Williams Joseph H, Edwards Jacob A, Ramsey Adam J
Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA
Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996 USA.
Am J Bot. 2016 Mar;103(3):471-83. doi: 10.3732/ajb.1500264. Epub 2016 Mar 2.
Pollen tube growth rate (PTGR) is an important aspect of male gametophyte performance because of its central role in the fertilization process. Theory suggests that under intense competition, PTGRs should evolve to be faster, especially if PTGR accurately reflects gametophyte quality. Oddly, we know remarkably little about how effectively the work of tube construction is translated to elongation (growth and growth rate). Here we test the prediction that pollen tubes grow equally efficiently by comparing the scaling of wall production rate (WPR) to PTGR in three water lilies that flower concurrently: Nymphaea odorata, Nuphar advena and Brasenia schreberi.
Single-donor pollinations on flower or carpel pairs were fixed just after pollen germination (time A) and 45 min later (time B). Mean PTGR was calculated as the average increase in tube length over that growth period. Tube circumferences (C) and wall thicknesses (W) were measured at time B. For each donor, WPR = mean (C × W) × mean PTGR.
Within species, pollen tubes maintained a constant WPR to PTGR ratio, but species had significantly different ratios. N. odorata and N. advena had similar PTGRs, but for any given PTGR, they had the lowest and highest WPRs, respectively.
We showed that growth rate efficiencies evolved by changes in the volume of wall material used for growth and in how that material was partitioned between lateral and length dimensions. The economics of pollen tube growth are determined by tube design, which is consequent on trade-offs between efficient growth and other pollen tube functions.
花粉管生长速率（PTGR）是雄配子体性能的一个重要方面，因为它在受精过程中起着核心作用。理论表明，在激烈竞争下，PTGR应该进化得更快，特别是如果PTGR准确反映配子体质量的话。奇怪的是，我们对花粉管构建工作转化为伸长（生长和生长速率）的效率了解甚少。在这里，我们通过比较三种同时开花的睡莲——香睡莲（Nymphaea odorata）、萍蓬草（Nuphar advena）和莼菜（Brasenia schreberi）的壁生成速率（WPR）与PTGR的比例关系，来检验花粉管生长效率相同的预测。
对花或心皮对进行单供体授粉，在花粉萌发后（时间A）和45分钟后（时间B）立即固定。平均PTGR计算为该生长期间花粉管长度的平均增加量。在时间B测量花粉管周长（C）和壁厚（W）。对于每个供体，WPR = 平均（C×W）×平均PTGR。
在物种内，花粉管的WPR与PTGR比值保持恒定，但不同物种的比值有显著差异。香睡莲和萍蓬草的PTGR相似，但对于任何给定的PTGR，它们的WPR分别是最低和最高的。
我们表明，生长速率效率是通过用于生长的壁材料体积的变化以及该材料在横向和长度维度之间的分配方式的变化而进化的。花粉管生长的经济性由管的设计决定，而管的设计是在有效生长和其他花粉管功能之间权衡的结果。
