Linking high light-induced cellular ionic and oxidative responses in leaves to fruit quality in tomato

Light regulates cellular responses in leaves through a myriad of signalling cascades that control the growth and fruit quality of tomatoes. The relationships between high light-induced cellular hydrogen peroxide (H2O2) production and Ca2+ signalling in leaves (source) and fruits (sink) are rarely investigated. Experiments were conducted in two greenhouse trials to study the effects of high light on tomatoes at the plant-, organ-, cellular-, and molecular-levels. Short-term (1-week) and long-term (7-weeks) high light treatment led to a significant increase of H2O2 whereas, the accumulation of Ca2+ in leaf mesophyll cells was decreased significantly after 1- and 2-weeks of high light. Furthermore, photoreceptor genes (e.g., PHYB2, CRY2) were significantly downregulated in the leaves, however, Ca2+ and K+ transporter genes were not affected in the long-term, high light treatment. Notably, high light significantly improved the total soluble solids in tomato fruit without affecting fruit firmness, pH, and titratable acidity. Interestingly, we found a significant correlation between leaf mesophyll H2O2 production and fruit colour, fruit fresh weight, and titratable acidity, in addition to a correlation between leaf mesophyll Ca2+ concentration and fruit firmness. This study proposed that leaf mesophyll H2O2 and Ca2+ may be linked to fruit quality under high light conditions, which is useful for the early prediction of yield and postharvest quality of tomatoes in protected horticultural production. We suggest that light-induced fruit development and fruit quality, and their synchronisation with light signals in the leaf should be investigated to elucidate long-distant light signalling transduction in plants.