High Temperature Inhibits Ascorbate Recycling and Light Stimulation of the Ascorbate Pool in Tomato despite Increased Expression of Biosynthesis Genes

Abstract

Understanding how the fruit microclimate affects ascorbate (AsA) biosynthesis, oxidation and recycling is a great challenge in improving fruit nutritional quality. For this purpose, tomatoes at breaker stage were harvested and placed in controlled environment conditions at different temperatures (12, 17, 23, 27 and 31°C) and irradiance regimes (darkness or 150 µmol m-2 s-1). Fruit pericarp tissue was used to assay ascorbate, glutathione, enzymes related to oxidative stress and the AsA/glutathione cycle and follow the expression of genes coding for 5 enzymes of the AsA biosynthesis pathway (GME, VTC2, GPP, L-GalDH, GLDH). The AsA pool size in pericarp tissue was significantly higher under light at temperatures below 27°C. In addition, light promoted glutathione accumulation at low and high temperatures. At 12°C, increased AsA content was correlated with the enhanced expression of all genes of the biosynthesis pathway studied, combined with higher DHAR and MDHAR activities and increased enzymatic activities related to oxidative stress (CAT and APX). In contrast, at 31°C, MDHAR and GR activities were significantly reduced under light indicating that enzymes of the AsA/glutathione cycle may limit AsA recycling and pool size in fruit pericarp, despite enhanced expression of genes coding for AsA biosynthesis enzymes. In conclusion, this study confirms the important role of fruit microclimate in the regulation of fruit pericarp AsA content, as under oxidative conditions (12°C, light) total fruit pericarp AsA content increased up to 71%. Moreover, it reveals that light and temperature interact to regulate both AsA biosynthesis gene expression in tomato fruits and AsA oxidation and recycling.

Foliar Application of Copper Nanoparticles Increases the Fruit Quality and the Content of Bioactive Compounds in Tomatoes

“…In tomato fruits, it has been shown that under conditions of high-temperature stress, the CAT enzymatic activity increases [73]. Similar results were obtained in tomato leaves [75]. Therefore, the increase in CAT activity has a positive response in fruits.…”

Ascorbate biosynthesis and its involvement in stress tolerance and plant development in rice (Oryza sativa L.)

“…It has been shown for Vicia faba that young seeds are not capable of producing AsA and are provided with AsA by the maternal tissues (Arrigoni et al 1992). Moreover, studies in tomato have shown that AsA can be transported from leaves to fruits (Giovanelli et al 1999;Massot et al 2013;Stevens et al 2007). …”

Differences in Blossom-end Rot Resistance in Tomato Cultivars is Associated with Total Ascorbate rather than Calcium Concentration in the Distal End Part of Fruits <i>per se</i>

“…Ascorbate concentrations were reported to be limited during green fruit development , which is also the stage of BER appearance (Spurr, 1959). Ascorbate concentration in tomato fruit was also found to be reduced under high salinity (D'Amico et al, 2003), heat (Massot et al, 2013) and light stress conditions (Ioannidi et al, 2009;, all conditions favorable for BER appearance (Olle and Bender, 2009). Interestingly, fruit calcium concentration, the major known factor in BER initiation, has also been proposed to be positively correlated with ascorbate levels in tomato fruit (Premuzic et al, 1998) and the conditions favorable to BER, like salinity, drought and heat stress, were also found to increase ROS levels in tomato fruit (Leyva et al, 2013;Murshed et al, 2013Murshed et al, , 2014.…”