Exogenous ABA effect on physiology of winter rapeseed( Brassica rapa L. ) seedling in northern China

To improve cold tolerance of winter rapeseed( Brassica rapa L.) in northern China,hormone effect of exogenous abscisic acid( ABA) was investigated on cultivar Longyou 8. ABA( 5,10,15,20,25 mg / L) were sprayed on leaves from 6-7 true-leaf seedlings. Cold tolerance,physiology and biochemistry characteristics were studied before winter( at 15℃) and during winter( at-5℃). Results showed that ABA spray significantly improved overwintering rate. The overwintering rate was 86. 3% under 20 mg / L ABA,which was the highest among other treatments,and was 26. 7% higher than water spray( CK). After spray,leaves protective enzymes( SOD,POD,CAT) were activated significantly. Contents of soluble protein( SP),soluble sugar( SS) and free proline( Pro) were significantly increased. Malonaldehyde( MDA) content was significantly reduced. Root vitality and lateral roots were significantly increased. Root collar diameter and root weight increased too,but the increase was not significant different from water control. Result showed that 20 mg / L ABA spray was the best concentration to improve the cold tolerance of Longyou 8. It was benefited by the increase of protective enzyme activity and osmotic up-regulation from the aerial part. Thus the increase of root vitality and lateral root quantity proved a well condition for the seedling to overcome the chilling.