Studies On Tissue Culture And Physiological And Biochemical Basis Of Drought Resistance Evaluation In New Clones Of Black Locust(Robinia Pseudoacacia L.)

Robinia pseudoacacia L, is a multiple purpose tree with approximate one hundred cultivate history. It distributes abroad. Tetroploid black locust is a new introduced exotic choiceness variety. It's predicted to be used in soil and water conservation, wind-breaking and sand-fixing, converting the reclaimed farmland to forest. The efficient propagate route and the theoretic foundation in popularizing the choiceness tetraploid black locust should be provided.The tissue culture systems of fast-growing (K2) and fodder-type (K3) tetraploid black locust have been established. Bud explants were selected from the shoots sprouting in growth chamber, sterilized by ethanol 70% and NaCIO 0.5%. The best proliferation medium of K3 is MS+ 6-BA1.0mg/L + NAA0.1mg/L + sugar30g/L + agar6g/L, and MS + 6-BA0.3mg/L + NAA0.05mg/L + sugar30g/L + agar6g/L is propitious to K2. The optimized rooting medium of K2 and K3 are 1/2MS + sugar3% + agar0.6% medium containing IBA 0.1mg/L and NAA 0.1mg/L respectively. In addition, the pH is 5.8, special illumination for 14h/d. Shoots cultured for 14 days which undergo two-phase training and two-step transplanting, 98% of the plantlets survived.By taking one-year-old micropropagated K2, K3 and ordinary duplation (contrast) black locust as study objects, the difference in drought resistance abilities among three clones were evaluated under stimulant natural drought and gradual drought of soil. The results indicate that the tetraploid clones have more biomass, especially K3 keeps optimal ratio of root to shoot and leaf biomass. Their water use efficiency (WUE) exceed that of duplation clone under drought stress, which show that tetraploid clones have more yield at the same irrigation. δ(13)^C compares well with long-term WUE and biomass, and the correlation between them is higher while water stress severer and severer. δ(13)^C will be the evaluate index to high WUE. The tetraploid clones have higher photosynthetic capacity, which can be explained from two parts. One is that the decline extent of leaf area is smaller,the other is the negative effect on photosynthetic apparatus is slight. Net photosynthetic rate (Pn) declines along with stomatal conductance (Gs) and the ratio intercellular/ambient (Ci/Ca). The reason of photosynthate decline is mainly nonstomatal limitation. In addition, the CO₂ compensation point is lower, the CO₂ saturation point rise under drought stress, and they maintain higher Pn. The lower MDA accumulation and higher activity of SOD and CAT are the other factors which are contribute to the higher drought resistance evaluation. The membrane permeability, free proline and soluble saccharides probably can't indicate drought resistance ability efficiently.