Comparing Four Red/Green-Leafed Vegetables Reveals the Complementary Photoprotective Roles of Anthocyanin Accumulation and Chlorophyllase

The photoprotective role of anthocyanins in leaves is debated, as some anthocyanin-rich red leaves do not exhibit greater tolerance to high-light conditions than their anthocyanin-deficient green counterparts. In this study, we studied four leafy vegetables with both red- and green-leafed varieties: Bok Choy and Choy Sum from <i>Brassica rapa</i>, and Ramosa and Asparagus lettuce from <i>Lactuca sativa</i>. Under normal-light conditions, the red cultivars accumulated anthocyanins, the green ones did not, and all presented no photoinhibition. However, the green-leafed varieties exhibited 3-5-fold higher chlorophyllase (CLH) activity than their red counterparts. Under high-light conditions, more anthocyanins were accumulated in the red cultivars, but again, none accumulated in the green cultivars; the green cultivars showed greater CLH activity than their red counterparts. Bok Choy and Choy Sum demonstrated comparable photoinhibition between their red and green counterparts, with a similar reduction in photosynthetic activity, <i>F_v</i>/<i>F_m</i>, ETR, and NPQ; red Ramosa and Asparagus lettuce exhibited worse high-light tolerance than their green counterparts, with greater reductions in <i>F_v</i>/<i>F_m</i> and ETR. In Arabidopsis, the anthocyanin-deficient mutant <i>tt3tt4</i> (green) also induced higher <i>AtCLH1/2</i> expression than the wild-type and constitutive anthocyanin accumulation line PAP1-D (red); the <i>AtCLH1</i> overexpressor and the <i>clh1-1/2-2</i> mutant accumulated less and more anthocyanin than the wild-type, respectively. The findings suggest that CLH induction may compensate for absent anthocyanin photoprotection in green cultivars and that the two strategies may play complementary roles in photoprotection.