GENERATION PROCESS OF GROWTH STRESSES IN CELL-WALLS .4. ACTION OF THE CELLULOSE MICROFIBRIL UPON THE GENERATION OF THE TENSILE STRESSES

The relationships between longitudinal shrinkages, microfibril angles (MFAs), and the longitudinal released strains of growth stresses were investigated to obtain evidence of the contribution of cellulose microfibrils (CMFs) to the generation of tensile growth stresses in cell walls. (1) Longitudinal shrinkages in broadleaved trees which contained tension woods increased in proportion to the contractive released strains. Longitudinal shrinkages in the gelatinous layers were estimated to be about four times greater than those in normal cell walls: namely, the CMFs tended to contract largely in length as a result of the loss of water. This indicates the possibility that the CMFs contract and generate large tensile stresses in their axial directions also during cell maturation. (2) Contractive released strains increased as MFAs decreased and as the alpha-cellulose contents increased in sugi (Cryptomeria japonica D. Don.) and yurinoki (Liriodendron tulipifera L.). (3) According to a simulation of the growth stress evolution by a cell model described in a previous report, the generation of tensile growth stresses was considered to be controlled by an interaction between the Young's modulus in the CMFs and the contractions of the CMFs in addition to the MFAs.