目的:花外蜜腺是植物营养部分上存在的蜜腺分泌结构,可间接防御草食动物的侵袭。克雷多姆的花外蜜腺是髌状的特殊毛滴虫结构。然而,全面描绘了一般的髌状花外蜜腺,特别是中国蜜腺,尚未建立对花蜜生物合成和分泌过程中涉及的细胞生理机制的基本了解。
方法:我们研究了形态学的时间变化,花外蜜腺结构的解剖和超微结构特征。我们还比较了花外花蜜的代谢物谱,蜜腺组织,非坏死组织和韧皮部汁液。进一步检查了与糖代谢有关的酶的原位组织定位和正常的体外活性。
结果:从组织化学表征中揭示了花蜜腺中四个不同的组织区域,其中发现中间蜜腺组织是代谢活跃的区域,而发现中间层富含脂质。超微结构研究表明,在食盐区存在大量线粒体和含淀粉的叶绿体。然而,随着蜜腺的成熟,注意到淀粉的消耗。代谢物分析显示花蜜之间的成分差异,韧皮部汁液,蜜腺和非蜜腺组织。转化酶活性在分泌阶段较高,并位于蜜腺组织和邻近区域。
结论:我们的研究表明,中国菜的花蜜分泌在本质上既是内分泌,也是分乳。发现了将表皮与蜜腺薄壁组织分开的明显的中间富含脂质的层,这可能是花蜜中水流的屏障。这项研究还揭示了花蜜和韧皮部汁液之间的区别,酶和超微结构研究证明,淀粉可以作为花蜜前体。因此,我们的研究发现,随着花外蜜腺的时间分泌而改变结构,揭示了一个参与蜜腺生物合成和分泌的细胞生理过程。
OBJECTIVE: Extrafloral nectaries are nectar-secreting structures present on vegetative parts of plants which provide indirect defences against herbivore attack. Extrafloral nectaries in Clerodendrum chinense are patelliform-shaped specialized trichomatous structures. However, a complete understanding of patelliform extrafloral nectaries in general, and of C. chinense in particular, has not yet been established to provide fundamental insight into the cellular physiological machinery involved in nectar biosynthesis and secretory processes.
METHODS: We studied temporal changes in the morphological, anatomical and ultrastructural features in the architectures of extrafloral nectaries. We also compared metabolite profiles of extrafloral nectar, nectary tissue, non-nectary tissue and phloem sap. Further, both in situ histolocalization and normal in vitro activities of enzymes related to sugar metabolism were examined.
RESULTS: Four distinct tissue regions in the nectar gland were revealed from histochemical characterization, among which the middle nectariferous tissue was found to be the metabolically active region, while the intermediate layer was found to be lipid-rich. Ultrastructural study showed the presence of a large number of mitochondria along with starch-bearing chloroplasts in the nectariferous region. However, starch depletion was noted with progressive maturation of nectaries. Metabolite analysis revealed compositional differences among nectar, phloem sap, nectary and non-nectary tissue. Invertase activity was higher in secretory stages and localized in nectariferous tissue and adjacent region.
CONCLUSIONS: Our study suggests extrafloral nectar secretion in C. chinense to be both eccrine and merocrine in nature. A distinct intermediate lipid-rich layer that separates the epidermis from nectary parenchyma was revealed, which possibly acts as a barrier to water flow in nectar. This study also revealed a distinction between nectar and phloem sap, and starch could act as a nectar precursor, as evidenced from enzymatic and ultrastructural studies. Thus, our findings on changing architecture of extrafloral nectaries with temporal secretion revealed a cell physiological process involved in nectar biosynthesis and secretion.