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BackgroundRice (Oryza sativa L.), one of the most important crops cultivated in both tropical and temperate regions, has a high sensitivity to cold stress. Chilling stress limits the N uptake and nitrogen metabolism in rice. To identify the genes and pathways involved in cold tolerance, and specifically associations with the nitrogen metabolism pathway, we have compared the gene and protein expression changes between a cold-tolerant cultivar, Dongnong428 (DN), and a cold-sensitive cultivar, Songjing10(SJ).ResultsUsing absolute quantification (iTRAQ) with high-throughput mRNA sequencing (RNA-seq) techniques, we identified 5,549 genes and 450 proteins in DN and 6,145 genes and 790 proteins in SJ, that were differentially expressed during low- water temperature (Tw) treatment. There were 354 transcription factor (TF) genes (212down, 142 up), 366 TF genes (220 down, 146 up), including 47 gene families, differentially expressed in the DN under control (CKDN) vs. DN under low-Tw (D15DN) and CKSJ vs. D15SJ, respectively. These results indicated that TF genes play a major role in post-translational regulations. Genes related to rice cold-related biosynthesis pathways, particularly the MAPK signaling pathway, zeatin biosynthesis, and plant hormone signal transduction pathways, were significantly differentially expressed in both rice cultivars. Differentially expressed proteins (DEPs) related to rice cold-related biosynthesis pathways and particularly glutathione metabolism were significantly differentially expressed in both rice cultivars. Transcriptome and proteome analysis of the nitrogen metabolism pathways showed that major genes and proteins were down-regulated that participated in γ-aminobutyric acid (GABA) and glutamine synthesis. ConclusionUnder cold stress conditions during reproductive growth, genes and proteins related to the biosynthesis pathways of cold stress, were significantly differentially expressed in the DN and SJ. The present study confirmed the known cold stress-associated genes and identified a number of putative new cold-responsive genes. It has also revealed that translational regulation under cold stress plays an important role in cold-tolerant DN. Low-Tw treatments affect the N uptake and N metabolism in rice, and promote Glu metabolism, and the synthesis of ornithine and proline in cold-sensitive SJ.

To explore the germination mechanism of salt-stressed rice improved by exogenous proline, and provide a theoretical basis to rice direct sowing technology for salinized soil, the effects of soaking with proline on germination status, amylase activity and isoenzyme were studied in this paper. The results showed that germination status including germination energy (GE), germination rate (GR), relative germination energy (RGE) and relative germination rate (RGR) significantly decreased as the same as the activities of alpha-amylase, beta-amylase and the total amylase under salt stress. Soaking with exogenous proline improved the germination status of rice under salt stress. Moreover, GE and RGE of salt-stressed rice were improved with increasing of proline concentration at the range of 5-45 mmol •L-1. Soaking with 15 mmol •L-1 and 30 mmol •L-1 proline significantly improved the amylase activities (e.g. alpha-amylase, beta-amylase and total amylase) of rice under salt stress. Salt stress inhibited the express of beta-amylase isoenzyme temporarily, but had few impacts on alpha-amylase isozyme. Soaking with 30 mmol •L-1 proline brightened District I and increased the width of ‘i’ brand in District II of alpha-amylase isoenzyme, but had few impacts on beta-amylase isoenzyme. In a word, soaking with proline could effectively alleviate the inhibitory effects of salt stress on seed germination.