目的:蕨类植物是维管植物的第二大类群,分布在全世界。尽管蕨类植物已被纳入一些比较生态学研究,重点是棘突,我们对这些分泌组织的功能解剖结构的理解存在相当大的差距,这些组织存在于许多蕨类植物叶的静脉末端。在这项研究中,我们的目的是调查系统发育分布,蕨类植物的结构和功能。
方法:我们对蕨类植物的棘突及其系统发育分布进行了全球综述,进行了祖先性格状态的重建,并研究了结构,八种盐残留物的内脏和元素组成,和两种植物木质部压力的日模式。
结果:从1189种蕨类植物中已知Hydathodes,92属19科2目,equisetales和Polypodiales。随机特征图表明,在属水平上,棘突具有多种得失,特别发生在蕨类植物进化的最后五千万年。Hydathodes位于正面叶表面,具有富含细胞质的特征,无孔表皮,并在几乎完全的叶片扩张后几周内发挥功能。在两个物种中,正木质部压力在夜间建立,可能会促进内脏。络合液中富含Ca和Si,但也包含P,Mg,Na和Al.
结论:随机特征作图和棘突的结构和功能多样性表明多种起源,它们在密切相关的类群中的存在/不存在意味着蕨类植物进化过程中的次生损失。正木质部压力和高空气湿度作为内脏的驱动因素起着重要作用。Hydathodes可能通过释放废物以外的过量化合物和矿物质来调节叶片养分化学计量,但是盐残留物中必需化学元素的存在也表明可能泄漏。
Ferns are the second largest group of vascular plants and are distributed nearly worldwide. Although ferns have been integrated into some comparative ecological studies focusing on
hydathodes, there is a considerable gap in our understanding of the functional anatomy of these secretory tissues that are found on the vein endings of many fern leaves. In this study, we aimed to investigate the phylogenetic distribution, structure and function of fern hydathodes.
We performed a global review on fern
hydathodes and their phylogenetic distribution, carried out an ancestral character state reconstruction, and studied the structure, guttation and elemental composition of salt residues of eight species, and the diurnal patterns of xylem pressure of two species.
Hydathodes are known from 1189 fern species, 92 genera and 19 families of 2 orders, Equisetales and Polypodiales. Stochastic character mapping indicated multiple gains and losses of hydathodes at the genus level, occurring especially during the last 50 million years of fern evolution.
Hydathodes were located on the adaxial leaf surface and characterized by a cytoplasm-rich, pore-free epidermis, and became functional for several weeks after nearly complete leaf expansion. In two species, positive xylem pressure built up at night, potentially facilitating guttation. Guttation fluid was rich in Ca and often Si, but also contained P, Mg, Na and Al.
Stochastic character mapping and the structural and functional diversity of hydathodes indicate multiple origins, and their presence/absence in closely related taxa implies secondary losses during fern evolution. Positive xylem pressure and high air humidity play an important role as drivers of guttation.
Hydathodes may contribute to the regulation of leaf nutrient stoichiometry by the release of excessive compounds and minerals other than waste products, but the presence of essential chemical elements in salt residues also indicates possible leakage.