Making and breaking of boron bridges in the pectic domain rhamnogalacturonan‐II at apoplastic pH in vivo and in vitro

作者：Rifat Ara Begum, David J. Messenger, Stephen C. Fry · 发表于：The Plant Journal · 年份：2023 · DOI：10.1111/tpj.16112 · 被引用次数：10 · 研究领域：Polysaccharides and Plant Cell Walls、Plant Reproductive Biology、Plant nutrient uptake and metabolism

SUMMARY Cross‐linking of the cell‐wall pectin domain rhamnogalacturonan‐II (RG‐II) via boron bridges between apiose residues is essential for normal plant growth and development, but little is known about its mechanism or reversibility. We characterized the making and breaking of boron bridges in vivo and in vitro at ‘apoplastic’ pH. RG‐II (13–26 μ m ) was incubated in living Rosa cell cultures and cell‐free media with and without 1.2 m m H 3 BO 3 and cationic chaperones (Ca 2+ , Pb 2+ , polyhistidine, or arabinogalactan‐protein oligopeptides). The cross‐linking status of RG‐II was monitored electrophoretically. Dimeric RG‐II was stable at pH 2.0–7.0 in vivo and in vitro . In‐vitro dimerization required a ‘catalytic’ cation at all pHs tested (1.75–7.0); thus, merely neutralizing the negative charge of RG‐II (at pH 1.75) does not enable boron bridging. Pb 2+ (20–2500 μ m ) was highly effective at pH 1.75–4.0, but not 4.75–7.0. Cationic peptides were effective at approximately 1–30 μ m ; higher concentrations caused less dimerization, probably because two RG‐IIs then rarely bonded to the same peptide molecule. Peptides were ineffective at pH 1.75, their pH optimum being 2.5–4.75. d ‐Apiose (>40 m m ) blocked RG‐II dimerization in vitro , but did not cleave existing boron bridges. Rosa cells did not take up d ‐[U‐ 14 C]apiose; therefore, exogenous apiose would block only apoplastic RG‐II dimerization in vivo . In conclusion, apoplastic pH neither broke boron bridges nor preve...