Pollen carbohydrates and water content during development, presentation, and dispersal: a short review

Abstract

Pollen accumulates starch reserves during development and the final stage of ripening. Before the anther opens, starch is totally or partially converted to pectins, glucose, fructose, sucrose, and to some unknown polysaccharides. Pollen is exposed to dispersing agents in an arrested developmental state which differs according to pollen water content. Pollen is classified as partially dehydrated or partially hydrated. The final water content may be reached before or after anther opening. Especially during exposure and dispersal, partially dehydrated pollen may interconvert soluble and insoluble reserves, modifying internal turgor pressure and hindering water loss or gain. Partially hydrated pollen is commonly devoid of mechanisms to conserve viability in time but has the advantage of quickly emitting pollen tubes on reaching the stigma.

Starch distribution in anthers, microspores and pollen grains in Aechmea recurvata (Klotzsch.) L.B.Sm., Dyckia racinae L.B.Sm. and Tillandsia aeranthos (Loisel.) L.B.Sm. (Bromeliaceae)

“…In various species, the sugars in the cytoplasm are associated with the quiescence of the pollen grains, maintaining their viability and also associated with dry environments or entomophily (Baker & Baker 1979;Lisci et al 1994;Pacini 2000;Pacini et al 2006). …”

“…When preparing for the developmental events of pollen grains, including the pollination period, sugars can be accumulated as starch, callose, pectins, insoluble polysaccharides, disaccharides or monosaccharides (Pacini 1996;Aouali et al 2001;Clément & Pacini 2001;Pacini et al 2006). The starch acts on the metabolism or has a structural function (Pacini 1996).…”

“…The effectiveness of the reproductive process in angiosperms depends on the viability of microspores, megaspores, pollen grains and embryo sac, where the dynamics and use of primary metabolites are essential in this process (Bhandari 1984;Delph et al 1997;Shivanna 2003;Pacini et al 2006;Konyar et al 2013). The accumulation and mobilization of sugars, lipids and proteins are common during sporangia development and were demonstrated by microscopy, histochemistry, and biochemical, physiological and molecular assays (Pacini & Viegi 1995;Oliver et al 2005;Lora et al 2012;Konyar et al 2013).…”

“…Thus, some patterns of sugars and starch dynamics are widely disseminated among the angiosperms. Others have a strong phylogenetic determination, as observed in some Asteraceae (Baker & Baker 1983), and others are connected to the strategies to ensure pollen viability as a function of the environment, including biotic and abiotic aspects, such as the type of pollinator and the humidity (Baker & Baker 1979, 1983Lisci et al 1994;Pacini 2000;Pacini et al 2006).…”

“…Thus, some patterns of sugars and starch dynamics are widely disseminated among the angiosperms. Others have a strong phylogenetic determination, as observed in some Asteraceae (Baker & Baker 1983), and others are connected to the strategies to ensure pollen viability as a function of the environment, including biotic and abiotic aspects, such as the type of pollinator and the humidity (Baker & Baker 1979, 1983Lisci et al 1994;Pacini 2000;Pacini et al 2006).According to Baker & Baker (1979), two classes of pollen grains can be found among the angiosperms -one called the starchless type, i.e., with pollen grains containing little or no starch at the time of dispersion; the second called starchy, with pollen grains containing large amounts of starch at the time of dispersion. Often it is thought that the type of reserve is related to pollen viability and to the pollinating agent, and starchy pollen grains are less viable temporally than the starchless pollen grains, although there are exceptions due to pollen grain size (Baker & Baker 1983).…”