Plants endemic to serpentine soils are adapted to harsh environmental conditions typical of those soils, particularly, low (<1) calcium (Ca) : magnesium (Mg) ratios. We compared survival of two perennial Alyssum species native to Iran under experimental manipulations of Ca : Mg ratio, including when Ca : Mg ratio was varied under conditions of high ammonium concentration and heat stress. Alyssum inflatum is a serpentine endemic capable of nickel (Ni) hyperaccumulation, whereas A. lanceolatum is found on non-serpentine soils and is not known to hyperaccumulate Ni. We grew plants of both species under four Ca : Mg ratios (0.4, 2, 20, 40) and tested survival when plants were exposed to elevated ammonium levels (0, 1 and 4 mM) and heat stress (control conditions vs a 5-h 36 C treatment daily for 5 days). Alyssum lanceolatum was more tolerant of Ca : Mg ratio variation (100% survival in all treatments), whereas A. inflatum survival was maximum at Ca : Mg = 2, reduced at Ca : Mg = 0.4, and very low for Ca : Mg ratios of 20 and 40. Alyssum lanceolatum also tolerated ammonium and heat stress, whereas survival of A. inflatum declined at higher Ca : Mg ratios when subjected to both stresses. We conclude that at higher Ca : Mg ratios, the serpentine endemic has reduced tolerance for these environmental stresses and may be more susceptible to human-driven climate change-associated stressors than the non-serpentine species.
Serpentine-endemic plants need to grow in substrates with low calcium (Ca). To test this hypothesis, we compared some of the survival-related physiological responses to different concentrations of Ca in Alyssum inflatum (serpentine endemic) and A. lanceolatum (non-serpentine plant). Accordingly, we grew the plants by using solution culture, and the death of root cells was estimated by using Evan’s blue staining. The electrolyte and protein leakage from roots and NADH oxidation activity in the leaked contents were measured as indices of cell death. The results showed that despite the higher growth of shoots in serpentine plants, the high concentration of Ca caused less root growth. Meanwhile, we observed root-cell death, whole-plant death, more electrolyte and protein leakage from roots and a greater NADH oxidation activity in Ca-treated serpentine plants. In non-serpentine plants, both root and shoot showed more growth, whereas no evidence of cell death in the roots was observed. On the basis of the responses to different concentrations of Ca, we introduce the serpentine plant A. inflatum as a stenocalcic that has to live in substrates with a narrow range of Ca concentrations so that it could prevent lethal Ca toxicity. The results demonstrated the reason behind the uneven distribution of the plant on serpentine patches in its habitat.
Lipid production in Dunaliella bardawil under autotrophic, heterotrophic and mixotrophic conditions Many microalgae are rich in lipid. Due to their low growth rates in the autotrophic culture, the best alternative is to cultivate cells under different conditions such as heterotrophic or mixotrophic, which results in the highest yield of biomass and lipid in the shortest duration. In this study, Dunaliela bardawil (UTEX 2538) green microalgae was cultivated under different culture conditions, autotrophic, heterotrophic and mixotrophic, and effects on cell concentration, lipid production and reactive oxygen species (ROS), total chlorophyll and beta-carotene concentrations were investigated. Due to very low cellular growth, this alga is not recommended for heterotrophic culture. In terms of mixotrophic conditions containing different concentrations of glucose or acetate, the highest cell growth and lipid production in 60mM glucose was similar to the control (autotrophic condition), while the concentrations of chlorophyll and beta-carotene decreased. However, at all concentrations of acetate, a slight increase in cell growth was achieved, while the lipid content decreased. Additionally, the concentrations of chlorophyll and beta-carotene increased. A positive correlation was observed between beta-carotene biosynthesis and lipid production, as well as levels of reactive species of oxygen and lipid production in the presence of glucose and acetate. This study showed that for D. bardawil the mixotrophic culture with 60mM glucose was the most suitable type of culture for increasing lipid content and cell growth rates in less time (one week).
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