Abstract
Cultivated tomato species develop leaf injury while grown in continuous light (CL). Growth, photosynthesis, carbohydrate metabolism and antioxidative enzyme activities of a cultivated (Solanum lycopersicum L. ‘Aromata’) and a wild tomato species (Solanum pimpinellifolium L.) were compared in this study aiming to analyze the species-specific differences and thermoperiod effects in responses to CL. The species were subjected to three photoperiodic treatments for 12 days in climate chambers: 16-h photoperiod with a light/dark temperature of 26/16°C (P16D10 or control); CL with a constant temperature of 23°C (P24D0); CL with a variable temperature of 26/16°C (P24D10). The results showed that both species grown in CL had higher dry matter production due to the continuous photosynthesis and a subsequent increase in carbon gain. In S. lycopersicum, the rate of photosynthesis and the maximum photochemical efficiency of photosystem II declined in CL with the development of leaf chlorosis, reduction in the leaf chlorophyll content and a higher activity of antioxidative enzymes. The normal diurnal patterns of starch and sugar were only present under control conditions. The results demonstrated that CL conditions mainly affected the photosynthetic apparatus of a cultivated species (S. lycopersicum), and to a less degree to the wild species (S. pimpinellifolium). The negative effects of the CL could be alleviated by diurnal temperature variations, but the physiological mechanisms behind these are less clear. The results also show that the genetic potential for reducing the negative effects of CL does exist in the tomato germplasm.
Highlights
Providing supplemental light as continuous light (CL) in protected plant production systems can increase plant growth and development
Chlorophyll Fluorescence and Photosynthesis The Fv/Fm of S. lycopersicum was significantly lower on day 8 and 12 in plants from the CL treatments compared to P16D10 (Figure 2A)
The assimilate partitioning differed in the two plant species showing that the increase in shoot dry weight (DW) in CL-conditions was pronounced for both leaves and stems of S. lycopersicum, whereas mainly stem DW increased in S. pimpinellifolium
Summary
Providing supplemental light as continuous light (CL) in protected plant production systems can increase plant growth and development. Plants grown in CL accumulate high amounts of leaf starch and soluble sugars (Dorais et al, 1996; Globig et al, 1997; Gestel et al, 2005) and a relationship between leaf chlorosis development and starch accumulation has been suggested in tomato and eggplant (Bradley and Janes, 1985; Murage et al, 1996; Demers and Gosselin, 2002), whereas no relationship was found between these parameters in cucumber (Wolf and Langerud, 2006). This increased source activity could initiate downregulation of PN at the protein or transcriptional level, thereby lowering the amount and/or activity of Rubisco (Stutte et al, 1996; Globig et al, 1997)
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