Cytological study of gibberellin regulated xylem development.

We conducted the studies on xylem development of tobacco stem by over-expressed PtGA20ox and PtGA2ox1 genes, NtGA20ox RNAi transgenic lines and added extra different hormones with paraffin-cut section method and microscopic observation. The results showed that rapid elongation of internodes as well as xylem formation and development were stimulated by increasing endogenous gibberellins (GAs) levels or exogenous application of GA3, while xylem growth was delayed by decreasing endogenous GAs levels or exogenous application of PAC (GAs biosynthetic inhibitor). Thus our experiment proved that GAs played positive regulatory roles in the development process of xylem and this happened through a GAs concentration-dependent mechanism. Besides, we proved that the positive effects of IAA on xylem development were realized through increasing the level of GAs syntheses at least in some degree.