Diospyros virginiana In respect to the power of making heartwood, the persimmon rarely develops any heartwood until it is nearly one hundred years old. This heartwood is extremely close-grained and almost black, resembling ebony (of which it is a true variety). It is a common misconception persimmon fruit needs frost to ripen and soften, called bletting. Some, such as the early-ripening varieties "pieper" and "NC21"(also known as "supersweet"), easily lose astringency and become completely free of it when slightly soft at the touch—these are then very sweet, even in the British climate. On the other hand, some varieties (like the very large
Genetically modified tomato cold and drought tolerance in transgenic "Arabidopsis thaliana" plants, was inserted into the tomato. This resulted in increased drought tolerance, but did not appear to have any effect on cold tolerance. Overexpressing a vacuolar Na/H antiport ("AtNHX1") from "A. thaliana" lead to salt accumulating in the leaves of the plants, but not in the fruit and allowed them to grow more in salt solutions than wildtype plants. They were the first salt-tolerant, edible plants ever created. Tobacco osmotic genes overexpressed in tomatoes produced plants that held a higher water content than wildtype plants increasing tolerance to drought and salt stress.