| Xylem cellulose component is an important source of raw materials for papermaking industry. The growing demand for wood and paper products with the social development, and the vital role of xylem in plant growth and human life fulfillment, more and more attention have been paid on the the regulatory mechanisms of plant xylem formation and development. In the present study, transgenic technology and exogenous hormone treatment method were used to up-regulate or down-regulate gibberellins (GAs) levels in tobacco lines, and stem xylem development of above plants were studied. Xylem development process of tobacco stem in35S::PtGA20ox,35S::PtGA2oxl, NtGA20ox RNAi lines and plants treated with different hormones were studied with paraffin-cut section method and microscopic observation. The regulatory role of GA in xylem development were researched and discussed. The main contents and major results are introduced as follows:1) Phenotypic changes associated with altered endogenous bioactive GA levels. High quality RNA was extracted from mature leaves of Populus tomentosa, and GA metabolism two key genes PtGA20ox and PtGA2oxl were amplified from cDNA of Populus tomentosa. Transgenic technology was used to obtain transgenic tobacco plants35S::PtGA20ox and35S::PtGA2oxl, of which transgenic genes were expressed under the control of consecutive35S promoter. A series of growth indicators in transgenic plants were measured, and the results showed that GA promote growth of plant height, ground stems, leaves and other traits.2) Transgenic genes and GA contents were changed in different transgenic plants. Expression levels of PtGA20ox and PtGA2ox1were measured by using real-time quantitative PCR and found out that PtGA20ox and PtGA2oxl were over-expressed in different tissues of35S::PtGA20ox and35S: PtGA2oxl lines respectively. liquid chromatography-mass spectrometry was used to detect GA levels in different tissues of transgenic plants, the results showed that bioactive GA levels in transgenic lines with PtGA20ox over-expressed were significantly increased, while GA levels were down-regulated in plants with PtGA2oxl over-expressed.3) GA has been found to play a positive regulatory role in xylem formation and development. The results revealed 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. Varied inhibition levels of GA in different transgenic lines showed differentiated lignification degree 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. |
