Some similarities to : Other Pansys.

Very strange that books seem not to mention the square stems.

Habitat : Farmers arable fields.

VIOLAXANTHIN CYCLE PROTECTION FROM EXCESS SUNLIGHT A yellow to orange pigment, violaxanthin (or Zeaxanthin diepoxide) is present in Pansies (such as Yellow Pansy). It is a di-epoxide xanthophyll, and it protects plants with it from photo-oxidative damage by minimizing the formation of dangerous oxygen radicals. When the light absorbed by plants exceeds the capacity of the photosynthesis machinery to convert it to sugars etc, then the extra light goes towards de-epoxidizing violaxanthin to Zeathanthin in a 2-step process via an intermediate antheraxanthin which has just a single epoxide group. This conversion is reversible - being called the violaxanthin cycle. This protective mechanism also operates in Thale Cress and other plants. The conversion of violaxanthin to zeathanthin is mediated by an enzyme called violaxanthin de-epoxidase which is activated by the incidence of strong sunlight and the presence of Ascorbate (Vitamin C) in a low pH environment. The effectiveness of this protective mechanism is thus limited by the availability of ascorbate and if lacking for any reason then the plant may suffer stress under strong sunlight. In low-light the reverse process happens, mediated by a different enzyme, zeaxanthine epoxidase which adds the epoxide group to both zeaxanthin and antheraxanthin in readiness to protect the plant when the sun shines strongly again (up-arrows). Antheraxanthin is a neutral-yellow carotenoid with an epoxide group.

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