Supplementary Red light results in the earlier ripening of tomato fruit depending on ethylene production

In greenhouse tomato production, the lower canopy of tomato plants is often shaded by the neighbouring tomato plants. Supplementary lighting can be used to provide sufficient light energy for plants. Red light is regarded as the most efficient spectrum in supplementary lighting. Whether and how supplementary red light in the ambient of sunlight affect the ripening of tomato remain to be elucidated. In this research, the impacts of supplementary red light on tomato ripening were examined by comparing the impacts of supplementary red light on ripening-related regulators, ethylene synthesis, ethylene signaling, carotenoid synthesis and light signaling in Micro-Tom wild type tomato fruit and ripening-inhibitor (rin) mutant. Supplementary red light did not affect the fruit ripening of rin mutant, because the deficiency of SlRIN resulted in down-regulation of genes encoding ripening-related regulators and suppression of ethylene biosynthesis. The wild type tomato fruit under supplementary red light showed accelerated color transition during ripening, which was associated with the increased expressions of genes encoding ripening-related regulators and ethylene biosynthesis. The increased expressions of genes encoding phytochrome in wild type tomato fruit under supplementary red light might reduce the level of phytochrome-interacting factors, resulting in higher activation of the phytoene synthase and overaccumulation of phytoene. Supplementary red light in ambient sunlight resulted in the accumulation of phytoene and the earlier ripening in tomato fruit, which depended on ethylene production.