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Plant Physiol, October 2000, Vol. 124, pp. 767-780
Effects of Elevated [CO2] and Nitrogen Nutrition on
Cytokinins in the Xylem Sap and Leaves of Cotton1
Jean W.H.
Yong,
S. Chin
Wong,
D. Stuart
Letham,
Charles
H.
Hocart, and
Graham D.
Farquhar*
Environmental Biology Group (J.W.H.Y., S.C.W., G.D.F.) and Plant
Cell Biology Group (D.S.L., C.H.H.), Research School of Biological
Sciences, Australian National University, G.P.O. Box 475, Canberra,
Australian Capital Territory 2601, Australia
We measured the level of xylem-derived cytokinins (CKs)
entering a cotton leaf, and the CK levels in the same leaf, thus
enabling xylem sap and foliar CKs to be compared concurrently. Although zeatin was the dominant CK in xylem sap, zeatin, dihydrozeatin, and
N6-(2-isopentenyl) adenine were present in approximately
equimolar levels in leaves. Elevated [CO2] (EC) has an
effect on the levels of cytokinins in sap and leaf tissues. This effect
was modulated by the two levels of root nitrogen nutrition (2 and 12 mM nitrate). Growth enhancement (70%) in EC over plants in
ambient [CO2] (AC) was observed for both nitrogen
nutrition treatments. Low-nitrogen leaves growing in EC exhibited
photosynthetic acclimation, whereas there was no sign of photosynthetic
acclimation in high-nitrogen grown leaves. Under these prevailing
conditions, xylem sap and leaf tissues were obtained for CK analysis.
Higher nitrogen nutrition increased the delivery per unit leaf area of
CKs to the leaf at AC. EC caused a greater increase in CK delivery to
the leaf at low nitrogen conditions (106%) than at high nitrogen
conditions (17%). EC induced a significant increase in CK content in
low-nitrogen leaves, whereas CK content in leaf tissues was similar for
high-nitrogen leaves growing in AC and EC.
1
J.W.H.Y. was supported by the Australian
National University, Nanyang Technological University, and the Tan Kah
Kee Foundation (Singapore).
*
Corresponding author; e-mail farquhar{at}rsbs.anu.edu.au; fax:
61-2-62494919.
© 2000 American Society of Plant Physiologists
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