Modifications of Etioplasts in Cotyledons during Prolonged Dark Growth of Sugar Beet Seedlings (Identification of Etiolation-Related Plastidial Aminopeptidase Activities)

Purification and Characterization of a Novel Aminopeptidase, Plastidial Alanine-Aminopeptidase, from the Cotyledons of Etiolated Sugar Beet Seedlings

“…We identified these two plastidial aminopeptidase activities as early markers of the degenerative process, since they significantly increased after the proplastid-etioplast transition and at the onset of Glc limitation and loss of greening capacity (E1 Amrani et al, 1994a). They could be distinguished by their mobility on native PAGE and by their substrate specificity.…”

“…Most studies have dealt with proplastid-chloroplast transition or with etioplast-chloroplast transition at a stage of development where this transition is assumed to be optimal (Dehesh and Apel, 1983). However, it has been shown that the stage of development of etioplasts, which depends on the period of dark growth, affects the efficiency of chloroplast formation (Robertson and Laetsch, 1974;Klein and Mullet, 1986;E1 Amrani et al, 1994aE1 Amrani et al, , 1994b.…”

“…However, the role of these aminopeptidases in relation to sink-source transition was not clear. They may be related to normal plastid development, since a number of proteolytic activities have been associated with plastid biogenesis (see Liu and Jagendorf, 1986), or to prolonged etiolation per se, or to one of its consequences, such as Glc limitation (see E1 Amrani et al, 1994a). A better knowledge of these aminopeptidases is therefore required.…”

“…109, 1995 presented a wide substrate specificity but could be specifically followed by its activity with Ala-NH-Nap, was studied in more detail. It was shown to segregate like carotenoids, which were taken as a marker of plastids (Journet and Douce, 1985), in the course of plastid isolation (E1 Amrani et al, 1994a). Given the qualities of purity and integrity of the etioplast preparations, this Ala-aminopeptidase activity was thus considered to be plastidial.…”

“…Thus, as pointed out by Faure et al (1994), the sink-source transition must be precisely regulated to prevent starvation of the seedling. We have previously described the sequence of metabolic events (E1 Amrani et al, 199410) and the modifications of proplastids and etioplasts in cotyledons (E1 Amrani et al, 1994a) during prolonged dark growth of sugar beet seedlings. Etioplasts, after the proplastid-etioplast transition, underwent a degenerative process characterized by ultrastructural modifications, protein loss, and the decrease of the capacity of carotenoid and Chl accumulation.…”