Response Of Asplenium Nidus To Drought Stress And Excavation And Identification Of AVP1 Gene

Bird’s nest fern（Asplenium nidus L.）is an important epiphytic fern in tropical forests,which plays an important ecological function.Under wild conditions,the bird’s nest fern showed a certain drought tolerance function.In the horticultural production process,the bird’s nest fern has a certain industrial foundation.Therefore,the bird’s nest fern has gradually become a research hotspot.To explore how Asplenium nidus responds to drought stress,and to mine drought-responsive genes for Asplenium nidus,this study conducted a pot experiment in the IOT smart greenhouse of Hainan University.The six pots of the bird’s nest fern with uniform growth were divided into a group and subjected to different degrees of drought treatment.The control group CK was watered daily,the moderate drought group T1 was watered every two weeks,and the severe drought group T2 was not watered.Each week,a series of physiological and biochemical indexes were determined for these three groups of bird’s nest fern.Four AVP1 family genes were excavated from the bird’s nest fern,and the expression levels of these genes were analyzed by RT-qPCR technology.The experimental results are as follows:1.Leaf growth parameters of bird’s nest fern with different drought degreesThis experiment measured four growth parameters:the increments of leaf length and leaf width,relative leaf water content（RLWC）and stomatal density.Among them,the increments of leaf length and leaf width and the RLWC,the T1 group fluctuates according to the watering time,and the three indexes return to normal values almost immediately after rehydration.In the T2 group,the leaf length and leaf width almost stopped growing,and the RLWC also decreased sharply.After rehydration,the RLWC quickly returned to normal values,while the leaf length and leaf width immediately resumed growth but were slightly slower.2.Photosynthetic index of bird’s nest fern leaves with different drought degreesIn this experiment,we measured four photosynthetic parameters:the maximum net photosynthetic rate(P_max),transpiration rate（T_r）,stomatal conductance（G_s）,and intercellular CO₂ concentration（C_i）.Among them,the P_max,T_r,and G_s are almost the same.The control group changed only within a small range within a reasonable range.The three indicators of the T1 and T2 groups dropped to near zero after water loss but recovered after rehydration.The C_i changed in the opposite direction to the other three indicators.After dehydration,the T2 group increased significantly,and then decreased to normal values after rehydration.The T1 group changed periodically with watering frequency.3.Biochemical index of bird’s nest fern leaves with different drought degreesIn this research,the contents of three drought-resistant compounds,including soluble protein,proline,and betaine,and the activities of three drought-resistant enzymes such as SOD,POD,and CAT were determined.Among them,soluble protein,proline content,and SOD and POD enzyme activities increased after drought treatment,while betaine content and CAT activity were not affected by drought.4.Identification of drought-resistant genesAVP1 gene,a gene that has been proven to be related to plant drought resistance many times in other species.In this experiment,four AVP1 family genes in the bird’s nest fern were screened through the identification of conservative domains,gene mining,sequence alignment,and the phylogenetic tree construction.After RT-qPCR quantitative and expression level analysis,it was found that the four genes AVP1-1,AVP1-2,AVP1-3,and AVP1-4 showed different response patterns to drought and rehydration.All four genes were up-regulated under drought stress,but only AVP1-1and AVP1-2 were down-regulated after rehydration.In summary,Bird’s Nest Fern has certain drought resistance and can survive for six weeks without watering at all.Although drought stress caused the leaves to stop growing,the contents of drought-related compounds and enzyme activities changed,they could recover after rehydration.This study systematically elaborated the drought response mechanism of the bird’s nest fern,which further enriched the research on the drought regulation mechanism and molecular biological mechanism of the bird’s nest fern.It lays the foundation for the in-depth study of drought tolerance mechanism and drought tolerance genes of bird’s nest fern,provides a theoretical basis for ornamental cultivation of bird’s nest fern,and provides a useful reference for strengthening the protection of wild bird’s nest fern.