ISHS Acta Horticulturae 508: XIX International Symposium on Improvement of Ornamental Plants
FLORAL ARCHITECTURE: HOW FLOWERS ARE BUILT |
| Author: | J. Traas |
| Abstract:
The main objective of this lecture is to give an overview of recent developments in the field of floral developmental biology. Recent genetic/molecular analyses using model species such as arabidopsis, Antirrhinum majus, maize or petunia have provided a first insight in the network of genes that control flower morphogenesis. The factors involved appear to operate at different overlapping levels. First, one set of genes is necessary for the specification of organ identity. In the crucifer arabidopsis, the flower consists of four organ types, which are arranged in four concentric whorls. The type of organ that develops in each whorl appears to depend on the activity of three classes of genes termed A, B and C. Each of these is active in two adjacent whorls. Thus, A activity functions in whorl 1 and 2, B-activity in whorl 2 and 3 and C-activity in whorl 3 and 4. The specific combination of activities in each whorl is thought to determine organ identity in the meristem. Another level of control concerns architectural aspects such as organ positions and numbers. Only very recently the first genes controlling these characteristics have been identified, such as the receptor kinase Clavata in arabidopsis, which limits meristem size and organ numbers, or genes like Cycloidea (Antirrhinum), Perianthia and Mgoun (arabidopsis) which appear to control organ initiation and primordium position. Some of these genes are active in all apical meristems and are highly conserved throughout evolution. Together, these two groups of genes must instruct the individual cells within the floral meristem to grow, divide and differentiate in specific patterns. How the behaviour of the cells within the floral meristem is linked to the activity of the genes controlling organ position and identity is largely unknown. During the last years, some of the components that directly control cell division and growth have been identified. These basic regulators are likely to be targets of the genes co-ordinating floral architecture. The exact link between these two levels of control is far from clear at present, and the integration of the basic cellular mechanisms in the growing plant is becoming a central issue in plant developmental research. | |
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