Stevens R, Page D, Gouble B, Garchery C, Zamir D, Causse M
INRA, UR1052, Unité de génétique et amélioration des fruits et légumes, Domaine St Maurice BP94, 84143 Montfavet, France.
Plant Cell Environ. 2008 Aug;31(8):1086-96. doi: 10.1111/j.1365-3040.2008.01824.x. Epub 2008 Apr 21.
Quantitative trait loci (QTL) mapping is a step towards the identification of factors regulating traits such as fruit ascorbic acid content. A previously identified QTL controlling variations in tomato fruit ascorbic acid has been fine mapped and reveals that the QTL has a polygenic and epistatic architecture. A monodehydroascorbate reductase (MDHAR) allele is a candidate for a proportion of the increase in fruit ascorbic acid content. The MDHAR enzyme is active in different stages of fruit ripening, shows increased activity in the introgression lines containing the wild-type (Solanum pennellii) allele, and responds to chilling injury in tomato along with the reduced/oxidized ascorbate ratio. Low temperature storage of different tomato introgression lines with all or part of the QTL for ascorbic acid and with or without the wild MDHAR allele shows that enzyme activity explains 84% of the variation in the reduced ascorbic acid levels of tomato fruit following storage at 4 degrees C, compared with 38% at harvest under non-stress conditions. A role is indicated for MDHAR in the maintenance of ascorbate levels in fruit under stress conditions. Furthermore, an increased fruit MDHAR activity and a lower oxidation level of the fruit ascorbate pool are correlated with decreased loss of firmness because of chilling injury.
数量性状基因座（QTL）定位是朝着鉴定调控果实抗坏血酸含量等性状的因子迈出的一步。先前鉴定出的控制番茄果实抗坏血酸变异的一个QTL已被精细定位，结果表明该QTL具有多基因和上位性结构。单脱氢抗坏血酸还原酶（MDHAR）等位基因是果实抗坏血酸含量增加部分的一个候选基因。MDHAR酶在果实成熟的不同阶段具有活性，在含有野生型（潘那利番茄）等位基因的渐渗系中活性增加，并且在番茄中与抗坏血酸氧化态/还原态比率一起对冷害作出反应。对具有全部或部分抗坏血酸QTL以及有或没有野生型MDHAR等位基因的不同番茄渐渗系进行低温贮藏，结果表明，与非胁迫条件下收获时38%的变异解释率相比，酶活性解释了4℃贮藏后番茄果实还原型抗坏血酸水平84%的变异。这表明MDHAR在胁迫条件下维持果实中抗坏血酸水平方面发挥作用。此外，果实MDHAR活性增加以及果实抗坏血酸库的氧化水平降低与冷害导致的果实硬度损失减少相关。
