Brassinosteroids and gibberellic acid actively regulate the zinc detoxification mechanism of Medicago sativa L. seedlings

Abstract

Background Zinc is one of the essential trace elements in plants. There are few studies on the phytohormone to rescue the toxicity of excessive zinc to plants. The aim of this research was to evaluate the alleviating effects of brassinosteroids (BR) and gibberellic acid (GA) on the toxicity of Medicago sativa L. (M. sativa) induced by excessive zinc. Results After zinc, BR and GA were applied to M. sativa seedlings for 7 weeks, their physiological and biochemical properties and gene expression patterns were evaluated. BR and GA significantly weakened the inhibition effect of zinc stress on growth and biomass of M. sativa. Under zinc stress, the zinc accumulation in M. sativa roots was over 5 times that in shoots. Application of BR and GA reduced zinc accumulation in roots. The content of lipid peroxides in M. sativa decreased and the activity of antioxidant enzymes increased under BR and GA treatments. In addition, BR and GA treatment down-regulated the transcription level of MsZIP1/3/5, the transporters of zinc uptake in root cells. And BR and GA up-regulated the expressions of zinc efflux, chelation, vacuolar storage and long-distance transport related genes: MsZIP7, MsHMA1, MsZIF1, MsMTP1, MsYSL1 and MsNAS1. Conclusions Our findings further showed that BR and GA application to M. sativa under zinc stress can reduce zinc accumulation, promote the response of the antioxidant defense system, and actively regulate the mechanism of heavy metal detoxification. Notably, 100 nM BR performed slightly better than 100 nM GA in all aspects of the detoxification of M. sativa by excessive zinc.

Exogenous Brassinosteroid Enhances Zinc tolerance by activating the Phenylpropanoid Biosynthesis pathway in Citrullus lanatus L

“…When a large amount of Zn is enriched in the soil, it will adversely affect the growth of plants, then affect the quality and yield 1 . Here, Zn stress treatment significantly inhibited the growth of watermelon, and also significantly inhibited the accumulation of Zn, chlorophyll content, and photosynthetic rate of watermelon ( Figure 1 ), which was consistent with the previous studies that plant growth was inhibited under Zn stress 4 , 5 , 28–30 . To reduce the serious impact of heavy metal stress (including Zn) on plants, many methods have been adopted, including foliar application of different chemicals/phytohormones 4 , 5 , 29 , 31–35 .…”

“…Here, Zn stress treatment significantly inhibited the growth of watermelon, and also significantly inhibited the accumulation of Zn, chlorophyll content, and photosynthetic rate of watermelon ( Figure 1 ), which was consistent with the previous studies that plant growth was inhibited under Zn stress 4 , 5 , 28–30 . To reduce the serious impact of heavy metal stress (including Zn) on plants, many methods have been adopted, including foliar application of different chemicals/phytohormones 4 , 5 , 29 , 31–35 . BRs act as multidimensional regulators of plant responses under different environmental stresses, and epibrassinolide (EBR) is a synthetic brassinolide analog, which has been widely used in production 7 .…”

“…Excessive Zn can cause the imbalance of nutrient and water absorption of plants, change the ultrastructure of chloroplasts to inhibit plant photosynthesis, destroy the membrane system and macromolecular substances of plant cells through accumulation of reactive oxygen species (ROS), and then seriously damage the growth, development, metabolism, and other plant physiological processes, causing plant death 3 , 4 . For example, high concentration of Zn in M. sativa produces a large amount of ROS, resulting in oxidative stress and cell damage, which seriously interferes M. sativa growth and quality 5 . Therefore, it has become a research hotspot in the field of environmental science to control Zn pollution, study the mechanism of plant tolerance to Zn and reduce the excessive absorption of Zn by plants.…”

“…Exogenous EBR further increases the levels of antioxidant enzymes, thus effectively eliminating ROS, alleviating the toxicity of Zn to soybean seedlings 11 . Recently, EBR application to M. sativa under Zn stress could reduce Zn accumulation, promote the response of antioxidant defense system, and actively regulate the mechanism of heavy metal detoxification 5 .…”