二重雌雄异型异熟物种色木槭3种表型花的细胞形态学研究

Morphology and cytology of three flower phenotypes in a duodichogamous tree species,Acer mono

二重雌雄异型异熟,即雌雄功能按雄-雌-雄顺序分别表达,是有花植物中较为少见的异熟机制。槭属(Acer)大部分物种具有二重雌雄异型异熟的开花物候,且第一期雄花与第二期在形态上差别较大。为深入探讨花发育模式对花形态和开花物候的影响,本文应用石蜡切片技术和光镜技术,对色木槭(Acer mono)各个发育时期的3种类型花(雄花I,II和雌花)的形态学和细胞学进行观察比较。结果发现:色木槭一期雄花(雄I)在大孢子四分体退化形成功能性大孢子时期,子房萎缩并迅速退化消失;而二期雄花(雄II)在此时期胚珠和子房表现为逐渐退化败育,但成熟子房内仅剩蘑菇云状的败育胚珠,形态上可见子房和二分裂柱头;雌花由于绒毡层延缓解体,并缺少与花药开裂有关的唇细胞,导致成熟花药无法开裂散粉,发生了结构性的雄性不育。结果表明,色木槭的3种类型的花均起源于两性花,在花发育过程中通过成熟花药的不开裂和子房胚珠的败育分别产生功能性雌花或雄花,而雄I和雄II在形态上的差异,是由子房是否迅速退化造成的。

Duodichogamy,where individual plants produce two batches of male flowers that are temporally separated by a batch of female flowers,is the rarest temporal sexual system in flowering plants.Duodichogamy is present in some species of Acer,whose flowers of the first（male I） and second male phases（male II） differ morphologically.To explore the influence of floral development on flower morphology and phenology,we used paraffin methods and light microscopy to compare morphological and cytological differences among male（I and II） and female flowers at different developmental stages.Our main results were as follows：the ovary of male I degenerated and disappeared quickly upon megaspore tetrad degeneration,and developed into macrosporocytes;while the ovary of male II degenerated gradually during this period and only traces of residual ovule remained in the fully-developed ovary;the failure of anthers of female flowers to dehisce might be caused by retardant degeneration of tapetum tissue and loss of lip cells,i.e.formation sterility.In conclusion,both pistil and stamen primordial could be found in male（I and II） and female flower buds at early phases of sex differentiation,but selective abortion occurred in later developmental phases.