Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo.
Eur J Histochem. 2024 Apr 2;68(1):4027. doi: 10.4081/ejh.2024.4027.
Nuptial glands are very diverse and associated with different pollination mechanisms. The greater the specificity in the pollen transfer mechanism from anther to stigma, the greater the morphological elaboration of flowers and functional complexity of the nuptial glands. In Apocynaceae, pollination mechanisms reached an extreme specificity, a fact that was only possible due to an extreme morphological synorganization and a profusion of floral glands. Although these glands are of different types, the vast majority have secretory cells only in the epidermis. In general, these epidermal cells produce many different compounds at the same time, and previous studies have demonstrated that in the style head, the functional complexity of epidermis has become even greater. Four types of style head are found in the family, which have different degrees of functional complexity in relation to the secretion produced and pollen dispersal mechanism. The secretion is fluid in types I, II and III, and the pollen is dispersed and adhered to the pollinator by the secretion produced by the style head. In type IV, the secretion hardens and acquires a specific shape, moulded by the spatial constraints of the adjacent floral organs. This evolutionary alteration is accompanied by changes in the structure and arrangement of the secretory cells, as well as in pollen aggregation and position of stigma. Histochemical analysis has shown that the secretion is mixed and highly complex, especially in the style head type IV, where the secretion, called translator, is formed by a rigid central portion, which adheres to the pollinator, and two caudicles that attach to two pollinia. The translator has a distinct composition in its different parts. Further studies are needed to answer the new questions that have arisen from the discovery of this highly functional complexity of the secretory tissue.
生殖腺多种多样，与不同的传粉机制有关。从花药到柱头的花粉转移机制特异性越高，花的形态结构就越复杂，生殖腺的功能也越复杂。在夹竹桃科中，传粉机制达到了极端的特异性，这一事实之所以成为可能，是因为花的形态结构发生了极端的协同进化，以及生殖腺的大量存在。虽然这些腺体有不同的类型，但绝大多数在表皮中只有分泌细胞。一般来说，这些表皮细胞同时产生许多不同的化合物，先前的研究表明，在花柱头上，表皮的功能复杂性甚至更大。该科有 4 种花柱头类型，它们与产生的分泌物和花粉传播机制的功能复杂性有关。类型 I、II 和 III 的分泌物为液体，花粉通过花柱头产生的分泌物传播并黏附在传粉者上。在类型 IV 中，分泌物变硬并获得特定的形状，由相邻花器官的空间限制塑造。这种进化改变伴随着分泌细胞的结构和排列的变化，以及花粉聚集和柱头位置的变化。组织化学分析表明，分泌物是混合的，非常复杂，尤其是在花柱头类型 IV 中，这种称为翻译器的分泌物由一个坚硬的中央部分组成，该部分黏附在传粉者上，还有两个尾状部分附着在两个花粉块上。翻译器在不同部位有明显的组成。需要进一步的研究来回答从发现这种高度复杂的分泌组织中产生的新问题。
