The Regulation Of Indoleacetic Acid And Melatonin In Response To Aluminum Toxicity Of Helianthus Tuberosus L.

Acid soil accounts for about 22.7%of the total land area in China,and aluminum（Al）is the main factor limiting the growth of Helianthus tuberosus L..Indole acetic acid（IAA）or melatonin（MT）can reduce Al toxicity in many plants,but the mechanism is still unclear.In this study,seedlings from Nanjing（with strong Al-tolerance）and Ziyang（with weak Al-tolerance）were cultivated in Al treated sand,and alleviated by foliar-applied method.The relative root length was set as the index to chose the optimal combination dosage of IAA and MT.Through the changes of growth indexes,photosynthetic characteristics,antioxidant system,osmotic regulation,root damage and organic acids,the effects of IAA and MT in response to Al toxicity of Helianthus tuberosus were learned.At last,the relationship between them was explored by inhibitors of auxin synthesis and transport,so as to provide clues for revealing the mechanism of Al tolerance in Helianthus tuberosus.The main results were showed as follows:1.Both IAA and MT had low promoting and high inhibiting effects.10 mg/L IAA reduced the relative root length of seedlings from Nanjing by 12.90%compared with the control group,and Ziyang plants were decreased by 14.68%at the level of 50mg/L MT.The effects of 4-6 mg/L IAA on Nanjing groups were prominent,while Ziyang seedlings had no significant difference（P>0.05）in MT 10-30 mg/L groups.The orthogonal experiments were designed for 2 factors and 6 levels with IAA（0,4,4.5,5,5.5,6 mg/L）and MT（0,10,15,20,25,30 mg/L）.The range value was A factor>B factor,both A4 and B2 were the maximum in two groups,thus the optimal combination was selected as 5 mg/L IAA+10 mg/L MT.2.The effects of MT on root length,plant height,leaf area and dry weight of Helianthus tuberosus that from two places were not as good as IAA.In each remission group,chlorophyll a（Chla）and chlorophyll b（Chlb）were increased,but Chla/Chlb was decreased.The initial fluorescence（F₀）,non-photochemical quenching coefficient（qN）and intercellular CO₂concentration（C_i）of plants were decreased,meanwhile,the maximum photochemical efficiency（F_v/F_m）,electron transfer rate（ETR）,photochemical quenching coefficient（qP）,net photosynthetic rate（P_n）,stomatal conductance（G_s）and transpiration rate（T_r）were all increased.In MT groups,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）were improved,glutathione（GSH）and ascorbic acid（ASA）were significantly increased（P<0.05）.Under Al stress,malondialdehyde（MDA）was increased,but proline（Pro）,soluble sugar（SS）and soluble protein（SP）were decreased.IAA+MT could effectively alleviate this phenomenon.In addition,the root activity of plants was decreased.And the fluorescence signal of Nanjing Al group was more obvious than that of Ziyang group by Morin staining.After relieving,both of them were significantly faded.The Al content in the roots of Nanjing seedlings was 1.28 times higher than that of Ziyang,which demonstrated that the Al tolerance of Nanjing cultivars were stronger than seedlings of Ziyang.The accumulation of Al in Nanjing and Ziyang IAA+MT groups were significantly reduced by 44.79%and 48.84%.3.Al,L-AOPP（L-2-aminooxy-3-phenylpropionic acid）or TIBA（triiodoberzoic acid）significantly（P<0.05）reduced IAA content in root tips.The effects of exogenous IAA on Al and L-AOPP groups were obvious,with an increase of 85.36%in Ziyang and 58.83%in Nanjing.But MT had no significant effect on Nanjing L-AOPP group.Neither IAA nor MT could play a role in TIBA group.These results indicated that exogenous IAA could reach the required position through polar transport when auxin synthesis was limited.The effect of MT was not as good as IAA,which may be related to the decrease of endogenous IAA.If auxin transport was obstructed,IAA in leaves could not be transported to root tips.In conclusion,the effects of IAA were better than MT in alleviating the growth indexes of Helianthus tuberosus that from two places.The effects of MT on photosynthesis and antioxidant system were better than that of IAA.MT promoted root elongation depending on the existence of IAA,and the combination of them could achieve a better effect.