The morphology and chemical composition of cuticular waxes in some Brazilian liverworts and mosses

The cuticle, by ensuring protection against water loss, was a key innovation in plant terrestrialisation. This layer is characterised by the cutin matrix embedded and covered with cuticular waxes. In this study we describe the cuticular waxes on gametophytes of several species of liverworts and mosses, including Brazilian endemics.
Cuticular waxes from 34 species from different locations in the São Paulo state, Brazil, were analysed by gas chromatography coupled with mass spectrometry. The compounds were identified based on mass spectra fragmentation. The morphology of the epicuticular waxes was analysed using scanning electron microscopy.
The wax content in the liverwort species varied from 0.1 to 4 μg cm−2, while in mosses the values ranged from 0.02 to 0.6 μg cm−2. The main classes of wax compounds were fatty acids, alkanes, and primary alcohols. Aldehydes, alkenes, esters, ketones, triterpenes, a diacid and a secondary alcohol had a more restricted distribution. The morphology of the epicuticular waxes was predominately of the film type.
In general, wax content was higher in the liverworts than in the mosses. Fatty acids and alkanes were the most common class whilst alkenes, ketones, diacid, and a secondary alcohol are described for the first time as wax compounds in bryophyte gametophytes.

角质层（cuticle）通过抵御水分流失，成为植物登陆过程中的一项关键创新性状。该结构以嵌入并覆盖有表皮蜡质（cuticular waxes）的角质基质（cutin matrix）为典型特征。本研究针对多种苔类植物（liverworts）与藓类植物（mosses）的配子体（gametophytes）展开表皮蜡质相关描述，研究对象涵盖巴西特有物种。
本研究对采自巴西圣保罗州不同区域的34个物种的表皮蜡质采用气相色谱-质谱联用（gas chromatography coupled with mass spectrometry）法进行分析，通过质谱碎裂（mass spectra fragmentation）模式对化合物进行定性鉴定，并借助扫描电子显微镜（scanning electron microscopy）观察表皮外蜡质（epicuticular waxes）的形态结构。
苔类植物的蜡质含量介于0.1~4 μg·cm⁻²之间，藓类植物的蜡质含量则为0.02~0.6 μg·cm⁻²。蜡质化合物的主要类别为脂肪酸（fatty acids）、烷烃（alkanes）与伯醇（primary alcohols）。醛类、烯烃（alkenes）、酯类（esters）、酮类（ketones）、三萜类（triterpenes）、二元酸及仲醇的分布范围相对狭窄。表皮外蜡质的形态以膜状结构为主。
总体而言，苔类植物的蜡质含量高于藓类植物。脂肪酸与烷烃为最常见的蜡质成分类别，而烯烃、酮类、二元酸及仲醇则是首次在苔藓植物（bryophytes）配子体中被报道的蜡质化合物。