Effects Of Soaking Seeds With Hydrogen Peroxide And Sowing Dates On Physiology And Growth Of Direct-seeded Rapeseeds

Rapeseed is the largest and only winter oil crop in China.Improving rapeseed yield and reducing production cost are of great significance to ensure oil security in China.Rape direct seeding cultivation mode has great prospects for development because it is suitable for large-scale,mechanized production,time-saving and labor-saving.Affected by the harvest time of the previous crop,the actual sowing date of rapeseed has a long span.Low temperature is an important factor limiting the development of late direct seeding rapeseed.Previous studies in the laboratory showed that soaking seeds with H2O2 could enhance cold resistance of late direct seeding rapeseed,promote growth and development of rapeseed,and increase yield.However,the effects of soaking seeds with H2O2 on the growth and development of Rapeseed under early sowing conditions and the correlation between growth period,accumulated temperature and yield of rapeseed treated with hydrogen peroxide at different sowing dates have not been reported.The effects of different sowing dates and soaking treatments with H2O2 on the growth process,biomass accumulation,economic shape,yield formation and the metabolism of reactive oxygen species(ROS),antioxidant system and sugar metabolism system of Brassica napus cv.Nan Nong you4 under low temperature stress in winter were studied in order to reveal the effects of H2O2 on cold resistance of Brassica napus.The physiological mechanism of the effect and the relationship between accumulated temperature and the growth period and yield of rapeseed provide a theoretical basis for cold-resistant cultivation of late direct seeding rapeseed.The main results are as follows:1.With the delay of sowing date,the accumulated temperature needed to germinate seedlings increased and the time to germinate seedlings prolonged in the sowing date B2,while the available accumulated temperature decreased in the seedling and bud-bolting stage,which resulted in the increase of seedling time and the significant shortening of bud-bolting period.The duration of flowering and pod stage of rapeseed in sowing date B2 was slightly shorter,but the accumulated temperature of flowering and pod stage was slightly higher than that of sowing date B1 because of the lag of growth period of rapeseed in sowing date B2 and the rapid increase of temperature.The total growth process of rapeseed accelerated,the whole growth period shortened and the available accumulated temperature decreased during the whole growth period.Except that soaking seeds with H2O2 in sowing date B2 promoted the emergence of rapeseed one day earlier and the length of budding period increased one day,the whole soaking seeds with H2O2 had no significant effect on the growth process of rapeseed in sowing dates B1 and B2.2.1n terms of agronomic traits and yield components of rapeseed at maturity stage,plant height,branching height and underground dry weight increased,while stem diameter and above ground dry weight decreased,and eventually 1000-grain weight and yield decreased significantly.Soaking with hydrogen peroxide had a negative effect on the whole rapeseed at the first sowing date,with a decrease in total dry weight and yield,and a positive effect on the rapeseed at the sowing date B2.The total dry weight,1000-grain weight and yield of rapeseed were all increased.Moreover,the positive effect of soaking seeds with H2O2 at sowing date B2 on rapeseed fully compensated for the negative effect caused by delayed sowing date.The biomass and yield of rapeseed were higher than those of control treatment at sowing date B1.3.Under low temperature stress,the accumulation of ROS and the content of MDA increased,and the antioxidant defense system of rape itself was induced and activated,such as superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),Monodehydroascorbate reductase(MDHAR),glutathione reductase(GR),glutathione peroxidase(GPX),glutathione transferase(GST).)The activity of antioxidant enzymes increased.The levels of antioxidants ascorbic acid(AsA)and glutathione(GSH)increased.when the temperature stress was mild in the early stage of overwintering,the anti-oxidant defense system of rapeseed was strengthened by soaking seeds with H2O2 in the first sowing date,and the cold resistance was stronger.With the temperature change and the growth and development of rapeseed in the later stage,the aging process of rapeseed was aggravated by soaking seeds with H2O2,and the accumulation of ROS and the degree of membrane lipid peroxidation were increased.At sowing date B2,soaking seeds with H2O2 improved the antioxidant ability and cold resistance of rapeseed in general and alleviated the oxidative damage caused by low temperature stress.4.Under low temperature stress,the photosynthesis of rapeseed was inhibited.The degree of photosynthesis inhibition of rapeseed at sowing date B2 was lighter than that at sowing date B1.The activity of most sucrose metabolism-related enzymes in rapeseed was increased and the efficiency of sugar metabolism was accelerated by low temperature signal.In sowing date B1,the sugar content of each component of rapeseed increased rapidly,and reached a higher level at the early stage of low temperature stress.The increase of sugar content enhanced the cell osmotic potential and enhanced the cold resistance of rapeseed,but at the same time,it also caused feedback inhibition to photosynthesis to a certain extent.In sowing date B2,rapeseed still had relatively vigorous growth activities under low temperature stress.It was more active in sugar transportation and decomposition and utilization,and the sugar content of each component was in a downward trend.Soaking with H2O2 at sowing date B2 had a negative effect on the carbon metabolism system of rapeseed in general.The growth of rapeseed was slow and its metabolic activity was weak.Soaking with H2O2 at sowing date B1 increased the activities of sucrose metabolism-related enzymes and the sugar content of each component,which made the physiological metabolic activities of rapeseed more vigorous during overwintering period and weakened the inhibition of low temperature stress on rapeseed growth.