HETEROGENEITY IN FORMATION OF LIGNIN .14. FORMATION AND STRUCTURE OF LIGNIN IN DIFFERENTIATING XYLEM OF GINKGO-BILOBA

Selective labelling of p-hydroxyphenyl-, guaiacyl- and syringyl-propane moieties in protolignin was achieved by administration of corresponding H-3-labeled monolignol glucosides to differentiating xylem of ginkgo. The growing process of the protolignin macromolecule in the specific morphological region was visualized by application of high resolution microautoradiography to the selectively labeled wood tissue. The process of lignification of ginkgo is very similar to that of conifers. p-Hydroxyphenyl lignin was formed mainly in the compound middle lamella and cell corner in an early stage of cell wall differentiation of tracheid. There were two peaks of deposition of guaiacyl lignin in the compound middle lamella at an early stage and in the secondary wall at a late stage. The content of condensed p-hydroxyphenyl or guaiacyl units was higher in the middle lamella than in the secondary wall lignin. The content of syringyl units was lower than that of other units, and localized mainly in secondary wall, but the period of deposition of this units was different from that of guaiacyl units. It does not seem that syringyl units belong to main parts of ginkgo lignin. During the formation of the cell wall, ginkgo protolignin grows under definite biological regulations to a heterogeneous macromolecule which consists of various structural moieties arranged in a regulated manner.