Responses Of Growth,physiological Characteristics Of Different Cultivars And Root Transcriptome To Potassium Deficiency Stress In Camellia Oleifera Abel

Potassium（K）is one of the essential macroelements for plants,and participates in many physiological metabolic activities such as plant photosynthesis,protein synthesis,ion transport and enzymatic reaction.K is also important for plant growth,development,stress resistance,product improvement and quality.Many plants had a series of complex mechanisms in response to K deficiency along with changes in morphology and physiology.While different mechanisms were observed in different cutivars/species in the same plant when under K deficiency.Camellia oleifera Abel（C.oleifera）is one of the important woody oil species in south China,where the areas of soils are usually lack of K.Thus,administration of K in intensive and commercial C.oleifera forest is one of the most important measures to acquire high quality products.The cultivars used in practice were clone breeds characterized by high productivity,and studies were mainly focused on the improvement of products.However,limited research was concerned in the tolerance in barren soils of C.oleifera cultivars.In this study,three cultivars（Ganwu1,Ganshi83-4,Ganwu11）of C.oleifera with phenotypic differences were chosen as experimental materials.The responses of these cultivars to K deficiency in growth,morphology,nutrient,reproductive,photosynthesis and oxidation perspectives were measured and analyzed.Root transcriptome of K sensitive cultivar Ganwu1 under K deficiency were analyzed,so as to explore the molecular mechanism of C.oleifera to K deficiency.The main results were as follows:（1）The growth of root and leaf phenotypes of different cultivars of C.oleifera showed different responses to K deficiency.The seeding heights,ground diameters,branch numbers,leaf areas and biomass of Ganwu1 and Ganshi83-4 were decreased when grown under K deficiency,but no effect on Ganwu11.K deficiency retarded the elongation of taproot and lateral roots of C.oleifera,while promoted the taproot and lateral root diameter and taproot root volume,and significantly increased the root volume of Ganwu11.The volumes of taproot and lateral root,taproot surface area and biomass for Ganwu11 were significantly larger than that for the other two cultivars under K deficiency.（2）The nutrition contents and accumulation in different cultivars of C.oleifera had different responses to K deficiency.Compared with K application treatments,K deficiency decreased the nitrogen（N）and phosphorus（P）accumulation of Ganwu1 and Ganshi83-4,and the P and sodium（Na）utilization efficiency of Ganwu1 was significantly decreased.Furthermore,K deficiency increased the accumulation of N,P and Na in Ganwu11,but the Na utilization efficiency of Ganwu11 was significantly decreased.K deficiency decreased the K contents and accumulations in the three cultivars of C.oleifera,but increased the K utilization rate of C.oleifera.The nutrition accumulation of Ganwu11 was higher than that in the other two cultivars under K deficiency.（3）K was the essential nutrient for pollen development of C.oleifera,and the optimal K concentration for pollen germination and pollen tube growth were different within different cultivars.For cultivars Ganwu1,Ganshi83-4 and Ganwu11,6 mol/L,12 mol/L,and 6 mol/L of K respectively in the cultivate nutrients lead to best pollen germination,and1 mol/L,3 mol/L,and 6 mol/L of K were best for the development of pollen tube in these species.The germination and tube growth of the pollens in the three studied cultivars were significantly inhibited by deficient of K or addition of barium chloride（Ba Cl₂）,a kind of K channel inhibitor.K deficiency decreased the bud numbers and inhibited pollen germination.The bud numbers in Ganwu1,Ganshi83-4 and Ganwu11 under K deficiency were decreased by 43.39%,42.37%,23.52%respectively when compared to that in K2treatment.Under the treatment of K deficiency,the rate of pollen germination and length of pollen tubes of Ganwu11 were significantly higher than that in the other two cultivars.（4）The photosynthetic response of three cultivars to K deficiency changed with the duration of stress.After 60d of K deficiency,the parameters of net photosynthetic rate（Pn）,stomatal conductance（Gs）,Transpiration rate（Tr）,fluorescence,photosynthetic enzymes of the three cultivars of C.oleifera were lower than K treatments.K2 treatment showed inhibition on the photosynthesis and photosynthetic enzymes of Ganshi83-4 at 90d of K deficiency,but K treatments were still better for photosynthesis of Ganwu1 and Ganwu11than that in K deficient treatment.（5）In the cold winter,K deficiency significantly increased the enzyme activities of superoxide dismutase（SOD）,catalase（CAT）,peroxidase（POD）and content of malonaldehyde（MDA）,but decreased the contents of soluble sugar and protein in root and leaf and nitrogen balance of index（NBI）.Under K deficiency,the leaf relative conductivity of Ganwu1 was significantly higher than that of Ganshi83-4 and Ganwu11,but the antioxidant enzyme activity of Ganwu1 was significantly lower than that in Ganshi83-4and Ganwu11,the results indicated that K deficiency caused serious damages to the leaf cell membrane of Ganwu1,while the ability of cell scavenging oxidation in Ganwu1 was lower than that in other cultivars.（6）There were positive correlations between the morphological indexes and the accumulated nutrients,and a negative correlation between the morphological indexes and the contents of antioxidant enzymes.The results of principal component analysis and membership function showed that leaf width,tissue biomass,total biomass and lateral root volume could be used as the key indexes to characterize the tolerance of C.oleifera to K deficiency.Ganwu1 and Ganshi83-4 were relatively sensitive to K deficiency,while Ganwu11 was tolerant to K deficiency.（7）The content and accumulation of ROS in root and leaf of C.oleifera were significantly increased from 0 to 24 h,and the content of ROS in root was higher than that in leaf.The transcriptome analysis on root cells under 0 h,12 h and 24 h treatment of K deficiency was analyzed.Compared with 0 h,roots under 12 h treatment of K deficiency had 332 genes differentially expressed（DEGs）,and in 24 h treatment,a total of 156 DEGs were observed.Compared with 12 h,roots under 24 h K deficiency had 221 DEGs.According to the gene ontology（GO）enrichment analysis,the enriched genes were mainly affected the K absorption of root cells,the metabolic process,cellular process,response to stimulus,catalytic activity,and cell membrane component.In metabolic function perspective,including metabolic pathways related to carbohydrates,lipids,energy,amino acids,cofactors and vitamins were responsed to K deficiency.（8）Based on the analysis of related-genes response to potassium,it was found that the root of C.oleifera responded to K deficiency by adjusting the expression of K related channel proteins（including K channel and water channel proteins）,oxidase and dehydrogenase enzymes,transcription factors,kinase protein gene expressed.Compared with 0 h treatment,the expression of AKT1 was significantly down-regulated at 12 h,and significantly up-regulated at 24 h.Compared with 12 h,the expression of K transporters POT6,TPK2 and the expressions of 9 water channel protein genes were significantly up-regulated at 24 h.The expression of transcription-factor family b HLH,Zinc finger protein C2H2,CO-like,Dof,DBB and Ethylene signal transduction related transcription factors were down-regulated significantly under K deficiency.The expression of hormone,transmembrane transporters,kinase coding genes were inhibited under K deficiency.In conclusion,the responses of growth and physiology characters of the three cultivars（Ganwu1,Ganshi83-4,Ganwu11）of C.oleifera to K deficiency were different.The comprehensive evaluation results showed that Ganwu1 and Ganshi83-4 were K sensitive cultivars,while Ganwu11 was K-tolerant cultivar.K deficiency affected the accumulations of N,P,K of Ganwu1 and Ganshi83-4,and restrained the growth of the trees,made them produce more oxidizing substances during the low temperature period in winter.On the contrast,K-tolerant cultivar Ganwu11 was still grown well under K deficiency,while most of its physiology indexes were inhibited.Root transcriptome analysis showed that a large number of genes were differentially expressed under K deficiency.The root cells adjusted the K-dificiency by up-regulated the gene expressions of K-related channel proteins and down-regulated parts of gene expression of transcription-factors,hormones,transmembrane transport,and glucose metabolism the root of C.oleifera could adapt to K deficiency.