Paiva E A S, Martins L C
Departamento de Botânica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.
Departamento de Biologia, Instituto Federal de Educação Ciência e Tecnologia do Sul de Minas Gerais, Inconfidentes, Brazil.
Plant Biol (Stuttg). 2014 Jan;16(1):244-51. doi: 10.1111/plb.12038. Epub 2013 Aug 8.
Nectaries occur widely in Convolvulaceae. These structures remain little studied despite their possible importance in plant-animal interactions. In this paper, we sought to describe the structure and ultrastructure of the receptacular nectaries (RNs) of Ipomoea cairica, together with the dynamics of nectar secretion. Samples of floral buds, flowers at anthesis and immature fruits were collected, fixed and processed using routine methods for light, scanning and transmission electron microscopy. Circadian starch dynamics were determined through starch measurements on nectary sections. The secretion samples were subjected to thin layer chromatography. RNs of I. cairica were cryptic, having patches of nectar-secreting trichomes, subglandular parenchyma cells and thick-walled cells delimiting the nectary aperture. The glandular trichomes were peltate type and had typical ultrastructural features related to nectar secretion. The nectar is composed of sucrose, fructose and glucose. Nectar secretion was observed in young floral buds and continued as the flower developed, lasting until the fruit matured. The starch content of the subglandular tissue showed circadian variation, increasing during the day and decreasing at night. The plastids were distinct in different portions of the nectary. The continuous day-night secretory pattern of the RNs of I. cairica is associated with pre-nectar source circadian changes in which the starch acts as a buffer, ensuring uninterrupted nectar secretion. This circadian variation may be present in other extrafloral nectaries and be responsible for full daytime secretion. We conclude that sampling time is relevant in ultrastructural studies of dynamic extranuptial nectaries that undergo various changes throughout the day.
蜜腺在旋花科中广泛存在。尽管这些结构在植物 - 动物相互作用中可能具有重要意义，但对它们的研究仍然很少。在本文中，我们试图描述五爪金龙花托蜜腺（RNs）的结构和超微结构，以及花蜜分泌的动态过程。采集花芽、开花期花朵和未成熟果实的样本，采用常规方法进行固定和处理，用于光学显微镜、扫描电子显微镜和透射电子显微镜观察。通过对蜜腺切片进行淀粉测量来确定昼夜淀粉动态。将分泌样本进行薄层色谱分析。五爪金龙的花托蜜腺不明显，有分泌花蜜的毛状体斑块、腺下薄壁细胞和界定蜜腺孔的厚壁细胞。腺毛为盾状类型，具有与花蜜分泌相关的典型超微结构特征。花蜜由蔗糖、果糖和葡萄糖组成。在幼花芽中观察到花蜜分泌，并随着花朵发育持续进行，一直持续到果实成熟。腺下组织的淀粉含量呈现昼夜变化，白天增加，夜间减少。蜜腺不同部位的质体明显不同。五爪金龙花托蜜腺的昼夜连续分泌模式与花蜜前体源的昼夜变化有关，其中淀粉起到缓冲作用，确保花蜜不间断分泌。这种昼夜变化可能存在于其他花外蜜腺中，并导致全天的充分分泌。我们得出结论，在对全天经历各种变化的动态婚外蜜腺进行超微结构研究时，采样时间是相关的。
