Medina Maria Camila, Sousa-Baena Mariane S, Capelli Natalie do Valle, Koch Raquel, Demarco Diego
Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo 05508-090, SP, Brazil.
Plants (Basel). 2021 Oct 28;10(11):2324. doi: 10.3390/plants10112324.
Stinging trichomes are rare in plants, occurring only in angiosperms, where they are reported for a few genera belonging to six families. Although there is no report of stinging trichomes in Apocynaceae, previous fieldwork collections of and caused us a mild allergic reaction on the skin when we contacted the dense indumentum of the plants. This fact associated with the well-known presence of glandular trichomes with acute apex in both genera raised suspicions that stinging trichomes could be present in the family. Hence, this study aimed to investigate the likely occurrence of stinging trichomes in and . We analyzed vegetative shoots and leaves of and through the usual procedures of light and scanning electron microscopy. We also performed several histochemical tests to investigate the chemical composition of trichome secretion. We detected that glandular trichomes occur throughout the surface of the leaf and stem. They are multicellular, uniseriate with an apical secretory cell, which has a dilated base and a needle-shaped apex. The secretion is compressed into the acuminate portion of the apical cell by a large vacuole, and crystals are deposited in the cell wall in a subapical position, providing a preferential site of rupture. The secretion, composed of amino acids and/or proteins, is released under mechanical action, causing skin irritation. Based on our detailed morphological and anatomical analyses, and in the functional aspects observed, we concluded that the glandular trichomes in and can indeed be classified as stinging. Thus, Apocynaceae is the seventh family for which this type of trichome has been reported. We also compiled information on stinging trichomes in all families of angiosperms. Their phylogenetic distribution indicates that they have evolved at least 12 times during angiosperm evolution and may represent an evolutionary convergence of plant defense against herbivory.
刺毛在植物中很罕见，仅出现在被子植物中，据报道在六个科的少数属中存在。尽管夹竹桃科没有刺毛的报道，但之前对[植物名称1]和[植物名称2]的野外采集样本，当我们接触其浓密的毛被时，皮肤会出现轻微过敏反应。这一事实，再加上这两个属中都存在顶端尖锐的腺毛，引发了我们对夹竹桃科可能存在刺毛的怀疑。因此，本研究旨在调查[植物名称1]和[植物名称2]中刺毛可能的存在情况。我们通过光学显微镜和扫描电子显微镜的常规方法，分析了[植物名称1]和[植物名称2]的营养枝和叶片。我们还进行了多项组织化学测试，以研究毛状体分泌物的化学成分。我们检测到腺毛遍布叶片和茎的表面。它们是多细胞的，单列，有一个顶端分泌细胞，该细胞基部膨大，顶端呈针状。分泌物被一个大液泡挤压到顶端细胞的渐尖部分，晶体沉积在亚顶端位置的细胞壁中，形成一个优先破裂位点。由氨基酸和/或蛋白质组成的分泌物在机械作用下释放，引起皮肤刺激。基于我们详细的形态学和解剖学分析，以及观察到的功能方面，我们得出结论，[植物名称1]和[植物名称2]中的腺毛确实可以归类为刺毛。因此，夹竹桃科是第七个被报道有这种类型毛状体的科。我们还汇编了被子植物所有科中刺毛的信息。它们的系统发育分布表明，在被子植物进化过程中它们至少进化了12次，可能代表了植物防御食草动物的一种进化趋同现象。
