The Mechanism Of Abscisic Acid (ABA) On Seed Oil Accumulation In Cruciferous Oilseeds

Rapeseed(Brassica napus L.)is a vital edible oil source.Comprehensive research on the factors influencing the seed oil accumulation is of utmost importance to improve the seed oil content and quality,as well as for the agricultural industry.The seed oil contains various fatty acid components which have different functions and qualitative indices.During the biosynthesis of seed fatty acid(FA)in cruciferous plants,oleic acid(C18:1)could be branched in two different pathways.By the action of desaturase genes fatty acid desturation2(FAD2)and fatty acid desaturation3(FAD3),it could be converted into linoleic and linolenic acid,which is the important source for edible oil.And/or by the enzymatic activity of fatty acid elongase gene FAE1,oleic acid could be converted into very long chain fatty acid VLCFA,including ecrucic acid(C22:1),which can be industrial raw material.Plant hormones regulate the processes involved in plant growth and development by interacting with each other,either synergistically or antagonistically.Previous researches from our lab revealed significant variations in seed fatty acid components and found promising reduction in seed total fatty acid when the gibberellin(GA)signal was enhanced,and significant increase in rapeseed oil was obtained with the exogenous applicantion of paclobutrazol(PAC,gibberellin biosynthesis inhibitor)at reproductive stage.Abscisic acid(ABA)could interact antagonistically with gibberellin(GA)in many processes.So there is paucity in knowledge about the role of ABA in oil accumulation in oilseed crops.The current study was conducted in three parts with the objectives to evaluate the effect of exogenous application of ABA in different concentrations on the oil accumulation in seeds of Arabidopsis and two genotypes of brassica napus.L,namely,Jiuer-13xi(JR)and Zheyou50(ZY).Moreover,seeds of brassica obtained at 28th day after pollination were grown on MS culture media with different ABA concentrations to perform in vitro growth analysis.The major findings of our research are as follow:1.The exogenous application of ABA accelerated yellowing of leaves in Arabidopsis and desiccation of pod walls in brassica genotype Jiuer-13xi(JR).Moreover,spraying high concentration(100?M,200?M)ABA in early phase(before bolting stage)inhibited the sillique development in Arabidopsis.2.Spraying suitable ABA could promote the FA accumulation,which is significant when spraying JR with 5?M ABA.There was no significant difference in the FA accumulation in ZY,which meant the spraying time and concentration should accord to the different growth period of special varieties.The effect of ABA on FA synthesis had a dual functions,it was not benefit for the FA accumulation when spraying high concentration ABA.3.Spraying ABA to the Arabidopsis and brassica resulted in the inhibition of ecrucic acid synthesis,whereas the average content of oleic acid,linoleic acid and linolenic acid were increased,which is significant in the JR seeds.The qRT-PCR results showed that the FAE1 gene in Arabidopsis pod and brassica seeds was down-regulated significantly which indicated that ABA could inhibit the oleic acid(C18:1)elongation pathway,and promote the synthesis of PUFA indirectly.4.After 18 days of incubation in vitro cultured 28 DAP Brassica napus seeds resulted in no significant change in the seed total FA.However,the compositions of FA derivatives were significantly affected.Contrary to the spraying experiment,the PUFA(C18:1 and C18:3)were markedly reduced,and the very long chain fatty acids VLCFA(C>18)were noticeable increased,especially in Zheyou50(ZY).These results illustrated that due to higher concentration of ABA,and most of the genes were inhibited.However,the expression of FAD genes was highly significant in both genotypes,whereas,FAE1 gene was no significantly or slightly affected.From the genes expression profile and FAs content analysis,we concluded that in vitro condition,ABA inhibited the FA desaturation pathway which resulted in the conversion of more C18:1 to VLCFA.5.Spraying 20 ?M ABA to Arabidopsis and 5?M to Jiuer-13xi(JR)resulted in significantly reduced protein contents whereas the average FA contents were comparatively higher than that of control plants,respectively.Therefore,ABA could also regulate the negative correlation between seed FA and protein contents.Because of the different sensitivity to ABA in pod and seeds,different FA components results were got in spraying and in vitro experiments.ABA could regulate the carbon flux to elongation or desaturation by FAD or FAE genes at different concentrations,and the findings could provide reference to produce special types of oil for special purposes.