With Over 60 Independent Losses, Stomata Are Expendable in Mosses
With Over 60 Independent Losses, Stomata Are Expendable in Mosses
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DOI：
10.3389/fpls.2020.00567
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发表时间：
2020-05
影响因子：
5.6
通讯作者：
K. Renzaglia;William B. Browning;Amelia Merced
中科院分区：
文献类型：
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作者：
K. Renzaglia;William B. Browning;Amelia Merced
由于气孔在britectes是唯一位于孢子囊，生理和进化的限制放在britecte气孔是根本不同的，从那些在导管植物的叶子。虽然在苔藓植物中已经记录了气孔的损失，但这种进化过程发生的程度仍然相对未知。我们开始这项研究，绘制已知的气孔损失发生率和数量每胶囊上最近的藓类植物。由此，我们确定了40个科和74个属缺乏气孔，其中至少有63个是独立的损失。在苔藓多样性的任何方向上，气孔损失或数量都没有明显的趋势。现存的分类群在早期分歧的苔藓谱系要么缺乏气孔或产生pseudostomata不形成孔。最早的陆地植物化石显示出与现存苔藓相似的孢子囊形态和气孔分布，这表明最早的苔藓可能具有和失去气孔，这在该组中是常见的。为了理解为什么气孔在苔藓中是消耗性的，我们对一系列有气孔和没有气孔的苔藓进行了比较解剖学研究。我们比较了气孔和无气孔类群的解剖结构和细胞间隙的发育，包括气孔下腔，横跨苔藓。两种类型的细胞间隙发育不同，被认为是在peristomate苔藓，那些与气孔和那些包围孢子囊。无气孔藓类的蒴果结构从早期分歧谱系中的实体到包含直接与传导组织相连的内部空间，并参与蒴果扩张和孢子的营养，水合和发育。这种解剖学揭示了苔藓被囊内组织的不同结构安排，它们在完成孢子发生和孢子传播的基本过程中同样有效。气孔不是这些过程的基础。
Because stomata in bryophytes are uniquely located on sporangia, the physiological and evolutionary constraints placed on bryophyte stomata are fundamentally different from those on leaves of tracheophytes. Although losses of stomata have been documented in mosses, the extent to which this evolutionary process occurred remains relatively unexplored. We initiated this study by plotting the known occurrences of stomata loss and numbers per capsule on the most recent moss phylogeny. From this, we identified 40 families and 74 genera that lack stomata, of which at least 63 are independent losses. No trends in stomata losses or numbers are evident in any direction across moss diversity. Extant taxa in early divergent moss lineages either lack stomata or produce pseudostomata that do not form pores. The earliest land plant macrofossils from 400 ma exhibit similar sporangial morphologies and stomatal distribution to extant mosses, suggesting that the earliest mosses may have possessed and lost stomata as is common in the group. To understand why stomata are expendable in mosses, we conducted comparative anatomical studies on a range of mosses with and without stomata. We compared the anatomy of stomate and astomate taxa and the development of intercellular spaces, including substomatal cavities, across mosses. Two types of intercellular spaces that develop differently are seen in peristomate mosses, those associated with stomata and those that surround the spore sac. Capsule architecture in astomate mosses ranges from solid in the taxa in early divergent lineages to containing an internal space that is directly connected to the conducing tissue and is involved in capsule expansion and the nourishment, hydration and development of spores. This anatomy reveals there are different architectural arrangements of tissues within moss capsules that are equally effective in accomplishing the essential processes of sporogenesis and spore dispersal. Stomata are not foundational to these processes.