Nectar is a major floral reward offered to pollinators by plants. In dichogamous plant species, differences in nectar production across sexual phases often occur, but both the male- and female-phase flowers have to attract pollinators to achieve effective pollination. Nectar-producing structures, i.e. floral nectaries, are a key component of floral organisation and architecture, and the knowledge of their structure and function contributes to better understanding of the plant–pollinator interactions. In the present study, we investigated the morphology and structure of nectaries and the nectar production pattern in two protandrous species Geranium macrorrhizum and G. phaeum. The flowers of the studied species have been shown to exhibit varied availability of nectar for insect visitors. Their nectaries differ in the shape, size and thickness. The other differences include the localisation of the stomatal field, the size and number of nectarostomata, the presence of non-glandular and glandular trichomes, the presence of tannin idioblasts, the mode of secretion and the occurrence of plastids functioning probably as autophagosomes and autolysosomes, whose presence in nectary cells has been described for the first time. The flowers of the studied species started nectar secretion in the non-receptive phase before pollen presentation and nectar was produced throughout both sexual phases. The nectar production was gender biased towards the female phase in the nectar amount, nectar sugar concentration and total sugar secreted in the nectar. We postulate that the nectar production patterns in G. phaeum and G. macrorrhizum might have evolved as a response to pollinators’ pressure.

中文翻译：

---

原花种 Geranium macrorrhizum 和 Geranium phaeum 的花蜜腺结构和雌性花蜜生产

花蜜是植物提供给传粉者的主要花卉奖励。在双生植物物种中，不同性期的花蜜产量经常发生差异，但雄性和雌性花都必须吸引传粉者才能实现有效授粉。产生花蜜的结构，即花蜜腺，是花卉组织和结构的关键组成部分，对其结构和功能的了解有助于更好地了解植物 - 传粉媒介的相互作用。在本研究中，我们调查了两种突出物种 Geranium macrorrhizum 和 G. phaeum 的蜜腺形态和结构以及花蜜生产模式。研究表明，所研究物种的花朵为昆虫游客展示了不同的花蜜可用性。它们的蜜腺的形状、大小和厚度各不相同。其他差异包括气孔场的定位、蜜口的大小和数量、非腺体和腺体毛状体的存在、单宁特异母细胞的存在、分泌方式以及可能作为自噬体和自溶酶体发挥作用的质体的出现，其在蜜腺细胞中的存在已被首次描述。研究物种的花在花粉呈现之前的非接受期开始分泌花蜜，并且在两个有性阶段都产生花蜜。花蜜生产在花蜜量、花蜜糖浓度和花蜜中分泌的总糖方面对雌性期有性别偏见。我们假设 G. phaeum 和 G. macrorrhizum 中的花蜜生产模式可能已经进化为对传粉媒介压力的反应。