Lettuce hypocotyl elongation

There is extensive evidence that GA increases auxin levels either by enhancement of auxin biosynthesis (Jindal and Hemberg 1976, Sastry and Muir 1965) or by retardation of auxin destruction (Kogl and Elema 1960). Nevertheless, there is convincing evidence that GA can also stimulate elongation independently of auxin (Kazama and Katsumi 1974, Cleland et al. 1968, Kaufman et al. 1969). In excised Avena stem internodes, for example, GA stimulates cell elongation, while auxin is inhibitory (Kaufman et al. 1969). Similarly, stimulation of lettuce hypocotyl elongation has been used as a bioassay for GA, while... 

Figure 1. Effects of CaCl2 on bioassays for auxin, gibberellin, and cytokinin. A effects of CaCl2 on elongation of oat coleoptile sections in the presence and absence of indoleactic acid B effects on elongation of lettuce hypocotyls in the presence and absence of gibberellic add and C effects on enlargement of Xanthium cotyledon pieces in the presence and absence of benzyladenine (13).

Shibata K, Kubota T, Kamisaka S (1974) Isolation and chemical identification of a lettuce cotyledon factor, a synergist of the gibberellin action in inducing hypocotyl elongation. Plant Cell Physiol 15 191-194... 

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