| Low temperature stress is one of the major abiotic factors affecting plant growth and the geographical distribution of many economically important plants.birch is not only the most important plants worldwide,but also cold-resistant plant.Proteomic techniques are effective approaches that have been adopted to discover new genes related to cold resistance and cold responsive protein.Therefore,it will be very significant for to study the mechanism of birch respond to cold stress.birch seedlings were treated in the 4℃and 23℃phytotron on the same day,the fourth days,the seventh day,the tenth days,and the fourth daycrespectively.The changes of growth status,leaf plasma-membrane permeability,chlorophyll relative content,and photochemical efficiency of PSⅡin the light(Fv'/Fm'),photochemical quenching coefficient(q_p),non-photochemical quenching coefficient(NPQ) and total soluble carbohydrate Conten were measured.The results showed that the height growth was primarily suspended by low temperature stress,the Chlorophyll Content was gradually decreased and the leaves got yellow on the fourteenth day.The relative conductivity was increased at first,then it was decreased,and returned to the control level in the end.Compared with the control level,the Fv'/Fm',q_p and NPQ were evidently decreased.The Fv'/Fm' and NPQ were decreased at first and then increased,q_p was decreased at first and then increased,and decreased in the end..total soluble carbohydrate Conten was increased.It indicated,the low temperature of 4℃led the membrane in the reversible damage,and the conversion of primary light energy of PSⅡto be restrained. The birch have relatively high adaptability to cold stress with the prolonging of cold stress time,and increased their freezing tolerance.By using 2 DE-GEL method we analyzed their protein profiles.37 differentially expressed protein spots with higher than 2-fold spotdensity were detected in gel image.Among them,15 high abundance protein spots were successfully identified with ESI-MS/MS.According to Swiss Prot database and related references,these proteins were classified into 4 functional groups,which mainly involved in signal transduction,photosynthesis,and metabolisms of carbon,nitrogen,energy,and stress.This analysis also elucidated that 50%of proteins detected under cold stresss are located in chloroplast,suggesting that the chloroplast is likely play important role in thecold-response in plants.The RNA binding proteins in chloroplast are important factors in regulating gene expression in the organelle.We separated chloroplast proteins with affinity to polyadenylate or single stranded DNA through affinity chromatography in the birch tree.2-D Electrophoresis and MALDI-TOF-MS as well as ESI-MS/MS have been used in the present work to identify a total of 13 proteins from intact chloroplasts.Most of the identified proteins were defined as to their function inSwiss-prot/TrEMBL database.including 4 RNA-binding proteins,3 ATP-binding proteins,an NAD- and a DNA-binding protein as well as 4 proteins with no apparent binding function reported previously.With these methods four abundance proteins including a transcriptional factor were also enriched and identified.These results should advance the understanding of the function of general chloroplast RNA-binding proteins in a tree species that suggest they may have some application to the study of native RNA-protein interactions in and chloroplasts of other plants.
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