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Relationships between benzyladenine uptake, endogenous free IAA levels and peroxidase activities during upright shoot induction of Cymbidium ensifoilum cv. Yuh Hwa rhizomes in vitro
Authors:I-lun Lu  Ellen Sutter  David Burger
Institution:(1) Oregon Plant Tissue Culture Laboratory, Clackamas, USA;(2) Department of Pomology, University of California, Davis, USA;(3) Department of Environmental Horticulture, University of California, Davis, USA
Abstract:Studies were undertaken in order to improve the micropropagation ofCymbidiun ensifolium 'Yuh Hwarsquo. It is easy toinduce rhizomes in vitro in this cultivar but not upright shoots, which areneeded for eventual production of a flowering plant. Exposure ofCymbidium ensifolium 'Yuh Hwarsquo rhizomeexplants in vitro to greater than 2.5 mgrM BA for 12weeks or longer inhibited both elongation of upright, aerial shoots and rootgrowth. Through transfer experiments, it was determined that the commitment toinduction of upright shoots occurred after 10–14 days of exposure to 2.5mgrM BA. BA supplied at 20 mgrM during the first 14days of culture was sufficient to induce upright shoot formation, but shootelongation did not continue under these conditions. Using radiolabelled BA,adenine was found to be a major metabolite found in the rhizome tissue at day14. BA comprised 37% of the total DPM recovered in rhizomes grown in 20mgrM BA compared to that of 61% of the total DPM recoveredfrom rhizomes grown in 2.5 mgrM BA. The total amount of BA takenup per gram fresh weight was similar for both green and etiolated rhizomesgrownin 2.5 mgrM BA. Rhizomes grown in 20 mgrM BA tookupapproximately five times as much BA as those grown in 2.5 mgrMBA.Free IAA levels were highest in the rhizome tip (12.7 ng/g FW) anddecreased to one fourth the value at 1 cm behind the tip. Free IAAlevels increased initially in rhizornes transferred to medium with or without20mgrM BA (although at different amounts) and then decreased. Whenactivated charcoal was added to the medium as well as BA there was no initialincrease in IAA. When 20 mgrM BA was added to the medium, solubleperoxidase activity increased while IAA concentrations remained at about thesame level over a 7-day period. Peroxidase activity in rhizomes eitherdecreasedor remained constant when activated charcoal was added to the medium containingBA.
Keywords:Auxin  Cytokinin metabolism  Morphogenesis  Orchid  Plant tissue culture
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