超量表达苹果酸脱氢酶基因提高苜蓿对铝毒的耐受性

在酸性土壤中，铝毒是许多作物正常生产的主要限制因子。虽可通过施用生石灰来改良土壤酸碱度，但只能改善土壤表层，在实际应用中受到很大限制。紫花苜蓿作为一种非常重要的牧草、饲料，在酸性土壤条件下苜蓿生长缓慢甚至死亡。我国南方水热资源丰富，但土壤多偏酸性，限制了苜蓿南移。有机酸能螯合铝离子，减轻铝对植物根系的危害。苹果酸是游离铝离子的有效螯合剂，而苹果酸脱氢酶(Malate Dehydrogenase，MDH)催化草酰乙酸形成苹果酸。本研究在苜蓿中超量表达苹果酸脱氢酶基因，通过抗生素筛选、组织化学染色和PCR扩增等技术鉴定出转化植株，并对转化株系进行了耐铝胁迫试验，比较分析了转基因株系与非转基因株系的的相对伸长量，转基因株系根相对伸长量比对照高出3．6％～22．5％。说明超量表达neMDH基因可提高了转基因苜蓿对铝毒的耐受性。

Transgenic Alfalfa Plants Overexpressing Nodule-enhanced Malate Dehydrogenase Enhances Tolerance to Aluminum Toxicity

In acidic soils, aluminum (Al) toxicity is a severe impediment to production of many crops. Though Al toxicity can be decreased through lime application to raise soil pH, this amendment only remedies surface soil, and liming is limited in practice. Alfalfa (Medicago Sativa L.) is a most important legume forage crop, and adapted well in natural and alkalescence, not in acidic soil. Malate is a key metabolite in plants and catalyzed by malate dehydrogenase (MDH) of oxaloacetate. It is one of commonly organic acid that can form sufficiently complexes with Al3+ to detoxicity. The neMDH gene was transformated into the alfalfa by suspension embryogenic callus. Root elongation in hydroponic solutions showed that the transgenic plant have increased Al3+ tolerance. The transgenic plants have higher relative root elongation under 20umol/L Al3+ stress than untransformed control. After 3d under 20umol/L Al3+, the root system of untransformed control was soft and rotted while transgenic plant grown well.