Abscisic acid is a hormone that has an important role in regulating stomatal closure. In response to drought stress, ABA can be synthesized in roots and translocated to leaves by way of the transpirational stream (Davies et al., 2005; Malladi and Burns, 2007), or produced within the leaves or shoots (Christmann et al., 2007; Galvez-Valdivieso et al., 2009). In leaves, ABA causes a reduction in stomatal aperture by triggering a signaling cascade that leads to the net movement of ions and water out of stomatal guard cells (Raghavendra et al., 2010). Abscisic acid may further regulate stomatal closure by lowering the hydraulic conductivity of leaf vascular tissue (Pantin et al., 2012). The resultant stomatal closure allows plants to more effectively tolerate drought stress by limiting the amount of water lost through transpiration (Buckley, 2005; Kim et al., 2012).
For ornamentals, ABA is an effective way to extend shelf life. Plants treated with exogenous ABA can tolerate a temporary lack of watering with little or no wilting. Using ABA to extend the shelf life of ornamentals could be beneficial to growers, especially if their plants will spend an extended period in shipping and retailing, or if their distributors operate by the pay-by-scan system (Starman et al., 2007; van Iersel et al., 2009; Waterland et al., 2010a; Yue and Behe, 2008). Unfortunately, spray and drench applications of ABA have been shown to cause chlorosis in several plant species. This unwanted side effect could limit the usefulness of ABA as a commercial holding agent (Kim and van Iersel, 2011; van Iersel et al., 2009; Waterland et al., 2010a; Weaver and van Iersel, 2014).
Nitrogen is an essential component of chlorophyll, and leaf nitrogen concentration correlates positively to leaf chlorophyll content (Evans, 1983; Loh et al., 2002). We hypothesized that increased fertilization can reduce the severity of ABA-induced chlorosis in pansy. Pansy was used as a model plant because previous research has shown that they are highly susceptible to chlorosis when treated with ABA sprays (Waterland et al., 2010a; Weaver and van Iersel, 2014).
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