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.

The role of some aquaporins as CO permeable channels has been controversial. Low CO permeability of plant membranes has been criticized because of unstirred layers and other limitations. Here we measured both water and CO permeability (P , P ) using stopped flow on plasma membrane vesicles (pmv) isolated from Pisum sativum (pea) and Arabidopsis thaliana leaves. We excluded the chemical limitation of carbonic anhydrase (CA) in the vesicle acidification technique for P using different temperatures and CA concentrations. Unstirred layers were excluded based on small vesicle size and the positive correlation between vesicle diameter and P . We observed high aquaporin activity (P 0.06 to 0.22 cm s ) for pea pmv based on all the criteria for their function using inhibitors and temperature dependence. Inhibitors of P did not alter P . P ranged from 0.001 to 0.012 cm s (mean 0.0079 + 0.0007 cm s ) with activation energy of 30.2 kJ mol . Intrinsic variation between pmv batches from normally grown or stressed plants revealed a weak (R = 0.27) positive linear correlation between P and P . Despite the low P , aquaporins may facilitate CO transport across plasma membranes, but probably via a different pathway than for water.

Endomembrane system cation/H+ exchangers affect male gametophyte and sperm function through membrane trafficking that is likely to remodel the plasma membrane and cell walls.