Prelimimary Research On The Effect Of Auxin During Physcomitrella Patens Development

Auxin is one of the most important phytohormones and involved in all of the plant growth and development regulation.At present,our knowledge of auxin functions is mostly about seed plants tissue or organ development.Few reports about auxin functions on cell level.The moss Physcomitrella patens has simple tissue structure.Protonema is composed only of mono linear cells,and it is suitable for the studies on cell level.There is little knowledge about the role of auxin in the growth and development of P.patens,expect auxin(NAA)can promote the differentiation of caulonema from chloronema.Observation methods of the growth and development of the P.patens had been established in our lab.In this study,the observation condition were further clarified.The function of auxin on P.patens vegetative development were observed in details.Development of S-type and L-type choloronema treated with auxin(IAA)and auxin synthesis inhibitor were studied.Yucasin and L-Kynurenine are auxin synthesis inhibitors in seed plants.They can reduce auxin signal in the P.patens choloronema.The results showed that the indolpyruvate synthesis pathway(IPA)was also an important auxin synthesis pathway in the P.patens,and was homologous with A.thaliana.Exogenous IAA could increased the branching rate and potential branching rate of the chloronema,and auxin synthesis inhibitor Yucasin inhibited chloronema branching.However the cell division rate were not altered,even enhanced.Elongation of new divided chloronema cells was significantly reduced,indicating that auxin does not directly promote the division,but it was necessary for chloronema elongation and growth.Caulonemata under exogenous IAA was more and longer.so auxin can promote the occurrence and growth of caulonema.The number of buds formed by single chloronema was significantly increased with exogenous IAA,and the emergence of buds under auxin synthesis inhibitors was significantly delayed and depressed.Therefore,auxin was necessary for bud emergence.Exogenous IAA could enhance gametophyte growth,leave and rhizoid differentiation.Auxin synthesis inhibitors could suppress cell elongation and all of the tissue development,while cell number were not altered significantly.Under L-Kynurenine treatment,leaves of gametophyte were not only significantly shorter,but also lobed.Therefore,Auxin plays an important role in game top hyte growth and development.In addition,1?mol/L IAA showed a certain degree of inhibition on the chloronema and gametophyte,which indicated that auxin has enhance functions in low concentration and suppress functions in high concentration.Both Yucasin and L-Kynurenine could inhibit differentiation and growth of chloronema and gametophyte,but Yucasin worked quickly and L-Kynurenine was relatively slow.L-Kynurenine significantly delayed the emergence time and number of gametophytes.These results showed that Yucasin and L-Kynurenine had different inhibitory effects on the growth and development of P.patens.We hypothesize that they inhibit the synthesis of auxin in different points.Further experiments could use different auxin inhibitors according to specific requirementsOur results suggest that,auxin plays an important role in Physcomitrella vegetative development.Auxin could promote P.patens cell elongation,promote in low concentration while suppress in high concentration,as in seed plants.In addition the auxin biosynthesis could be inhibited by seed plants auxin synthesis inhibitors also.So the role of auxin in higher plants is likely to be highly conserved.It is further indicate that the P.patens is an excellent material for studying the mechanism of auxin at the cellular level.The results of this study not only clarify the essential functions of auxin for cell development of P.patens,but also prepare good prerequisites for further analysis of auxin on cellular level.