THE ROLE OF CARBOHYDRATES IN THE INDUCTION OF FLOWERING IN ARABIDOPSIS-THALIANA - COMPARISON BETWEEN THE WILD-TYPE AND A STARCHLESS MUTANT

In order to test whether an increased export of carbohydrates by leave s and starch mobilization are critical for floral transition in Arabid opsis thaliana, the Columbia ecotype as well as its starchless mutant pgm and starch-in-excess mutant sex1 were investigated. Induction of f lowering was achieved by exposure of plants to either one long day (LD ) or one displaced short day (DSD). The following conclusions were dra wn: (i) Both the pgm and sex1 mutants have a late-flowering phenotype in days shorter than 16 h. (ii) When inductive treatments cause a larg e percentage of induced plants, there is always a large, early and tra nsient increase in carbohydrate export from leaves. By contrast, when an inductive treatment results in only a low percentage of induced pla nts (pgm plants exposed to one DSD), the export of carbohydrates from leaves is not increased, supporting the idea that phloem carbohydrates have a critical function in floral transition. (iii) Starch mobilizat ion is not required to obtain an increased carbohydrate export when in duction is by one LD (extended period of photosynthesis), but is absol utely essential when induction is by one DSD (period of photosynthesis unaffected). (iv) Floral induction apparently increases the capabilit y of the leaf phloem-loading system.