Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China.
University of Chinese Academy of Sciences, Beijing, China.
BMC Plant Biol. 2023 Jun 22;23(1):331. doi: 10.1186/s12870-023-04344-2.
Floral nectar is the most common reward flowers offered to pollinators. The quality and quantity of nectar produced by a plant species provide a key to understanding its interactions with pollinators and predicting rates of reproductive success. However, nectar secretion is a dynamic process with a production period accompanied or followed by reabsorption and reabsorption remains an understudied topic. In this study, we compared nectar volume and sugar concentration in the flowers of two long-spurred orchid species, Habenaria limprichtii and H. davidii (Orchidaceae). We also compared sugar concentration gradients within their spurs and rates of reabsorption of water and sugars.
Both species produced diluted nectar with sugar concentrations from 17 to 24%. Analyses of nectar production dynamics showed that as flowers of both species wilted almost all sugar was reabsorbed while the original water was retained in their spurs. We established a nectar sugar concentration gradient for both species, with differences in sugar concentrations at their spur's terminus and at their spur's entrance (sinus). Sugar concentration gradient levels were 1.1% in H. limprichtii and 2.8% in H. davidii, both decreasing as flowers aged.
We provided evidence for the reabsorption of sugars but not water occurred in wilted flowers of both Habenaria species. Their sugar concentration gradients vanished as flowers aged suggesting a slow process of sugar diffusion from the nectary at the spur's terminus where the nectar gland is located. The processes of nectar secretion/reabsorption in conjunction with the dilution and hydration of sugar rewards for moth pollinators warrant further study.
花卉花蜜是花朵向传粉者提供的最常见的奖励。植物物种产生的花蜜的质量和数量为了解其与传粉者的相互作用和预测繁殖成功的速度提供了关键信息。然而，花蜜分泌是一个动态过程，具有伴随或随后发生的分泌期和重吸收期，而重吸收仍然是一个研究不足的课题。在这项研究中，我们比较了两种长距兰花，Habenaria limprichtii 和 H. davidii（兰科）花朵的花蜜体积和糖浓度。我们还比较了它们的距内的糖浓度梯度和水及糖的重吸收率。
两个物种都产生了稀释的花蜜，糖浓度为 17%至 24%。对花蜜产生动态的分析表明，随着两种物种的花朵萎蔫，几乎所有的糖都被重吸收，而原始的水则保留在它们的距内。我们为两个物种建立了一个花蜜糖浓度梯度，在距的末端和入口（窦）处的糖浓度存在差异。H. limprichtii 的糖浓度梯度为 1.1%，H. davidii 的糖浓度梯度为 2.8%，随着花朵的衰老，糖浓度梯度都降低了。
我们提供了证据表明，在两种 Habenaria 物种萎蔫的花朵中，糖被重吸收而水没有被重吸收。随着花朵的衰老，它们的糖浓度梯度消失，这表明糖从位于距末端的蜜腺的缓慢扩散过程，蜜腺是花蜜腺所在的位置。花蜜分泌/重吸收过程以及对鳞翅目传粉者的糖奖励的稀释和水合作用需要进一步研究。
