Studies On The Relationship Between Fruit Setting And Polyamines And Cloning Of Related Genes In Litchi

Polyamines,as physiological active materials with broad functions of regulation,play a critical role in flowering and fruit setting of fruit trees.In the present paper,the relationship between fruit setting and endogenous polyamine was studied.The changes of endogenous polyamine contents in fruit setting and effects of exogenous polyamines on the promotion of fruit growth as well as fruit setting were investigated.We also report the cloning of S-adenosylmethionine decarboxylase(SAMDC) cDNA fragment from litchi (Litchi chinensis 'Guiwei') leaves,an enzyme involved in the polyamine biosynthesis pathway,and 1-aminocyclopropane-1-carboxylicacidsynthase(ACS) cDNA fragment,a key enzyme responsible for the ethylene biosynthesis.In theory,SAM metabolism and biosynthesis of polyamine and ethylene during litchi fruit growth and their molecular mechanism in fruit setting and physiological fruit dropping can be established.In practice, this research can also offer theoretical foundation for developping a new way to produce high quality litchi fruit with low investment.The main results were listed as follows:1.Use of exogenous polyamines on bagged flower without pollination showed that parthenocarpy can be induced in Feizixiao but not in Guiwei and Nuomici.Spm was more effective for the induction,followed by Spd and Put.The three polyamines all can obviously improve percentage of fruit setting especially Put.2.HPLC analysis of Put,Spd and Spm contents in litchi was established,which was completed in 15 minutes.All the relative coefficients were above 0.999 when the linear arrange of the three polyamines was from 0.03125 to 2 nmol.The relative standard deviation of precision and stability experiments was lower than 5%,indicating that the method was a simple and rapid method with more accuracy and stability.3.The contents of Put,Spm and Spd in the leaf,floral organ and fruitlet of three litchi varieties were analyzed during their development.Put,Spm and Spd in the leaf of normal flowering Litchi plant increased and then declined after a abrupt peak at anthesis. However,the contents of polyamines in the leaf of non-flowering 'Feizixiao' changes in an opposite trend.The contents of polyamine in the leaves of non-flowering 'Guiwei' continuously declined which may be related to new flushing in this phase.The contents of total PAs in floral organ and fruitlet were much higher than in leaves.In floral organ and fruitlet of Litchi chinensis 'Feizixiao',Spd was the most abundant and kept high during the initial stage of fruitset. 4.The influence of exogenous polyamines on endogenous polyamine contents was analyzed.Exogenous Spd decreased the endogenous Spd content,and exogenous Spm enhanced endogenous Spm greatly.Exogenous Put can only improve endogenous Put and did not alter endogenous Spd and Spm.A combination of these three polyamines notably increased the content of endogenous Put and mildly changed Spd and Spm.Among the three polyamines,Spd and Spm influenced each other.5.A 728bp ACS gene fragment named LcACS1 was isolated from litchi for the first time using a homology-based method.Sequence analysis revealed that the coding sequence fragment ofACS gene was 493bp which deduced 165 amino acids.The result of BLAST showed the ACS amino acid showed 82%to 89%homology with ACS genes from other 9 plants reported.Four conserved catalytic domains in the ACS gene were found and there is respective 109bp intron and 125bp intron in the domain l and domain3.6.A 584bp SAMDC gene fragment named LcSAMDC1 was isolated from litchi via RT-PCR for the first time.Sequence analysis revealed that the fragment of SAMDC gene encode product of 194 amino acids.BLAST seach demonstrated that LcSAMDC1 showed above 78%sequence identity with other plants SAMDC genes.The deduced amino acids of LcSAMDC1 showed 75%to 85%identity with SAMDC from 9 other plants.Four conserved catalytic domains in the SAMDC gene were found.