Responses Of Two Broussonetia Papyrifera Varieties To NaCl Stress

The physiological and biochemical characteristics and ultra-structure of the 1a seedlings of Broussonetia papyrifera Vent and Broussonetia kazinoki Sied under different NaCl treatments (CK, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%) were studied. The main results were drawn as follows:(1)The membrane permeability of two seedlings under 0.1% NaCl was lower than the contrast. With the increasing salinity and time, the membrane permeability and MDA contents increased. POD activity increased firstly and decreased later and the soluble protein contents decreased gradually. For Broussonetia papyrifera, SOD activity increased gradually under 0.1% NaCl, increased firstly and decreased later under other salt concentrations, while SOD activity of Broussonetia kazinoki was higher than contrast under any concentration, and changed slowly along with the time.(2)The Na+ contents of root and stem increased remarkably while K+, Ca2+ and Mg2+ contents changed slowly and the Na+ and K+ contents of leaf increased while Ca2+ and Mg2+ contents changed irregularly. Compared with the contrast, the ratios of K+ to Na+, Ca2+ to Na+ and Mg2+ to Na+ of different organs decreased gradually with the increasing salinity.(3)22 days after salt stress, the net photosynthetic rate(Pn), stomatal conductance(Gs) and transpiration rate(Tr) all were up firstly and down later under NaCl treatments while intercellular CO2 concentrations(Ci) was opposite. With the increasing NaCl and time, the relative chlorophyll contents, the PSII maximal photochemical efficiency (Fv/Fm), the PSII effective photochemical efficiency (Fv'/Fm'), the photochemical quench(qP) and the PSII actual photochemical efficiency(ΦPSⅡ) declined while the non-photochemical quench increased.(4)The cell ultra-structure, the cellular organs and the nucleolus of two seedlings'leaves were unabridged under low salt concentrations (0.1% and 0.2% NaCl), While under 0.3% and 0.4% NaCl, the cell ultra-structure were destroyed seriously. The cytoderm became deformed and the cellular organs structure were disordered. Besides, the nucleolus diminished obviously and the nucleolus matter agglomerated.