Arabinogalactan proteins in XXXX coleoptiles: developmental relationship to cell death during xylem differentiation but not to extension growth.

@entity2829 @entity73243 @entity4583 @entity10786 @entity3649 @entity1521
The spatial and temporal expression of arabinogalactan proteins (AGPs) in the coleoptile of @entity2829 seedlings was investigated with monoclonal antibodies (MAC207, JIM13, JIM14) raised against particular @entity73243 epitopes in @entity10786 . MAC207 binds to a buffer-soluble @entity73243 fraction of 90-210 kDa that also reacts with beta-glucosyl Yariv reagent and the lectin RCA120. Immunogold-labelling showed that the MAC207 epitope is exclusively localized in the plasma membrane. JIM13 binds to a 120 kDa component of the buffer-soluble @entity73243 fraction localized in the plasma membrane of future sclerenchyma cells and secondary-wall thickenings of future tracheids of vascular bundles. JIM14 binds to a 50 kDa component of the salt-extractable fraction from cell walls localized in the innermost wall layer of sclerenchyma cells. These @entity73243 epitopes demonstrate different temporal expression patterns which do not correlate with extension growth. Auxin had no effect on the amount of soluble @entity73243 from coleoptile sections, containing the growth-controlling epidermis but no vascular bundles, as measured by crossed electrophoresis. Moreover, incorporation of radioactive @entity4583 , @entity3649 or @entity1521 into this fraction was not stimulated by auxin. These results contradict the hypothesis that AGPs function as wall-loosening agents in auxin-mediated extension growth. The results are compatible with the notion that AGPs serve as developmental markers defining particular features of future cell differentiation. The specific association of the epitopes recognized by JIM13 and JIM14 with disintegrating cells suggests that the related AGPs identify those cells of the coleoptile which are committed to programmed cell death.
