Growth of the tocopherol-deficient vte1 mutant and Col-0 wild type of Arabidopsis thaliana in a sunlit glasshouse revealed both similarities and differences between genotypes. Photosynthetic capacity and leaf mesophyll features did not differ between mutant and wild type. Likewise, the total volume of water conduits (tracheary elements, TEs), sugar conduits (sieve elements, SEs), and sugar-loading cells (companion and phloem parenchyma cells) on a leaf area basis were unaffected by tocopherol deficiency. However, tocopherol deficiency yielded smaller and more numerous minor veins with fewer phloem cells and smaller TEs, resulting in greater ratios of TEs to SEs. The smaller TEs in the vte1 mutant may present a decreased risk for cavitation under high evaporative demand or in response to freezing. In turn, compensation for fewer phloem cells and smaller TEs by more numerous veins may bolster resistance to cavitation at no cost to photosynthetic capacity., J. J. Stewart, W. W. Adams, C. M. Cohu, B. Demmig-Adams., and Obsahuje bibliografické odkazy
Cadmium is often detected in areas contaminated by heavy metals and the incidence of this element in dangerous concentrations has been increasing due to anthropogenic activities. The aim of this research was to determine Cd concentrations in tissues, quantify compounds, pigments and enzymes, and to evaluate the gas exchange. Our aim was also to identify components that can modify and contribute to tolerance of Cassia alata against Cd toxicity. We used five Cd concentrations (0, 22, 44, 88, and 132 μM) to validate our hypothesis. The Cd concentrations in tissues of C. alata plants increased significantly, compared with the control treatment, in the following graduated sequence: root > leaf > stem. Progressive enhancement in glutathione (GSH) was verified in plants treated with all Cd concentrations used, when compared with treatment without Cd. Antioxidant enzyme activities presented similar patterns with progressive enhancements, being a desirable characteristic for plants with a potential to hyperaccumulate Cd. Our results suggest that C. alata plants can be used for phytoremediation programs. Their defense mechanism is based on Cd accumulation in roots, coupled with increase in GSH and the efficient activity of antioxidant enzymes that contribute to minimize the oxidative stress and consequently improve the protection of the metabolic machinery., J. R. R. Silva, A. R. Fernandes, M. L. Silva Junior, C. R. C. Santos, A. K. S. Lobato., and Obsahuje bibliografii
Increase in salinity is predicted to affect plant growth and survival in most arid and semiarid regions worldwide. Mitragyna parvifolia (Roxb.) Korth. is an important medicinal tree species distributed throughout the semiarid regions of India; however, it is facing a threat of its extinction in its natural habitat. We examined the effects of increasing NaCl salinity on two-month-old M. parvifolia seedlings grown in an environment-controlled chamber and exposed to soils of different electrical conductivity (EC) caused by NaCl [0-5 (control), 5-10, 10-15, 15-20, and 20-25 dS m-1)] for 85 days. Seedlings transferred to soil of EC >15 dS m-¹ did not survive beyond 1 week. Increase in the Na+ concentration negatively correlated with their height and positively correlated with their water-use efficiency (WUE). However, leaf area, net photosynthetic rate (PN), stomatal conductance, and transpiration rate showed varying correlations and an overall decrease in these parameters compared with the control. At EC of 10-15 dS m-1, the seedling height was reduced by 37% and PN was lowered by 50% compared with those of the control. An increase in the Na+/K+ ratio was observed with increasing salinity. The maximum quantum efficiency of PSII significantly decreased with increasing salinity compared with the control. Our results suggest that the increase in salinity reduced the overall performance of the M. parvifolia seedlings. However, the maintenance of WUE and maximum quantum efficiency of PSII might help M. parvifolia to tolerate NaCl salinity of 15 dS m-1., A. Bidalia, M. Hanief, K. S. Rao., and Obsahuje bibliografii