The Initial Investigation For Function Of ABA Involved In Starch Accumulation In Storage Root Of Cassava

Cassava is an important food crop and resources for industry starch and bioethanol globally, because of it’s extremely biological characteristics as high biomass, tolerance to drought and barren soil and high quality starch.Cassava could be he a candidate crop to resolve the energy and food crisis in the near future. Up to now, we known less about the molecular mechanism of the high yield and drought tolerance in cassava. but it is indicated that ABA will play a key role in the process. However, it almost was in a black of the knowledge.In the study, using two cultivars, SC124and Arg7, we designed the experiment with treatment of ABA and sodium tungstate. While the plant grow to60days in pot culture condition, we take the ABA treatment each two weeks, the introgrovious ABA and other hormones were investigated after the first treatment at2h,4h,8h,12h,24h and48h. Then we evaluated the yield and components after3times of treatment.Other ways, we screened the expression levels of genes for ABA synthesis, regression and starch synthesis. The main results have been described as the followings:1. In the pre experiment, the moderate concentration of ABA and sodium tungstate treatment were selected with10mg/Land2000mg/L respectively. According to it, we found the ABA treatment changed the expression of genes for ABA synthesis, receptor such as PYL, and SUSY involved in starch synthesis.2.ABA and sodium tungstate really modified the growth, accumulation of biomass and fresh storage root yield compared to their control. Although we could not find a clear trend according to the pot culture experiment. It seems that ABA treatment increased tuber root yield and biomass but it need to be confirmed further under a better controllable condition.3.Changes of Endogenous ABA in cassava shows circadian tendency controlled by the light signal: the same trend of endogenous ABA in two cassava varieties, SC124and Arg7under normal condition illuminates that the endogenous ABA level in plants is significantly regulated by the light cycle which reaches higher level before noon and has lower level in the afternoon till light, and the same tendency is observed in the following day. 4. In cassava there is regulating mechanism balancing the homeostasis of ABA Based on the level changes of endogenous ABA and also changes in related plant hormone levels and the expression changes regarding ABA biosynthetic and repression genes in cassava plants under ABA and sodium tungstate treatment we speculate there is a flexible ABA regulating mechanism within cassava which can keep ABA in a stable level.①ABA has degraded only2hours after sodium tungstate and ABA treatment and the concentration is even lower compared with the controls and ABA concentration remained at lower level during the following4to12hours after treatment. This means that the exogenous ABA absorbed by the plants begins to degrade within2hours after treatment so as to balance the homeostasis.②Different with the level changes of ABA, other plant hormones IAA and GA that have antagonism with ABA express rather contrast changes. There has been reports on the antagonism between IAA and ABA, GA and ABA, thus we propose that this antagonism might be a way to balance the ABA homeostasis in Cassava.③After the treatment of sodium tungstate and ABA, the expression levels of main ABA synthesizing genes ZEP%ALDO are significantly declined, on the other hand, UTG, the ABA regression gene’s expression level increases though it is merely obvious at midnight when ABA level reaches lowest and this means that UTG is submitted to the dual regulation of ABA feedback and light signal.5.The relationship of ABA and starch metabolism remains unclear based on this study There is no evidence supporting certain stimulating or repression regulation based on the expression analysis of ABA signaling receptor genes and core starch biosynthetic genes from plants both under normal growth condition and under ABA treatment. The main question could be that the ABA homeostasis with cassava can’t simply be explained by mere positive or negative effects. In this study we used leafs rather than starch storage organs and we need more gene expression data and other information on ABA levels and other plant hormones in storage roots to reach a final conclusion.