Introduction and Definitions

Pollen is the male gametophyte of gymnosperms and angios-perms. Its size ranges from 15 to 200 mm. Pollination is transport of pollen from its site of production to the female landing site. If successful, it is followed by fertilization and seed development. Irrespective of systematic group, pollination is always affected by biotic and abiotic factors (Table 1).

Pollen presentation is the manner in which pollen is presented for dispersal. Pollen may be dispersed as single grains, as in many plants relying on wind dispersal, or in

Table 1 Effects of the main climatic parameters on pollination

Temperature

High Tdamages flowers and pollen during

presentation or dispersal

Moderate Tfacilitates flower and anther

opening

Low T slows pollen ripening and flower opening

and reduces pollinator activity

Rain and

Purge pollen from air, especially at low T

mist

Slow flower opening and anther-pollen

dehydration

May inappropriately rehydrate and reactivate

pollen

Hinder small animal movements

Sky

Brightness facilitates diurnal pollinator flight

brightness

Dullness hinders diurnal pollinator flight

Air currents

Facilitate pollen removal and dispersal in

anemophilous species

Facilitate flower opening and anther

dehydration

High wind speeds hinder pollinator flight

Pressure

Ascending air currents facilitate long-distance

variations

pollen dispersal

Descending air currents facilitate pollen fallout

groups of grains, as in almost all zoophilous species.

Pollen grains may be held together by:

1. common walls, as in tetrads where grains derived from the same meiotic division stay together, or multiple tetrads which may number up to several thousand, as in orchids;

2. threads on the pollen surface or derived from the anther; and

3. viscous fluids, of which pollenkitt is the most common, which also have other functions, such as to keep pollen in the anther until dispersal, to stick pollen to pollinators, to make pollen attractive through scent or color, and to hide or expose pollen to insect sight.

Pollen dispersal in clumps is typical of angiosperms.

Gymnosperm pollen is produced by pollen sacs in male cones. It is transported by air currents to the ovule micropyle. Angiosperm pollen is produced by anthers of flowers. It is carried to stigmas by animals, air currents, and sometimes water (Table 2).

At the end of its flight, pollen may land on female parts of the same or another species, giving rise to legitimate and illegitimate pollination, respectively (Figure 1). Pollen has two walls and when accepted by the female part, emits a tube leading the male gametes toward the female ones inside the ovule. Possible crosses in angiosperms depend on the sexual expression of the plant and on pollen vectors (Figure 1).

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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