Effect Of Plant Hormone And Aluminum On Organic Acid Metablism And Secretion In Wheat Root Apcies

Aluminum toxicity has been recognized as a major limiting factor of plant productivity on acidic soils.Al toxicity is manifest by inhibition of root elongation, variation in Al resistance between cultivars does exist.The Al-induced release of malic acid has been suggested as an important mechanism for Al resistance in wheat. But the mechanism of Al-induced efflux of malic acid and the mechanism of Al inhibit elongation of wheat roots are not clear.We selected two different Al-resistant wheat lines:Atlas 66(Al-resistant) and Scout 66(Al-sensitive) and hydroponics in this research.On the one hand,Al-induced variation in the endogenous content of plant hormones includes ABA,IAA and GA_s and the effect of plant hormones on the efflux of malate was investigated in these two different Al- resistant wheat lines,which aimed to expatiate the effect of plant hormones regulated Al-induced efflux of malic acid;On the other hand,we investigated variation on elongation and endogenous content of plant hormones in these two different Al-resistant wheat roots which induced by aluminum,we also investigated Al and IAA-induced ROS metabolism in these two different Al-resistant wheat,which were purpose-made for explain mechanism of Al toxicity and plant hormones mediated inhibition of elongation of wheat roots by aluminum.The main results were as followed:1.Atlas 66 and Scout 66 were treated with 0,10,20,50,100μmol/L AlCl₃ after 24 h,Al inhibits elongation of wheat roots in dose-dependent manner,and root elongation was inhibited more extensively in Scout 66 than Atlas 66.Al content in 0～1 cm root apices increased with the increment of Al among all treatments. Microscopic observation revealed that the root apex was the most Al-sensitive part of the root.The root apex of Al-sensitive genotype accumulated more Al than Al-resistant genotype is related to their Al toxicity expression and resistance.The order of wheat resistant capacity to Al toxicity was Atlas 66＞Scout 66.2.The secretion of malic acid increased with the time,the malic acid secretion rate of Atlas 66 was higher than that of Scout 66.The malic acid secretion rate increased with the increment of Al after 6h.The secretion of malic acid of the root tips inhibited by anion channels NIF and A-9-C.It shows that the secretion of malic acid of the root tips by the secretion of anion channels.3.The activities of PEPC,MDH,and CS in 0～1 cm root apices of Atlas 66 and Scout 66 had no obvious change at different Al concentration,and there were no significant change in MDH activity,the content of citric acid and malic acid between Atlas 66 and Scout 66.The results indicated that the secretion of malic acid which under Al stress has no correlation with the regulation of the organic acids synthesis in the root apices4.The content of ABA and IAA increased with the increment of Al,and will show an accumulative tendency with the time,the content of IAA in Scout 66 were higher than that of Atlas 66,the content of ABA in Scout 66 was lower than that of Atlas 66.The content of GA_s decreased with the increment of Al.The conclusion showed that Al stress effect the plant hormone metabolism in root apices.5.The malic acid secretion rate increased with the increment of IAA among all treatments,the malic acid secretion rate which induced by 200μmol/L IAA were significant higher than that of control.The malic acid secretion rate decreased progressively when induced by GA_s,and there was no obvious change between Atlas 66 and Scout 66.The malic acid secretion rate did not change with the increment of ABA.Same results were achieved in 3 weeks aged wheat.6.The secretion of malic acid of the root apices had no delay under the Al stress and IAA-induced;there were much malic acid which secret by root apices could be detected in 15 min.Temp.had no effect on the organic acids secretion under 6℃or 25℃.The secretion of malic acid of the root apices inhibited by anion channel inhibitor NIF and A-9-C.It showed that the secretion of malic acid of the root apices under Al stress was similar to that under IAA-induced.7.Induced by 200μmol/L IAA,the level of citric acid and malic acid was not changed in 0～1 cm root apices of tested cultivars.The activities of PEPC,MDH,and CS had not obvious change either.It showed that the secretion of malic acid which induced by IAA did not involved in the control of the organic acids metabolism, which can further explained that IAA may participate in the secretion of malic acid under Al stress.8.The activities of SOD,APX,and GR in 0～1 cm root apices of Atlas 66 were obviously lower than Scout 66 under 50μmol/L AlCl₃ stress,but Atlas 66 showed a higher CAT activity than that of Scout 66 in 0～1 cm root apices,the results showed that there are differences in oxidation resistance between Atlas 66 and Scout 66. Under 50μmol/L AlCl3 stress,POD activity was increased significantly in the two wheat lines.The activity of POD in Scout 66 was higher than that in Atlas 66.It was suggested that the effiux of malic acid root apices and the resistance to oxidative stress were the two principal factors controlling the inhibition of the root elongation, more accumulation of ROS,more higher activity POD,which promoted the cross linking sclerosis of cell walls and inhibits the root elongation.9.The activities of SOD,APX,and GR of Atlas 66 were obviously lower than Scout 66 which induced by 200μmol/L IAA,Atlas 66 showed a higher CAT activity than that of Scout 66,POD activity were increased significantly in the two wheat lines. The activity of POD in Scout 66 was higher than that in Atlas 66;it was similar to that under Al stress.Microscopic observation revealed that fibrosis degree was higher where IAA accumulated;the degree of fibrosis was higher in Scout 66 than that in Atlas 66.Al³⁺ is mainly accumulated in the cortex and epicortex under Al stress,it cannot enter the IAA accumulate region to induce oxidation stress easily.The IAA content in root tips were increased under Al stress,and the relative cumutant in the root tips of Scout 66 were much higher,it suggests that IAA content increased under Al stress was related to the root inhibit elongation.