Jespersen David, Zhang Jing, Huang Bingru
Dep. Of Plant Biology and Pathology, Rutgers University, New Brunswick, NJ 08901, USA.
College of Agro-grassland Science, Nanjing Agricultural University, Nanjing 210095, PR China.
Plant Sci. 2016 Aug;249:1-12. doi: 10.1016/j.plantsci.2016.04.016. Epub 2016 May 3.
Heat stress-induced leaf senescence is characterized by the loss of chlorophyll from leaf tissues. The objectives of this study were to examine genetic variations in the level of heat-induced leaf senescence in hybrids of colonial (Agrostis capillaris)×creeping bentgrass (Agrostis stolonifera) contrasting in heat tolerance, and determine whether loss of leaf chlorophyll during heat-induced leaf senescence was due to suppressed chlorophyll synthesis and/or accelerated chlorophyll degradation in the cool-season perennial grass species. Plants of two hybrid backcross genotypes ('ColxCB169' and 'ColxCB190') were exposed to heat stress (38/33°C, day/night) for 28 d in growth chambers. The analysis of turf quality, membrane stability, photochemical efficiency, and chlorophyll content demonstrated significant variations in the level of leaf senescence induced by heat stress between the two genotypes, with ColXCB169 exhibiting a lesser degree of decline in chlorophyll content, photochemical efficiency and membrane stability than ColXCB190. The assays of enzymatic activity or gene expression of several major chlorophyll-synthesizing (porphobilinogen deaminase, Mg-chelatase, protochlorophyllide-reductase) and chlorophyll-degrading enzymes (chlorophyllase, pheophytinase, and chlorophyll-degrading peroxidase) indicated heat-induced decline in leaf chlorophyll content was mainly due to accelerated chlorophyll degradation, as manifested by increased gene expression levels of chlorophyllase and pheophytinase, and the activity of pheophytinase (PPH), while chlorophyll-synthesizing genes and enzymatic activities were not differentially altered by heat stress in the two genotypes. The analysis of heat-induced leaf senescence of pph mutants of Arabidopsis further confirmed that PPH could be one enzymes that plays key roles in regulating heat-accelerated chlorophyll degradation. Further research on enzymes responsible in part for the loss of chlorophyll during heat-induced senescence could aid in the development of genotypes with stay-green traits either through marker assisted selection or transgenic approaches.
热胁迫诱导的叶片衰老的特征是叶片组织中叶绿素的丧失。本研究的目的是检测耐热性不同的匍匐翦股颖（Agrostis capillaris）×匍匐翦股颖（Agrostis stolonifera）杂交种中热诱导叶片衰老水平的遗传变异，并确定在冷季多年生禾本科植物中，热胁迫诱导叶片衰老过程中叶绿素的丧失是否是由于叶绿素合成受抑制和/或叶绿素降解加速所致。两种杂交回交基因型（‘ColxCB169’和‘ColxCB190’）的植株在生长室中经受28天的热胁迫（38/33°C，日/夜）。对草坪质量、膜稳定性、光化学效率和叶绿素含量的分析表明，两种基因型之间热胁迫诱导的叶片衰老水平存在显著差异，与ColXCB190相比，ColXCB169在叶绿素含量、光化学效率和膜稳定性方面的下降程度较小。对几种主要叶绿素合成酶（胆色素原脱氨酶、镁螯合酶、原叶绿素酸酯还原酶）和叶绿素降解酶（叶绿素酶、脱镁叶绿素酶和叶绿素降解过氧化物酶）的酶活性或基因表达分析表明，热胁迫诱导的叶片叶绿素含量下降主要是由于叶绿素降解加速，表现为叶绿素酶和脱镁叶绿素酶基因表达水平的增加以及脱镁叶绿素酶（PPH）的活性增加，而两种基因型中叶绿素合成基因和酶活性并未因热胁迫而发生差异变化。对拟南芥pph突变体热诱导叶片衰老的分析进一步证实，PPH可能是在调节热加速叶绿素降解中起关键作用的一种酶。进一步研究在热胁迫诱导衰老过程中部分导致叶绿素丧失的酶，可能有助于通过标记辅助选择或转基因方法培育具有持绿性状的基因型。
