Abstract Detail

Developmental and Structural Section

Williams, Joseph [1].

A comparative metric for studying the efficiency of pollen tube growth.

Pollen tube growth rate (PTGR) is an important arbiter of male fitness in flowering plants, yet it varies by over four orders of magnitude. PTGR is controlled by wall production rate (WPR) and wall dimensions. In this study, I explored the relationship between tube construction costs and growth rate in Nymphaea odorata Aiton (Nymphaeaceae). Single-donor pollinations were done on pairs of nearest-neighbor flowers and fixed in FAA at 30 and 75 minutes after pollination (map) (N = 15 pollen donors x 2 replicate experiments/donor). Lengths of 10 leading pollen tubes per carpel were measured for each time. PTGR for each replicate was the mean of the longest 75 map tube minus the longest 30 map tube divided by the duration of growth, and so on for the 10 tube pairs. An adjacent carpel was embedded in glycol methacrylate, serial-sectioned, and stained with aniline blue/calcofluor. Cross-sections of tube diameters (D) or circumferences (C), and wall thicknesses (W) were measured at 630x magnification (1 pixel = 0.0352 µm²). Mean WPR for each replicate was calculated as the average of individual (C x W) x (mean PTGR). Between 30 map and 75 map, tubes had grown primarily within substigmatic tissues. Mean PTGRs ranged from 147 to 936 μm/h. In an ANOVA, variation among pollen donors accounted for 74% of the variance, whereas among-replicate variation within donors was 17%. The high among-pollen donor variation is explained by a positive linear relationship between mean pollen donor PTGR and temperature (R² = 0.725). Thickness of the intine did not differ from the proximal tube wall (P = 0.9302), and thickness of distal tube walls did not differ at four sequential locations (P = 0.4073). Mean W was 0.2288 ± 0.0025 μm and mean D was 8.45 ± 0.58 μm. Wall area (C x W) did not vary with temperature, and its among-replicate coefficient of variation was 10.3 % versus 50.2 % for PTGR. Wall production rate was strongly correlated with PTGR (WPR = 6.42*PTGR – 52.63; R² = 0.97; N = 28). Since wall and tube dimensions were relatively invariant over a broad range of temperatures and growth rates, the >10-fold variation in PTGR can be attributed largely to changes in wall synthesis rate at different temperatures. The conservation of tube architecture supports its strong genetic basis. The WPR to PTGR ratio (6.4 in N. odorata) is a cost:benefit ratio. Tubes with lower ratios have more efficient growth.

Broader Impacts:

Related Links:
Williams lab website

1 - University of Tennessee, Department of Ecology & Evolutionary Biology, 341 HESLER BUILDING, 1406 Circle Drive, KNOXVILLE, TN, 37996-1100, USA

Keywords:
pollen tube
growth rate
evolution of development
cell wall
phenotypic plasticity
reproductive biology.

Presentation Type: Oral Paper:Papers for Sections
Session: 15
Location: Jasperwood/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 9:15 AM
Number: 15006
Abstract ID:324
Candidate for Awards:None