From anther and pollen ripening to pollen presentation

The events and processes occurring between pollen maturation, opening of th e anther and presentation of pollen to dispersing agents are described. In the final phases of pollen development, starch is always stored; this occur s before the anther opens, Depending on the species, this starch may be tot ally or partially transformed into: (a) other types of polysaccharides (fru ctans and rarely callose); (b) disaccharides (sucrose); (c) monosaccharides (glucose and fructose, all situated in the cytoplasm. While awaiting dispe rsing agents and during dispersal, polysaccharides, especially fructans, an d sucrose may be interconverted to control osmotic pressure and prevent los s and uptake of water. Opening of the anther is preceded by disappearance o f the locular fluid and in many cases by partial dehydration of the pollen. Pollen generally has a water content between 5 and 50%. Pollen with a high water content may or may not be able to control water retention during pol len exposure and dispersal. Pollen may be dispersed in monads or grouped in pollen dispersing units by the following mechanisms: (i). tangling of fila mentous pollen; (ii). adhesion by viscous substances (pollenkitt, tryphine, elastoviscin) derived from the tapetum, (iii). common walls. When the anth er opens, the pollen may be dispersed immediately, remain until dispersed ( primary presentation), or be presented to pollinators in another part of th e flower (secondary presentation).