The Effect And Mechanism Of Exogenous Silicon On Salt Resistance Of Tomato Seedlings

Tomato(Solanum lycopersicum L.) is one of the main vegetables cultivated in protected facilities. However, due to the special cultivation environment and the man-made soil salinization, secondary soil salinization in protected facilities is becoming more and more serious, which has caused heavy loss of production and decrease of quality in tomato fruits. A large number of studies have shown that silicon can enhance the resistance of plants to various stresses including disease, drought, cold and salt, etc. However, previous studies were mostly focused on monocotyledons, such as rice, wheat and maize, which are usually silicon accumulators. In dicotyledonous plants including vegetables, which usually have low capabilities of silicon accumulation, the silicon effects on stress resistance have received less attention. Tomato is a silicon-excluding plant, which accumulates much less silicon compared with silicon accumulators. Study on the effect and mechanism of exogenous silicon on salt resistance of tomato not only has important theoretical significance, but also provides theoretical basis for application of silicon fertilizer to improve salt resistance in tomatoes and other vegetables and therefore their yields and qualities. In this experiment, the effects of exogenous silicon on salt resistance of tomato were investigated in seedlings grown in culture solution or in sand culture. The main results were as follows:1. Under salt stress, the dry weight of tomato was decreased, while it was significantly increased after addition of exogenous silicon. Under salt stress, the tomato leaves turned yellow and wilt, the leaf area became smaller and the plant height was lower, while these parameters were improved after silicon addition. In both culture conditions, the net photosynthetic rate and chlorophyll content were decreased under salt stress, while they were significantly increased when treated with exogenous silicon. These results indicate that exogenous silicon improved the plant growth by increasing the net photosynthetic rate and chlorophyll content under salt stress. In the hydroponic or sand culture conditions, the root length, surface area and root volume were decreased under salt stress, while they were increased by addition of exogenous silicon, indicating the improvement of root growth of tomato under stress.2. Under salt stress, the leaf relative water content and water potential were obviously decreased, while addition of exogenous silicon improved the leaf water status. The waterconductanceoftomatorootsdramaticallydecreasedundersaltstress,whileexogenoussiliconpartlyinhibitedthedecrease.undersaltstress,siliconadditionincreasedtheexpressionsofplasmamembraneaquaporingenespip1:1andpip1:3,whileitonlypromotedtheexpressionsofpip1;5,pip2;1,pip2;4,pip2;5,pip2;6,pip2;8andpip2;12attheearlystageofsaltstress.theresultssuggestthatexogenoussiliconimprovedtherootwateruptakebypromotingtheexpressionsofplasmamembraneaquaporingenes,andthereforeimprovedtheplantwaterstatus.3.undersaltstress,theactivitiesofsuperoxidedismutase(sod),peroxidase(pod)andcatalase(cat),andthecontentsofascorbicacidandnon-proteinthiolweredecreasedintomatoplants,meanwhile,reactiveoxygenh2o2andmalondialdehyde(mda)–aproductoflipidperoxidationwereaccumulated.exogenoussiliconincreasedtheactivitiesofsod,podandcat,andcontentsofbothascorbicacidandnon-proteinthiol;whileitreducedthecontentsofmdaandh2o2.theseresultssuggestthatexogenoussiliconcouldenhancetheantioxidantdefensecapabilitiesoftomatoseedlingsundersaltstress,andthereforealleviateoxidativedamageofplasmamembranes.4.exogenoussiliconinhibitedtheaccumulationofna+andcl-,whileincreasedthemg2+,ca2+,k+contentsintomatoundersaltstress,therebyreducingtheiontoxicity.5.undersaltstress,thesolublesugarandprolinewereaccumulatedintherootsandleavesoftomatoseedlings;whileexogenoussiliconfurtherpromotedthesolublesugaraccumulationbutinhibitedtheprolineaccumulation.theosmoticpotentialintomatoplantswasdecreasedundersaltstress,anditwasincreasedbyadditionofexogenoussilicon.theresultsshowthatosmoticadjustmentwasnotthemainmechanismforsilicon-mediatedincreaseinsaltresistanceoftomatoseedlings.inconclusion,exogenoussiliconcouldimprovethegrowthandstressresistanceoftomatoseedlingsundersaltstress.silicon-mediatedsaltresistanceintomatowasassociatedwithenhancedrootwateruptakeandantioxidantdefensecapabilities.