Effects Of 24-Epibrassinolide On Growth And Cadmium Uptake,Transfer And Accumulation In Wheat

With the development of science and technology,the problem of heavy metal pollution is becoming more and more serious,and it is also one of the important sources of agricultural product pollution.Among them,cadmium has strong mobility in the soil,is easy to be absorbed by plant roots,and transfers to the edible parts of the ground,and enters the human body through the food chain,causing harm to the human body.As one of the important food crops in China,wheat plays an important role in food security.Plant growth regulators have differences in the growth and development of wheat and the absorption,transport and accumulation of cadmium.Exploring the effect of plant growth regulators on the growth and development of wheat under heavy metal stress is of great significance for further adopting effective agronomic measures to reduce the content of cadmium in wheat grains.In this paper,24-EBL was selected through the previous hydroponic experiment.Through hydroponic and pot experiment,the effect and mechanism of 24-EBL on the growth and development of wheat and the absorption,transport and accumulation of cadmium were studied with Bainong 207 as the research carrier.The results showed that:(1)In the screening test of plant growth regulators.Plant growth regulators could significantly promote the growth of wheat seedlings,decreased the Cd concentrations in different parts of wheat,improved the root morphology,and enhance the photosynthetic rate.There was a significant positive correlation between plant Cd concentration and root Cd uptake capacity(r=0.66**),and root morphological indexes are positively and negatively related to the dry matter accumulation(r=0.59*～0.69*)and root Cd uptake capacity(r=-0.51*～-0.67**).This indicates that plant growth regulators could reduce Cd concentrations in plants,through the improvement of root morphology,which increasing dry matter accumulation and inhibiting Cd uptake by roots.It is worth noting that all plant plant growth regulators significantly inhibited the ratio of the number of tips to the number of bifurcations in root,which are positively related to the Cd uptake capacity(r=0.97*～1.00**)in the treatments of IAA,ABA,and MLT.It may suggest that the reduction of root tips/forks may reduce the uptake of Cd by wheat.Grey correlation analysis shows that 100 μmol·L-1 ABA and 0.1/1 μmol·L-1 24-EBL had the best comprehensive performance,in consideration of biomass,root Cd uptake capacity and Cd distribution between root and shoot.(2)In the hydroponic system,24-EBL increased biomass by promoting root development,improving root morphological structure,promoting photosynthesis and endogenous growth hormone concentration,and reduced cadmium content in Wheat by biological dilution effect under different cadmium levels;At the same time,by changing the hydrogen peroxide accumulation part of root system(from meristematic area and elongation area to mature area or lateral root),reduce the root hair and root tip bifurcation ratio,so as to reduce the cadmium absorption capacity of root system and reduce the cadmium content of wheat;In addition,24EBL promoted the transfer of cadmium from root to shoot in wheat,mainly by alleviating the extrusion deformation of cadmium on wheat root phloem cells,promoting the formation of pericycle sheath,increasing the proportion of root deionized water and ethanol extracted cadmium,and improving transpiration rate and stomatal conductance;The mechanisms of 24-EBL alleviating cadmium toxicity are as follows:most cadmium is accumulated in cell wall and soluble components,which can reduce cadmium toxicity and increase cell membrane tissue through the fixation of cell wall and the regionalization of vacuole,which is also one of the reasons to avoid cadmium toxicity of organelles;Improve the activity of antioxidant enzymes(POD,CAT),regulate the balance of reactive oxygen species in wheat and reduce oxidative damage.(3)In the pot system,both 24-EBL and propiconazole could promote wheat grain biomass under Cd3 and Cd10 stress,and reduce the cadmium accumulation of the whole plant by reducing the cadmium absorption capacity of roots.However,the effects of 24-EBL and propiconazole on grain cadmium content under different cadmium levels were quite different.Spraying 24-EBL and propiconazole before anthesis could reduce the content of cadmium at Cd0.5 and Cd3 stress significantly reduced the content of cadmium in main stem grains;Under Cd10 stress,cadmium content in main stem grain was significantly increased;Under Cd0.5 and Cd3 stress,spraying E100 and B5 before anthesis significantly reduced the content of cadmium in grains by reducing the PN transfer coefficient;Spraying hormone under Cd10 stress can significantly improve the content of cadmium in grains by promoting the increase of N1 vascular bundle area,more complete development of medullary cavity,increasing N1 transfer coefficient.