In comparison, figleaf gourd ( Cucurbita ficifolia) is unique among cucurbit species with an optimal root temperature at approx. In a previous study, it was found that chilling under low light significantly decreased the capacity of RuBP carboxylation but increased H 2O 2 accumulation in cucumber leaves ( Zhou et al., 2004, 2006). In this case, accumulation of the reactive oxygen species (ROS) both in shoots and roots occurred frequently, together with photosystem I (PSI) photoinhibition and an inhibited CO 2 assimilation in chilled leaves, and a reduction in the activity of plasma membrane H +-ATPase in chilled roots ( Terashima et al., 1994 Sonoike, 1995, 1996, 1997 Lee et al., 2004 a, b). Like other thermophilic plants grown in an unheated greenhouse, chilling under low light is a common episode during its growth (Yu et al., 2002 b Zhou et al., 2006). Chill has a direct impact on the photosynthetic apparatus, essentially by disrupting all major components of photosynthesis, including the thylakoid electron transport, the carbon reduction cycle and the stomatal control of the CO 2 supply, together with an increased accumulation of carbohydrates, peroxidative destruction of lipids and disturbance of the water balance ( Allen and Ort, 2001).Īs a chilling-sensitive species, cucumber plants for most genotypes show their optimal growth at 24–26/18 ☌ (day/night), with an optimal root temperature at approx.
Photosynthetic processes are often the first to be inhibited at chilling temperatures ( Berry and Björkman, 1980). Root-to-shoot communication has been intensively investigated in plants exposed to drought, salinity or flooding conditions ( Sauter et al., 2001, 2002 Sobeih et al., 2004) however, there are few reports on plants subjected to low temperatures and even less attention has been devoted to investigating the involvement of roots in the regulation of the photosynthetic apparatus and chilling tolerance of leaves.Ĭhilling is a major limiting factor for the productivity and geographical distribution of many thermophilic plants such as cucumber and tomato, and growing these plants during winter requires a large energy input to protect plants from low temperatures. A recent study also showed that roots affect the gene expression patterns of the shoot ( Jensen et al., 2003). ABA has been implicated in a number of studies as the likely chemical substance used for root-to-shoot signalling especially under drought conditions, while cytokinins are known to be involved in the regulation of chloroplast build-up, chlorophyll formation and the expression of some photosynthesis-related genes ( Schmülling et al., 1997 Kato et al., 2002). It has been shown that the transpiration stream or xylem sap contains compounds such as ABA and cytokinins ( Incoll et al., 1990 Beck and Wagner, 1994 Pospisilova, 2003). Roots change the mineral and water states in leaves by ion and water uptake and influence leaf growth and stomatal functioning by the root-sourced chemicals such as abscisic acid (ABA) ( Sauter et al., 2001, 2002 Sobeih et al., 2004). In higher plants, organs that contribute to the organization of the whole plant body have different functions and the growth of the organs depends on interactions among the different organs. ABA and cytokinins) protect leaf photosynthesis in shoots of chilling-sensitive plants.Ĭhilling, chlorophyll fluorescence, Cucumis sativus, electron transport flux, grafting, photosynthesis, reactive oxygen species, water–water cycle INTRODUCTION These results suggest that some signals coming from chilling-resistant roots (i.e. Improved plant growth was also observed in grafted plants after the chill.
In comparison, ABA and cytokinin concentrations increased by 10♵-fold and 36♹ %, respectively, for the grafted plants. In addition, ABA concentration increased by 48♴-fold whilst cytokinin concentration decreased by 91♵ % in the xylem sap of own-rooted plants after exposure to a 7 ☌ chill. Higher activity of antioxidant enzymes with less ROS production was found in grafted plants. However, grafted plants showed weaker inhibition, together with decreased electron flux in the water–water cycle. Chill at 7 ☌ irreversibly reduced A sat, and significantly decreased maximum carboxylation activity, Rubisco content and initial Rubisco activity. Grafted plants showed a significantly higher light-saturated rate of CO 2 assimilation ( A sat) than own-rooted plants when roots were gradually cooled, but no differences were detected when shoots were cooled.
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