Morphological and biochemical responses to gibberellic acid in Magnolia × 'spectrum' in vitro.

Abstract

The total soluble sugar content and antioxidant enzyme activities were studied for the first time during axillary shoot formation in Magnolia × ‘Spectrum’ in vitro in response to BAP (0.3 mg l -1 ), different levels of gibberellic acid (GA 3 ; 0.0, 0.1, 0.5, 1.0 mg l -1 ), sucrose (20 and 30 g l -1 ) and nitrogen salts (KNO 3 /NH 4 NO 3 ; 100/100% and 75/50% relative to MS medium). Among various GA 3 and sucrose/nitrogen salts ratios, the most effective axillary multiplication (5.9 shoots/explant) and leaf formation (25.7 leaves per multiplied clumps) were obtained after addition of GA 3 at 0.1 mg l -1 to a BAP medium containing 20 g l -1 sucrose and reduced levels of nitrogen salts (75% KNO 3 and 50% NH 4 NO 3 ). The addition of GA 3 to the BAP medium enhanced shoot formation by 36% and leaf formation by 27%. The highest shoot formation capacity of M. × ‘Spectrum’ in vitro coincided with enhanced levels of soluble sugar and peroxidase (POD) activity. Increasing GA 3 concentration from 0.1 to 1.0 mg l -1 in the above medium resulted in inhibition of shoot and leaf formation and a decrease in the soluble sugar content. The influence of GA 3 on the activities of catalase (CAT) and POD depended on its concentration and the levels of sucrose and nitrogen salts in the medium. The highest increase in CAT and POD activities, that coincided with the enhanced shoot formation capacity of M. × ‘Spectrum’ in vitro, was observed after addition of GA 3 to the medium containing high levels of sucrose and nitrogen salts. presence of different concentration of GA 3 , sucrose and nitrogen salts were studied.