Page 315 - PC2019 Program & Proceedings

PLANT CANADA 2019

P203. Nitrogen isotope composition and content varied along xylem transport pathway of black
cottonwood (Populus trichocarpa) under near steady-state hydroponics
Hu, Y. *
University of British Columbia

Xylem is essential for water and nutrient transport in plants. To investigate nitrate uptake, assimilation
and translocation in trees, 60 black cottonwoods from three randomly selected genotypes were grown
hydroponically under glasshouse conditions. A large and regularly replaced volume (2000 L) of 1/10th
Johnson’s solution was used to ensure a realistic rate of nutrient supply with little change in isotopic
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(d N) composition or concentration (<10%). After 90 days of growth, xylem sap was collected by
pressure bombing at different position (root, lower shoot and upper shoot) at 0-1MPa and 1-1.5MPa,
sequentially. An elemental analyzer–isotope ratio mass spectrometer (EA-IRMS) was used to analyze the
N content and isotopic composition of bulk N in xylem sap. A denitrifying method followed by gas
chromatography–IRMS was used to analyze the N content and isotopic composition of nitrate in xylem
sap. Our results showed the overall average nitrate concentration in the xylem sap is ~1.18 mM, while the
bulk N in xylem sap is ~5.28 mM. The average nitrate discrimination against the hydroponic source is
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~19.35‰. There were changes in d N of xylem nitrate and bulk N at the different bomb pressures, with
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lower nitrate concentrations and higher d N at the higher pressure, suggesting that nitrate assimilation
occurs progressively along the xylem transport pathway.
Yi Hu (yi.hu@ubc.ca)

P204. Development of an efficient temporary immersion system for the micropropagation of
American chestnut (Castanea dentata (Marsh.) Borkh.)
Liu, Z. ; M. Shukla; P. Saxena
*
University of Guelph

American chestnut (Castanea dentata), a native species of eastern North America, is an economically
important deciduous hardwood tree that has been designated as endangered in Canada. The population of
American chestnut trees has dwindled significantly across Southern Ontario due to chestnut blight disease
and many of the surviving trees continue to show blight disease symptoms. Micropropagation is a highly
effective tool to rapidly clone disease-free germplasms from limited material to large-scale production
under controlled environmental conditions. Facilitating long-term plant conservation and reintroduction,
the objective of this study was to develop an efficient micropropagation protocol for in vitro
multiplication of American chestnut in a temporary immersion system (TIS). The highest rate of shoot
multiplication was observed in cultures grown in DKW (Driver and Kuniyuki 1984) basal medium
supplemented with 2.2 µmol L-1 6-benzylaminopurine and 1.0 µmol L-1 gibberellic acid. More than 95%
of microshoots 30-40 mm in size developed roots after 30 days in vitro within bioreactor vessels
containing DKW basal medium supplemented with 15 µmolL-1 3-Indolebutyric acid. Rooted plantlets
transplanted to the greenhouse expressed a survival rate of 52% after one month in ex vitro conditions.
This study confirms the potential of TIS for micropropagation in ex-situ conservation and reintroduction
of endangered American chestnuts in their natural habitat.

Zhuoya Liu (zhuoya@uoguelph.ca)

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