Insights into the Roles of Melatonin in Alleviating Heavy Metal Toxicity in Crop Plants

Alleviating heavy metal pollution in farmland soil,and heavy metal toxicity in plants is the focus of global agricultural environmental research.Melatonin is a kind of indoleamine compound that wide exists in organisms;it is currently known as an endogenous free radical scavenger with the strongest antioxidant effect.As a new plant growth regulator and signaling molecule,melatonin plays an important role in plant resistance to biotic or abiotic stress.Recent studies indicate that melatonin can effectively alleviate heavy metal toxicity in crop plants,which provides a new strategy to minimize heavy metal pollution in crop plants.This study summarizes the research progress on the role of melatonin in alleviating heavy metal toxicity in crop plants and the related physiological and ecological mechanisms such as reducing the concentration of heavy metals in the rhizosphere,fixing and regionally isolating of heavy metals,maintaining the mineral element balance,enhancing the antioxidant defense system and interacting with hormonal signaling.Furthermore,future prospects for the mechanism of melatonin in regulating heavy metal toxicity,the pathway regulating synthesis and catabolism,and the interaction mechanism of melatonin signaling and other phytohormones are presented in this paper,with the goal of providing a theoretical basis for controlling heavy metal ion accumulation in crop plants grown in contaminated soil.

Advances in Cotton Tolerance to Heavy Metal Stress and Applications to Remediate Heavy Metal-Contaminated Farmland Soil

Heavy metal-contaminated soil is one of the major environmental pollution problems of agricultural production and human health in the world.Remediation of heavy metals in soil is one of the most popular research subjects.Different remediation strategies have been reported to remove heavy metals from contaminated soil,among which phytoremediation is the most important one.Compared with other major crops,cotton shows the strongest and most widespread resistance to abiotic stresses,such as heavy metals.Although heavy metal stress adversely affects the growth and development of cotton,cotton possesses a set of sophisticated stress-resistance strategies.As the main product of cotton is nonedible fibers,which have a large biomass and strong heavy metal absorption and enrichment capacities,cotton is an ideal crop to restore heavy metal-contaminated soils and has unique advantages in terms of both ecological and economic benefits,with great application prospects.In this review,based on domestic and foreign research results in recent years,the effects of heavy metals on cotton growth and product quality were analyzed,the heavy metal absorption,accumulation,translocation and enrichment characteristics of cotton plants were summarized,and the adaptation and tolerance mechanisms of cotton to heavy metals were explored.Furthermore,the view that cotton is an effective crop to remediate heavy metal pollution in farmland soil has been proposed,and popularization and application suggestions for planting cotton to repair heavy metal pollution have been put forward to provide a reference for the comprehensive evaluation of the economic feasibility of cotton to repair heavy metal pollution in farmland soil.

Cadmium-Induced Structure Change of Pigment Glands and the Reduction of the Gossypol Content in Cottonseed Kernels

The risk of cotton production on arable land contaminated with heavy metals has increased in recent years.Cotton shows stronger and more extensive resistance to heavy metals,such as cadmium(Cd)than that of other major crops.Here,a potted plant experiment was performed to study Cd-induced alterations in the cottonseed kernel gossypol content and pigment gland structure at maturity in two transgenic cotton cultivars(ZD-90 and SGK3)and an upland cotton standard genotype(TM-1).The results showed that Cd accumulation in cottonseed kernels increased with increasing Cd levels in the soil.The seed kernel Cd content in plants grown on Cd-treated soils was 10-20 times greater than the amount in the corresponding controls.There was a significant difference in Cd accumulation in cottonseed kernels at the 400 and 600μM Cd levels.Cd accumulation was higher in SGK3 and ZD-90 than in TM-1.However,the gossypol content in cottonseed kernels was lower in SGK3 and ZD-90 than in TM-1.There was a negative correlation(r=0.550)between Cd accumulation and the gossypol content in cottonseed kernels.The density of cottonseed kernel pigment glands decreased under Cd stress.This is consistent with the change in gossypol content,which decreased under Cd stress.The damage of the cultivars ZD-90 and SGK3 from Cd poisoning was relatively low under Cd stress,while TM-1 was seriously affected and exhibited Cd sensitivity.Further studies are necessary to understand the cause of the reduced gossypol content in cotton seeds under Cd stress.