Abstract
BackgroundThe elongating maize internode represents a useful system for following development of cell walls in vegetative cells in the Poaceae family. Elongating internodes can be divided into four developmental zones, namely the basal intercalary meristem, above which are found the elongation, transition and maturation zones. Cells in the basal meristem and elongation zones contain mainly primary walls, while secondary cell wall deposition accelerates in the transition zone and predominates in the maturation zone.ResultsThe major wall components cellulose, lignin and glucuronoarabinoxylan (GAX) increased without any abrupt changes across the elongation, transition and maturation zones, although GAX appeared to increase more between the elongation and transition zones. Microarray analyses show that transcript abundance of key glycosyl transferase genes known to be involved in wall synthesis or re-modelling did not match the increases in cellulose, GAX and lignin. Rather, transcript levels of many of these genes were low in the meristematic and elongation zones, quickly increased to maximal levels in the transition zone and lower sections of the maturation zone, and generally decreased in the upper maturation zone sections. Genes with transcript profiles showing this pattern included secondary cell wall CesA genes, GT43 genes, some β-expansins, UDP-Xylose synthase and UDP-Glucose pyrophosphorylase, some xyloglucan endotransglycosylases/hydrolases, genes involved in monolignol biosynthesis, and NAM and MYB transcription factor genes.ConclusionsThe data indicated that the enzymic products of genes involved in cell wall synthesis and modification remain active right along the maturation zone of elongating maize internodes, despite the fact that corresponding transcript levels peak earlier, near or in the transition zone.
Highlights
The elongating maize internode represents a useful system for following development of cell walls in vegetative cells in the Poaceae family
Microarray analyses have been used to define gene transcript profiles along the elongating internode and have enabled changes in wall composition to be reconciled with the transcriptional activities of genes involved in wall polysaccharide, protein and lignin synthesis, together with transcription factor genes that are known to regulate the expression of genes responsible for wall synthesis and re-modelling
The trend in the GAX contents of the walls was generally similar to that of cellulose, GAX appeared to increase more between the elongation and transition zones
Summary
The elongating maize internode represents a useful system for following development of cell walls in vegetative cells in the Poaceae family. Cells in the basal meristem and elongation zones contain mainly primary walls, while secondary cell wall deposition accelerates in the transition zone and predominates in the maturation zone. We have measured changes in cell wall composition along an elongating maize internode, which represents a useful model system for the examination of walls of the stalk at different stages of development. The basal region of the internode includes the intercalary meristem, above which is an elongation zone where cell expansion occurs and primary cell walls are deposited [2,3]. At the upper or distal end of the internode is the maturation zone, where cells have stopped growing and secondary wall deposition predominates [2]. Microarray analyses have been used to define gene transcript profiles along the elongating internode and have enabled changes in wall composition to be reconciled with the transcriptional activities of genes involved in wall polysaccharide, protein and lignin synthesis, together with transcription factor genes that are known to regulate the expression of genes responsible for wall synthesis and re-modelling
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