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Developmental changes in guard cell wall structure and pectin composition in the moss Funaria: implications for
Amelia Merced1, Karen Renzaglia2
1Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901, USA ameliamerced@siu.edu.
Annals of Botany
|August 18, 2014
Summary
Moss stomatal movement is limited by pectin composition changes during development. Guard cell walls gain rigidity from homogalacturonan (HG) and flexibility from arabinan rhamnogalacturonan I (RG1).
Area of Science:
- Plant cell wall biology
- Pectin biosynthesis and function
- Stomatal development and evolution
Background:
- Guard cell walls in seed plants use pectins (arabinan rhamnogalacturonan I for flexibility, unesterified homogalacturonan for rigidity) for movement.
- Mosses, as early land plants, offer insights into guard cell evolution and function.
- Moss stomata exhibit limited movement, primarily during capsule expansion.
Purpose of the Study:
- To investigate the ultrastructure and pectin composition of guard cell walls during stomatal development in the moss Funaria hygrometrica.
- To correlate these features with the observed limited movement of moss stomata.
Main Methods:
- Transmission electron microscopy was used to examine developing stomata.
- Immunogold labeling with monoclonal antibodies identified five pectin epitopes: LM19 (unesterified HG), LM20 (esterified HG), LM5 (galactan RG1), LM6 (arabinan RG1), and LM13 (linear arabinan RG1).
- Pectin localization and abundance were quantified across different developmental stages.
Main Results:
- Guard cell walls were significantly thinner before pore formation compared to mature stomata.
- Unesterified homogalacturonan (HG) was abundant in early wall layers, while arabinan rhamnogalacturonan I (RG1) strongly labeled guard cell walls, particularly linear arabinan RG1.
- Pectin content decreased during development, with a shift in the proportion of HG to arabinans, and esterified HG and galactan RG1 were present in low amounts.
Conclusions:
- This study provides the first evidence of pectin composition changes during stomatal development in any plant species.
- The limited movement of Funaria stomata is associated with incomplete wall layering and decreased pectin content in mature stages.
- The specialization of moss guard cells involves the incorporation of linear arabinans into their cell walls.
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