Comparison of Sugars, Iridoid Glycosides and Amino Acids in Nectar and Phloem Sap of Maurandya barclayana, Lophospermum erubescens, and Brassica napus
Comparison of Sugars, Iridoid Glycosides and Amino Acids in Nectar and Phloem Sap of Maurandya barclayana, Lophospermum erubescens, and Brassica napus
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DOI：
10.1371/journal.pone.0087689
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发表时间：
2014-01-29
期刊：
影响因子：
3.7
通讯作者：
Schwerdtfeger, Michael
中科院分区：
文献类型：
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作者：
Lohaus, Gertrud;Schwerdtfeger, Michael
背景：花蜜中含有糖和氨基酸，可以吸引传粉者。此外，花蜜还含有不同的次生化合物，但对其来源和功能了解甚少。花蜜成分是否反映韧皮部成分，或花蜜是在蜜腺中合成和/或修饰的？同时对同一植物的花蜜和韧皮部汁液进行分析的研究很少。因此，对不同植物(毛果、芥菜和甘蓝型油菜)的韧皮部汁液和花蜜进行了比较。方法和主要发现：用微毛细管采集花蜜，韧皮部汁液采用激光-蚜虫-针刺技术。所有三种植物的花蜜都含有大量的糖，其中葡萄糖、果糖和蔗糖的比例不同，而韧皮部汁液中的糖几乎完全由蔗糖组成。其中一个可能的原因可能是蜜腺中蔗糖酶的活性。蜜汁中氨基酸总量远低于韧皮部汁液，说明蜜汁形成过程中氮素溶质有选择性地滞留。不同植物的花蜜氨基酸浓度与花蜜体积呈负相关。车前亚族(车前科车前族)M.barclayana和L.erubescens均合成了环烯醚萜糖苷类化合物。两种植物的韧皮部汁液中均含有大量的抗大黄苷，而蜜汁中的抗大黄素含量较低。结论/意义：对蜜汁和韧皮部汁液的平行分析表明，除己糖外，蜜汁中的所有代谢物都可在韧皮部汁液中检测到。另外，两种水溶液的组成不同。蜜汁中几种代谢物的浓度低于韧皮部汁液中的浓度，说明某些代谢物具有选择性保留。此外，花蜜中抗大黄苷的存在可能是由于韧皮部被动分泌的结果。
Background: Floral nectar contains sugars and amino acids to attract pollinators. In addition, nectar also contains different secondary compounds, but little is understood about their origin or function. Does nectar composition reflect phloem composition, or is nectar synthesized and/or modified in nectaries? Studies where both, the nectar as well as the phloem sap taken from the same plant species were analyzed in parallel are rare. Therefore, phloem sap and nectar from different plant species (Maurandya barclayana, Lophospermum erubescens, and Brassica napus) were compared.Methodology and Principal Findings: Nectar was collected with microcapillary tubes and phloem sap with the laser-aphid-stylet technique. The nectar of all three plant species contained high amounts of sugars with different percentages of glucose, fructose, and sucrose, whereas phloem sap sugars consisted almost exclusively of sucrose. One possible reason for this could be the activity of invertases in the nectaries. The total concentration of amino acids was much lower in nectars than in phloem sap, indicating selective retention of nitrogenous solutes during nectar formation. Nectar amino acid concentrations were negatively correlated with the nectar volumes per flower of the different plant species. Both members of the tribe Antirrhineae (Plantaginaceae) M. barclayana and L. erubescens synthesized the iridoid glycoside antirrhinoside. High amounts of antirrhinoside were found in the phloem sap and lower amounts in the nectar of both plant species.Conclusions/Significance: The parallel analyses of nectar and phloem sap have shown that all metabolites which were found in nectar were also detectable in phloem sap with the exception of hexoses. Otherwise, the composition of both aqueous solutions was not the same. The concentration of several metabolites was lower in nectar than in phloem sap indicating selective retention of some metabolites. Furthermore, the existence of antirrhinoside in nectar could be based on passive secretion from the phloem.