Proceedings of the XLVII Italian Society of Agricultural Genetics - SIGA Annual Congress

Verona, Italy - 24/27 September, 2003

ISBN 88-900622-4-X

Poster Abstract - 4.04

PLANT BODY MODIFICATION IN TWO SUNFLOWER MUTANTS WITH ALTERATIONS IN MERISTEM STRUCTURE

V. MICHELOTTI*, D. BERTINI*, G. CIONINI**, A. CONTI*, M. FAMBRINI*, C. PUGLIESI*

*) Università di Pisa, Dipartimento di Biologia delle Piante Agrarie - Sezione di Genetica, via Matteotti 1/B, 56124 Pisa, Italy

**) Consiglio Nazionale delle Ricerche, Istituto di Biologia e Biotecnologie Agrarie IBBA - Sezione di Pisa, via Moruzzi 1, I-56124 Pisa, Italy

Helianthus annuus, axillary meristems, flowers, phyllotaxy

A vascular plant can be viewed as a branched axis that grows at its tips where two populations of unspecialized cells, the shoot and the root apical meristems, constantly produce organs reiteratively (Clark, 2001). In the post-embryonic vegetative growth, plant form is established by continuos formation of lateral organs and axillary shoots and this phenomenon, is ensured by stem cell homeostasis that requires a negative regulatory feedback loop (Lenhard and Laux, 2003). During the transition of shoot apical meristem from vegetative to reproductive development a change of branching pattern has key importance to differentiate a more complex structure, the inflorescence. Genetic analysis of shoot meristem biology has progressed significantly in recent years especially in the plant model Arabidopsis thaliana (Fletcher, 2002). In this context, the study of mutants affecting the meristem size (with defects in meristem formation and maintenance or characterized by meristem enlargement) is particularly significant (Leyser and Furner, 1992; Barton and Poethig, 1993).

Here we report the morphological and histological analyses of two mutants of sunflower (Helianthus annuus L.) with strong alteration of plant body organization. The missing flowers (mf) mutant show the absence of axillary meristems such as side shoots and flowers (Fambrini et al., 2003), while the stem fasciated (stf) mutant, is characterized by stem fasciation, abnormal phyllotaxy and very short apical internodes. Decapitation experiments and histological analyses indicate that the mf phenotype is the result of a defect in axillary shoot meristem initiation. In addition, we demonstrate that the formation of flowers at the axil of bracts is precluded, in mf/mf plants, by the absence of a subdivion in dyads of floret primordia. On the contrary, a significative enlargement of shoot apical meristem is the primary genetic alteration of the stf mutant.

References

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Clark SE. (2001) Cell signalling at the shoot meristem. Nature Reviews Molecular Cell Biology 2: 276-284.

Fambrini M., Cionini G., Bertini D., Michelotti V., Conti A., Pugliesi C. (2003) MISSING FLOWERS gene controls axillary meristems initiation in sunflower. genesis 36: 25-33.

Fletcher JC. (2002) Shoot and floral meristem maintenance in Arabidopsis. Annual Review Plant Biology 53: 45-66.

Lenhard M., Laux T. (2003) Stem cell homeostasis in the Arabidopsis shoot meristem is regulated by intercellular movement of CLAVATA3 and its sequestration by CLAVATA1. Development 130: 3163-3173.

Leyser HMO., Furner IJ. (1992) Characterization of three shoot apical meristem mutants of Arabidopsis thaliana. Development 116: 397-403.