PLANT PHYSIOLOGY , Vol 109, Issue 1 231-238, Copyright © 1995 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Correlated Changes in the Activity, Amount of Protein, and Abundance of Transcript of NADPH:Protochlorophyllide Oxidoreductase and Chlorophyll Accumulation during Greening of Cucumber Cotyledons
K. Yoshida, R. M. Chen, A. Tanaka, H. Teramoto, R. Tanaka, M. P. Timko and H. Tsuji
Department of Botany, Faculty of Science, Kyoto University, Kyoto, 606 Japan (K.Y., A.T., H. Teramoto, R.T., H. Tsuji)
Changes in the activity and abundance of NADPH:protochlorophyllide
oxidoreductase (NPR) and the abundance of mRNA encoding it were examined
during the greening of 5-d-old etiolated cucumber cotyledons under
continuous illumination. To measure NPR activity in the extracts from fully
greened tissues, we have developed an improved method of assay. Upon
exposure of etiolated cotyledons to light, NPR activity decreased rapidly
within the first 2 h of exposure. Thereafter, enzymatic activity increased
transiently, reaching a submaximum level at 12 h, and decreased slowly. The
level of immunodetectable NPR protein followed the same pattern of changes
during 96 h of greening as observed for NPR activity. The NPR mRNA in
etiolated cotyledons disappeared quickly in the 1st h of irradiation.
However, the level of mRNA increased thereafter to reach 3-fold or more of
the dark level at 12 h and then decreased. The changes in the activity,
protein level, and mRNA level after the first rapid decreases corresponded
chronologically and nearly paralleled the increase in the rate of
chlorophyll accumulation. These findings suggest that the greening of
cucumber cotyledons is regulated basically by the level of NPR protein
without activation or repression of enzymatic activity and that NPR mRNA
increased by light maintains the level of enzyme protein necessary for
greening.
