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Chlorophyll Biosynthesis During Plant Greening
Benoît Schoefs
University of South Bohemia, Budejovice, Czech Republic*
265I. INTRODUCTION
The development and the maintenance of life on earth are predominantly dependent on photosynthesis, which
transforms the radiant energy, coming from the sun, into the chemical energy stored in various molecules.
In photosynthetic eukaryotic organisms, this process takes place in the chloroplast. At the heart of
the photosynthetic process are chlorophyll (Chl) and carotenoid (Car) pigments, which are principally, if
not completely, associated with proteins (reviewed in Ref. 1).
In angiosperms, chloroplast formation is a light-dependent process, which starts from the proplastid
stage. This stage is characterized by the presence of few internal membranes and of starch. In further de-
velopment of the proplastid, two pathways are possible: in the light, proplastids directly differentiate into
chloroplasts, whereas in the dark, they develop into etioplasts [2,3]. The light dependence of the chloro-
plast formation lies in the absolute requirement of light for enzymatic transformation of protochloro-
phyllidea(Pchlide) to chlorophyllide a(Chlide)†. In contrast, green algae and most of the other eukary-
otic groups of land plants are able to form chloroplasts in the absence of light (reviewed in Ref. 3). This
ability lies in the additional presence of a light-independent enzyme that transforms Pchlide to Chlide (re-
viewed in Refs. 7 and 8).
In the first part of this chapter, the chlorophyll biosynthetic pathway is briefly described. Then the
transformation of Pchlide under the impact of the first photons in angiosperms, cultivated in conditions
similar to those found in the natural environment and in fields, is discussed. The third part concerns how
Chl is synthesized during greening and in green plants. The fourth part of this chapter describes light-de-
pendent and light-independent Chl formation in gymnosperms, and the last part gives information about
the regulation of Chl synthesis.
II. OUTLINE OF THE CHLOROPHYLL BIOSYNTHETIC PATHWAY
Chl biosynthesis starts with the formation of -aminolevulinic acid (-ALA), the universal precursor of
tetrapyrroles. All photosynthetic organisms, except those of the -proteobacterial group, synthesize -
*Current affiliation:Université Joseph Fourier, Grenoble, France.
†Dark-grown tissues can contain some traces of chl. It seems that they are deposited in the embryo during its formation rather
than synthesized in vivo during dark growth [4]. For a full discussion of the possibility of Chl synthesis in the dark in an-
giosperms tissues, see Adamson et al. [5]. There is no protochlorophyll b in nonilluminated tissues [6].