Effects Of Foliar Applied Gibberellin And Brassinolide On The Growth And Accumulation Of Cadmium In Rice

Cadmium(Cd)pollution in paddy soil is one of the major environmental pollution problems in southern China.It not only affects the safety of rice production,but also poses a threat to human health through the food chain.It has become a research hotspot to explore the technology of Cd minimization in rice.The literatures have been reported on plant growth and development affected by exogenous plant hormones as gibberellin(GA)and brassinolide(BR).However,a few reports have found that plant hormones can improve plant resistance under heavy metal stress.The mechanism of gibberellin and brassinolide on rice growth and Cd accumulation under the Cd stress is still unclear.The current study was performed to investigate(1)the effects of GA and BR on the growth,photosynthetic characteristics,antioxidant enzyme system and Cd content of rice seedlings under Cd stress,and clarified its protective mechanism against Cd toxicity in rice seedlings.(2)the effects of application of gibberellin and brassinolide on rice growth,Cd subcellular distribution,Cd chemical forms and Cd concentration in each part of rice grown in Cd contaminated soil were analyse,and clarified its the response mechanism of reducing Cd accumulation in rice.The main research results are as follows:(1)In hydroponic experiment,the effect of foliar applications of GA and BR on the growth and physiological responses of rice seedlings under Cd stress were discussed.The results showed that exposure to Cd significantly inhibit the plant growth,showing the decreased biomass of shoot(18.23%)and root(26.32%),the root length(9.08%)and root surface area(19.13%),and maximum fluorescence(8.9%),however,increased the content of MDA by 37.04%,compared to the without Cd treatment.While under Cd stress,foliar applications of GA and BR can effectively relieve the Cd toxicity to rice seedlings.Compared with single Cd treatment,applications of GA and BR could promote the growth of rice seedling by increasing the root biomass(84.35% and 45.66%,respectively),shoot biomass(48.2% and 30.94%,respectively),root length(13.01% and16.06%,respectively),root surface area(24.1% and 20.25%,respectively)and maximum fluorescence(7.47% and 6.89%,respectively).Moreover,foliar applications of GA and BR could significantly decreased MDA content by 9.52%and 14.59%,respectively.while foliar applications of GA and BR could significantly increased in antioxidant enzyme activities(SOD,POD,CAT),while significantly decreased in APX activity.Futuremore,foliar application of GA and BR could significantly reduce the Cd concentrations in the root(by 13.03% and7.78%,respectively)and shoot(by 18.4% and 8.5%,respectively)of rice seedlings.Among them,the effective of GA was the best.Thus,the these results suggested that foliar applications of GA and BR could effectively enhance the tolerance of rice under Cd stress and alleviate the damage of Cd stress on rice seedlings by maintaining normal growth,promoting photosynthetic performance and regulating antioxidant system,and declining the Cd uptake of rice.In the pot experiment,the effects of foliar applications of GA and BR on Cd translocation and accumulation characteristics in rice grown in Cd contaminated soil were investigated.The results showed that GA and BR applicaitons could significantly increase the biomass of rice plants(p<0.05).Compared with single Cd contaminated control,GA application could root biomass,straw biomass and grain yield by 40.46%、38.52% and 23.74%,respectively(p<0.05).BR application had no effect on gain yield(p>0.05).No significant different in photosynthetic rate(Pn)of rice was observed in GA and BR treatment,however GA decreased transpiration rate.Moreover,chemical extraction method was used to determine the Cd form in rice.The results found that foliar application of GA and BR could change the percentage of Cd form in roots and shoots of rice(p<0.05).Compared with single Cd pollution controls,GA and BR applications could significantly increase the proportion of Cd in sodium chloride extraction by 26.99% and 9.52%,respectively.while decrease deionized water,ethanol extraction forms of Cd proportion by 65.89% and 81.5%,44.63% and 64.96%,respectively.Similar trend was found in root,GA and BR applications could increase Cd proportion in the extracted form of sodium chloride in root by 12.23% and 17.87%,respectively,while decreased the proportion of Cd in the extracted form of deionized water and ethanol by 46.35% and 71.59%,46.53% and 59.62%,respectively.In additionally,subcellular distributions of Cd in plant cell components were analyzed by differential centrifugation.It was found that GA and BR applications could change the distribution ratio of Cd in subcellular of rice shoot and root.Compared with single Cd contaminated control,GA and BR applications could increase the proportion of Cd in cell wall of roots by 18.77% and 20.06%,respectively,while decreased organelles component(F3)by 58.86% and 42.98%,respectively.Similar found in root.GA and BR applications could increase the proportion of Cd in cell wall of shoot while decreased organelles component.Futuremore,Cd concentration in root,straw and grain was significant decreased by GA and BR applications.The effective of GA was better than BR.The GA application could significant decreased Cd concentration in root,straw and grain by 42.79%,79.72%和 39.43%,respectively.These results suggested that GA and BR application could regulate the subcellular distributions of Cd in plant cell components,enhancing the fixation of Cd in cell walls,forms of 1 M Na Cl,2% HAc,1 M Na Cl extracted Cd with low mobility,thus reduce the mobility and accumulation of Cd in rice.In addition,GA may also reduce the accumulation of Cd through biological dilution.In conclusion,under the stress of Cd,foliar application of gibberellin and brassinolide can effectively alleviate Cd toxicity and Cd accumulation in rice.In this study,GA resulted in a pronounced effect in alleviating Cd stress in rice.