白鹃梅属(Exochorda Lindl.)花发育揭示蔷薇科雄蕊演化新证据

Floral development study of Exochorda Lindl.reveals new evidence for the evolution of the androecium in Rosaceae

蔷薇科具有独特的成对外轮雄蕊、多数的雄蕊轮、高度的雄蕊群形态多样性和发育多样性.如何解释蔷薇科的雄蕊群发育是长期研究而未解决的问题,此前,Linfenhofer和Weber提出了一种蔷薇科特殊的雄蕊群发生模式——绣线菊模式,但该模式能否作为蔷薇科雄蕊发生的一般模式还存在极大的争议,且蔷薇科内部分属的特殊雄蕊群结构如何发生仍然不清楚.白鹃梅属具有蔷薇科中少见的束状雄蕊,而此前的研究并未解释这种束状雄蕊的成因.本研究以白鹃梅和齿叶白鹃梅为研究对象,利用扫描电子显微镜详细研究了从花原基到成熟花的整个发育过程.结果显示,对萼雄蕊的消失和对萼位置被丝托的扩张共同促成了雄蕊束的形成.同时,白鹃梅属的雄蕊发育模式还修正了绣线菊模式的雄蕊群排列,并验证了绣线菊模式的重复叠加作为蔷薇科雄蕊发育基础的可能性.

Rosaceae have a unique outer whorl of stamen pairs,numerous stamen whorls,and high morphological and developmental diversity of the androecium.Explanations of the developmental mode of the androecium in Rosaceae are controversial.Linfenhofer and Weber proposed a specific developmental mode of the androecium in Rosaceae called“the spiraeaoid pattern”,but whether this pattern can be used as a general type in Rosaceae remains highly controversial.Additionally,the developmental modes of the specific androecia in some genera are unknown.Exochorda has fascicular stamens,which have rarely been reported in Rosaceae,and previous studies have not explained how fascicular stamens are formed in Exochorda.Our study used scanning electron microscopy to study floral development in E.racemosa and E.serratifolia.The results showed that the disappearance of antesepalous stamens and expansion of the antesepalous hypanthium contributed to the formation of the fascicular stamens.The androecium developmental mode also revises the androecium arrangement of the“spiraeaoid pattern”,and verifies the possibility of repetition of the“spiraeoid pattern”as the developmental basis of polyandry in Rosaceae.