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Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies.

ABSTRACT: BACKGROUND:Grass phytoliths are the most common phytoliths in sediments; recognizing grass phytolith types is important when using phytoliths as a tool to reconstruct paleoenvironments. Grass bulliform cells may be silicified to large size parallelepipedal or cuneiform shaped phytoliths, which were often regarded as of no taxonomic value. However, studies in eastern Asia had identified several forms of grass bulliform phytoliths, including rice bulliform phytolith, a phytolith type frequently used to track the history of rice domestication. Identification with a higher level of taxonomic resolution is possible, yet a systematic investigation on morphology of Poaceae bulliform phytoliths is lacking. We aimed at providing a morphological description of bulliform phytoliths of Poaceae from Taiwan based on morphometric measurements in anatomical aspect. The results are important references for paleo-ecological studies. RESULT:The morphology of grass bulliform phytoliths is usually consistent within a subfamily; the end profile is relatively rectangular in Panicoideae and Micrairoideae, whereas cuneiform to nearly circular in Oryzoideae, Bambusoideae, Arundinoideae, and Chloridoideae. Bulliform phytoliths were seldom observed in Pooideae. Certain morphotypes are limited to plants growing in specific environments. For example, large, thin, and pointed bulliform phytoliths are associated with wet habitat; Chloridoideae types are mostly from C4 plants occupying open arid places. CONCLUSION:Grass bulliform phytoliths can be identified at least to the subfamily level, and several forms were distinguished within large subfamilies. Previously un-reported silicified cell types, i.e., arm cells and fusoids, and two special trichome phytolith types associated with bulliform phytoliths, were described. Morphometric methods were great tools for delimiting morphotypes; with refined morphological classification the association between forms and habit/habitats was revealed. The knowledge provides new ways to interpret phytolith assemblage data, and it is especially useful when the sediments are enriched in large blocky phytoliths.

SUBMITTER: Chen I

PROVIDER: S-EPMC7052108 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies.

Chen Iju I Li Kuang-Ti KT Tsang Cheng-Hwa CH

Botanical studies 20200302 1

<h4>Background</h4>Grass phytoliths are the most common phytoliths in sediments; recognizing grass phytolith types is important when using phytoliths as a tool to reconstruct paleoenvironments. Grass bulliform cells may be silicified to large size parallelepipedal or cuneiform shaped phytoliths, which were often regarded as of no taxonomic value. However, studies in eastern Asia had identified several forms of grass bulliform phytoliths, including rice bulliform phytolith, a phytolith type frequ ...[more]

PMID: 32124105

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Project description:Chloridoideae is one of the largest subfamilies of Poaceae, containing many species of great economic and ecological value; however, phylogenetic relationships among the subtribes and genera of Cynodonteae are controversial. In the present study, we combined 111 plastomes representing all five tribes, including 25 newly sequenced plastomes that are mostly from Cynodonteae. Phylogenetic analyses supported the five monophyletic tribes of Chloridoideae, including Centropodieae, Triraphideae, Eragrostideae, Zoysieae and Cynodonteae. Simultaneously, nine monophyletic lineages were revealed in Cynodonteae: supersubtribe Boutelouodinae, subtribes Tripogoninae, Aeluropodinae, Eleusininae, Dactylocteniinae, supersubtribe Gouiniodinae, Cleistogenes and Orinus, and subtribe Triodiinae. Within the tribe of Cynodonteae, the basal lineage is supersubtribe Boutelouodinae and Tripogoninae is sister to the remaining lineages. The clade formed of Aeluropodinae and Eleusininae is sister to the clade composed of Dactylocteniinae, supersubtribe Gouiniodinae, Cleistogenes and Orinus, and subtribe Triodiinae. The clade comprising Dactylocteniinae and supersubtribe Gouiniodinae is sister to the clade comprising Cleistogenes, Orinus, and Triodiinae. Acrachne is a genus within Eleusininae but not within Dactylocteniinae. Molecular evidence determined that Diplachne is not clustered with Leptochloa, which indicated that Diplachne should not be combined into Leptochloa. Cleistogenes is sister to a clade composed of Orinus and Triodia, whereas the recently proposed subtribe Orininae was not supported. Cynodonteae was estimated to have experienced rapid divergence within a short period, which could be a major obstacle in resolving its phylogenetic relationships. Ancestral state reconstructions of morphological characters showed that the most recent common ancestor (MRCA) of Chloridoideae has a panicle, multiple florets in each spikelet, the peaked type of stomatal subsidiary cells, and a saddle-shaped phytoliths, while the ancestral morphological characters of Cynodonteae are the panicle, peaked type of stomatal subsidiary cells, sharp-cap cell typed and equal-base-cell microhair, and square-shaped phytoliths. Overall, plastome phylogenomics provides new insights into the phylogenetic relationships and morphological character evolution of Chloridoideae.

Project description:In the last decade, our understanding of rice domestication has improved by new archaeological findings using advanced analytical techniques such as morphological and morphometric analyses on rice grains, spikelet bases and phytoliths, and ancient DNA analysis on rice remains. Previous studies have considered the size of rice bulliform phytoliths as a proxy for tracking the domestication process. These phytoliths are often abundant and well preserved in sediments, and their shape is under the control of numerous genes, which may shift toward larger sizes by genetic mutation in domestication. Therefore, it has been assumed that the bulliforms of domesticated rice are usually larger than those of wild ones; however, morphometric data supporting this assumption are lacking in the literature, thereby requiring additional evidence to test its veracity. In this study, the vertical and horizonal lengths of bulliform phytoliths were measured in four rice species (domesticated Oryza sativa and wild Oryza rufipogon, Oryza officinalis, and Oryza meyeriana) from different regions of southern China. We found that the bulliform morphometric data of wild and domesticated rice overlapped and that there was no statistically significant difference between them. Therefore, bulliform size could not be used as a diagnostic indicator to distinguish domesticated rice from wild species and is a supporting rather than conclusive proxy for determining the domesticated status of rice in archaeological research. We further found that larger rice bulliform sizes likely occurred at the locations with higher temperature, precipitation, and water levels, indicating hydrothermal environment is an alternative factor influencing the size of rice bulliform phytoliths. For further archaeological use of an increasing size trend of bulliform phytoliths to reveal the process of rice domestication, we present some suggestions for controlling the influence of hydrothermal factors. Even so, the combination of bulliform phytolith size with other established criteria is strongly suggested to provide precise identification of wild and domesticated rice in future research.

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Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies.

Publications

Silicified bulliform cells of Poaceae: morphological characteristics that distinguish subfamilies.

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