| Tomato(Solanum lycopersicum)is one of the main vegetables in the facilities in China,which is sensitive to low temperature.Low temperature is a prominent obstacle in protected horticultural industy of China,tomao often suffers from sub-low temperature(8~15℃)stress.The potassium requirement of greenhouse tomatoes is very high for vegetative growth and fruit production.Higher K tissue concentration reduced chilling damage and increased cold resistance.In order to study the effects of sub-low temperature on potassium absorption,translocation and circulation.Tomato cultivars with different cold tolerance were used as expermental materials.The tomato seedlings were grown in growth chamber at 25/18℃and 15/10℃temperature.After treatment 5 d,10 d,the growth and potassium content were measured.The differences of K~+flux rate and root transcriptional regulation of two tomato seedlings at sub-low temperatures were studied.Main results of this paper were presented as follows:1.At 15/10℃,a significant sub-low temperature induced reduction in plant growth rate,dry mass growth rate,root length,root surface,chlorophyll content,maximum photochemical efficiency,PSII actual photochemical efficiency,photosynthetic electron transfer rate at 5 and 10days after treatment and this reduction was significantly higher in cold-sensitive than in cold-tolerant plants at both time points.2.Sub-low temperature(15/10℃)induced reduction in K~+concentration,K~+accumulation in stems and leaves at 5 and 10 days after treatment and this reduction was significantly higher in cold-sensitive than in cold-tolerant plants at both time points.At 25/18℃and 15/10℃,the absorption of K~+in cold-tolerant was higher than that in cold-sensitive.3.After treatment 5 d,sub-low temperature increased the K~+concentration and distribution rate in roots,and decreased in stems.After treatment 5 h,24 h and 5 d,sub-low temperature inhibited the expression of LKT1、LeKC1、LeHAK5、SIHAK9 in both cultivars roots,but induced increase the expression in cold-tolerant leaves.The expression of LKT1 in cold-tolerant cultivar leaves was significantly higher than that in cold-sensitive cultivar at each time points.4.At 15/10℃,the K~+concentration in shoots decreased,K~+transported amount in the phloem was decreased.At 25/18℃and 15/10℃,the ratio of the circulation of potassium to the content transporting to the shoot were 91.24%,74.27%in cold-sensitive,respectively,and 78.16%,68.78%in cold-tolerant respectively.5.RNA-seq was used to analyze the gene expresssion response of the two cultivars of tomato seedlings under sub-low temperature stress.(1)Compared to CK1,GO analysis of DEGs in T1showed the DEGs with the“biological process”,“molecular function”,“catalytic activity”were enriched.Compared to CK2,GO analysis of DEGs in T2 showed the DEGs with the“biological process”,“response to stimulus”,“response to stress”were encirched.Compared to control,pathway enrichment analysis showed the DEGs of two cultivars involved in“phenyllpropanoid biosynthesis”,“plant hormone signal transduction”,“inositol phosphate metabolism”were enriched.Most of the defense related genes up-regulated in cold-tolerant cultivar.The DEGs involved in calcium dependent protein kinase gene,mitogen activated protein kinase genes,antioxidant enzyme genes,AP2/ERF,MYB,ZFP transcription factor genes.Under sub-low temperature condition,with respect to HAK5 transporter,the three genes in RCI3-RAP2.11-HAK5phthway were down-regulated,plays a negative role of K~+absorption,the gene NRT1.5/NRF7.3down-regulated,inhibited the K~+translocation to the shoot.To sum up,sub-low temperature affect the absorption and translocation of K by regulating the expression of K~+channel and transporter genes.Compared to cold-sensitive cultivar,the up-regulated expression of defense related genes in roots,and the higher K~+absorption in plants are the most important characteristics of cold-tolerant cultivar. |
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