Long-day conditions increase internode length, leaf area, and dry weight and reduce the interval between the appearance of successive leaf pairs in <it>S. rebaudiana</it> as compared with short days. Total soluble leaf sugars, protein, and stevioside content are also augmented in both absolute and relative terms and the biosynthesis of steviol, the aglucone present in stevioside, is increased by 45%. The interaction between dry matter, stevioside content, and day length is discussed and a theory for the biological role of stevioside as a possible defence mechanism against insect herbivory is proposed: as such this is the first known case of a tetracyclic diterpene glycoside assuming this function.
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METIVIER et al. (1979) studied this question.