Effect Of Seed Priming With Chitosan And Ca(NO₃)₂ On Germination And Physiological Characteristics Of Maize Under Low Temperature Stress

Low temperature stress is an important constraint of maize production, and seed priming has been shown to improve seed vigor especially under adversity conditions. In present thesis, the effects of seed priming with acidic and near neutral chitosan solutions on seed germination and physiological characteristics of seedlings were investigated using four maize (Zea mays L.) varieties;the effects of seed priming with chitosan solutions of different concentrations on seed germination and physiological changes of seedlings using two maize inbred lines, HungC (chilling-tolerant) and Mo17 (chilling-sensitive), subjected to low temperature stress (before low temperature stress, after 5℃ low temperature stress for 3 days and after recovering growth for 3 days) were discussed;the effects of seed priming with Ca(NO₃)₂ solutions on changes of leaf photosynthesis and chlorophyll fluorescence at normal temperature, effects on seed germination and growth of seedling under low temperature stress, and the changes of priming effects during short time storage were studied using HungC and Mo 17 maize inbred lines. Main results were as follows:Priming treatments with acidic (pH 5.1) and near neutral (pH 6.4) chitosan solutions significantly improved the emergence percentage, enhanced the energy of germination, reduced mean germination time, increased shoot height and chlorophyll content in four maize varieties. There were no significant difference in germination percentage between primed new seeds of three materials and un-treated control. The germination percentage of old seed of Chaotian No.3 was, however, lowers than that in the control. The peroxidase (POD) activity and malondialdehyde (MDA) content of the shoots of Suyu No.1 and Chaotian No.3 were obviously increased and reduced respectively after priming with pH5.1 chitosan solution. The POD activity was significantly reduced, and MDA content had no significant difference in the shoots of Chaotian No.3 old-aged seeds compared to the control. Concerning the catalase (CAT) activity in the shoots of the three maize materials, including old-aged seeds, there were no markedly differences between the treatments and the control. Thus, it seems that chitosan is a new promising priming material for maize seed treatment, and no significant difference was found between the two acidic chitosan solutions and both are efficient in improving vigor of maize seeds.The seedling growth of two maize inbred lines, HungC (chilling-tolerant) and Mo17 (chilling-sensitive) was determined in three stages (before low temperature stress, after 5℃ low temperature stress for 3 days and after recovering growth for 3 days) after seed priming with three concentrations of chitosan solutions (0.25%, 0.5% and 0.75%). The priming significantly increased the final germination index and reduced mean germination time of the two maize inbred lines, there was no significant difference among the threepriming solutions in HuangC, and the 0.5% solution was better than 0.25% and 0.75% treatments in Mo 17. The priming with all three concentration solutions did not significantly increase the germination percentage of maize, however, increased the shoot height and root length of both inbred lines in the three stages, as well as the dry weight of shoot and root, and the 0.5% solution treatment was better than 0.25% and 0.75% treatments. After suffering 5℃ low temperature stress for 3 days, the priming significantly reduced the MDA content and relative permeability of plasmmemembrance, and enhanced the soluble sugars and proline concentrations in the shoots of the two maize inbred lines. The priming obviously increased POD and CAT activities in Mo 17, and did not significantly increase those of HuangC after 5℃ low temperature stress for 3 days. It suggests that seed priming with chitosan at a suitable concentration can improve germination speed and seedling growth of maize under low temperature stress. The priming with 0.5% concentration chitosan for 60 - 64 h seemed to have the best effects. Mol7 gained more advantage than HuangC from the priming.The effects of seed priming with 0.1mol/L Ca(NO₃)₂ solutions on seed germination and growth of seedling of HuangC and Mo 17 maize inbred lines at normal temperature were investigated. Compared to the control, the priming significantly enhanced the emergence percentage of both lines, increased the shoot height and root length, as well as dry weight of seedlings of Mo 17, had no significant effect on MDA content in both inbred lines. The priming obviously increased POD and CAT activities of maize seedlings, significantly increased the chlorophyll content and leaf photosynthetic rate of Mo 17. The priming also reduced stomatal conductance and substomatal CO₂ concentration of maize leaves, these effects were more obvious in Mo17 than in HuangC. The priming reduced the chlorophyll fluorescence parameter Fv/Fm of HuangC leaves, but increased Fv/Fm of Mo 17 leaves. It seems that Ca(NO₃)₂is a new practical priming material for maize seed treatment, which could improve seed germination speed, seedling growth and leaf photosynthetic efficiency.The effects of seed priming with 0.1mol/L Ca(NO₃)₂ solution on seed germination and growth of seedling of maize inbred lines, HuangC and Mo 17 at 15℃ low temperature stress for 14 days or during seedling low temperature stress (before low temperature stress, after 5℃ low temperature stress for 3 days and after recovering growth for 3 days) were investigated. Ca(NO₃)₂ priming significantly improved emergence percentage, shoot height, root length, shoot and root dry weight and the content of chlorophyll and reduced the MDA content in both inbred lines under 15 ℃ low temperature stress.The priming also enhanced seed emergence percentage of Mo 17 and had no significant enhancement for HuangC before low temperature stress, after 5℃ low temperature stress for 3 days and after recovering growth for 3 days. Before low temperature stress and after 5℃ low temperature stress for 3 days, the priming significantly increased shoot height, root length, shoot and root dry weight of Mo 17, after recovering growth for 3 days, shoot and root dry weight were significantly increased. The primingsignificantly increased the content of chlorophyll in Mo 17 before low temperature stress, after 5°C low temperature stress for 3 days and after recovering growth for 3 days. Before low temperature stress, the priming reduced MDA content of Mo 17, after low temperature stress for 3 days and after recover growth for 3 days, MDA content of Mo 17 had no significant difference compared to the control. The priming increased shoot height, root length, shoot and root dry weight of HungC before low temperature stress, after 5°C low temperature stress for 3 days and after recovering growth for 3 days, increased the content of chlorophyll before low temperature stress and after 5°C low temperature stress for 3 days, and had no significant difference compared to the control after recover growth for 3 days. The priming reduced MDA content of HuangC before low temperature stress and after recover growth for 3 days, and had no significant difference compared to the control after 5°C low temperature stress for 3 days.The effect changes of seed priming with O.lmol/L Ca(NO3)2 solution after storage for 15 days at 15°C in HuangC and Mo 17 maize inbred lines were investigated. The priming treatment significantly accelerated seed germination, increased shoot height, root length, shoot and root dry weight and the content of chlorophyll and reduced MDA content after 0, 5 and lOd storage of Mo 17. After Mo 17 storage for 15d, the priming treatment reduced the energy of germination, germination percentage, germination index, vigor index, mean germination time, root length and shoot and root dry weight in Mo 17. The priming had not significant increase in the energy of germination, germination percentage, germination index and vigor index after 0 and 5d storage of HungC, but significantly increased shoot height, root length, the content of chlorophyll and reduced MDA content after storage for 5d. The priming significantly reduced the energy of germination, germination percentage, germination index and vigor index of HungC, and significantly reduced shoot dry weight and the content of chlorophyll of seedlings after storage for 10 and 15d. It suggests that Ca(NO3)2 priming can enhance seed vigor of maize, and this effect can be kept 10 d for Mo 17 and 5d for HungC at 15°C, respectively. It gave great advantage to avoid improper conditions in sowing time.