Molecular Plant Science/Plant Biochemistry, University of Wuppertal, Wuppertal, Germany.
Molecular Cell Biology and Microbiology, University of Wuppertal, Wuppertal, Germany.
BMC Plant Biol. 2024 Oct 9;24(1):940. doi: 10.1186/s12870-024-05630-3.
Nectar is offered by numerous flowering plants to attract pollinators. To date, the production and secretion of nectar have been analyzed mainly in eudicots, particularly rosids such as Arabidopsis. However, due to the enormous diversity of flowering plants, further research on other plant species, especially monocots, is needed. Ananas comosus (monocot) is an economically important species that is ideal for such analyses because it produces easily accessible nectar in sufficient quantities. In addition, the analyses were also carried out with Nicotiana tabacum (dicot, asterids) for comparison.
We performed transcriptome sequencing (RNA-Seq) analyses of the nectaries of Ananas comosus and Nicotiana tabacum, to test whether the mechanisms described for nectar production and secretion in Arabidopsis are also present in these plant species. The focus of these analyses is on carbohydrate metabolism and transport (e.g., sucrose-phosphate synthases, invertases, sucrose synthases, SWEETs and further sugar transporters). In addition, the metabolites were analyzed in the nectar, nectaries and leaves of both plant species to address the question of whether concentration gradients for different metabolites exist between the nectaries and nectar The nectar of N. tabacum contains large amounts of glucose, fructose and sucrose, and the sucrose concentration in the nectar appears to be similar to the sucrose concentration in the nectaries. Nectar production and secretion in this species closely resemble corresponding processes in some other dicots, including sucrose synthesis in nectaries and sucrose secretion by SWEET9. The nectar of A. comosus also contains large amounts of glucose, fructose and sucrose and in this species the sucrose concentration in the nectar appears to be higher than the sucrose concentration in the nectaries. Furthermore, orthologs of SWEET9 generally appear to be absent in A. comosus and other monocots. Therefore, sucrose export by SWEETs from nectaries into nectar can be excluded; rather, other mechanisms, such as active sugar export or exocytosis, are more likely.
The mechanisms of nectar production and secretion in N. tabacum appear to be largely similar to those in other dicots, whereas in the monocotyledonous species A. comosus, different synthesis and transport processes are involved.
许多开花植物都会分泌花蜜，以吸引传粉者。迄今为止，人们主要在真双子叶植物中（尤其是蔷薇目植物，如拟南芥）分析了花蜜的产生和分泌。然而，由于开花植物种类繁多，还需要对其他植物物种（尤其是单子叶植物）进行进一步研究。菠萝（单子叶植物）是一种经济上很重要的物种，非常适合进行此类分析，因为它能够产生容易获取且数量充足的花蜜。此外，还对烟草（真双子叶植物，木兰类植物）进行了分析，以作比较。
我们对菠萝和烟草的蜜腺进行了转录组测序（RNA-Seq）分析，以验证在拟南芥中描述的花蜜产生和分泌机制是否也存在于这些植物物种中。这些分析的重点是碳水化合物代谢和运输（例如，蔗糖磷酸合酶、转化酶、蔗糖合酶、SWEET 及其他糖转运蛋白）。此外，还分析了这两个物种的花蜜、蜜腺和叶片中的代谢物，以解决蜜腺和花蜜之间是否存在不同代谢物浓度梯度的问题。烟草花蜜中含有大量的葡萄糖、果糖和蔗糖，且花蜜中的蔗糖浓度似乎与蜜腺中的蔗糖浓度相似。该物种的花蜜产生和分泌过程与其他一些双子叶植物中的过程非常相似，包括蜜腺中的蔗糖合成和 SWEET9 介导的蔗糖分泌。菠萝花蜜中也含有大量的葡萄糖、果糖和蔗糖，且该物种花蜜中的蔗糖浓度似乎高于蜜腺中的蔗糖浓度。此外，SWEET9 的直系同源物似乎普遍不存在于菠萝和其他单子叶植物中。因此，SWEET 从蜜腺向花蜜中的蔗糖输出可以排除；相反，可能涉及其他机制，如主动糖输出或胞吐作用。
烟草花蜜产生和分泌的机制与其他双子叶植物中的机制大致相似，而在单子叶植物菠萝中，则涉及不同的合成和运输过程。
