PLANT PHYSIOLOGY , Vol 111, Issue 1 39-47, Copyright © 1996 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Developmental Stage-Specific and Nitrate-Independent Regulation of Nitrate Reductase Gene Expression in Rapeseed
H. Fukuoka, T. Ogawa, H. Minami, H. Yano and Y. Ohkawa
Chugoku National Agricultural Experiment Station, Fukuyama, Hiroshima 721, Japan (H.F., T.O., H.Y., Y.O)
cDNA clones for two isogenes of nitrate reductase (NR) have been isolated
from rapeseed (Brassica napus L.) androgenetic haploid embryos induced by
microspore culture. NR mRNA accumulation can be detected by northern
hybridization at 14 d after culture initiation when embryos develop to the
heart/torpedo-shaped stage. Whole-mount in situ hybridization experiments
demonstrate that the mRNA accumulation is developmental stage specific. In
addition, even when cultured in media containing no nitrate, embryos
accumulated NR mRNA to almost the same level as the control. This indicates
the unique regulation of NR in embryogenesis in which NR mRNA transcription
is activated in a developmental stage-specific manner that is independent
of nitrate induction. In zygotic embryogenesis, a stage-specific
accumulation of NR mRNA was also observed. By contrast, the obvious effect
of nitrate on NR expression that has been reported in many plant species
was also confirmed in rapeseed leaf. Quantitative combined reverse
transcription-poly-merase chain reaction analysis suggests that the
flexible and variable regulation of NR expression, which is organ specific,
nitrogen metabolite specific, and developmental stage specific, is caused
principally by regulation of one major structural gene.
