| Populus tomentosa Carr. (Chinese white poplar) is a native species of great greening and timber value, yet serious catkin-caused pollution of which at flowering phase inconveniences people's normal work and life. Herein, our research on general process of floral development with female Populus tomentosa using paraffin section initially uncovers a complete morphogenesis of seed hair, and that seed hair developing from the superficial cells of ovary placentas and funicles was confirmed. Study on accumulation of soluble sugar and activity of sucrose-metabolizing enzyme in fibrogenesis reveals that, the change of glucose content and that of SS activity are temporally accordant with the morphology of seed hair fiber, thus providing convincing physiological supports for morphogenesis of seed hair, and identifying SS as a key enzyme during the whole fibrogenesis. Furthermore, analysis of PtSS family members encoding SS through semiquantitative PCR technique shows a far-ranging expression of PtSS1 and PtSS2 in all tissues, while essentially equal amounts of PtSS3 and PtSS4 and PtSS6 transcript in all tissues but stem and leaf, and a low transcript of PtSS7 in stem only. More specifically, PtSS1 expresses most highly in both root and floral bud, which is not the case for that in other tissues. PtSS2 expresses in all tissues in a critical high and constant fashion.A complete seed hair genesis process is firstly represented in this paper, and its physiological support has been obtained. Ultimately, expression patterns of each member in PtSS family for this process identify PtSS7 as a member expressing specifically to stem. The above-mentioned results do not only make a profound theoretical sense for illuminating molecular mechanism of such gene family in the genesis of seed hair, but also lay a theoretical foundation for addressing the flying catkin-caused pollution through gene engineering and further breeding a new poplar cultivar without seed hair.
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