PLANT PHYSIOLOGY , Vol 106, Issue 1 211-215, Copyright © 1994 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
Poplar Bark Storage Protein and a Related Wound-Induced Gene Are Differentially Induced by Nitrogen
G. D. Coleman, M. P. Banados and THH. Chen
Department of Horticulture, 4017 Agricultural and Life Sciences (G.D.C., M.P.B., T.H.H.C.), and Center for Gene Research and Biotechnology (G.D.C., T.H.H.C.), Oregon State University, Corvallis, Oregon 97331-7304
Poplars (Populus deltoides Bartr. ex Marsh) accumulate a 32-kD bark storage
protein (BSP) in phloem parenchyma and xylem ray cells during autumn and
winter. Accumulation of poplar BSP is associated with short-day (SD)
photoperiods. Poplar BSP shares sequence similarity with the product of the
wound-inducible poplar gene win4. The influence of nitrogen availability
and photoperiod on the levels of BSP, BSP mRNA, and win4 mRNA was
investigated. In long-day (LD) plants BSP, BSP mRNA, and win4 mRNA levels
were correlated with the amount of NH4NO3 provided to the plant. BSP mRNA
and BSP were detected only in bark, whereas win4 mRNA was detected only in
leaves. In LD plants treated with NH4NO3, BSP mRNA levels were
significantly greater than those of win4. In nitrogen-deficient plants
exposed to SD conditions, the accumulation of BSP mRNA and BSP was delayed
for 2 weeks. This delay was eliminated by further SD exposure, and after 6
weeks of SD treatment similar levels of BSP and BSP mRNA were detected in
the bark of SD plants regardless of the level of NH4NO3 treatment. win4
mRNA levels declined to undetectable levels in young leaves of SD plants
but increased in mature leaves. These results indicate that BSP
accumulation in both LD and SD plants is influenced by nitrogen
availability. Although both BSP and win4 appear to be involved in nitrogen
storage, our data suggest that BSP is probably the primary protein involved
in both seasonal and short-term nitrogen storage in poplar. These results
also suggest that nitrogen cycling and storage in poplar could involve a
two-component system. In this system the win4 gene product may modulate
accumulation and mobilization of leaf nitrogen, whereas BSP is involved in
seasonal and short-term nitrogen storage during periods of excess nitrogen
availability.
