Physiological Mechanisms Of Hydrogen Sulfide In Regulating Seed Germination And Seedlings Growth Of Processing Tomato Under NaCl Stress

Salt stress is the main stress factor that causes inhibition in plant growth and development,seriously restricts the sustainable development of agriculttre.To improve the tolerance of plants to high salinity has been an important goal for a long time.It is imperative to control this increasing problem by adapting some suitable strategies.As a new kind of signal molecule,hydrogen sulfide（H₂S）has been proved to regulate a variety of plant physio bgical processes under biotic stress.In the present study,processing tomato（KT-7,KT-16,KT-32）was used to investigate whether exogenous H₂ S has any alleviating role on seed germination and seedling stages of processing tomato under salt stress.For this purpose,the different concentration NaCl were applied at both germinating and seedling stages with or without application of different concentration H₂ S donor,sodium hydrosulfide（NaHS）.Seed germination rate,germination potential,germination index,vigor index,biological accumulation,relative water content,root activity,chlorophyll content,antioxidant enzyme activity were studied in order to understand the mechanism of exogenous H₂ S to salt stress.The main findings of the study were as follows:1)In this work,processing tomato cultivar KT-7,KT-16 and KT-32 were treated with Na Cl and screened semi-lethal concentration for 85,120 and 100mmol·L-1,respectively.Application of NaHS（H₂S donor）can alleviate the inhibitory effect of NaCl stress and show the protective effect of 0.4mmol·L-1NaHS on Na Cl-stressed processing tomato seed germination.Soaking time also affect the seed germination.The results show that with 0.4mmol/l Na HS seed soaking for 24 hours significant increase the germination and epicotyl fresh weight of KT-7,KT-16 and KT-32 under NaCl stress.Further studies show that NaHS can promote SOD,POD and CAT activities and reduce the accumulation of MDA.These data indicate that H₂ S was involved in the mechanism of germinating seeds responses to salt stress.2)The results showed that: With increasing NaHS level,the germination rate,germination energy,germination index,vigor index,SOD,POD and CAT activities first increased and then decreased.Compared with salt stress,treatments with 0.4mmo/l NaHS significantly increased seed germination rate,germination index,vigor index and the activities of SOD,POD and CAT in KT-7（70%,250%,120%,130%,6.7%,150% and 180%,respectively）and KT-16（50%,250%,60%,80%,4.3%,160% and200%,respectively）.The mitigation effect of hydrogen sulfide on KT-7 is stronger than KT-16.3)The results showed that the low concentration of sodium hydrosulfide were used to spray on the leaves of seedling,and to study the seedling biomass,photosynthetic pigment content,relative water content,root activity,free proline accumulation,autioxidant enzyme（SOD,POD,CAT）activities,electrolytic leakage and malondialdehyde（MDA）contents.According to the results,under the salt stress,exogenous H₂ S treatment significantly improved the processing tomato seedling biomass,photosynthetic pigment content,relative water content,root activity,proline content and autioxidant enzyme activities.However,electrolytic leakage and MDA contents had a significantly drop.Among them,50 μmol·L-1concentration had the best effect.Compared with salt stress alone,50 μmol/L NaHS increased seedling biomass,chlorophyll a content,chlorophyll b content,carotenoids content,SOD activities by 30.8%-66.7%,61.8%,56.3%,57.0%,9.1%,respectively,however,the electrolytic leakage and MDA contents descend 15 percentage points and 23.7%,in KT-7.50 μmol·L-1NaHS increased seedling biomass,chlorophyll a content,chlorophyll b content,carotenoids content,SOD activities by 24.0%⁹6.4%,49.8%,52.0%,46.7%,10.2%,respectively,however,the electrolytic leakage and MDA contents descend 12 percentage points and 24.2%,in KT-32.These illustrated that the exogenous H₂ S regulated the antioxidant levels in leaves to reduce oxidative damage on processing tomato seedling during salt stress that improved the processing tomato seedling adaptability to salt stress.4)The results showed that: Exogenous hydrogen sulfide improved the growth and chlorophyll a,b,carotenoids contents,net photosynthetic rate（Pn）,stomatal conductance（Gs）,transpiration rate（Tr）,maximal PSII quantum yield（Fv/Fm）and PSII actual photochemical efficiency（ΦPSII）of processing tomato seedling,but the level of concentration of CO2（Ci）,parameters of quantum yield of regulated energy dissipation [Y（NPQ）] and non-photochemical quenching coefficient（NPQ）were decreased.Quantum yield of non-regulated energy dissipation [Y（NO）] kept a lower level.The mitigation effect of hydrogen sulfide on KT-32 is stronger than KT-7.It is concluded that exogenous hydrogen sulfide could increase photosynthetic pigment content and improve photochemical electron transport efficiency and efficiently protect processing tomato leaves from PSII damage.