| Thuja sutchuenensis, which was discovered first time by the French missionary P. G.Farges at April1892but has disappeared for over100years, is an evergreen tree of Thuja forthe Cupressaceae. It is an endemic to China that distributes at Daba mountain of ChongqingMunicipality. The World Conservation Union (IUCN-SSC) listed T. sutchuenensis as an EW(extinct in the wild) in1998. In2003, however, IUCN-SSC added it as a Critically Endangeredplant after it had been rediscovered in1999.Propagation of the population is a key step for Endangered plant conservation. In recentyears, the following key findings have been obtained by the scientific community throughcontinuous observation. First, the seed quantity of T. sutchuenensis is too small to meet theneeds of sexual propagation. Therefore, cuttage breeding and tissue culture technology are themain ways of artificial propagation for T. sutchuenensis. Second, its main habitat is steepsouth-facing slopes or precipices. Moreover, although the underlying mechanism ofdrought-resistance remains unclear, T. sutchuenensis does have a strong adaptability to drought.Here, we conducted a cuttage experiment, in order to provide propagation technology forpopulation expansion, reveal drought resistance and corresponding mechanisms, and provide ascientific basis for the introduction and ex-situ conservation of T. sutchuenensis. The mainresults are as the following:1) The contamination rate is up to100%while using the shoot apex collected from wildadult trees in tissue culture experiment. Nonetheless, shoot tip of young trees that cultivated ongreenhouse are easily for disinfection, and the contamination rate is only25%. In the initialphase of the experiment, all treatment can induce shoot growth. The culture medium hassignificant effects on multiplication (P <0.01), but plant growth regulator only has significanteffects on multiplication in1/2SH medium (P <0.05). The best medium for plant multiplica-tion is1/2SH with No.1(2mg·L-12-ip)or No.3(2mg·L-1ZT) hormone. Plant enlongation is also significantly affected by the culture medium (P <0.05), while the content of AC (2g·L-1or1g·L-1) has no effect on enlongation, and the best medium for enlongation is DCR. Thevitrificated shoots cultured on multiplication medium will turn to normal after being transferedto enlongation medium that content AC. We puted the buds in100mg·L-1IBA for5minutesand then cultured them on the1/2QP or DCR medium with AC (2g·L-1or1g·L-1) for rootingexperiment. However, after5months, no buds took roots, and now the rooting experiments isstill on.2)Rooting rate of cuttage is related to trees'age, hormone types and concentration.1-2years lignify branchs collected from adult trees cutting in Chengkou county, ChongqingMunicipality, in spite of many ways have been used for induce root, the highest rooting ratewas only20.83%; the cuttage collected from4years old trees disposed to2000mg·L-1IBA,1000mg·L-1IBA and1000mg·L-1IBA plus500mg·L-1NAA respectively (water as control),and then cultivated on medium of vermiculite, peat and pearlite (v:v:v,1:1:1), rooting rate wasup to74.76-96.7%when cutting at ChengKou in summer, the results of4treatments forrooting are:2000mg·L-1IBA＞water＞1000mg·L-1IBA＞1000mg·L-1IBA+500mg·L-1NAA. The same medium and cuttages of yong trees at same age were be uesd for cutting atgreenhouse in autumn, the plant growth regulator uesed for induce root are2000mg·L-1IBA,and1000mg·L-1IBA+50mg·L-1NAA (water as control), rooting rate with a range from25.93%to45.37%after120days, the results of3treatments are:1000mg·L-1IBA+50mg·L-1NAA=2000mg·L-1IBA＞water.3) At the process of gradually drought on T. sutchuenensis, the leaf relative water content(LWC) decreased after soil relative water cnotent (SWC) fell below30%under water stress;net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2concentration (Ci),light saturation point (LSP) and the maximum photosynthetic rate(Pmax) decreased alongwith the reduce of available water, leaf wilting when the drought stress last50days; quantumyield (Q), apparent quantum requirement (1/Q), and light compensation point (LCP) keptstable under water stress; water use efficiency (WUE) gradually increased with the decline inSWC; chlorophyll content increased under water stress while the three kinds of osmotic adjustment substances such as proline, soluble protein and soluble sugar increased after30days of last drought.All the physiological parameters can be gradually restored after rewatered,after3days of rewater, Pnrecoved to88.59%of control group when WUE decrease to88.63%,LWC be normal, after7days of rewatered, Pn, gas exchange parameters, WUE were recoveryto normal, meanwhile, three kinds of osmotic adjustment substances decreased to the controllevel. Through the analysis of physiological indicators above, we conclude that Thujasutchuenensis is a drought-avoiding plant. |
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