Different pigment and antioxidant profiles in field-collected and lab-cultured plants
Comparison of the photosynthetic pigment profiles in field-collected and lab-cultured S. caninervis supports this hypothesis of relaxation of sustained NPQ. Zeaxanthin, which is associated with both rapidly reversible (qE) and sustained NPQ mechanisms such as photoinhibitory quenching (qI; Demmig-Adams, 1990; Verhoeven et al. , 1996), was more than five times higher in field-collected plants than in lab-cultured plants (Table 3). In fact, the relative VAZ pool was larger in field-collected plants, which is unsurprising as these pigments increase in abundance in high-light environments (Siefermann-Harms 1985; Demmig-Adams 1990; Jahns, Latowski & Strzalka 2009). Similarly, the total chlorophyll pool was reduced and the ratio of chlorophylla :b was increased in field-collected plants, also consistent with acclimation to high light intensity (Björkman 1981; Leong & Anderson 1984; Lindahl, Yang & Andersson 1995). Tocopherol abundance was much higher in field-collected plants than those cultured in the lab, as well (Table 5). Tocopherols are membrane-bound antioxidants that may be increased due to the higher light intensity and UV exposure in the field site (Delong & Steffen 1998; Yao et al.2015) or due to other stresses such as desiccation and freezing that these plants frequently face in their natural habitat (Munné-Bosch 2005).