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.
摘要 苝酮是一种具有 18 碳饱和苝基尾部的取代 1,4-萘醌,在光合系统 I(PSI)的 A1 位点上起结合单电子载体辅助因子的作用。一个编号为 2755 的费尔德曼标记线突变体(以下称为 abc4)显示出淡绿色的嫩叶和白色的老叶。突变的核基因编码 1,4-二羟基-2-萘乙酸酞基转移酶(一种植物醌生物合成酶),高效液相色谱分析显示,abc4 突变体不含植物醌,只含有约 3% 的质醌。在abc4突变体中没有观察到PSI的P700发生光氧化,还原与氧化差分光谱显示abc4突变体没有P700。在abc4突变体中,光系统II(PSII)的最大量子产率大大降低,并且在abc4突变体中没有发生从PSII到PSI的电子传递。在abc4突变体的淡绿色叶片中,叶绿体的超微结构与野生型植株几乎相同。然而,突变体白化叶片中的叶绿体较小,且颗粒状叶绿体较多,基质状叶绿体较少。与野生型相比,abc4 突变体中 PSI 和 PSII 核心亚基的数量明显减少。这些结果表明,由于质醌的大量减少,PSI中的质醌缺乏导致了PSI的废止和PSII的部分缺陷,但并不影响幼叶叶绿体的超微结构。