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. 2012 Oct 29;3:236. doi: 10.3389/fpls.2012.00236

Figure 1.

Figure 1

Metabolic pathway of tetrapyrrole biosynthesis in plants. The color code comprise the five sections of the tetrapyrrole biosynthetic pathway: ALA synthesis purple, porphyrin synthesis blue, the Fe branch red, Mg branch green, siroheme synthesis yellow. The universal precursor of all tetrapyrroles 5-aminolevulinic acid (ALA) is synthesized from glutamate via a three-step reaction. ALA is further metabolized to protoporphyrin IX before the pathway branches into heme (and phytochromobilin) and chlorophyll biosynthesis. The ratio of chlorophyll a and b is balanced in the chlorophyll cycle. The end products of the pathway are underlined. Mutants of tetrapyrrole biosynthetic enzymes that play a role in plastid-to-nucleus signaling and inhibitors of certain enzymatic steps are shown. ALAD, ALA dehydratase; CAO, Chl a oxygenase; CBR, chlorophyll b reductase; ChlS, chlorophyll synthase; CPO, coproporphyrinogen III oxidase; DVR, divinyl protochlorophyllide reductase; FeCh, Fe chelatase; FLU, flourescent; GluRS, glutamyl-tRNA synthetase; GluTR, glutamyl-tRNA reductase; GluTRBP, GluTR binding protein; GSAT, glutamate-1-semialdehyde aminotransferase; HBS, hydroxymethylbilane synthase; HCAR, 7-hydroxymethyl chlorophyll a reductase; HO, heme oxygenase; MgCh, Mg chelatase; MTF, Mg protoporphyrin IX methyltransferase; PBS, phytochromobilin synthase; POR, light dependent NADPH-protochlorophyllide oxidoreductase; PPOX, protoporphyrinogen IX oxidase; UROD, uroporphyrinogen III decarboxylase; UROM, uroporphyrinogen III methyltransferase; UROS, uroporphyrinogen III synthase.