PLANT PHYSIOLOGY , Vol 106, Issue 4 1555-1565, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Modifications of Etioplasts in Cotyledons during Prolonged Dark Growth of Sugar Beet Seedlings (Identification of Etiolation-Related Plastidial Aminopeptidase Activities)
A. E. Amrani, I. Couee, J. P. Carde, J. P. Gaudillere and P. Raymond
Station de Physiologie Vegetale, Institut National de la Recherche Agronomique, BP 81, 33883 Villenave d'Ornon Cedex, France (A.E.A., I.C., J.-P.G., P.R.)
We studied the effects of prolonged dark growth on proplastids and
etioplasts in cotyledons of sugar beet (Beta vulgaris L.) seedlings.
Differentiation of proplastids into etioplasts occurred between d 4 and d 6
after imbibition, with the typical characteristics of increased synthesis
of plastidial proteins, protein and carotenoid accumulation, size increase,
development of plastid membranes and of the prolamellar body, and increase
of the greening capacity. However, this situation of efficient greening
capacity was short-lived. The greening capacity started to decline from d 6
after imbibition. This decline was due in part to reserve depletion and
glucose limitation and also to irreversible damage to plastids. Indeed,
electron microscopy observations in situ showed some signs of plastidial
damage, such as accumulation of plastoglobuli and membrane alterations. The
biochemical characterization of purified plastids also showed a decrease of
proteins per plastid. Aminopeptidase activities, and to a lesser extent,
neutral endopeptidase activities, were found to increase in plastids during
this degenerative process. We identified two plastidial aminopeptidases
showing a sharp increase of activity at the onset of the degenerative
process. One of them, an alanyl aminopeptidase, was shown to be inactivated
by exposure to light or addition of exogenous glucose, thus confirming the
relationship with prolonged dark growth and indicating a relationship with
glucose limitation.
