Effect of shading on ascorbic acid accumulation and biosynthetic gene expression during tomato fruit development and ripening

Abstract

The purpose of the current study was to determine the effect of leaf shading, fruit shading, and a combination of both, on the accumulation of ascorbic acid (AsA) and the expression levels of AsA biosynthetic genes at the immature green, mature green, breaker, and red ripe stages of <i>Ailsa craig</i> tomato during fruit development. Shading (72% reducing of light intensity) imposed on the leaves significantly reduced AsA content and AsA biosynthetic gene expression in the fruits. Leaf shading, fruit shading, and a combination of both significantly decreased the amount of total AsA and reduced AsA to a range of 18.5%−31.5% at mature green, breaker, and red ripe stages of tomato fruits, with no significant change at the immature green stage of fruits. Moreover, reducing the light intensity in tomato leaves, fruits or both resulted in reduced expression of most AsA biosynthetic genes in the fruits, except for <i>PMM, cAPX, tAPX,</i> and <i>APX7</i> genes under leaf shading, <i>GPI, PMI, PMM, GP1, GP2, cAPX,</i> and <i>tAPX</i> genes under fruit shading, and <i>PMM, cAPX, APX1,</i> and <i>APX7</i> genes under both shading. The expression level of <i>GMP, GP1,</i> and <i>GalDH</i> showed an up-regulation at the red ripe stage in fruits with leaf shading, and also an up-regulation at the immature green and red ripe stages with both shading. Furthermore, positive correlations between expression of AsA biosynthetic genes and AsA accumulation were recorded under leaf shading, fruit shading, and both types of shading, while a negative correlation was recorded under normal conditions without shading.