Effect Of Light Intensity On Ascorbic Acid Accumulation And Biosynthetic Gene Expression In Tomato Fruit

Light is the main effector in photosynthesis essential in tomato growth,development and metabolites accumulation.The quality of metabolite accumulation largely depends on light intensity;therefore,it is important to study the influence of light intensity on fruit quality.The purpose of current study was the determination of the leaves-shading impacts,fruit shading,and both shading on the accumulation of ascorbic acid(AsA)and the level expression of AsA biosynthetic genes at the immature green,mature green,breaker,and red ripe stages of “Ailsa craig” tomato during fruit development.A shading(72% reducing of light intensity)imposed on the leaves significantly impacted AsA content and AsA biosynthetic gene expression in the fruits.Shading leaves resulted in 18.5%,22.4% and 26% reduction in total AsA levels at the mature,breaker and red ripe stages of fruits,respectively.Shading decreased reduced AsA by22.2% at mature green stages,24.7% at the breaker,and 25.2% at the red ripe stages of fruits,respectively,relative to the control(non-shading).Also,we observed a significant reduction in both total-AsA and reduced AsA at MG,BR,and RR stages of the fruit shaded and both shaded fruits;However,fruit shading resulted in the amount of total AsA a decreasing by 25.8%,28.9% and 30.6%,respectively at MG,BR,and RR stages relative to the control,while IMG stage of the shaded fruits showed a reduction by 3.2%,which was not significant.In addition,the amount of r-AsA was decreased by 3.5% at IMG,23.9% at MG,26.9% at BR,and 28.2% at RR stages in shaded fruits,relative to the control,which means that this reduction was not significant only at IMG stage of fruits.In fruits with both leaf and fruit shading,similar to leaf shading and fruit shading,it was observed that total AsA content decreased significantly by 26.1%,29.4%,and 31.5% respectively,at IMG,MG,BR,and RR stages of tomato fruits,and the reduced AsA content exhibited a significant decreasing by 25.9%,27.7%,and 28.4%,at,MG,BR,and RR fruits,respectively.Moreover,reducing the light intensity in tomato leaves resulted in reduced expression of most genes in the fruits,except for PMM,cAPX,tAPX,and APX7 genes which displayed a nonsignificant change under low light condition.In shaded fruits we observed a low expression level in most genes except for GPI,PMI,PMM,GP1,GP2,cAPX,and tAPX genes which indicated no significant in response to low light condition.However,in both shading fruits the transcription level of the genes,showed us a further impact reduction in most genes,in relative to the fruit shading,which means only the PMM,cAPX,APX1,and APX7 genes exhibited a non-significant efficacy.Interestingly,the regulation level of the GPM,GP1,and Gal DH showed an up-regulation at the red ripe stage in leaf shaded fruits,and also an up-regulation at the immature green and red ripe stages in both shaded fruits under low light intensity.Furthermore,positive correlations between expression of AsA biosynthetic genes and AsA accumulation were recorded in leaf shaded,fruit shaded,and both shaded fruits,while a negative correlation was recorded for non-shaded fruits.