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Abstract Detail



Developmental and Structural Section

Williams, Joseph H. [1].

Economy, efficiency and the evolution of pollen tube growth rates.

Pollen tube growth rates of flowering plants are one to four orders of magnitude faster than those of non-flowering seed plants. Yet we know very little about which determinants of pollen tube growth rate actually evolve. Pollen tubes grow via tip growth, and tip extension rate is controlled by the rate at which walls are constructed and reinforced in the tube tip region. Given similar construction materials, pollen tube growth rates (PTGRs) should evolve by changes in wall production rate (WPRs), but PTGR might also evolve by changing the economy of tube construction (i.e. using more or less wall material to achieve a given WPR). To test this idea, we compared the relationship between WPR and PTGR in three water lilies growing in the same pond, Nymphaea odorata (N.o.), Nuphar advena (N.a.) and Brasenia schreberi (B.s.). Single-donor pollinations were done and then flowers were fixed in FAA either soon after pollen germination (time A), or 45 min later (time B). Lengths of 5 leading pollen tubes were measured for each carpel and mean PTGR was calculated for each donor over the 45 minute growth period. For each time B collection, an adjacent carpel was embedded in glycol methacrylate, serial-sectioned, and stained with purified aniline blue. Cross-sectional circumferences (C) and wall thicknesses (W) were measured at 630x magnification. For each male, WPR was calculated as the average of individual (C x W) x (mean PTGR). Temperature was used as a covariate. Pollen tubes of all species grew primarily within substigmatic tissues. Nymphaea odorata pollen tubes grew the fastest (P = 0.0004) and made significantly less wall material per unit of growth than the other two species (6.2 μm3 material per μm growth vs. 7.7 μm3 and 8.7 μm3 for B.s. and N.a., respectively; P = 0.002). The relationship of WPR to PTGR was linear for all species. Pollen tubes with a low WPR to PTGR ratio are using less wall material to extend their tube tip at a given rate towards the egg, a measure of growth efficiency. The WPR:PTGR ratio of N.o. was only 76% of that of the highest value, in N.a. Hence, the faster PTGRs of N.o. were achieved with a more efficient growth pattern, which is attributed largely to its smaller diameter tube.


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1 - University Of Tennessee, Ecology & Evolutionary Biology, 341 Hesler Building, 1406 Circle Drive, Knoxville, TN, 37996-1100, USA

Keywords:
Development
pollen tube growth
life history.

Presentation Type: Oral Paper:Papers for Sections
Session: 69
Location: Salon 11/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 2:00 PM
Number: 69003
Abstract ID:1204
Candidate for Awards:None


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