NADP-ME And PEPC Gene Expression During The Fruit Development Of Loquat

Organic acid and composition is one of the important factors determining fruit flavor and quality. High fruit acidity is one of the main problems affecting loquat (Eriobotrya japonica Lindl.) industry in China. Therefore, low acid 'Changhong 3' and high acid 'Jiefangzhong' , which are two leading cultivars of loquat growing in Fujian province, were selected as experimental material in this study. Changes in NADP-ME and PEPC gene expression as well as malic acid content in the pulp during the fruit development were investigated in this study. This objectives were to determine the relationship between NADP-ME and PEPC gene expression and malic acid content in the pulp, provide some theoretic basis for making reasonable and effective measures to reduce fruit organic acid content, and improve its quality. The main results were summarized as follows:1. Malic acid content of the two cultivars increased at the earlier stages of fruit development and decreased at the latter stages. Malic acid content decreased to a larger degree in the low acid cultivar than in the high acid one at the latter stages of fruit development. This is the main cause of malic acid content difference between the two cultivars.2. The conservative regions of NADP-ME and PEPC cDNA were cloned from loquat pulp by RT-PCR technology. NADP-ME gene shared the highest identity at both the nucleotide (94%) and amino acid (96%) levels with apple. PEPC gene shared the highest identity at the nucleotide level with caster (83%) and at the amino acid level with cotton (92%).3. Northern bloting showed that the trends of changes in NADP-ME gene expression in the pulp of the two cultivars during the fruit development were basically similar. As fruit developed, the mRNA level decreased firstly, then increased, and stayed high although decreased slightly at the last sampling date. At each given date, mRNA level was lower in the low acid cultivar than in the high acid one. It was found that PEPC gene probe was hybridized to two mRNA bands in the pulp of the two cultivars. The abundance of the two bands in the pulp of the low acid cultivar was high at the earlier stages of fruit development, and reached a peak on April 12^th, then gradually declined at the latter stages. However, the abundance of the two bands in the pulp of the high acid cultivar decreased gradually with fruit development, and reached a valley on March 29^th and April 12^th respectively, then increased at the latter stages and stayed high although decreased slightly at the last sampling date.4. During the fruit development, malic acid content in the pulp of the two cultivars may be regulated by NADP-ME transcript level. In the low acid cultivar, the changes in PEPC gene expression in the pulp were basically concomitant with malic acid accumulation and degradation during the fruit development; however, in the high acid cultivar, the changes in PEPC gene expression in the pulp differred from the changes in malic acid content during the fruit development. The difference in malic acid content between the two cultivars may be regulated not only by NADP-ME and PEPC gene expression, but also by the post-transcript and post-translation levels.