The pollen-stigma interaction in the grasses. 2. Pollen-tube penetration and the stigma response in Secale
Acta botanica neerlandica , Volume 30 - Issue 4 p. 289- 307
After an initial period of hydration on the stigma, viable pollen grains release an exudate which becomes continuous with the stigma surface secretions. This is accompanied by an enhancement of surface esterase activity, and eventually the stigma cuticle is eroded at the contact face. Simultaneously the pectin-rich outer layer of the wall of the stigma papilla gelatinises. Germination of the grain begins with the gelatinisation of the pectins of the Zwischenkorper, which displaces the operculum. The emerging tip passes through the eroded stigma cuticle and enters the outer pectin-rich layer of the wall. Enzymic removal of the proteinaceous part of the stigma surface secretion before pollination interferes with the capacity of the tube tip to penetrate, but does not prevent germination. During further growth in the stigma, the tube passes through the intercellular material of the branch axis, which occupies some 10% of the volume of the branch before pollination. The advent of the tube brings about a rapid increase in the permeability of the affected cells, preceded in some species by the blockage of the plasmodesmata by callose. The membranes of the cells immediately adjacent to the pollen-tube pathway undergo dissolution, and the nuclei become pycnotic. Calculations based upon the changes of volume of the grain during the first 500 pm of pollen tube growth show that the water requirement of the tube may be met entirely by transfer from the hydrated grain, and not by uptake from the stigma tissues. This implies that all of the initial events of germination, tube emergence and growth through the secondary stigma branches are driven by the hydrostatic pressure built up in the grain during the period of hydration following upon capture.
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J. Heslop-Harrison, & Y. Heslop-Harrison. (1981). The pollen-stigma interaction in the grasses. 2. Pollen-tube penetration and the stigma response in Secale. Acta botanica neerlandica, 30(4), 289–307.
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