Carotenoid content, leaf gas-exchange, and non-photochemical quenching in transgenic tomato overexpressing the β-carotene hydroxylase 2 gene (CrtR-b2)

Abstract

Non-photochemical quenching (NPQ) of chlorophyll a fluorescence and leaf gas-exchange were investigated in relation to the chlorophyll and carotenoid content, and the xanthophyll cycles in wild type tomato ( Solanum lycopersicum, L. cv Red Setter (RS)) and in two transgenic lines (UO and UU) over-expressing β-carotene hydroxylase. Potted plants were grown in a glasshouse under low light (LL, 100 μmol m −2 s −1) or high light (HL, 300 μmol m −2 s −1). The maximum quantum efficiency of photosystems II (PSII) photochemistry in dark-adapted leaves ( F v/ F m) was higher than 0.82 in all treatments while photosynthetic CO 2 assimilation ( A) was higher than 14 μmol m −2 s −1, and stomatal conductance ( g s) higher than 0.4 mol m −2 s −1 in HL plants, indicating no effects induced by the genetic modification. Chlorophyll content and composition changed little, whereas transgenic plants had up to 47% higher total carotenoid content than wild type plants. Violaxanthin was the most abundant carotenoid in transgenic plants, with more than 2-fold higher content than the average 0.586 mg g −1 found in RS plants. Transgenic plants had similar light-induced steady-state NPQ compared to wild type plants, but had slower dark relaxation because of the decreased de-epoxydation state index due to the higher violaxanthin accumulation, despite the higher zeaxanthin content.