Abstract
Tracheary elements deposit secondary cell walls in appropriate patterns during plant development. To analyze regulatory mechanism of the secondary wall patterns, we have developed in vitro metaxylem vessel differentiation system using Arabidopsis suspension cells harboring inducible VND6, a master regulator of metaxylem vessel differentiation. In this study, we focused on roles of microtubules and actin microfilaments in secondary cell wall patterning. During the differentiation, the cortical microtubules were mainly distributed beneath the region of secondary wall synthesis. Detailed observation revealed that the microtubules soon depolymerized after growing into secondary wall-free pits. Depolymerization of actin microfilaments caused abnormal microtubule distribution and secondary wall patterns. Interestingly, the microtubule stabilizing agent taxol suppressed the effect of actin microfilament depolymerization. Actin microfilaments didn't show significant co-localization with secondary walls. These results suggested that indirect regulation of microtubules by actin microfilaments is essential for appropriate secondary wall patterning.
