The Salt Tolerance Clons Screening Of Broussonetia Papyrifera And Its Response To NaCl Stress

Using Broussonetia papyrifera(L.) Vent(common name:paper mulberry),an economically important tree species,we established efficient experimental system of tissue culture and studied the effect of NaCl stress on plantlet growth,partial physiological nature, membrane lipid peroxidation,protective enzyme system,photosynthetic characters and Dehydrin gene expression.The major results were summarized as follows:1.The shoots of Bronssonetia Papyrifera disinfected for 10-15 minutes with 0.1% mercuric chloride could efficiently control contamination in sterile culture.The most suitable proliferation medium was MS+1.0mg/L 6-BA+0.1 mg/L IBA+3.0%sucrose+6.5 g/L carrageenan.Rooting medium is 1/2MS+0.5 mg/L IBA+0.3 mg/L NAA+3.0%sucrose+6.5 g/L carrageenan.2.The injury rate and salt stress index of Broussonetia papyrifera plantlet was increased with increased NaCl concentration.However,shoot height,fresh weight and dry weight decreased with the increased concentration.The suitable concentration for the selection of salt tolerance plant was 100 mM-125 mM.Meanwhile,the stress time was important to select salt tolerance plantlet.3.NaCl treatment caused a lot of changes in protein content,antioxidant enzyme activities and the content of proline and MDA.The results demonstrated that soluble protein content increased at low level of NaCl concentration,and when NaCl concentration exceeded 100mM it decreased.Moreover,proline contents markedly increased in response to salt stress.In our study,there was a positive relationship between salt concentration and proline content of tissues.Proline content significantly increased in tissues with increase in salinity.MDA content increased at low levels of salinity and then decreased at 125mM and 150 mM NaCl concentration. The decrease of MDA content probably results from up-regulation of the antioxidative system in response to salt stress.4.Under salt stress chla and total chlorophyl contents in the leaves tended to decline while chlb and carotenoid contents were increased,chla/chlb was decreased while car/chl was higher than control.NaCl stress could accelerate the senescence of leaves.Photosynthetic rate, evaporate and stomatal conductance of Broussonetia papyrifera plantlet was decreased with increased salt concentration.But CO₂ concentration was higher than control.The decrease of net photosynthetic rate of Broussonetia papyrifera plantlet was caused by non-stomatal limitation.The results of correlation analysis showed that: Pn(Photosynthesic rate),Tr(Evaporate) and Gs(Stomatal conductance) had significant negative correlation with treatment concentration,and the correlation between WUE(water use efficiency) and treatment concentration was not significant, Ci(CO₂ concentration) had no correlation with treatment concentration.The effects of 50 mM NaCl on the gas exchange parameters was not significant,which indicated that Broussonetia papyrifera has certain salt tolerance.5.Salt stress induced the expression of dehydrin gene in transcriptional levels. There was only a little expression for dhnl gene in control plantlet.When treatment concentration was more than 75mM,the expression of dhnl gene was increased obviously.The transcription level reached the highest when stress concentration was 100mM.