| Due to the impact of climate change and human activities,it is difficult to regenerate desert seedlings naturally.Therefore,it is very important to study desert seed germination characteristics and seedling adaptation mechanisms for vegetation restoration in desert areas.Desert plants survive in extremely harsh environments and have their own special seed germination and seedling regeneration mechanisms.The adaptability of different plant seeds to adversity stress greatly affects the growth and development of plants.Anabasis aphylla belongs to the cryptoviviparous plant of the Anabasis of Chenopodiaceae,which has the characteristics of high salt and alkali resistance,cold resistance,drought resistance,sand fixation and soil improvement.Anabasis aphylla is the major dominant species and constructive species in the desert area of Junggar.Field investigation found that Anabasis aphylla seeds had the phenomenon of snow-melt germination in early spring.At this time,the temperature difference between day and night in the desert area is large,and the land surface is repeatedly frozen and thawed.Seeds and germinated seedlings are often affected by low temperature.Therefore,this paper studies the adaptability to low temperature of the seed germination process,and it is mainly divided into three parts.Firstly,to study the response of Anabasis aphylla and Haloxylon ammodendron seeds germination to low temperature.Secondly,to study the low temperature tolerance and physiological changes of the Anabasis aphylla and Haloxylon ammodendron seeds at different germination stages.Thirdly,using transcriptome sequencing and iTRAQ technology to analyze the differential genes and differential proteins at different germination stages of the Anabasis aphylla seeds at low temperatures.This paper have revealed the low-temperature germination characteristics of the cryptoviviparous plant Anabasis aphylla,and have discussed the adaptability of seed germination process to low temperature.The main results are as follows:(1)Through the study of the influence of temperature on the seeds germination and the law of water absorption of the seeds of Anabasis aphylla and Haloxylon ammodendron,it was found that the water absorption characteristics of the two desert seeds were the same.The water absorption capacity of the seeds is strong,and the whole swelling process takes a short time.It is the rapid water absorption period in 0~20min,and the water absorption in 60 min gradually reaches saturation.There was no significant difference in water absorption between the two desert seeds at normal temperature and low temperature,but compared with Haloxylon ammodendron,the water absorption of the seeds of Anabasis aphylla was not easily affected by low temperature.The two desert plant seeds can germinate at different temperatures.With the decrease of temperature,the initial germination time was prolonged,and the germination rate and germination index were reduced.But the final germinationpercentage has no significant difference at different temperatures,and the germination percentage can reach 90%.Through the analysis of thermal time effect,the base temperature of the seeds of Anabasis aphylla and Haloxylon ammodendron were 0.54 ? and 0.79 ?,respectively,and the thermal time were 9.89?·d and 7.26?·d,respectively.(2)This study found that the characteristics of low temperature tolerance at different germination stages of the seeds of Anabasis aphylla and Haloxylon ammodendron were roughly the same.The low temperature tolerance of the two plants was stronger in the stages of imbibition(I)and testa rupture(II),while the survival rate decreased sharply with the decrease of temperature in the stage of testa removal(?)and elongation(?).The low temperature tolerance of the seeds of Anabasis aphylla and Haloxylon ammodendron were???>?>? and ?>?>?>?,respectively,and the low temperature tolerance of Anabasis aphylla seeds was stronger than Haloxylon ammodendron seeds.With the germination at low temperature,the POD and soluble protein of the Anabasis aphylla seeds increased first and then decreased,while the activities of SOD and CAT always decreased,and MDA and soluble sugar always increased.The changes of POD and soluble protein of Haloxylon ammodendron seeds were consistent with Anabasis aphylla seeds,and the SOD,POD,CAT and soluble proteins of the two plant seeds were higher in stages ? and ? than in stages ? and ?.(3)Based on the above research,this study uses RNA-Seq technology to sequence the transcriptome of the four germination stages(W1: ripe and dry seeds;W2: imbibition;W3:testa removal;W4: elongation)of the Anabasis aphylla seeds.A total of 582580 Transcripts and 484941 Unigenes were obtained,and the average length of Unigenes was 864 bp and the length of N50 was 15661 bp.Further analysis of the down-regulated genes in the comparison group at different stages,there were 5096,5438,and 1474 down-regulated genes in the W2 vs W1,W3 vs W2,and W4 vs W3 comparison groups,respectively.Compared with W1 stage,the number of down-regulated genes in other stages was W4>W3> W2,and there were 2787 common down-regulated genes,mainly cytochrome P450,BURP domain-containing protein,oleosin,cysteine proteinase inhibitor,late embryogenesis abundant protein and so on.In the four stages,the continuously down-regulated genes are mainly the late embryogenesis abundant protein,oleosin,probable protein phosphatase 2C and so on.(4)Based on transcriptome sequencing,iTRAQ technology was used to perform protein identification and analysis on the four germination stages of the Anabasis aphylla seeds.The total number of proteins identified in all samples was 11,304,and the number of differential proteins in the W2 vs W1,W3 vs W2,and W4 vs W3 comparison groups were 112,3274,and73,respectively.GO analysis found that W2 vs W1 differential proteins were mainly significantly enriched in biological stimulus response,defense response and other processes.W3 vs W2 mainly enriches in cell localization,intracellular transport and transport.W4 vsW3 is mainly enriched in oxidative stress response,biosynthesis and metabolism.According to the protein expression during germination,the protein expression patterns are divided into6 categories,among which the protein expression in Cluster 1 and Cluster 6 shows downward trend during germination.Correlation analysis between proteome and transcriptome revealed that the down-regulated proteins were mainly concentrated in stress response,defense response,metal ion response,carbohydrate metabolism and other processes.By comparing with the differential proteins of Anabasis aphylla seedlings at low temperature,it was found that 16 low temperature differential proteins were differentially expressed in different germination stages of Anabasis aphylla.The expression of S-adenosylmethionine synthase,chloroplast ATP synthase delta and fimbrin-1 first increased and then decreased during germination,and the expression of other proteins overall showed downward trend during germination,including glyceraldehyde-3-phosphate dehydrogenase,peroxiredoxin Q and heat shock cognate 70 kDa protein and so on. |
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