Heavy metals reduce the plant growth and adversely affect plant performance potential. Heavy metals also induce the formation of reactive oxygen species leading to cell damage. Plants deal with heavy metal stress by activating enzymatic and non-enzymatic antioxidant systems such as Superoxide Dismutase which converts superoxide anion to hydrogen peroxide. Then Peroxidase and Catalase convert hydrogen peroxide to water. Another method employed by pl-ants to deal with heavy metals is mycorrhizal symbiosis. In this study, mycorrhizal and non-mycorrhizal barley seedlings (Hordeum vulgar), var. Rayhan, grown in a greenhouse were treated with four concentrations of nickel (0,100,200 and 400 µg/g). Results showed greater antioxidant activity in mycorrhizal plants compared with non-mycorrhizal plants.  Also, it was determined that the accumulation of nickel in roots of mycorrhizal plants was greater compared with non-mycorrhizal plants.

Astragalus semnanensis Bornm. & Rech. belongs to sect. Semnanensis, of thorny astragali and A. fridae, of non-thorny astragali, belongs to sect. Incani are the only endemic gypsophyllic species in western Semnan. The morphological and systematical studies available on these two species are scarce. Nor have the anatomical, distribution and adaptive capabilities in relation to soil and elevation of these species been investigated yet. Therefore, this study is aimed to comparatively investigate these features. The effect of soil and elevation on the anatomy, morphology and micro-morphology of the leaves of both species, as well as associated plant species, were analyzed using RDA and CCA analytical methods, Canoco 4.5 software. Comparison of RDA analysis of both species indicated that gypsum had the highest effect on the abundance of both species, while elevation had a strongly positive correlation with A. fridae and a negative correlation with A. semnanensis. Both species adsorb gypsum on their epidermis and part of the gypsum absorbed is accumulated in leaf parenchyma cells as calcium sulfate crystals. Adaptability of leaf surface is in the form of long and dense hairs which, in A. semnanensis, are longer and basifixed and, in A. fridae, thicker and medifixed. Increase in soil Ec and Na, K and Mg content and content of CaCO₃ reduce both species abundances. Species such as Acantholimon cymosum and Prunus lycioides were found to be associated with A. semnanensis and species such as Moltkia gypsaceae and Euphorbia gypsicola with A. fridae.