Abstract:

Objective: The development of bamboo culm has always been a research hotspot. This study aims to reveal the physiological mechanism of culm lodging, by exploring the dynamic changes in the morphological, anatomical, and cell wall composition characteristics of the culm of the somatic clone variant strain of Pseudosasa japonica f. akebonosuji. Method: The dwarf and lodging mutant (DWF) of P. japonica f. akebonosuji with somaclonal variation was used as the research object, and the normal tissue-cultured P. japonica f. akebonosuji (WT) served as the control. After 90, 180, 270, and 360 days of transplanting, the phenotype, cross-sectional anatomical structure, and changes in cell wall component content of the newly-grown bamboo culm were investigated. Result: There were significant differences in culm morphology, anatomical structure, and cell wall component content between DWF and WT at different transplanting stages. 1) Compared to WT, DWF culms experienced varying degrees of lodging during all four transplanting periods. At 90 days after transplanting, the angle between the stem and the ground was 35.27°, indicating the greatest degree of culm lodging. At 360 days after transplanting, the angle between the culm and the ground was 73.13°, indicating the least degree of culm lodging. 2) The stem diameter, stem height, and basal internode length of DWF were extremely significantly lower than those of WT, with the largest difference occurring at 360 days after transplanting. DWF grew slowly, and the height increase of new culms from 270 to 360 days after transplanting was only 21.41% of that of WT, and the diameter increase of new culms was only 17.49% of that of WT. 3) The number and area of vascular bundles in DWF were significantly lower than those in WT. At 360 days after transplanting, the number and area of large vascular bundles in DWF were 65.71% and 55.35% lower than those in WT, respectively, while the number and area of small vascular bundles were 75.44% and 55.51% lower than those in WT, respectively. When the number and area of vascular bundles of the new culms of WT increased rapidly, the increase in DWF was slow. The thickness of the DWF sclerenchyma decreased, and there were significant differences in sclerenchyma thickness between WT and DWF in all four periods, with DWF being 50.21%, 55.77%, 54.59%, and 45.41% smaller than WT, respectively. The development of the DWF pith cavity was slow, and the pith cavity appeared at 270 days and 360 days after transplanting, with a significantly smaller diameter than that of WT. 4) With the extension of transplanting time, though the lignin and cellulose content of the new culms of DWF increased, their content in DWF was significantly lower than that in WT. The degree of lignin and cellulose deposition in the internodes was also lower than that of WT, however there was no significant difference in hemicellulose content between WT and DWF. 5) There was a significant negative correlation between the degree of DWF stem lodging and its stem diameter, and there were highly significantly negative correlations between the degree of DWF stem lodging and the number and area of large and small vascular bundles, the thickness of sclerenchyma, as well as the content of lignin and cellulose. Conclusion: Compared to WT, DWF shows stunted growth and dwarfism in the development process, with weak culm strength and lodging. DWF stem diameter is smaller, the number and area of large and small vascular bundles are smaller, and the thickness of the sclerenchyma is also smaller, which all are the reason for its lodging. The low content of lignin and cellulose in the cell wall of DWF results in weak stem strength, which is another reason for its lodging.

Key words: Pseudosasa japonica f. akebonosuji, mutant, culm lodging, lignin, cellulose