Reference "Two routes of chlorophyllide synthesis that are differentially regulated by light in barley (Hordeum vulgare L.)"

Reference ID

8718

Title

Two routes of chlorophyllide synthesis that are differentially regulated by light in barley (Hordeum vulgare L.)

Source

Proceedings of the National Academy of Sciences of the United States of America, 1995, vol. 92, pp. 3254-3258

Authors (5)

Holtorf-H	Reinbothe-S
Reinbothe-C	Bereza-B
Apel-K

Abstract

NADPH-protochlorophyllide oxidoreductase (POR; EC 1.6.99.1) catalyzes the only
known light-dependent step in chlorophyll synthesis of higher plants, the
reduction of protochlorophyllide (Pchlide) to chlorophyllide. In barley, two
distinct immunoreactive POR proteins were identified. In contrast to the light-
sensitive POR enzyme studied thus far (POR-A), levels of the second POR protein
remained constant in seedlings during the transition from dark growth to the
light and in green plants. The existence of a second POR-related protein was
verified by isolating and sequencing cDNAs that encode a second POR polypeptide
(POR-B) with an amino acid sequence identity of 75% to the POR-A. In the
presence of NADPH and Pchlide, the in vitro-synthesized POR-A and POR-B proteins
could be reconstituted to ternary enzymatically active complexes that reduced
Pchlide to chlorophyllide only after illumination. Even though the in vitro
activities of the two enzymes were similar, the expression of their genes during
the light-induced transformation of etiolated to green seedlings was distinct.
While the POR-A mRNA rapidly declined during illumination of dark-grown
seedlings and soon disappeared, POR-B mRNA remained at an approximately constant
level in dark-grown and green seedlings. Thus these results suggest that
chlorophyll synthesis is controlled by two light-dependent POR enzymes, one that
is active only transiently in etiolated seedlings at the beginning of
illumination and the other that also operates in green plants.