Mitigative Effects Of Exogenous Melatonin On Seedling Growth Of Apple Rootstock Under Hypoxia

Molecular oxygen?O₂?is the terminal electron acceptor in the mitochondrial electron transport chain and is an absolute requirement for efficient production of ATP though oxidative phosphorylation in aerobic organisms.Higher plants are aerobic organisms requiring molecular oxygen to support respiration and various other life-sustaining oxidations.But they frequently experience a low oxygen?hypoxia?environment mainly due to soil waterlogging or complete flooding,soil compaction,or poor soil drainage.Apple?Malus×domestica Borkh?is one of the most cultivated fruit crops in China.While apple tree frequently encounters waterlogging stress mainly due to excess rainfall,soil compaction,or poor soil drainage,resulting in yellowing leaf,declined fruit quality and yield in some region.In this study,we investigated the effect of exogenous melatonin on seedling growth,photosynthetic characteristics and mineral elements content in M.hupehensis and M.Toringoides under hypoxia stress.The main results were as follows:1.Under hypoxia stress,biomass of M.hupehensis and M.Toringoides decreased significantly compared with the control,but the decline rate was different due to the imparity of hypoxia tolerance.Exogenous 0.1 mmol?L^-1 melatonin could relieve the harm caused by hypoxia stress and result in improved growth of M.Toringoides and M.Toringoides,The results suggested treatment with 0.1 mmol?L^-1 melatonin mitigated the growth inhibitions in M.Toringoides and M.Toringoides under root-zone hypoxia stress.Under root-zone hypoxia stress,the relative water content and relative membrane permeability of two apple rootstock were decreased compared with their control.Exogenous melatonin significantly ireased the relative water content and relative membrane permeability of two apple rootstock under hypoxia stress.It was proposed that exogenous melatonin as a chemical activator could induce resistance,raise the relative water content,and decrease the membrane lipid peroxidation.therefore it alleviated the damage degree of hypoxia stress of M.hupehensis and M.Toringoides.2.Chlorophyll synthesis is significantly impeded under hypoxia stress condition,the content of Chla,Chlb and Chlt of two apple rootstocks decreased in response to hypoxia stress,but with significantly differences in intensity of two genotypes.The reduction in Chla,Chlb and Chlt was more drastic in M.Toringoides than M.hupehensis under hypoxia stress.Exogenous melatonin significantly ireased the chorophyll content of two apple rootstock under hypoxia stress.The stomatal conductance?Gs?,transpiration?TRAN?,intercellular carbon dioxide concentration?CINT?and net photosynthetic rate?Pn?of M.Toringoides showed different degrees changes under hypoxia treatment.The decline degree of hypoxia-sensitive M.Toringoides is more significant than hypoxia-resistant M.hupehensis.But two apple rootstocks change tendency of four kinds of index under HM treatment rise significantly compared to hypoxia treatment.3?Under hypoxia treatment,six kinds of mineral elememts content of apple rootstock showed different changes.They change differently due to different material and part,and the changes range of content of different mineral elememts is different.The changes of potassium content is not obvious,and sodium content of stem is increased,while calcium and nitrogen content of whole plant is lower than contrast?CK?;The six kinds of mineral elememts of M.Hupehensis present decline trend under hypoxia,but the decline tendency is no larger than hypoxia sensitive M.Toringoides.Under hypoxia and melatonin treatment,six kinds of mineral elememts content of apple rootstock also present different degree changes.But mineral elememts content is higher obviously compared to hypoxia.4?We extract the RNA of two apple stock root and leaf.The result shows that RNA integrity of CTAB extraction is great.The electrophoresis detection shows obvious stripes.The 28s RNA is twice as bright as 18s RNA basicly in the leaf.Ultraviolet absorbance value measured is around 2.0,which suggests that RNA is of good quality and high purity.