Peterson R B, Havir E A
Department of Biochemistry and Genetics, Connecticut Agricultural Experiment Station, 123 Huntington St., New Haven, CT 06511, USA.
Planta. 2001 Nov;214(1):142-52. doi: 10.1007/s004250100601.
We describe the properties of npq4-9, a new mutant of Arabidopsis thaliana (L.) Heynh. with reduced nonphotochemical quenching (NPQ) capacity that possesses a single amino acid substitution in the PsbS gene encoding PSII-S, a ubiquitous pigment-binding protein associated with photosystem II (PSII) of higher plants. Growth, photosynthetic pigment contents, and levels of the major PSII antenna proteins were not affected by npq4-9. Although the extent of de-epoxidatin of violaxanthin to antheraxanthin plus zeaxanthin for leaves displaying the mutant phenotype equaled or exceeded that observed for the wild type, the relative effectiveness of de-epoxidized xanthophylls in promoting NPQ was consistently lower for the mutant. Energy partitioning in PSII was analyzed in terms of the competition for singlet chlorophyll a among the processes of fluorescence, thermal dissipation, and photochemistry. The key processes of NPQ and photochemistry in open PSII centers are represented by the relative in vivo rate constants kN and kP0, respectively. The magnitude of kP0 in normal leaves declined only slightly with increasing kN, consistent with localization of NPQ primarily in the antenna complex. Conversely, a highly significant linear decline in kP0 with increasing kN was observed for the mutant, consistent with a role for the PSII reaction center in the NPQ mechanism. Although the PSII absorption cross-section for white light was not significantly different relative to that of the wild type, PSII quantum yield was significantly lower in the mutant. The resulting lower capacity for linear electron transport in the mutant primarily affected reduction of terminal acceptors other than CO2. Parallel measurements of fluorescence and in vivo absorbance at 820 nm indicated a consistently higher steady-state level of reduction of PSII acceptors and accumulation of P700+ for the mutant. This suggests that inter-photosystem electron transport in the mutant is restricted either by a higher transthylakoid delta pH or by diminished accessibility to reduced plastoquinone.
我们描述了拟南芥（Arabidopsis thaliana (L.) Heynh.）新突变体npq4 - 9的特性，该突变体的非光化学猝灭（NPQ）能力降低，其编码PSII - S的PsbS基因中有一个氨基酸替换，PSII - S是一种与高等植物光系统II（PSII）相关的普遍存在的色素结合蛋白。npq4 - 9对生长、光合色素含量和主要PSII天线蛋白水平没有影响。尽管表现出突变表型的叶片中紫黄质脱环氧化为花药黄质加玉米黄质的程度等于或超过野生型，但突变体中脱环氧化叶黄素促进NPQ的相对有效性始终较低。根据荧光、热耗散和光化学过程中单线态叶绿素a的竞争情况分析了PSII中的能量分配。开放PSII中心中NPQ和光化学的关键过程分别由相对体内速率常数kN和kP0表示。正常叶片中kP0的大小仅随kN增加略有下降，这与NPQ主要定位于天线复合体一致。相反，在突变体中观察到kP0随kN增加呈高度显著的线性下降，这与PSII反应中心在NPQ机制中的作用一致。尽管突变体中PSII对白光的吸收截面与野生型相比没有显著差异，但突变体中的PSII量子产率显著较低。突变体中线性电子传递能力降低主要影响了除CO2以外的末端受体的还原。荧光和820 nm处体内吸光度的平行测量表明，突变体中PSII受体的还原稳态水平和P700 + 的积累始终较高。这表明突变体中的光系统间电子传递要么受到较高的类囊体跨膜ΔpH的限制，要么受到还原型质体醌可及性降低的限制。
