do Valle Capelli Natalie, Alonso Rodrigues Bruna, Demarco Diego
Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo 05508-090, Brazil.
AoB Plants. 2017 Feb 10;9(1):plw083. doi: 10.1093/aobpla/plw083. eCollection 2017 Jan.
Stipules are leaf structures common in many groups of plants that can take a variety of forms. In Gentianales, interpetiolar stipules are considered a synapomorphy of Rubiaceae; however, some reports in the literature refer to their presence in other families. The goal of this study was to analyze the development of leaf primordia to investigate the possible presence of reduced or modified stipules in Apocynaceae. Shoot apices of 12 genera were analyzed under light and scanning electron microscopy comparatively with one species of Rubiaceae. Early in their development, leaf primordia form two lateral expansions at the base of the petiole (stipules) that give rise to colleters in 11 of the 12 genera of Apocynaceae studied, similarly to the Rubiaceae species. The basal genera have pairs of stipules modified into colleters positioned laterally to the petiole, while other species belonging to the derived subfamilies have interpetiolar stipules that each project towards the opposite stipule and merge, forming a sheathing stipule and from this arc the interpetiolar colleters originate. The ontogenetic study proved for the first time that Apocynaceae is a stipulate family whose stipules are modified into colleters and their absence might be a secondary loss, changing the interpretation of stipule evolution in Gentianales.
托叶是许多植物类群中常见的叶结构，可呈现多种形态。在龙胆目植物中，叶间托叶被认为是茜草科的一个共衍征；然而，文献中的一些报道提及它们在其他科中的存在情况。本研究的目的是分析叶原基的发育，以探究夹竹桃科中是否可能存在退化或变异的托叶。对12个属的茎尖进行了光学显微镜和扫描电子显微镜分析，并与一种茜草科植物进行了比较。在发育早期，叶原基在叶柄基部形成两个侧向扩展部分（托叶），在所研究的夹竹桃科12个属中的11个属中，这些托叶会发育出分泌结构，这与茜草科植物类似。基部的属有一对托叶变异为分泌结构，位于叶柄两侧，而其他属于衍生亚科的物种具有叶间托叶，每个托叶向相对的托叶伸出并融合，形成一个鞘状托叶，叶间分泌结构由此弧形结构产生。个体发育研究首次证明夹竹桃科是一个有托叶的科，其托叶变异为分泌结构，托叶的缺失可能是次生丢失，这改变了对龙胆目托叶进化的解释。
