Group of Biotechnology of Pharmaceutical Plants, Laboratory of Pharmacognosy, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece; Laboratory of Microbiology, School of Medicine, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece.
Group of Biotechnology of Pharmaceutical Plants, Laboratory of Pharmacognosy, Department of Pharmaceutical Sciences, Aristotle University of Thessaloniki, 541 24, Thessaloniki, Greece; Instituto de Biología Molecular y Celular de Plantas (IBMCP), Universidad Politécnica de Valencia (UPV)-Consejo Superior de Investigaciones Científicas (CSIC), Ciudad Politécnica de la Innovación, Ed. 8E, Ingeniero Fausto Elio s/n, Valencia, Spain.
Plant Physiol Biochem. 2020 Nov;156:291-303. doi: 10.1016/j.plaphy.2020.08.040. Epub 2020 Aug 27.
Ascorbate oxidase (AO, EC 1.10.3.3) is a copper-containing enzyme localized at the apoplast, where it catalyzes the oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHA) via monodehydroascorbic acid (MDHA) intermediate. Despite it has been extensively studied, no biological roles have been definitively ascribed. To understand the role of AO in plant metabolism, fruit growth and physiology, we suppressed AO expression in melon (Cucumis melo L.) fruit. Reduction of AO activity increased AA content in melon fruit, which is the result of repression of AA oxidation and simultaneous induction of certain biosynthetic and recycling genes. As a consequence, ascorbate redox state was altered in the apoplast. Interestingly, transgenic melon fruit displayed increased ethylene production rate coincided with elevated levels of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase (ACO, EC 1.14.17.4) activity and gene expression, which might contribute to earlier ripening. Moreover, AO suppressed transgenic melon fruit exhibited a dramatic arrest in fruit growth, due to a simultaneous decrease in fruit cell size and in plasmalemma (PM) ATPase activity. All the above, support for the first time, the in vivo AO participation in the rapid fruit growth of Cucurbitaceae and further suggest an alternative route for AA increase in ripening fruit.
抗坏血酸氧化酶（AO，EC 1.10.3.3）是一种定位于质外体的铜结合酶，在质外体中，它通过单脱氢抗坏血酸（MDHA）中间产物催化抗坏血酸（AA）氧化为脱氢抗坏血酸（DHA）。尽管它已经被广泛研究，但尚未明确赋予其任何生物学功能。为了了解 AO 在植物代谢、果实生长和生理中的作用，我们在甜瓜（Cucumis melo L.）果实中抑制了 AO 的表达。AO 活性的降低增加了甜瓜果实中的 AA 含量，这是 AA 氧化受到抑制和某些生物合成和循环基因同时诱导的结果。因此，质外体中的抗坏血酸氧化还原状态发生了改变。有趣的是，转基因甜瓜果实表现出乙烯生成速率的增加，同时伴随着 1-氨基环丙烷-1-羧酸氧化酶（ACO，EC 1.14.17.4）活性和基因表达的升高，这可能有助于果实更早成熟。此外，AO 抑制的转基因甜瓜果实的生长急剧停止，这是由于果实细胞大小和质膜（PM）ATP 酶活性同时降低所致。所有这些都首次支持了 AO 参与葫芦科果实快速生长的体内作用，并进一步表明 AA 在成熟果实中增加的另一种途径。
