Carotenoid content, leaf gas-exchange, and non-photochemical quenching in transgenic tomato overexpressing the β-carotene hydroxylase 2 gene (CrtR-b2)
2012
Giorio, P. (Pasquale) | Giorio, Giovanni | Guadagno, Carmela R. | Cellini, Francesco | Stigliani, Lucia A. | D’Ambrosio, Caterina
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, 100μmolm⁻²s⁻¹) or high light (HL, 300μmolm⁻²s⁻¹). The maximum quantum efficiency of photosystems II (PSII) photochemistry in dark-adapted leaves (Fᵥ/Fₘ) was higher than 0.82 in all treatments while photosynthetic CO₂ assimilation (A) was higher than 14μmolm⁻²s⁻¹, and stomatal conductance (gₛ) higher than 0.4molm⁻²s⁻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 0.586mgg⁻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.
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