Yin Xiaofeng, Meicenheimer Roger D
Department of Botany, Miami University. 316 Pearson Hall, Oxford, Ohio 45056 USA.
Am J Bot. 2017 Jan;104(1):8-23. doi: 10.3732/ajb.1600346. Epub 2016 Dec 30.
Fibonacci phyllotactic patterns in seed plants are well documented, but whether such predominance holds true for lower vascular plants is relatively unknown. We investigated Diphasiastrum digitatum (Lycopodiaceae) phyllotaxis throughout its ontogeny to extend our knowledge of pattern frequency of lower vascular plants and to measure quantitative variables associated with discontinuous phyllotactic transitions. These investigations allowed us to test whether the same mechanisms inherent in shoot apical meristem (SAM) development of seed plants are applicable to early-diverged lower vascular plants SAM development.
Divergence angle, plastochron ratio, leaf insertion angle, circumferential ratio, radial ratio, half conic angle, area, circumference, and circularity of the shoot apical meristem were compared among different phyllotactic patterns and different meristem types observed throughout D. digitatum ontogeny, using scanning electron microscopy.
Fibonacci patterns were not predominant during six stages of D. digitatum ontogeny. In all five cases of discontinuous transition associated with strobili formation, divergence angle was the only variable that has changed consistently.
The predominance of non-Fibonacci patterns/series in D. digitatum is inconsistent with the prediction of interpretive model of phyllotaxis. We hypothesize this is because its SAM, due to its frequent dichotomy, is not circular and primordia initiation is restricted spatially and temporally at the beginning of pattern formation. Change in divergence angle associated with discontinuous transitions is most likely due to the change of the location of new auxin maxima, due to the change of SAM shape and size.
种子植物中的斐波那契叶序模式已有充分记载，但这种优势在低等维管植物中是否成立相对未知。我们研究了石松科的多穗石松在其个体发育过程中的叶序，以扩展我们对低等维管植物模式频率的认识，并测量与不连续叶序转变相关的定量变量。这些研究使我们能够测试种子植物茎尖分生组织（SAM）发育中固有的相同机制是否适用于早期分化的低等维管植物SAM发育。
使用扫描电子显微镜，比较了在多穗石松个体发育过程中观察到的不同叶序模式和不同分生组织类型之间的发散角、叶序比率、叶插入角、圆周率、径向率、半锥角、面积、周长和茎尖分生组织的圆形度。
在多穗石松个体发育的六个阶段中，斐波那契模式并不占主导地位。在与球果形成相关的所有五个不连续转变案例中，发散角是唯一持续变化的变量。
多穗石松中非斐波那契模式/序列的优势与叶序解释模型的预测不一致。我们推测这是因为其茎尖分生组织由于频繁的二歧分枝而不是圆形，并且在模式形成开始时原基起始在空间和时间上受到限制。与不连续转变相关的发散角变化最有可能是由于茎尖分生组织形状和大小的变化导致新的生长素最大值位置的改变。
