CHLOROPHYLL SYNTHESIS IN A DEETIOLATED-(DET340) MUTANT OF ARABIDOPSISWITHOUT NADPH-PROTOCHLOROPHYLLIDE (PCHLIDE) OXIDOREDUCTASE (POR)-A AND PHOTOACTIVE PCHLIDE-F655
N. Lebedev et al., CHLOROPHYLL SYNTHESIS IN A DEETIOLATED-(DET340) MUTANT OF ARABIDOPSISWITHOUT NADPH-PROTOCHLOROPHYLLIDE (PCHLIDE) OXIDOREDUCTASE (POR)-A AND PHOTOACTIVE PCHLIDE-F655, The Plant cell, 7(12), 1995, pp. 2081-2090
Chlorophyll (Chl) synthesis in Arabidopsis is controlled by two light-
dependent NADPH-protochlorophyllide (PChlide) oxidoreductases (PORs),
one (FOR A) that is active transiently in etiolated seedlings at the b
eginning of illumination and another (FOR B) that also operates in gre
en plants, The function of these two enzymes during the light-induced
greening of dark-grown seedlings has been studied in the wild type and
a deetiolated (det340) mutant of Arabidopsis. One of the consequences
of the def mutation is that FOR A is constitutively down-regulated, a
nd therefore, synthesis of the FOR A enzyme is shut off. When grown in
the dark, the det340 mutant lacks FOR A and the photoactive PChlide-F
655 species but maintains the second PChlide reductase, FOR B, Previou
sly, photoactive PChlide-F655 has often been considered to be the only
PChlide form that leads to Chi formation. Despite its deficiency in F
OR A and photoactive PChlide-F655, the det340 mutant is able to green
when placed in the light. Chi accumulation, however, proceeds abnormal
ly, At the beginning of illumination, seedlings of det340 mutants are
extremely susceptible to photooxidative damage and accumulate Chi only
at extremely low light intensities, They form core complexes of photo
systems I and II but are almost completely devoid of light-harvesting
structures. The results of this study demonstrate that in addition to
the route of Chi synthesis that has been studied extensively in illumi
nated dark-grown wild-type plants, a second branch of Chi synthesis ex
ists that is driven by POR B and does not require POR A.