水稻（Oryza sativa L.）是我国第一大粮食作物，在我国超过65%的人口以水稻为主食，镉（Cd）污染不但对水稻产量造成极大的影响，对食品安全也造成极大的威胁。研究表明镉在不同水稻亚种籽粒中的积累存在很大的差异，通常籼稻＞粳稻，关于水稻镉吸收和转运方面国内外已有大量报导，但关于短时间镉处理对籼稻和粳稻苗期的在转录组水平不同影响的报导很少。本实验以高镉积累型水稻‘Kasalath’和低镉积累型水稻‘Nipponbare’为材料，通过生理、表型及转录组分析比较了两个品种水稻对短时间Cd胁迫的响应机理。所得结果如下：

（1）在短时间（6 h）Cd处理下，与对照相比，两种水稻株高、根长、鲜重均受到显著抑制，随时间延长，抑制作用越明显，且‘Kasalath’比‘Nipponbare’受抑制更显著； Cd 处理后两个水稻品种地上部和根部积累的镉含量均显著上升，随时间延长，累积的镉含量越高，且‘Kasalath’累积的Cd比‘Nipponbare’显著增多，但在短时间（6 h）处理下Cd积累无显著差异。进一步测定了Cd处理6 h后两个水稻品种根系H2O2、MDA含量及根系活力，结果显示短时间（6 h）Cd处理下两个水稻品种中H2O2、MDA含量显著增加，根系活力均显著降低，但两个品种无显著差异。比较两个水稻品种抗氧化酶活性和谷胱甘肽代谢产物及叶绿素含量，结果显示与对照相比两个水稻品种SOD、POD和CAT活性以及Cys、PCs、叶绿素含量均显著增加。‘Nipponbare’中抗氧化酶活性及叶绿素含量均高于‘Kasalath’，而‘Kasalath’中Cys、PCs含量显著高于‘Nipponbare’。

（2）采用Illumina测序平台对四个处理（K-Con、K-Cd、N-Con、N-Cd）的cDNA进行了测序。构建了四个比较组（K-Con vs N-Con，K-Con vs K-Cd，N-Con vs N-Cd，K-Cd vs N-Cd）进行转录组比较分析，结果显示，四个比较组均检测出大量差异表达基因（DEGs）（FDR<0.05 且 |log2（FC）|>1）。镉处理与对照相比，两个水稻品种检测到的DEGs数量均显著上升，在‘Kasalath’和‘Nipponbare’中分别检测到5963和6339个DEGs。通过GO富集分析和KEGG途径分析对DEGs进行功能分类。结果显示大量DEGs在谷胱甘肽代谢、抗氧化、光合作用等途径富集，但两个水稻品种DEGs富集表现出差异。通过热图分析两个品种水稻对短时间镉处理响应不同的关键基因，结果显示，与对照相比，镉处理的‘Kasalath’ 中DEGs主要富集在谷胱甘肽代谢途径，而‘Nipponbare’中DEGs主要富集在抗氧化、光合作用等途径。综上，

‘Nipponbare’通过提高抗氧化能力和增强光合作用抵御Cd胁迫，而‘Kasalath’通过提高谷胱甘肽代谢能力在根部积累更多的Cd，减少Cd向地上部的转运。

Rice (Oryza sativa L.) is the largest cereal crop in china and is the staple food for more than 65% of Chinese population, and cadmium pollution not only has a great impact on rice yield but also poses a great threat to food safety. A large number of studies have shown that there are great differences in cadmium accumulation between different rice subspecies, usually indica rice > japonica rice, but there are few reports on the different effects of short-term exposure to Cd between indica rice and japonica rice at the transcriptome level. In this study, seedlings of high cadmium accumulation rice ‘Kasalath’ and low cadmium accumulation rice ‘Nipponbare’ were used as materials to compare the responses of the two varieties of rice to short time Cd stress by physiological, phenotypic and transcriptome analysis. The results are as follows：

• Compared to control, the plant height, root length and fresh weight of the two rice seedlings were significantly inhibited under cadmium treatment, and the inhibition was more obvious with time, which was more significant in ‘Kasalath’ than in ‘Nipponbare’ . And the accumulation of cadmium in the shoots and roots of the two rice varieties increased significantly, and the higher the accumulation with time, and ‘Kasalath’ accumulated more Cd than ‘Nipponbare’ , but there was no significant difference between the two rice varieties within a short term (6 h) treatment of Cd. The indexes of root oxidative damage in the two rice varieties after 6 h of Cd treatment were determined and found that the contents of H2O2 and MDA significantly increased while the root activities remarkably decreased, but there was no significant difference between the two subspecies. Further comparison of antioxidant enzymes and glutathione metabolites and chlorophyll contents in the two rice varieties after 6 h of Cd treatment was performed, of which the activities of SOD, POD and CAT as well as the contents of Cys, PCs and chlorophyll increased significantly. The antioxidant enzyme activities and chlorophyll contents increased much more in ‘Nipponbare’ than those in ‘Kasalath’, but the contents of Cys and PCs increased more significant in ‘Kasalath’ than those in ‘Nipponbare’ .
• Seedlings of ‘Kasalath’ and ‘Nipponbare’ treated with or without 10 μM CdCl2 were used in this study and cDNA from the four treatments (K-Con, K-Cd, N-Con, N-Cd) was subjected to the Illumina sequencing platform. Four comparable groups (K-Con vs N-Con, K-Con vs K-Cd, N-Con vs N-Cd and K-Cd vs N-Cd) were constructed to proceed  comparative transcriptomic analysis, the results showed that a large number of  differentially expressed genes (DEGs) (FDR<0.05 and |log2(FC)|>1) were found in the four groups. The numbers of DEGs in the two rice varieties increased both significantly under cadmium stress compared to control while 5963 and 6339 DEGs were expressed by Cd stress in ‘Kasalath’ and ‘Nipponbare’ respectively. GO enrichment analysis and KEGG pathway analysis were used for functional classification to identify the key different expression genes between the two rice subspecies response to short-term cadmium stress. A large number of DEGs were enriched in glutathione metabolism, antioxidant and photosynthesis pathway. However there were much different regulations between ‘Kasalath’ and ‘Nipponbare’ in response to Cd stress. The results of heat map analysis showed that under cadmium stress compared to control, the DEGs in ‘Kasalath’ mainly enriched in the glutathione metabolism pathway, while the DEGs in ‘Nipponbare’ mainly enriched in the antioxidant and photosynthesis pathway. Over all, ‘Nipponbare’ resist Cd stress by increasing antioxidant capacity and enhancing photosynthesis, while ‘Kasalath’ have a stronger capacity in glutathione metabolism, thus accumulating more Cd in root and reducing Cd transport to the aboveground.