Study On The Physiological And Molecular Mechanisms Of Silicon Regulating Tomato Responses To Low-iron Stress

The low bioavailability of iron（Fe）in the soil can easily lead to Fe deficiency in plants,which is one of the abiotic stresses that restrict plant growth and development.It has become a research hotspot in recent years to improve the absorption and utilization of Fe by crops and reduce the damage of low Fe stress to crops through biological methods.Silicon（Si）is a beneficial element for plant growth and can improve plant tolerance to adversity stress.However,the regulatory effect and mechanism of exogenous Si on tomato growth and development under low Fe stress are still unclear.For this reason,this experiment uses the ‘Microtom’ tomato as the material,adopts the hydroponic method,and sets three Fe concentrations of 100,10 and1 μmol·L-1.Among them,100 μmol·L-1 Fe is used as the control to study the root The effect of Si application（1.5 mmol·L-1）on the growth and physiological and biochemical characteristics of tomato seedlings under different low Fe stresses.On this basis,RNA-Seq technology was used to analyze the effect of Si on the transcriptome of tomato leaves and roots under low Fe（1 μmol·L-1）stress.The main results are as follows:1.Compared with the control,under low Fe stress,tomato plant dry and fresh weight,total root length,volume and surface area were significantly reduced,Fe³⁺ reductase activity and root activity were significantly increased;after adding Si,tomato dry and fresh weight and total Root length,surface area and volume increased significantly,and root activity decreased,but Fe³⁺ reductase activity increased significantly,indicating that Si significantly alleviated the inhibitory effect of low Fe stress on tomato seedling growth.Compared with the control,under low Fe stress,the Fe element content in tomato leaves significantly decreased,the Ca element content increased significantly,and the stem Ca,K,Mg,Fe element content increased significantly,and the roots’ absorption of Cu showed varying degrees Increased application of Si promotes the absorption of mineral elements by roots,and significantly increases the distribution ratio of K,Ca,Mg,Fe,Zn,and Cu in stems and leaves under low Fe stress,promotes the redistribution of nutrient elements,and maintains The nutrient balance of tomato seedlings.Compared with the control,under low Fe stress,leaf chlorophyll content decreased significantly,net photosynthetic rate（Pn）,transpiration rate（Tr）and stomatal conductance（Gs）decreased significantly,and PSⅡ maximum photochemical quantum efficiency（Fv/Fm）,Photosynthetic electron transfer efficiency（ETR）,PSⅡ effective photochemical efficiency（Fv’/Fm’）,PSⅡ actual photochemical efficiency（ΦPSⅡ）and photochemical quenching coefficient（q P）all decreased;after adding Si,the content of chlorophyll and carotenoids And Pn,Gs,Tr,Fv/Fm,Fv’/Fm’,ETR,ΦPSⅡ,and non-photochemical quenching coefficient（NPQ）all increased significantly,indicating that Si significantly alleviated the decline in photosynthetic capacity of tomato leaves caused by low Fe stress.2.Compared with the control,under low Fe stress,tomato plant plasma membrane integrity is impaired,malondialdehyde（MDA）content and electrolyte permeability increase significantly,superoxide anion（O2（?））and hydrogen peroxide（H₂O₂）Accumulate in a large amount,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）are all reduced;the increase of Si treatment can promote the increase of SOD,POD and CAT activities of tomato seedlings,MDA,electrolyte Permeability,O2（?） and H₂O₂ content were significantly reduced,indicating that Si can reduce the production rate of reactive oxygen species and reduce the degree of membrane lipid peroxidation by increasing plant antioxidant enzyme activities,thereby maintaining the stability of cell membranes under low Fe stress.Compared with the control,under low Fe stress,the content of soluble sugar and soluble protein in tomato plants decreased significantly;while the increase in Si effectively promoted the accumulation of soluble sugar and soluble protein in tomato plants and maintained a higher osmotic rate.Regulating ability,has a good protective effect on plant cells.3.Compared with the control,under low Fe stress,the activities of leaf neutral invertase（NI）,acid invertase（AI）,sucrose synthase（SS）and sucrose phosphate synthase（SPS）were significantly reduced,and the sucrose content was significant Decrease;increased Si application effectively promoted the activities of SS and NI,while the activities of AI and SPS decreased significantly,which promoted the increase of sucrose content.It shows that the addition of Si significantly regulates the activities of enzymes related to sucrose metabolism and promotes the accumulation of sucrose content.Compared with the control,under low Fe stress,the contents of free,bound and bound polyamines in leaves and roots all increased significantly;after increasing Si,it promoted putrescine（Put）to spermine（Spm）and spermidine The conversion of amine（Spd）leads to a significant decrease in Put content,and a significant increase in Spm and Spd content.It shows that the increased application of Si can regulate the mutual transformation between different forms of polyamines,improve the tolerance of tomatoes to low Fe stress,and then maintain their normal growth.Compared with the control,low Fe stress promoted the increase in the content of oxalic acid,acetic acid,malic acid and citric acid in the root system;after increasing Si,the content of oxalic acid decreased significantly,while the content of acetic acid,malic acid and citric acid increased significantly It shows that the increased application of Si significantly regulates the root organic acid content,promotes the absorption and transport of Fe,and then maintains the normal growth of plants.4.Through RNA-Seq analysis,in tomato leaves,low Fe stress compared with the control,there are 1209 differentially expressed genes,of which 915 genes are up-regulated and 294 genes are down-regulated;exogenous application under low Fe stress Compared with low Fe stress alone,Si was differentially expressed in 1835 genes,of which 1377 genes were up-regulated and 458 genes were down-regulated.In tomato root system,there are 909 genes differentially expressed under low Fe stress compared with exogenous Si application under low Fe stress,of which 521 genes are up-regulated and 388 genes are down-regulated.Compared with low Fe stress,after the addition of exogenous Si,56 and 27 differentially expressed transcription factors were identified in tomato leaves and roots,including WRKY,MYB,and NAC.These transcription factors are related to regulating root Fe absorption and Transport,induction of antioxidant response,regulation of carbohydrate metabolism and hormone signal transduction,etc.,play an important role in improving plant resistance to stress.The fluorescence quantitative PCR（q-PCR）method was used to analyze and verify the 6 candidate differentially expressed genes in the process of Fe absorption and transport.The quantitative detection results are basically consistent with the sequencing results,which proves the reliability of the transcriptome database established in this experiment.It has laid a foundation for the cloning of low-Fe-tolerant genes and the further study of the molecular mechanism of exogenous Si-mediated lowFe stress tolerance.