Heckathorn Scott A, Ryan Samantha L, Baylis Joanne A, Wang Dongfang, Hamilton Iii E William, Cundiff Lee, Luthe Dawn S
Department of Biology, Syracuse University, Syracuse, NY 13244, USA.Corresponding author; email:
Department of Biology, College of Charleston, Charleston, SC 29424, USA.
Funct Plant Biol. 2002 Aug;29(8):935-946. doi: 10.1071/PP01191.
Previous in vitro experiments indicated that chloroplast small heat-shock proteins (sHsp) could associate with thylakoids and protect PSII during heat and other stresses, possibly by stabilizing the O2-evolving complex (OEC). However, in vivo evidence of sHsp protection of PSII is equivocal at present. Using previously characterized selection genotypes of Agrostis stolonifera Huds. that differ in thermotolerance and production of chloroplast sHsps, we show that both genotypes contain thylakoid-associating sHsps, but the heat-tolerant genotype, which produces an additional sHsp isoform not made by the sensitive genotype, produces a greater quantity of chloroplast and thylakoid sHsp. Following a pre-heat stress to induce sHsps, in vivo PSII function decreased less at high temperatures in the tolerant genotype. Differences in PSII thermotolerance in vivo were associated with increased thermotolerance of the OEC proteins and O2-evolving function of PSII, and not with other PSII proteins or functions examined. In vivo cross-linking experiments indicated that a greater amount of sHsp associated with PSII proteins during heat stress in the tolerant genotype. PSII was the most thermosensitive component of photosynthetic electron transport, and no differences between genotypes in the thermotolerance of other electron transport components were observed. These results indicate that in vivo chloroplast sHsps can protect O2 evolution and the OEC proteins of PSII during heat stress.
先前的体外实验表明，叶绿体小热激蛋白（sHsp）可与类囊体结合，并在高温及其他胁迫条件下保护光系统II（PSII），可能是通过稳定放氧复合体（OEC）来实现的。然而，目前关于sHsp在体内对PSII保护作用的证据并不明确。利用先前已鉴定的匍匐翦股颖不同耐热性和叶绿体sHsp产生量的选择基因型，我们发现两种基因型均含有与类囊体结合的sHsp，但耐热基因型除了产生敏感基因型所没有的一种额外sHsp异构体之外，还产生了更多量的叶绿体和类囊体sHsp。在进行预热胁迫以诱导sHsp产生后，耐热基因型在高温下体内PSII功能的下降幅度较小。体内PSII耐热性的差异与OEC蛋白耐热性的提高以及PSII的放氧功能有关，而与所检测的其他PSII蛋白或功能无关。体内交联实验表明，在耐热基因型的热胁迫过程中，有更多量的sHsp与PSII蛋白结合。PSII是光合电子传递中对热最敏感的组分，未观察到不同基因型在其他电子传递组分耐热性上的差异。这些结果表明，体内叶绿体sHsp在热胁迫期间可保护PSII的放氧过程及OEC蛋白。
