Nucellar beak structure and pollen tube growth in Cucurbitaceae

LIZARAZU, M. A; POZNER, E. R.

FLORA

ELSEVIER GMBH

Año: 2014 p. 340 - 348

0367-2530

. The nucellar beak is a proboscis-like outgrowth of the nucellus at the micropylar end, being the obliged path for the pollen tube entering the ovule. Among the few angiosperm families with nucellar beak, Cucurbitaceae is remarkable because the pollen tube may develop at least two types of growth within the nucelar beak: tubular, and ampulliform. Wondering about the possibility that Cucurbitaceae ovules may express some histological variation that could be related to pollen tube growth within the nucellar beak, we performed a compared anatomical, histochemical study of the nucellar beak and pollen tube growth of ten species of Cucurbitaceae. Results show that Cucurbitaceae ovules are diverse in size, and proportions (of integuments, nucellar body, and nucellar beak), and they have at least four types of nucellar beak histology: pectic-tracked, secretory-like, amylaceous, and mixed. Amylaceous and mixed nucellar beaks are related to the ampulliform growth of the pollen tube, but the understanding of this relation is pending. However, it may constitute an interesting model of pollen tube ? ovule co-evolution in angiosperms. In this sense, an evolutionary view of the ovule and nucellar beak structure in Cucurbitacae would be useful, but information about ovule structure of the basal tribes is still needed.