MODIFICATIONS OF ETIOPLASTS IN COTYLEDONS DURING PROLONGED DARK GROWTH OF SUGAR-BEET SEEDLINGS - IDENTIFICATION OF ETIOLATION-RELATED PLASTIDIAL AMINOPEPTIDASE ACTIVITIES
A. Elamrani et al., MODIFICATIONS OF ETIOPLASTS IN COTYLEDONS DURING PROLONGED DARK GROWTH OF SUGAR-BEET SEEDLINGS - IDENTIFICATION OF ETIOLATION-RELATED PLASTIDIAL AMINOPEPTIDASE ACTIVITIES, Plant physiology, 106(4), 1994, pp. 1555-1565
We studied the effects of prolonged dark growth on proplastids and eti
oplasts in cotyledons of sugar beet (Beta vulgaris L.) seedlings. Diff
erentiation of proplastids into etioplasts occurred between d 4 and d
6 after imbibition, with the typical characteristics of increased synt
hesis of plastidial proteins, protein and carotenoid accumulation, siz
e increase, development of plastid membranes and of the prolamellar bo
dy, and increase of the greening capacity. However, this situation of
efficient greening capacity was short-lived. The greening capacity sta
rted to decline from d 6 after imbibition. This decline was due in par
t 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 plasto
globuli and membrane alterations. The biochemical characterization of
purified plastids also showed a decrease of proteins per plastid. Amin
opeptidase activities, and to a lesser extent; neutral endopeptidase a
ctivities, 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 exposu
re to light or addition of exogenous glucose, thus confirming the rela
tionship with prolonged dark growth and indicating a relationship with
glucose limitation.