Difference On The Mechanism Of Starch Accumulation And Degradation In The Pulp Of Bananas

Banana is not only a popular fruit around the world, but also an important food crop in Areas. Content of green banana pulp is about 70%(DW), and starch is a votial role in supporting energy, which means bananas could be recover energy as food. Amylose and amylopectin make up the complex polysaccharides that named starch. According to the digestion time, starch can be divided into non-resistant starch and resistant starch. Resistant starch in the pulp of banana is much higher than conventional crops and fruits. Resistant starch is helpful to digestion. Besides, the function of resistant starch contribute to prevention of intestinal diseases and obesity. Banana is characteristic with high starch content, which lighted banana processing industry up. This research focuses on the starch synthesis and degradation of banana fruit, elaborate the difference and changes on physiological and biochemical level.In this study, ZJ3 and EAHB were used as material. Determine the content of total starch, resistant starch and amylose through AOAC method. The expression of starch branching enzyme family was analysised by Real-time PCR. Screening the transcription factors of starch branching enzyme through yeast one-hybrid. Besides, Cavendish, Plantain and Pisang awak were used as material. Comparing the difference of starch, resistant starch and amylose content in postharvest stage. Obserbing the scale and shape of starch among three banana cultivars under the SEM. Analysis the pathway by Real-time PCR, explored the difference of starch degradation in three bananas. Mainly results and conclusion are described as follows.1. The content of water dropped in developmental banana fruit, and starch accumulated obviously. Resisrant starch and non-resistant starch of ZJ3 fruit accumulated at 1-5 weeks after flower. Resisrant starch of EAHB fruit obviously accumulated at 1-3 weeks after flower. Amylose of ZJ3 increased during development and finally reach 40%. Amylose of EAHB was 20% at first and finally reach 35%. The accumulation of starch in banana was affect by different cultivars.2. Starch branching enzyme was a key enzyme in starch synthesis. By cloning and genetic analysis of six banana GBE full-length sequence, named as Ma GBE. Sequence analysis found α-amylase catalytic domain in the amino acids sequence of Ma GBE1, Ma GBE2, Ma GBE4, Ma GBE5 and Ma GBE6, which indicated that those genes belong to starch branching enzyme family(1,4-alpha-glucan-branching enzyme). Phylogenetic analysis showed that, Ma GBE1 belong to type I, Ma GBE2, Ma GBE4 and Ma GBE6 belong to type II, Ma GBE5 belong to type III. Type II GBE played as an votal role in amylopectin synthesis. Real-time PCR result showed that Ma GBE4 was much higher expressed than others in every developmental stage of EAHB and Cavendish, indicating type II GBE was a key enzyme in the formation of amylopectin.3. The promoter of Ma GBE4 was mainly regulated by hoemones and other stress response factors. Transcription factors of Ma GBE4 were screened by Yeast one-hybrid screening system. Out result indicated that NAC, zinc finger transcription factor and leucine zipper protein involved in the regulation of expression Ma GBE4.4. Contents of starch and resistant starch decreased in postharvest banana fruit. The content of amylose was stable in Pisang awak. The content of amylose in Cavendish dropped from 35% to 10%. Amylose in Plantain rised first and decreased finally. Amylose content of was positively correlated to resistant starch content.5. Starch granual from bananas(Cavendish, Plantain and Pisang awak) were observed through scanning electron microscope(SEM). The granual of Cavendish and Plantain was round, and the Pisang awak starch was much larger. The starch of Plantain was longer than others and look like a stick. Starch granual become smaller during ripening.6. Real-time PCR results indicated that β-amylase and α-amylase genes were significantly upregulated, phosphorylase differentially expressed in Cavendish and Plantain. Combined with changes in starch content, it concluded the following conclusions as follow. β-amylase enzyme is the major role in starch degradation. α-amylase might involved in the degradation of amylopectin. phosphorylation-dependent degradation of starch contribute to the difference of Plantain and Cavendish.In summary, this research studied the synthesis and degradation of banana starch, which lay the foundation for breeding and food processing. Research on the transcription factors of starch branching enzyme(Ma GBE4), make the mechanism of regulation of GBE clear. This work could be used for improving the content of resistant starch. Inhibition of starch degradation in banana, which was great to food processing industry.