ISHS Acta Horticulturae 420: Ornamental Plant Improvement: Classical and Molecular
HORMONAL REGULATION OF COROLLA GROWTH AND PIGMENTATION IN PETUNIA FLOWERS |
| Author: | D. Weiss |
| Abstract:
In many cases, the economic success of plants as ornamentals depends on flower size, structure and color. These characteristics result mainly from petal growth and pigmentation, the latter being is an integral part of the former. Petunia corolla elongation is accompanied by the accumulation of the flavonoid pigment anthocyanin. We found both processes to be controlled by the developing anthers and the plant hormone gibberellic acid (GA3). Anthers and GA3 induce corolla pigmentation by activating the transcription of several genes encoding flavonoid enzymes such as chalcone synthase (chs), chalcone isomerase (chi), dihydroflavonol 4-reductase (dfr), anthocyanidin synthase (as), and ramnosyl transferase (rt). GA controls flavonoid gene transcription in an indirect manner and our data support a model in which the hormone induces the production of a regulatory protein. Analysis of endogenous GA indicated the presence of biologically active GAs such as GA1 and GA4 in anthers and corollas at the stage of flavonoid gene induction. These GAs were also able to induce pigmentation and chs gene transcription in in-vitro grown corollas. The plant hormone abscisic acid (ABA) inhibited all GA- and anthers-inducible processes. At this point, we do not know whether ABA plays a role in planta. We cloned several other GA-inducible genes such as those encoding S-adenosylmethionone synthetase (SAM) and triosephosphate isomerase (TPI). The expression patterns of these genes were similar to those of the flavonoid genes. We suggest that during flower development the anthers produce GAs that are transported into the corollas where they induce the activities of many genes involved in growth and pigmentation. | |
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