SummaryPhylloquinone, a substituted 1,4‐naphthoquinone with an 18‐carbon‐saturated phytyl tail, functions as a bound one‐electron carrier cofactor at the A1 site of photosystem I (PSI). A Feldmann tag line mutant, no. 2755 (designated as abc4 hereafter), showed pale‐green young leaves and white old leaves. The mutated nuclear gene encoded 1,4‐dihydroxy‐2‐naphtoic acid phytyltransferase, an enzyme of phylloquinone biosynthesis, and high‐performance liquid chromatography analysis revealed that the abc4 mutant contained no phylloquinone, and only about 3% plastoquinone. Photooxidation of P700 of PSI in the abc4 mutant was not observed, and reduced‐versus‐oxidized difference spectroscopy indicated that the abc4 mutant had no P700. The maximum quantum yield of photosystem II (PSII) in the abc4 mutant was much decreased, and the electron transfer from PSII to PSI in the abc4 mutant did not occur. For the pale‐green leaves of the abc4 mutant plant, the ultrastructure of the chloroplasts was almost the same as that of the wild‐type plant. However, the chloroplasts in the albino leaves of the mutant were smaller and had a lot of grana thylakoids and few stroma thylakoids. The amounts of PSI and PSII core subunits in the abc4 mutant were significantly decreased compared with those in the wild type. These results suggested that a deficiency of phylloquinone in PSI caused the abolishment of PSI and a partial defect of PSII due to a significant decrease of plastoquinone, but did not influence the ultrastructure of the chloroplasts in young leaves.