Abstract
Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed. Comprehensive histological investigation of these feeding sites is complicated by their variable shape and their positions deep within root tissue. Using tissue clearing and confocal microscopy, we examined thick (up to 150 μm) sections of wheat roots infected by cereal cyst nematodes (Heterodera avenae). This approach provided clear views of feeding sites and surrounding tissues, with resolution sufficient to reveal spatial relationships among nematodes, syncytia and host vascular tissues at the cellular level. Regions of metaxylem vessels near syncytia were found to have deviated from classical developmental patterns. Xylem vessel elements in these regions had failed to elongate but had undergone radial expansion, becoming short and plump rather than long and cylindrical. Further investigation revealed that vessel elements cease to elongate shortly after infection and that they later experience delays in secondary thickening (lignification) of their outer cell walls. Some of these elements were eventually incorporated into syncytial feeding sites. By interfering with a developmental program that normally leads to programmed cell death, H. avenae may permit xylem vessel elements to remain alive for later exploitation by the parasite.
Highlights
Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed
In the seminal roots of wheat (Triticum aestivum L.) and other cereal crops, there are multiple peripheral metaxylem vessels arranged around one large central metaxylem vessel
This has been thoroughly investigated for root knot nematodes (RKN, Meloidogyne spp.), which induce the development of new vascular tissue around their ‘giant cell’ feeding sites[7]
Summary
Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed. Using tissue clearing and confocal microscopy, we examined thick (up to 150 μm) sections of wheat roots infected by cereal cyst nematodes (Heterodera avenae) This approach provided clear views of feeding sites and surrounding tissues, with resolution sufficient to reveal spatial relationships among nematodes, syncytia and host vascular tissues at the cellular level. Further investigation revealed that vessel elements cease to elongate shortly after infection and that they later experience delays in secondary thickening (lignification) of their outer cell walls. Some of these elements were eventually incorporated into syncytial feeding sites. Such expansion may enhance water uptake to support nematode development[18] and/or help maintain high turgor pressure[19] within the syncytia
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