Style morphology and pollen tube pathway

Abstract

The style morphology and anatomy vary among different species. Three basic types are: open, closed, and semi-closed. Cells involved in the pollen tube pathway in the different types of styles present abundant endoplasmic reticulum, dictyosomes, mitochondria, and ribosomes. These secretory characteristics are related to the secretion where pollen tube grows. This secretion can be represented by the substances either in the canal or in the intercellular matrix or in the cell wall. Most studies suggest that pollen tubes only grow through the secretion of the canal in open styles. However, some species present pollen tubes that penetrate the epithelial cells of the canal, or grow through the middle lamella between these cells and subepithelial cells. In species with a closed style, a pathway is provided by the presence of an extracellular matrix, or by the thickened cell walls of the stylar transmitting tissue. There are reports in some species where pollen tubes can also penetrate the transmitting tissue cells and continue their growth through the cell lumen. In this review, we define subtypes of styles according to the path of the pollen tube. Style types were mapped on an angiosperm phylogenetic tree following the maximum parsimony principle. In line with this, it could be hypothesized that: 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 appeared in Rosids, Ericales, and Gentianales. The open style seems to have been lost in core Eudicots, with reversions in some Rosids and Asterids.

Structure and ontogeny of inflorescence and flower of Bactris simplicifrons Mart. (Arecaceae, Arecoideae, Bactridinae)

“…On the other hand, it could be a synapomorphy of the Cocoseae, since they have been observed in several of the species of this group (Table 3). However, it is necessary to pay more attention to the features of this structure, since although there are studies on the morphology and anatomy of palm owers, they do not usually describe the style in detail, as indicated by Gotelli et al (2017) for angiosperms in general. In B. simplicifrons, the absence of rigid emergencies stands out, indicated as a common trait in Bactris (Henderson 2000), and recently reported in the oral parts of B. acanthocarpoides and B. hirta (Briceño et al 2023).…”

“…The open style is characterized by a canal lined with a glandular epidermis or secretory epithelium and is more common among the monocots; the closed style, usually present in Eudicots, has a core of transmitting tissue; and, in semi-closed style, the transmitting tissue is limiting the stylar channel (Gotelli et al 2017). In the studied species, the characteristics indicated for the style do not strictly correspond to these de nitions, since it is open, but the internal epidermis is papillose, probably secretory, which possibly releases products into the channel, which can act as the extracellular matrix or transmission tissue in solid styles.…”

“…It is necessary to study in detail the ultrastructure of these cells to con rm their function. We must remember that the characteristics of the style play a relevant role in the interactions with the developing pollen tubes, since they provide favorable or unfavorable conditions for their development and nutrition, as has been indicated by various works, including Gotelli et al (2017).…”

Spatio-Temporal Distribution of Cell Wall Components in the Placentas, Ovules and Female Gametophytes of Utricularia during Pollination

“…Sporophytic tissues not only protect the female gametophyte and transport nutrients to it, but also guide the male gametophyte to the female gametophyte e.g., [ 3 , 4 , 5 , 6 , 7 ]. The great success of angiosperms is associated with the diverse structure of their styles and ovules and the sites of the pollen tube pathway [ 8 , 9 , 10 , 11 ]. During pollen tube growth, there is a dialogue between the male gametophytes and sporophytic tissues [ 12 ], but there is also competition between the pollen tubes, i.e., gametophytic competition [ 9 , 13 ].…”

Wrinkled surface on helical cell wall thickening of vessel elements in flower style

“…During angiosperm reproduction, pollen grains that are germinated on the stigma surface form a pollen tube that grows through the transmitting tissues to the ovule micropyle (Palanivelu et al, 2003). The style is a fragile and short-lived tissue (Gotelli et al, 2017) which grows and wilts fast, within no longer than 2 weeks. The helical thickening vessel is the only tissue to provide water for the stigma, transmitting tissue, female gametophyte, and pollen tube.…”