1,721,040 research outputs found
Pollination, pollen viability and pistil receptivity in Cucurbita pepo
No full textCucurbita pepo carries male and female flowers on the same plant, and is pollinated by nectar-collecting bees. The nectaries are dimorphic in the two sexes and pollen is loaded and unloaded as the bees gain access to the nectar. Both types of flower are open for only 6 h (from 0600 h to 1200 h); male flowers open and close half an hour earlier than female flowers. The latter produce more nectar and are visited more often by the bees than the male flowers. Pollen viability determined by fluorescein diacetate (fluorochromatic reaction) decreases by 20% during anthesis and more rapidly after the flower closes. This decrease is due to dehydration of the grain, especially around the pore where the intine is exposed. An unusual feature of this species is that the grains do not dehydrate before anther dehiscence. Female receptivity has two aspects, that of the stigma lasting 4 d, and that of the ovules lasting 2 d. The receptivity of the two sexes and the short period of anthesis are discussed in the light of the reproductive ecology of the species
Pollen biodiversity – why are pollen grains different despite having the same function? A review
No full textThe main morphological, cytological and physiological characters of ripe pollen are described, compared, analysed
and discussed individually, in multiple combinations and in respect to the female counterpart and the biotic and
abiotic components of the environment. This is to try to understand the reasons why pollen grains have the same
reproductive function, but at dispersal are morphologically and physiologically different in many respects. The
considered characters are: one or more types of grain per species; shape and size; number of cells; types of pollen
dispersal unit; sporoderm stratification, furrows, colpori and other kinds of apertures; pollen presentation and array;
water content percentage; and mature pollen reserves and osmotics. Some of the pollen features are correlated
between themselves, some with the female counterpart or male and female competition, and others with the different
components of the environment where the species lives, when it flowers and when pollen presentation occurs
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