苹果果实GalDH和GalLDH基因的表达与AsA的关系

 【目的】进一步探明苹果果实是否具有抗坏血酸（AsA）合成的能力。【方法】从‘嘎拉’苹果果实中克隆AsA合成关键酶L-半乳糖脱氢酶（L-galactose dehydrogenase, GalDH）全长cDNA序列,检测它与另一合成酶L-半乳糖-1,4-内酯脱氢酶（L-galactono-1,4-lactone dehydrogenase, GalLDH）在苹果不同组织中的表达及酶活性与AsA含量的关系。【结果】克隆获得的苹果GalDH cDNA含有975 bp的完整开放阅读框,编码一条分子量为34.97kD、含324个氨基酸残基的蛋白质,登录号为GQ131419。在叶片和苹果果实不同组织中,均能检测到GalDH和GalLDH基因mRNA表达和活性,叶片高于果实,幼果高于成熟果,果皮高于果肉。同时,苹果果皮中的AsA含量受光的调控,二者在阳面果皮的表达和活性明显高于阴面果皮,而阳、阴面果肉间无明显差异。不同组织中的AsA含量与GalDH和GalLDH活性均呈显著正相关性。【结论】进一步证明了苹果果实自身具有经L-半乳糖途径合成AsA的能力,且合成可能是苹果果实AsA形成的主要决定因子。

Relationship Between Expressions of GalDH and GalLDH and Ascorbate Content in Apple Fruits

Objective] The objective of this experiment was to further investigate whether apple fruit has the capability of AsA biosynthesis. Method] L-galactose dehydrogenase (GaIDH) cDNA which encode a enzyme involved in synthesizing As A in plants was isolated from young fruit of Malus domestica Borkch cv. Gala, then the relationship of the mRNA expression level and enzyme activities of GalDH and L-galactono-l,4-lactone dehydrogenase(GalLDH) on AsA in different tissues of apple was studied. Result] cDNA of GalDH, which was cloned from young fruit exocarp of apple, has an 975 bp open reading frame and encodes a protein of 324 amino acid residues with a molecular mass of 34.97 kD, its accession no in GenBank is GQ131419. The mRNA expression levels and enzyme activities of GalDH and GalLDH were detected in leaves as well as different tissues of apple fruits. Both of mRNA expression levels and activities of the two enzymes in leaves were higher than that in fruit, in young fruit was higher than that in mature fruit, while in peel was higher than that in flesh. Meanwhile, AsA content in apple peel was regulated by light condition. The mRNA expression levels and enzyme activities of both in sun side peel were higher than that in shaded side peel, but no significant differences between sun side flesh and shaded side flesh. A significant positive correlation was detected between AsA content and enzymes activities of GalDH and GalLDH in different tissues of apple. Conclusion ] These results further suggest that apple fruit has the capability of AsA biosynthesis by L-galactose pathway, and synthesis may be a major reason of AsA formation in apple fruit.