membranes within chloroplasts of BAP treated plantlets and control ones. In the BAP treated plantlets the chloroplasts were smaller and had a profound accumulation of starch inclusions and a more flattened shape than the chloroplasts of control plantlets. The volume density of plastoglobuli in chloroplasts did not decrease under the influence of BAP,
WN6 (a stay-green wheat cultivar) and JM20 (control) were used to evaluate the effects of exogenous cytokinin on photosynthetic capacity and antioxidant enzymes activities in flag leaves. Results showed that WN6 reached the higher grain mass, which was mainly due to the higher photosynthetic rate resulting from the higher maximal quantum yield of PSII photochemistry (ΦPSII) and probability that a trapped exaction transfers an electron into the electron transport chain beyond QA (Ψo), and lower relative variable fluorescence intensity at the J-step (Vj). Exogenous 6-benzylaminopurine (6-BA) enhanced antioxidant enzymes activities and decreased malondialdehyde (MDA) content. Enhanced Ψo and electron transport rate (ETR), and decreased Vj contributed to improved photosynthetic rate in the 6-BA treatment. In addition, exogenous 6-BA significantly increased endogenous zeatin (Zt) content, which was significantly and positively correlated with the antioxidant enzyme activity and ΦPSII, implying that higher Zt content was responsible for the improved antioxidant status and photosynthetic performance., D. Q. Yang, Y. L. Luo, W. H. Dong, Y. P. Yin, Y. Li, Z. L. Wang., and Obsahuje bibliografii
The carboxylating activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39), and other soluble proteins in young seedlings and mature leaves of Lutescens-758, a drought-sensitive cultivar of soft spring wheat Triticum aestivum L., were studied under the conditions of drought and subsequent rehydration. Seedlings and mature plants preliminarily treated with the cytokinin-like compound kartolin-4 were compared to untreated plants. Drought-induced decrease in RuBPCO activity should be attributed not only to proteolytic decomposition of the enzyme protein itself but also to a partial inhibition of its catalytic activity. The decrease in RuBPCO activity was larger than that in RuBPCO content. Water stress induced a marked decrease in the soluble protein content. Kartolin-4 increased the resistance to drought. and I. I. Chernyad'ev, O. F. Monakhova.