| Turfs can beautify environment and purify air,occupy an important position in landscapes.However,many turfs are facing with low-light（LL）environment for a long time due to the shielding of some tall macrophanerophytes and urban buildings,resulting in decrease of turf quality and increase of management costs,which greatly restricts the development of turf industry.5-aminovulinic acid（ALA）has been proven to participate in the anti-inverse reactions of multiple plants,so has been widely used in agricultural production.Tall fescue（Festuca arundinacea Schreb.）,an important perennial cold-season turfgrass,is widely planted in worldwide.Owing to its strong adaptation to stress,trampling,and disease,tall fescue is widely used in the fields of urban greening and soil and water conservation.However,LL stress reduces the turf quality and range of application of of eminent tall fescue cultivars,thus limiting its popularization and application.So far,the research of the effects on ALA under LL stress in plants has not yet been reported.This study adopted the experimental method for exogenous ALA application and endogenous ALA inhibitory,combined with filed experiment and in-door planting experiment,to reveal the important role of exogenous ALA in regulating LL tolerance of tall fescue from aspects of turf quality,morphological characteristics,antioxidant system,chlorophyll biosynthesis,photosynthesis,photosynthetic enzymes activity,and chloroplast ultrastructure.The mechanism was elucidated from physiological and biochemical level,subcellular structure level,and excepted to provide theoretical basis and technological guidance for the construction and management of turf under LL stress.It also supplied theoretical basis for the breeding of LL-tolerant tall fescue cultivars.The main research results were as follows:1.Under LL stress,the turf quality,tiller numbers,and chlorophyll content in tall fescue significantly decreased（P<0.05）.However,the application of the exogenous ALA on the leaves significantly increased the NTEP value,tiller number,and relative chlorophyll content of tall fescue under LL stress.And the application of LA（synthetic inhibitor of ALA）reversed the effect of ALA on LL stress.These results showed that the appropriate application of ALA could improve the turf quality of tall fescue under LL stress,during the construct and management of tall fescue turf.2.LL stress significantly affected the morphological characteristics and antioxidant capability of tall fescue（P<0.05）.The plant height,leaf width,and total biomass were remarkably reduced under LL stress,and antioxidant capabilities was suppressed.However,the application of exogenous ALA increased the activity of antioxidant enzymes（SOD,POD,CAT,APX,and GR）and their gene expression level were up-regulated,it also improved non-enzyme antioxidant substance（GSH,As A）.ALA enhanced the cycle rate of As A-GSH,so as to reduced the contents of MDA,H2O2,superoxide radical（O2·-）,and the value of relative conductivity,thereby relieved the membrane lipid peroxidation of tall fescue.3.Under LL stress,the activities photosynthetic enzymes in tall fescue leaves were reduced,the photosynthetic capacity decreased significantly,and the accumulation of photosynthesis products were suppressed（P<0.05）.However,the application of ALA increased the contents of photosynthetic pigments and the value of chlorophyll b/a in tall fescue under LL stress.The gas exchange parameters（Pn,gs,Ci,and Tr）and chlorophyll fluorescence parameters(Fv/Fm,ΦPSII,q P,and ETR)were enhanced significantly,and the accumulation of soluble sugar was increased,which indicated that ALA promoted the process of photosynthesis in tall fescue,thereby maintaining the accumulation of carbohydrates and active chemical energy in tall fescue.4.LL stress significantly reduced the gene expression level of chlorophyll biosynthetic enzymes gene and the content of precursor substances in tall fescue leaves（P<0.05）,and destroyed the normal structure of the chloroplast and even caused the disintegration of chloroplast membrane.However,the application of ALA improved the content of seven important chlorophyll precursor substances（ALA,PBG,Coprogen III,Urogen III,Proto IX,Mg IX,and Pchld）,and up-regulated the relative expression levels of chlorophyll biosynthetic enzymes genes（Fa CHLG,Fa HEMA,Fa CAO,and Fa POR）in tall fescue under LL stress.Furthermore,ALA alleviated the damage of chloroplast ultrastructural caused by LL stress,and promoted the more regular morphology of chloroplasts,caused the more order lamellar arrangement of granules and induced the formation of more starch granules,to protect the order process of photosynthesis in tall fescue under LL stress.In conclusion,ALA effectively removed the accumulation of intracellular reactive oxygen species（ROS）,inhibited membrane lipid peroxidation,enhanced the activity and gene expression level of photosynthetic enzymes,promoted chlorophyll biosynthesis,and alleviated chloroplast damage,improved the antioxidant system in tall fescue under LL stress,so as to improved the photosynthetic and then finally enhanced the adaptability of tall fescue to LL stress,thus enhanced the turf quality of tall fescue. |
