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

Accepted 22 August 2011Keywords:Tomato?-Carotene hydroxylase CarotenoidsXanthophyll cycleChlorophyll a fluorescence Non-photochemical quenching1. IntroductionUnder high irradiance, the absorbed light energy exceeds the saturation point of photosynthesis and the photosynthetic appa- ratus can experience a potentially harmful condition (Foyer et al., 1994; Oguchi et al., 2009). As a result, reactive species of oxygen (ROS) may be generated (Blankeship, 1998), with a consequent photooxidative damage (Macpherson et al., 1993; Telfer et al., 1994; Niyogi, 1999). A line of defense against ROS reactions is developed by carotenoids (Cars). These molecules are able to harvest the exci- tation energy and they contemporary play a fundamental role in the photoprotective mechanism, quenching the excited state of chloro- phylls (Krinsky, 1978; Blankeship, 1998; Bassi and Caffarri, 2000; Kalituho et al., 2007b). Improved stress tolerance was found in rice after exogenous application of ?-carotene (?-car) (Yang et al., 2002). On the contrary, a very low viability of tomato ghost mutants has been demonstrated and it seems to be caused by the inhibi- tion of the carotenoid biosynthetic pathway (Scolnik et al., 1987;* Corresponding author. Fax: +39 0817718045. E-mail address: pasquale.giorio@cnr.it (P. Giorio).0098-8472/$ - see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.08.009abstractNon-photochemical quenching (NPQ) of chlorophyll a fluorescence and leaf gas-exchange were inves- tigated 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 ?-carotene hydroxylase. Potted plants were grown in a glasshouse under low light (LL, 100 ?mol m-2 s-1 ) or high light (HL, 300 ?mol m-2 s-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 14 ?mol m-2 s-1 , and sto- matal conductance (gs ) 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 0.586mgg-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.