5-ALA Promotes Plant Root Growth By Up-regulating Auxin Transport

The root system not only has the function of fixing and absorbing water and nutrients,but also can affect the growth and development of the aboveground parts through the storage of photosynthetic products and synthetic plant hormones.Therefore,the regulation of root growth and development is important in plant physiology.5-ALA is a key precursor for the biosynthesis of tetrapyrrole(porphyrin)compounds in all living organisms,which can be converted to heme,chlorophyll and vitamin B12.The results showed that 5-ALA,as a potential plant growth regulator,has the dual properties of auxin and cytokinin,which can promote the adventitious roots and buds formation.However,the mechanism by which 5-ALA affects plant root growth is not clear.In this study,strawberry seedlings(Fragaria X ananassa Duch.cv.'Benihoppe')with root revomed and five genotypes of Arabidopsis thaliana(including Col-0?DR5::GFP?PIN1::GFP?PIN2::GFP and PIN7::GFP)seedlings were used as experimental materials.Then,using qRT-PCR to analysis the molecular basis of the promotion effect of 5-ALA on root elongation,and using laser confocal fluorescence microscope to observe the fluorescence intensity of Arabidopsis related auxin proteins,we focused on the relationship between auxin polar transportion and the effect of 5-ALA on promoting plant root elongation growth.The main results are as follows:1.Through the experiment,the optimal concentration of 5-ALA to promote the root growth of strawberry was 10 mg·L-1.On this basis,we empolyed the qRT-PCR to analysis the effect of 5-ALA on expression of auxin related genes in strawberry.The results showed that the expressions of auxin receptor protein and auxin transport gene were up-regulated after 5-ALA treatment.These results suggest that 5-ALA promotes the growth of strawberry roots,which may be related to auxin transport and signal transduction.2.In order to further explore the mechanism of 5-ALA regulating auxin transport,we used the auxin transport inhibitor(TIBA).First of all,we found the optimal concentration of TIBA to inhibit strawberry root growth was 1 mg·L-1.Then,we observed that the inhibition of 1 mg·L-1 TIBA was relieved by 10 mg·L-1 5-ALA.The quantitative analysis showed that TIBA down regulated the expressions of auxin receptor protein and auxin export carrier gene expression,while 5-ALA up-regulated these genes expression.Therefore,the auxin export carrier and the receptor protein play an important role in 5-ALA promoting strawberry root growth.3.There is evidence to suggest that auxin is an important hormone involved in plant root growth.Meanwhile,some studies have shown that 5-ALA can significantly enhance the accumulation of underground biomass under stress conditions.In previous work,we found that 5-ALA induced the upregulation of the expression of auxin delivery and receptor proteins genes expression in strawberry.However,the role of auxin transport in 5-ALA promoting root growth remains unclear.Here,we proved that 5-ALA treatment can promote the root growth of Arabidopsis thaliana,and enhanced the auxin biosynthesis gene YUC2,ABP1 gene and polar auxin transport genes(AUX1,PIN],PIN2 and PIN7)expression levels,confirming that 5-ALA can improve the endogenous auxin synthesis,transport and signal transduction,and related physiological and biochemical reaction.Then,with 5-ALA treatment on 5 different genotypes of Arabidopsis,we found that DR5,PIN1,PIN2 and PIN7 protein fluorescence intensity were all enhanced.The results showed that 5-ALA promoted the root growth of Arabidopsis thaliana,which might be related to auxin synthesis,transport and signal transduction.4.Using TIBA to treat Arabidopsis seedlings,we found that 5-ALA mitigated the TIBA inhibition on the root growth of Arabidopsis.The results of qRT-PCR analysis showed that TIBA inhibited the expression of the auxin receptor protein and the transport carrier proteins PIN1,PIN2 and PIN7,while 5-ALA up-regulated the expressions all of the genes.In addition,we observed that the TIBA reduced the fluorescence intensity of auxin synthesis and auxin output protein,5-ALA reversed this phenomenon.Therefore,5-ALA may be involved in the process of root growth by auxin export and its signal transduction pathway,but the 5-ALA promoting root growth is not entirely dependent on the output of auxin.In summary,the use of strawberry and Arabidopsis,we show that 5-ALA promoted root growth may be associated with the receptor protein and auxin transport.These results provide new insight into the mechanism of 5-ALA promoting root growth.