Effect Of Exogenous ABA On Starch Synthesis In Lotus Root Rhizomes

Lotus(Nelumbo nucifera Gaertn.)is a perennial aquatic herb of the lotus family(Nelumbonaceae),native to China and India,and is the largest cultivated aquatic vegetable in China.The expanded rhizome of lotus root is the main edible organ,and starch is the main component of the rhizome.The starch content of lotus root rhizomes accounts for more than 70%of the total dry matter mass of rhizomes.The starch synthesis pathway in plants is well understood,and ABA can regulate starch synthesis in a variety of plants,however,the mechanism of ABA regulation of starch synthesis and expression in lotus root is less studied.In-depth analysis of ABA-regulated starch synthesis in lotus root rhizomes will not only help us understand the physicochemical properties of starch,but also provide a theoretical basis for the cultivation and production of lotus root.In this paper,the effects of exogenous ABA on starch synthesis in the rhizome of lotus root were studied using ’Meirenhong’ and ’X5’ as experimental materials.The main results as below:1.Effects of exogenous ABA on photosynthesis and starch content in lotus rootWhen exogenous ABA was applied to the leaves in the non-expanded stage of lotus root rhizome,the stomatal conductance of both leaves was lower than that of CK at the 5th day of treatment.From the 3rd day,the transpiration rate of treatment group was lower than the net photosynthetic rate of CK and gradually increased than that of CK after exogenous ABA treatment.During the process of rhizome enlargement,the total starch content of ’Meirenhong’and ’X5’ was both higher than that of the control,especially the total starch content at the beginning of rhizome enlargement was 1.29,0.77 times that of the control,respectively.Exogenous ABA treatment could reduce the stomatal conductance,transpiration rate of lotus root leaves,increase the net photosynthetic rate,promote the synthesis of more starch in the rhizome,and increase the content of total starch.2.Effects of exogenous ABA on expression of key genes in starch synthesis in lotus rootThe expression of NnSS1 gene in ’Meirenhong’rhizome was significantly higher than that in the control group at the beginning of expansion.The expression of NnSBE1 gene was significantly higher than that of the control at the beginning and early stage of expansion.In ’X5’rhizome,the expression of NnSBE1 gene was up-regulated at the beginning and middle of enlargement,and the difference was significant.After exogenous ABA treatment,the expression of NnABI4 gene in the two lotus root materials during rhizome enlargement was significantly higher than that in the control lotus root rhizome.The genes that were up-regulated by ABA induction were NnSS1,NnSBE1 and NnAB14 gene related to ABA signal transduction.3.Interaction between ABI4 and NnSS1 in the rhizome of lotus rootThe results of subcellular localization showed that NnAB14 encoded a nucleoprotein and NnSS1 was localized in the chloroplast.The yeast monoheterozyme and dual luciferase assays showed that NnABI4 protein could directly bind to the NnSS1 promoter,and the FLUC/RLuc value was 2.67 times that of the contrastive irradiation.NnABI4 could bind and activate the NNSS1 promoter and enhance the expression of NnSS1 gene.