Irreversible Flower Initiation of Chenopodium rubrum Seedlings and Excised Stem Tips

Abstract

It was concluded that the first week of culture of excised stem tips might be concerned with other than flowering processes, and that only after 1 week's growth can flowering be manipulated by exposure to short or long days. A period of 14 short days, after the first week's growth, appears to be threshold for the flowering of excised stem tip cultures, and a period of no longer than 24 days led to 100% cultures in flower. Excised stem tips from 3- to 4-day-old seedlings normally do not flower if they are exposed to long-day conditions. However, stem tips, excised from seedlings given 6 short days, flowered even though they were exposed to long days only; tips from seedlings exposed to fewer than 6 short days did not flower when exposed to long days. Similarly, excised stem tips from seedlings, exposed to either 7 short days or to 7 long days, revealed the effect of the seedling induction on exposure to short days: the tips from the long-day seedlings flowered much later than those from the short-day seedlings. Seedlings exposed to various periods of long days, prior to exposure to short days, all flowered after 10-11 short days. These and other results were difficult to explain entirely on the basis of a postulated relationship between amount of leaf and amount of production of the flower stimulus.