Zhang Miao, Chavan Ramesh R, Smith Bronwen G, McArdle Brian H, Harris Philip J
School of Biological Sciences, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland, 1142, New Zealand.
School of Chemical Sciences, The University of Auckland, Private Bag 92019, Auckland Mail Centre, Auckland, 1142, New Zealand.
BMC Plant Biol. 2016 Sep 7;16(1):194. doi: 10.1186/s12870-016-0884-3.
Compression wood (CW) forms on the underside of tilted stems of coniferous gymnosperms and opposite wood (OW) on the upperside. The tracheid walls of these wood types differ structurally and chemically. Although much is known about the most severe form of CW, severe CW (SCW), mild CWs (MCWs), also occur, but less is known about them. In this study, tracheid wall structures and compositions of two grades of MCWs (1 and 2) and SCW were investigated and compared with OW in slightly tilted radiata pine (Pinus radiata) stems.
The four wood types were identified by the distribution of lignin in their tracheid walls. Only the tracheid walls of OW and MCW1 had a S3 layer and this was thin in MCW1. The tracheid walls of only SCW had a S2 layer with helical cavities in the inner region (S2i). Using immunomicroscopy, (1 → 4)-β-D-galactans and (1 → 3)-β-D-glucans were detected in the tracheid walls of all CWs, but in only trace amounts in OW. The (1 → 4)-β-D-galactans were located in the outer region of the S2 layer, whereas the (1 → 3)-β-D-glucans were in the inner S2i region. The areas and intensities of labelling increased with CW severity. The antibody for (1 → 4)-β-D-galactans was also used to identify the locations and relative amounts of these galactans in whole stem cross sections based on the formation of an insoluble dye. Areas containing the four wood types were clearly differentiated depending on colour intensity. The neutral monosaccharide compositions of the non-cellulosic polysaccharides of these wood types were determined on small, well defined discs, and showed the proportion of galactose was higher for CWs and increased with severity.
The presence of an S3 wall layer is a marker for very MCW and the presence of helical cavities in the S2 wall layer for SCW. The occurrence and proportions of (1 → 4)-β-D-galactans and (1 → 3)-β-D-glucans can be used as markers for CW and its severity. The proportions of galactose were consistent with the labelling results for (1 → 4)-β-D-galactans.
针叶裸子植物倾斜茎干的下侧形成压缩木（CW），上侧形成对应木（OW）。这些木材类型的管胞壁在结构和化学性质上有所不同。尽管人们对最严重形式的压缩木，即重度压缩木（SCW）了解很多，但轻度压缩木（MCW）也会出现，不过对其了解较少。在本研究中，对两种等级的轻度压缩木（1级和2级）以及重度压缩木的管胞壁结构和组成进行了研究，并与轻度倾斜的辐射松（Pinus radiata）茎干中的对应木进行了比较。
通过木质素在管胞壁中的分布确定了这四种木材类型。只有对应木和1级轻度压缩木的管胞壁有S3层，且1级轻度压缩木的S3层较薄。只有重度压缩木的管胞壁在内部区域（S2i）有带有螺旋状空洞的S2层。使用免疫显微镜技术，在所有压缩木的管胞壁中检测到了（1→4）-β-D-半乳聚糖和（1→3）-β-D-葡聚糖，但在对应木中仅检测到微量。（1→4）-β-D-半乳聚糖位于S2层的外部区域，而（1→3）-β-D-葡聚糖位于S2i内部区域。标记的面积和强度随压缩木严重程度的增加而增加。用于（1→4）-β-D-半乳聚糖的抗体还用于根据不溶性染料的形成来确定全茎横切面中这些半乳聚糖的位置和相对含量。根据颜色强度，包含这四种木材类型的区域清晰可辨。在小的、明确界定的切片上测定了这些木材类型非纤维素多糖的中性单糖组成，结果表明压缩木中半乳糖的比例较高，且随严重程度增加。
S3细胞壁层的存在是极轻度压缩木的标志，S2细胞壁层中螺旋状空洞的存在是重度压缩木的标志。（1→4）-β-D-半乳聚糖和（1→3）-β-D-葡聚糖的出现和比例可作为压缩木及其严重程度的标志。半乳糖的比例与（1→4）-β-D-半乳聚糖的标记结果一致。
