Growth habit of Lotus tenuis shoots and the influence of photosynthetic photon flux density, sucrose and endogenous levels of gibberellins A1 and A3.

The tropic response of Lotus tenuis shoots under conditions of full sunlight (FS) or artificial shade (AS) has been studied in relation to their endogenous levels of gibberellins (Gas) and sucrose. Single-node explants with one axillary branch each were incubated in darkness with different concentrations of sucrose, GA₃, B9 or their combinations, or whole plants were treated with FS, AS, AS + uniconazole, or AS + cimectacarb. High sucrose concentration supplied via xylem turned the axillary branch growth diagravitropic. GA₃ reversed the effect of sucrose, both in shoot sections and whole plants, turning the axillary branch growth ortotropic and diminishing the sucrose levels at the shoot bases. High irradiance induced a prostrate growth of the shoots. Artificial shade increased both internode and branch length and induced an upward curvature of the shoots. This was correlated with a lower sucrose concentration and increased content of GA ₁and GA₃ Cimectacarb and uniconazole reversed the AS effects, although the sucrose content in the shoots remained low. These results are direct evidence that gravitropism of L. tenuis shoots under different light intensities, but of similar light quality, is controlled by the levels of GA₁ and GA₃ and sucrose. [ABSTRACT FROM AUTHOR]