Alleviation of cadmium-induced phytotoxicity and growth improvement by exogenous melatonin pretreatment in mallow (Malva parviflora) plants.

The present work was aimed to study the effect of melatonin pretreatments on growth, oxidative stress modulation, cadmium (Cd) accumulation, and tolerance in mallow (Malva parviflora, Malvaceae) plants under the hydroponic system. Application of substances that can modulate the harmful effects of Cd on plant yield and reduce its accumulation in the edible parts is of particular importance. Therefore, the mallow plants pretreated with 15, 50, and 100 µM of melatonin were exposed to 50 µM Cd. Our results showed that melatonin, especially at 15 and 50 µM, led to positive effects on Cd tolerance, including a significant increase in growth, photosynthetic pigments, and soluble protein content. Exogenous melatonin could improve relative water content (RWC) and stomatal conductance in the plants treated with Cd, probably through an increase in proline. Further, lower concentrations of melatonin led to a decrease in Cd translocation to the shoots. Based on the results, melatonin considerably increased catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (GPX) activities as well as the production of phenols. The increased activity of antioxidant enzymes led to a decrease in electrolyte leakage (EL), lipid peroxidation, and H2O2 content in the plants exposed to Cd stress. Under Cd stress, the increased phenols content in melatonin-pretreated plants could be due to the induction of phenylalanine ammonia-lyase (PAL) activity and an increase in shoot soluble carbohydrates. The results showed that the use of melatonin could reduce oxidative stress and improve biomass in the plants exposed to Cd. At least in our experimental conditions, this information appears to be useful for healthy food production.

A newly found cadmium accumulator--Malva sinensis Cavan.

Screening hyperaccumulators and accumulators is a key step in the phytoremediation of soils contaminated by heavy metals. A pot experiment was conducted involving a soil Cd concentration gradient (0, 50, 75, 100, 125, 150, 175, and 200 mg kg(-1)) to determine if Malva sinensis Cavan. from two lead-zinc mines in Kangding and Yajiang in western Sichuan, China, is a Cd-hyperaccumulator. The highest Cd concentrations in plant shoots from Kangding and Yajiang were 154.30 and 122.77 mg kg(-1), respectively, at a soil Cd concentration of 200 mg kg(-1). The largest amounts of accumulation in plant shoots from Kangding and Yajiang were 700.5 and 1403.2 microg pot(-1), respectively. The bioconcentration factors in shoots were 0.53-1.03 for Kangding and 0.69-1.25 for Yajiang. Moreover, all translocation factors of plants from the two sites were over 1.0. Therefore, M. sinensis can be classified as a Cd-accumulator or non-standard Cd-hyperaccumulator.

Mutual feedbacks maintain both genetic and species diversity in a plant community.

The forces that maintain genetic diversity among individuals and diversity among species are usually studied separately. Nevertheless, diversity at one of these levels may depend on the diversity at the other. We have combined observations of natural populations, quantitative genetics, and field experiments to show that genetic variation in the concentration of an allelopathic secondary compound in Brassica nigra is necessary for the coexistence of B. nigra and its competitor species. In addition, the diversity of competing species was required for the maintenance of genetic variation in the trait within B. nigra. Thus, conservation of species diversity may also necessitate maintenance of the processes that sustain the genetic diversity of each individual species.