2 NADPH-PROTOCHLOROPHYLLIDE OXIDOREDUCTASES IN BARLEY - EVIDENCE FOR THE SELECTIVE DISAPPEARANCE OF PORA DURING THE LIGHT-INDUCED GREENING OF ETIOLATED SEEDLINGS
S. Reinbothe et al., 2 NADPH-PROTOCHLOROPHYLLIDE OXIDOREDUCTASES IN BARLEY - EVIDENCE FOR THE SELECTIVE DISAPPEARANCE OF PORA DURING THE LIGHT-INDUCED GREENING OF ETIOLATED SEEDLINGS, The Plant cell, 7(11), 1995, pp. 1933-1940
Chlorophyll synthesis in barley is controlled by two different light-d
ependent NADPH:protochlorophylide oxidoreductases, termed PORA and POR
E, PORA is present abundantly in etioplasts but selectively disappears
soon after the beginning of illumination, This negative light effect
is mediated simultaneously at three different levels, First, the conce
ntration of porA mRNA declines drastically during illumination of dark
-grown seedlings, Second, the plastids' ability to import the precurso
r of PORA (pPORA) is reduced during the transition from etioplasts to
chloroplasts. This effect is due to a rapid decline in the plastidic l
evel of protochlorophyllide (Pchlide), which is required for the trans
location of the pPORA, Third, PORA becomes selectively destabilized in
illuminated seedlings, When illuminated, PORA-Pchlide-NADPH complexes
formed in the dark photoreduce their Pchlide to Chlide and become sim
ultaneously susceptible to attack by plastid proteases, The PORA-degra
ding protease activity is not detectable in etioplasts but is induced
during illumination, In contrast to PORA, the second Pchlide-reducing
enzyme, PORE, remains operative in both illuminated and green plants,
Its translocation into plastids does not depend on its substrate, Pchl
ide.