Zeaxanthin Epoxidation Inhibition by EPTC (S-Ethyl Dipropylthiocarbamate)

Abstract

Wheat (Triticum aestivum L. ''Holley'') was grown at 3 light levels (270, 20 and 0 .mu.Einsteins/m2 s-1) in sand in which EPTC (0, 15.6, 31.25, 62.5, or 125.0 .mu./kg sand) was incorporated. The EPTC-mediated height and fresh-weight decreases were light dependent. As EPTC concentration increased, CHL [chlorophyll] and total CAR [carotenoid] contents (.mu.g/g fresh wt) increased under 270 .mu.Einsteins/m2 s-1, while CHL a:b, CHL b:CAR, and CHL a + b:CAR ratios decreased. Under 270, but not at 20 .mu.Einsteins/m2 s-1, the quantities of .beta.-carotene, luteine-epoxide, lutein, violaxanthin, antheraxanthin and zeaxanthin decreased per milligram CHL b as EPTC concentration increased. Under 270 .mu.Einsteins/m2 s-1, violaxanthin content (7mg/g fresh wt) was not altered by EPTC treatment, but antheraxanthin and zeaxanthin contents increased, resulting in decreases in the ratio of epoxidized/de-epoxidized components of the violaxanthin cycle.