| Maize is one of the most important food crops. The planting area, output, and commodity grain of maize in Heilongjiang province had given rise to the first in china. Spring chilling damages is the most frequent meteorological disasters in heilongjiang province, seriously influence the maize stable production and high yield. Abscisic acid(abscisic acid, ABA) as a plant stress resistance factor and plays an important role in regulating of plant cold resistance. This study selected cold resistance Zhengdan 958 as test material,to investigate the effect of exogenous ABA on corn seedling root system under low temperature stress. The experiment was carried on the experimental base in Northeast Agricultural University from 2014 to 2015, Setting treatment of ABA at five levels(0, 10-7, 10-6, 10-5 and 10-4 mol· L-1) and watering the roots of maize seedlings under different low temperature(day/night = 14± 0.5 ℃ / 5± 0.5 ℃) last for 0, 2, 4, 6 and 8 days stress to measure root characteristics, osmotic regulation substances content, endogenous hormones content, phenolics metabolism and changes in cell ultrastructure. The results showed that:The application of exogenous ABA presented a promoting effect at low concentration and all inhibiting effect at high concentration at the same time under low temperature stress(performance for 10-5 mol·L-1 >10-6 mol·L-1 >10-7 mol·L-1 >0 mol· L-1), Wherein 10-5 mol·L-1 treatment was significant. Under the same concentration of ABA treatment,the growth rate of seedling under the middle of low temperature stress(2-4 d and 4-6 d) was greater than the prophase of low temperature stress(0-2d) and the late stage of low temperature stress(6-8d), above results indicated that, within a certain range of low temperature stress, appropriate concentration of ABA could regulate the root growth of maize seedling and alleviate low temperature stress in some degree, so as to improve the cold resistance of maize.With the time prolonged of low temperature stress, proline content increased gradually, soluble sugar and soluble protein was first increased and then decreased, and exogenous applied ABA significantly improve these indicators’ content. There was a concentration effect between each treatment, performance as low concentration promotion and high concentration inhibition, and the optimal concentration is 10-5mol·L-1. The effect on soluble sugar is most significant. The ABA and ZR content and ABA/IAA, ABA/GA3 was first increased and then decreased, GA3 and IAA content decreased gradually. ABA/ZR ratio increased gradually.The suitable concentration of exogenous ABA could promote the synthesis of endogenous ABA and may delay the drop points of endogenous ABA during of low temperature stress, the contents of ZR, IAA and GA3 were also decreased at the same time.Along with the cold stress time,the content of total phenolics and total flavonoid showed first increased and then decreased, but FRAP and ABTS antioxidant capacity showed continued downward trend, the polyphenol oxidase(PPO) showed gradually increased trend. The congtent of free phenol,combined phenol and total phenolic among 670-830 mg GAE/100 g DW, 531-640 mg GAE/100 g DW and 1310-1460 mg GAE/100 g DW in maize root with 5 different concentrations of exogenous ABA; free state flavonoids, bound flavonoids and total flavonoids contents were between 473-518 mg GAE/100 g DW, 262-426 mg GAE/100 g DW 744-906 mg and GAE/100 g DW. The free, bound and the total FRAP antioxidant capacity values were among 106-168 mg GAE/100 g DW, 19-31 mg GAE/100 g DW, 131-189 mg GAE/100 g DW. The phenolic acids related with low temperature mainly contain coumaric acid, chlorogenic acid, caffeic acid and ferulic acid. At the beginning of low temperature stress, the composition and content of phenolic monomer of control experiment was significantly more than that of ABA treatment, however there would be an opposite result with prolonged low temperature stress.Under low temperature stress, the cell wall was separated, the nucleus was deformed,the kernel was loose, the mitochondria were deformed and inclusions appear within vacuoles. In the late stage of low temperature stress, the separation of cell and wall was serious, the nucleus was largely disappeared, the mitochondria were not completely empty, and the vacuole was filled with a large number of inclusions. Exogenous ABA significantly reduce d the damage caused by low temperature stress on the cell structure. |
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