Boron-dependent cytoarchitecture in plants: In vivo visualization of vacuolar compartments and the cytoskeleton in Arabidopsis root hairs after disruption of boron-dependent structural cross-links with phenylboronate

摘要

Boron in plants acts as a cross-linking molecule by forming reversible covalent bonds with cis-diols on either side of borate. Phenylboronates can form the same reversible bonds with cis-diols but cannot cross-link two discrete molecules, and therefore have been previously used to selectively disrupt possible boron-dependent structural cross-links. In cultured tobacco (Nicotiana tabacum cv BY-2) cells, phenylboronates caused the disruption of cytoplasmic strands and cell-to-cell wall detachment, suggesting borate involvement in cross-links somewhere along the putative cytoskeleton-plasma membrane-cell wall continuum (Baluska et al. 2003). Here we report the effects of 3-nitrophenylboronic acid (3-NBA) on vacuolar and cytoskeleton organization, and endosomal trafficking, using several lines of transgenic Arabidopsis harboring GFP-fusion constructs that label actin, microtubules, and FYVE-endosomes. Results indicate that within 2 min following treatment with 30 μM 3-NBA, dramatic reorganization of dynamic, tip-directed tubular vacuoles can be observed, including the formation of numerous spherical vacuoles behind the tip that continue to fuse and split before eventually joining to form a large central vacuole. Vacuolar reorganization was concomitant with the disruption of transvacuolar cytoplasmic strands. Actin and microtubule organization, as well as cytoplasmic streaming were not significantly affected in the short term, as evidenced by the presence of actin filaments, microtubule bundles and continued movements of FYVE-endosomes in treated root hairs. These results support a structural role for boron that is likely critical for the maintenance of cytoarchitecture, especially the integrity of cytoplasmic strands and tip-directed tubular vacuoles.