ZINI lucia melisa
Style morphology and pollen tube pathway
GOTELLI, M. M.; LATTAR, E. C.; ZINI, L. M.; GALATI, B. G.
The style morphology and anatomy vary amongdifferent species. Three basic types are: open, closed, andsemi-closed. Cells involved in the pollen tube pathway inthe different types of styles present abundant endoplasmicreticulum, dictyosomes, mitochondria, and ribosomes. Thesesecretory characteristics are related to the secretion wherepollen tube grows. This secretion can be represented by thesubstances either in the canal or in the intercellular matrixor in the cell wall. Most studies suggest that pollen tubesonly grow through the secretion of the canal in open styles.However, some species present pollen tubes that penetratethe epithelial cells of the canal, or grow through the middlelamella between these cells and subepithelial cells. In specieswith a closed style, a pathway is provided by the presenceof an extracellular matrix, or by the thickened cell wallsof the stylar transmitting tissue. There are reports in somespecies where pollen tubes can also penetrate the transmittingtissue cells and continue their growth through the celllumen. In this review, we define subtypes of styles accordingto the path of the pollen tube. Style types were mapped on anangiosperm phylogenetic tree following the maximum parsimonyprinciple. In line with this, it could be hypothesizedthat: the open style appeared in the early divergent angiosperms;the closed type of style originated in Asparagales,Poales, and Eudicots; and the semi-closed style appearedin Rosids, Ericales, and Gentianales. The open style seemsto have been lost in core Eudicots, with reversions in someRosids and Asterids.