角苔类气孔对外源和环境信号没有积极响应。
Hornwort stomata do not respond actively to exogenous and environmental cues.
机构信息
Life Sciences Department, Natural History Museum, London, UK.
Plant Biology Department, Southern Illinois University, Carbondale, USA.
出版信息
Ann Bot. 2018 Jun 28;122(1):45-57. doi: 10.1093/aob/mcy045.
BACKGROUNDS AND AIMS
Because stomata in bryophytes occur on sporangia, they are subject to different developmental and evolutionary constraints from those on leaves of tracheophytes. No conclusive experimental evidence exists on the responses of hornwort stomata to exogenous stimulation.
METHODS
Responses of hornwort stomata to abscisic acid (ABA), desiccation, darkness and plasmolysis were compared with those in tracheophyte leaves. Potassium ion concentrations in the guard cells and adjacent cells were analysed by X-ray microanalysis, and the ontogeny of the sporophytic intercellular spaces was compared with those of tracheophytes by cryo-scanning electron microscopy.
KEY RESULTS
The apertures in hornwort stomata open early in development and thereafter remain open. In hornworts, the experimental treatments, based on measurements of >9000 stomata, produced only a slight reduction in aperture dimensions after desiccation and plasmolysis, and no changes following ABA treatments and darkness. In tracheophytes, all these treatments resulted in complete stomatal closure. Potassium concentrations are similar in hornwort guard cells and epidermal cells under all treatments at all times. The small changes in hornwort stomatal dimensions in response to desiccation and plasmolysis are probably mechanical and/or stress responses of all the epidermal and spongy chlorophyllose cells, affecting the guard cells. In contrast to their nascent gas-filled counterparts across tracheophytes, sporophytic intercellular spaces in hornworts are initially liquid filled.
CONCLUSIONS
Our experiments demonstrate a lack of physiological regulation of opening and closing of stomata in hornworts compared with tracheophytes, and support accumulating developmental and structural evidence that stomata in hornworts are primarily involved in sporophyte desiccation and spore discharge rather than the regulation of photosynthesis-related gaseous exchange. Our results run counter to the notion of the early acquisition of active control of stomatal movements in bryophytes as proposed from previous experiments on mosses.
背景与目的
由于藓类植物的气孔出现在孢子体上，因此它们受到的发育和进化限制与维管束植物的叶片气孔不同。目前尚无确凿的实验证据表明角苔气孔对外源刺激的反应。
方法
比较了角苔气孔对脱落酸（ABA）、干旱、黑暗和质壁分离的反应与维管束植物叶片的反应。通过 X 射线微分析分析保卫细胞和相邻细胞中的钾离子浓度，并通过冷冻扫描电子显微镜比较孢子体细胞间隙的发生与维管束植物的发生。
主要结果
角苔气孔的孔径在发育早期就开始打开，此后一直保持打开状态。在角苔中，基于对>9000 个气孔的测量，实验处理仅在干旱和质壁分离后略微减小孔径尺寸，而 ABA 处理和黑暗处理后没有变化。在维管束植物中，所有这些处理都导致气孔完全关闭。在所有处理和所有时间点，角苔保卫细胞和表皮细胞中的钾浓度相似。角苔气孔对干旱和质壁分离的尺寸变化很小，可能是所有表皮和海绵状叶绿体细胞的机械和/或应激反应，影响了保卫细胞。与维管束植物中初生充满气体的对应物不同，角苔的孢子体细胞间隙最初是充满液体的。
结论
与维管束植物相比，我们的实验表明角苔气孔的开放和关闭没有生理调节，这支持了越来越多的发育和结构证据，表明角苔气孔主要参与孢子体的干燥和孢子释放，而不是光合作用相关气体交换的调节。我们的结果与先前关于藓类植物的实验提出的关于藓类植物早期获得主动控制气孔运动的观点相悖。
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