Pollen-pistil interactions in tristylous Pontederia sagittata (Pontederiaceae). II. Patterns of pollen tube growth
1991
Scribailo, R.W. | Barrett, S.C.H.
Pollen tube behavior was compared after legitimate and illegitimate pollinations of tristylous Pontederia sagittata. All pollinations resulted in substantially fewer pollen tubes in the style than pollen grains on the stigma surface. Number of pollen tubes showed a characteristic attrition, particularly by the midpoint of the style in all pollination types. Two classes of illegitimate pollination could be identified. In pollinations with pollen smaller than the legitimate size class for a given morph, pollen tubes ceased growth in characteristic regions of the style. In pollinations with pollen larger than the legitimate size class, pollen tubes entered the ovary. In the latter class of pollination, pollen tube behavior in the M morph was similar to that of legitimate pollinations. In the S morph illegitimate pollen tube behavior was distinctive. Pollen tubes entered the ovary but rarely contacted the obturator most often growing down the funiculus of the ovule and terminating growth at its base. The associations between pollen size, pollen tube length and width, and callose plug length regardless of pollination type suggest that incompatibility in P. sagittata is governed by the interaction of heteromorphic characters rather than by an active rejection mechanism mediated by molecular specificities. The distinctive features of incompatibility in P. sagittata are discussed in relation to structural features of the pollen tube pathway, incongruity mechanisms, and gametophytic incompatibility in monocotyledonous families.
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