Relationships between benzyladenine uptake, endogenous free IAA levels and peroxidase activities during upright shoot induction of Cymbidium ensifolium cv. Yuh Hwa rhizomes in vitro
2001
Lu, I.L. | Sutter, E. | Burger, D.
Studies were undertaken in order to improve the micropropagation of Cymbidium ensifolium 'Yuh Hwa'. It is easy to induce rhizomes in vitro in this cultivar but not upright shoots, which are needed for eventual production of a flowering plant. Exposure of Cymbidium ensifolium 'Yuh Hwa' rhizome explants in vitro to greater than 2.5 micromolar BA for 12 weeks or longer inhibited both elongation of upright, aerial shoots and root growth. Through transfer experiments, it was determined that the commitment to induction of upright shoots occurred after 10-14 days of exposure to 2.5 micromolar BA. BA supplied at 20 micromolar during the first 14 days of culture was sufficient to induce upright shoot formation, but shoot elongation did not continue under these conditions. Using radiolabelled BA, adenine was found to be a major metabolite found in the rhizome tissue at day 14. BA comprised 37% of the total DPM recovered in rhizomes grown in 20 micromolar BA compared to that of 61% of the total DPM recovered from rhizomes grown in 2.5 micromolar BA. The total amount of BA taken up per gram fresh weight was similar for both green and etiolated rhizomes grown in 2.5 micromolar BA. Rhizomes grown in 20 micromolar BA took up approximately five times as much BA as those grown in 2.5 micromolar BA. Free IAA levels were highest in the rhizome tip (12.7 ng/g FW) and decreased to one fourth the value at 1 cm behind the tip. Free IAA levels increased initially in rhizomes transferred to medium with or without 20 micromolar BA (although at different amounts) and then decreased. When activated charcoal was added to the medium as well as BA there was no initial increase in IAA. When 20 micromolar BA was added to the medium, soluble peroxidase activity increased while IAA concentrations remained at about the same level over a 7-day period. Peroxidase activity in rhizomes either decreased or remained constant when activated charcoal was added to the medium containing BA.
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