Tomato Leaf Types Part 2 of 6
Anthocyanin, which can appear in a number of different leaf shapes, involves a blue/purple pigment on the epidermis of the fruit. The gene responsible for that expression was the “Aft” gene (anthocyanin fruit). Anthocyanin can also be found in plant foliage and stems, but it is controlled and expressed by another recessive anthocyanin gene called atroviolaceum or “atv” which expresses in the plant body as well as sometimes in the fruit. Most of the atv expressions we see in today’s modern tomatoes relates back to the wild species Solanum Cheesmaniae (L. Cheesmanii).
This pigment will appear soon after the seedling develops it’s first true leaves and will typically stay with the plant until it is planted out in the final growing spot. Then as seasonal temperatures begin to climb, the heat can make it fade or disappear for some time. It is controlled not only by sun exposure, but also temperature. As you move into cooler early fall weather, you will see the ‘atv’ return to the foliage, some can turn almost black.
This expression can be very hard to capture or judge the exposure rate because it is so highly affected by temperature changes. Some will confuse this with the normal purpling of the leaves and stems that a non-atv plant will exhibit under cooler conditions. This effect happens due to a phosphorus mobility issue and has nothing to do with the ‘atv’ gene.