Kerr Ellen M, Fry Stephen C
The Edinburgh Cell Wall Group, Institute of Cell and Molecular Biology, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, EH9 3JH, Edinburgh, UK.
Planta. 2004 May;219(1):73-83. doi: 10.1007/s00425-004-1210-0. Epub 2004 Feb 11.
Cell-suspension cultures of maize ( Zea mays L.) released soluble extracellular polysaccharides (SEPs) into their medium. Some or all of the SEPs had feruloyl ester groups. Pulse-labelling with [(3)H]arabinose was used to monitor changes in the SEPs' M(r) (estimated by gel-permeation chromatography) with time after synthesis. Newly released (3)H-SEPs were 1.3-1.6 MDa, but between 2 days and 3 days after radiolabelling (in one experiment) or between 5 days and 6 days (in another), the (3)H-SEPs abruptly increased to approximately 17 MDa, indicating extensive cross-linking. The cross-linking involved both [(3)H]xylan and [(3)H]xyloglucan components of the SEPs. The cross-links could be cleaved by alkali, returning the SEPs to their original M(r). In 0.1 M NaOH at 37 degrees C, 58% cleavage was effected within 24 h. The requirement for such prolonged alkali treatment indicates that ester-bonded (e.g. diferuloyl) groups were not solely responsible for the cross-linking. Bonds cleaved only by relatively severe alkali could include benzyl ether linkages formed between sugar residues and oxidised phenolics that had quinone methide structures. The ability of alkali to cleave the cross-links was independent of the age of the (3)H-SEP molecules. Cross-linking of (3)H-SEPs in vivo was delayed (up to approx. 7 days after radiolabelling) by exogenous sinapic acid, chlorogenic acid or rutin-agents predicted to compete with the oxidative coupling of feruloyl-polysaccharides. The cross-linking was promoted by exogenous ferulic acid or l-tyrosine, possibly because these compounds acted as precursors for polysaccharide feruloylation, thus providing additional partner substrates for the oxidative coupling of previously formed (3)H-SEPs. The ability of certain phenolics to prevent the cross-linking of (3)H-SEPs supports the idea that the cross-linking involved phenolic oxidation.
玉米（Zea mays L.）的细胞悬浮培养物会向培养基中释放可溶性细胞外多糖（SEPs）。部分或全部SEPs含有阿魏酸酯基团。用[³H]阿拉伯糖进行脉冲标记，以监测合成后不同时间SEPs的相对分子质量（通过凝胶渗透色谱法估算）变化。新释放的³H-SEPs相对分子质量为1.3 - 1.6 MDa，但在放射性标记后的2天至3天（在一项实验中）或5天至6天（在另一项实验中），³H-SEPs的相对分子质量突然增加到约17 MDa，表明发生了广泛的交联。交联涉及SEPs的[³H]木聚糖和[³H]木葡聚糖成分。交联键可被碱裂解，使SEPs恢复到原来的相对分子质量。在37℃的0.1 M NaOH中，24小时内可实现58%的裂解。需要如此长时间的碱处理表明酯键连接（如二阿魏酸酯）并非交联的唯一原因。仅在相对强碱条件下才能裂解的键可能包括糖残基与具有醌甲基结构的氧化酚类之间形成的苄基醚键。碱裂解交联键的能力与³H-SEP分子的年龄无关。外源性芥子酸、绿原酸或芦丁（预计可与阿魏酸多糖的氧化偶联竞争）会延迟³H-SEPs在体内的交联（放射性标记后长达约7天）。外源性阿魏酸或L-酪氨酸会促进交联，可能是因为这些化合物作为多糖阿魏酸化的前体，从而为先前形成的³H-SEPs的氧化偶联提供了额外的配对底物。某些酚类物质阻止³H-SEPs交联的能力支持了交联涉及酚类氧化的观点。
