Effects And Physiological Mechanism Of PEG Priming On Germination Of Dormancy Released Fraxinus Mandshurica Seeds

The secondary dormancy of seeds is widespread in nature,It has a certain impact on agricultural and forestry production,resulting in reduced output and economic losses.PEG priming has the effect of promoting seed germination,but it is not clear whether it can inhibit seed secondary dormancy.This study take the dormancy released Fraxinus mandshurica seeds as the research material,in order to study that the PEG priming treatment and the hormones or the cell cycle inhibitors with PEG solution co-priming treatments on the seed germination capacities,cell wall degradation enzymes activity and the effect of endogenous hormones content,aiming at providing references for ensuring the suit priming treatment of Fraxinus mandshurica seeds,intensive studing the physiological mechanism of seed heat dormancy regulation.The main research results are as follows:(1)Different PEG priming treatments have different effect on the germination of Fraxinus mandshurica seeds which have broken dormancy.Under optimal germination temperature condition,at the priming temperature of 10?,priming the seed with low mass fraction(5%)PEG solution for short duration(1 d)can improve the germination index of seeds significantly.Under high germination temperature condition(25?),at the priming temperature of 10?,priming the seed with high mass fraction(50%)PEG solution for medium duration(3 d)or long duration(7 d)can significantly improve the germination rate and germination index of seeds,and prevent the entering of seed thermal dormancy effectively.(2)Under the germination condition of high temperature,osmotic priming treatment has effect on improving germination capacities,partly,PEG co-priming treatments with different hormones and cell cycle inhibitors can improve the PEG priming effects.Moreover,the germination performance of un-preabsorbent seeds after initiation treatment was better than that of pre-absorbent seeds.PEG solution co-priming with 1 mmol/L GA4+7 have the best prevent effect on the seed secondary dormancy of the pre-inbibition seed,which could significantly improve the germination rate(94%)of the seeds,but could not improve the germination index or reduce the germination time of the seeds.PEG solution co-priming with 100 mmol/L hydroxyurea have the best prevent effect on the seed secondary dormancy of not pre-inbibition seed,it can significantly increase the germination rate(85%)and germination index(1.84)of Fraxinus mandshurica seeds,but have no significant effect on the seed germination time.(3)Under the germination condition of high temperature,PEG osmotic priming treatment can induce the changes of seeds endogenous hormones contents and cell wall degrading enzymes activities,there are some differences of these changes between seeds are pre-imbibition or not pre-imbibition.For the seeds of pre-imbibition,compare with the control seeds without priming treatment,PEG priming can increase the contents of GA3,GA7,IAA and CTK in seeds,increase the cellulase activities and decrease the ABA contents.For seeds are not pre-imbibition,PEG priming treatment can increase the contents of GA3,GA7 and IAA in seeds,compare with the control seeds without priming treatment.(4)Under the germination condition of high temperature,for the Fraxinus mandshurica seeds are pre-imbibition,compare to the seeds which are priming by PEG,PEG+hydroxyurea co-priming can increase of the contents of GAs?IAA and CTK,decrease ABA contents.For the seeds are not pre-imbibition,PEG+hydroxyurea co-priming can increase of the contents of GA3 and IAA,increase the pectinase activities and decrease ABA contents.In summary,at high germination temperature,PEG priming treatment promote seeds germination by improving the cellulase activity of seed endosperm weakens the resistance of endosperm to breakthrough of seed embryo.And by changing the endogenous hormones contents(In general,GAs,IAA and CTK contents are increase,ABA contents are decrease)and regulating the hormonal effect.Hench,PEG priming treatment can prevent the thermal dormancy of the seeds effectively.