Department of Plant Biology, Rutgers University, New Brunswick, New Jersey, USA.
Physiol Plant. 2022 Sep;174(5):e13766. doi: 10.1111/ppl.13766.
Heat stress is a major abiotic stress for temperate plant species with characteristic symptoms of premature leaf senescence. The objectives of this study were to evaluate the physiological effects of cytokinins (CK) and an ethylene inhibitor, aminoethoxyvinylglycine (AVG) on heat-induced leaf senescence in the temperate perennial grass species, perennial ryegrass (Lolium perenne), and to investigate whether WRKY transcription factors (TFs) could be associated with CK- or ethylene-mediated regulation of heat-induced leaf senescence by exogenously applying CK or AVG to perennial ryegrass. Perennial ryegrass plants foliar-sprayed with 6-benzylaminopurine (6-BA), and AVG exhibited prolonged stay-green phenotypes and a lesser degree of leaf senescence under heat stress (35/30°C), as shown by a decline in electrolyte leakage, malondialdehyde content, hydrogen peroxide, and superoxide content, and increased chlorophyll (Chl) content along with reduced activities of Chl-degrading enzymes (pheophytinase and chlorophyllase) and increased activity of Chl-synthesizing enzyme (porphobilinogen deaminase) due to 6-BA or AVG application. The suppression of heat-induced leaf senescence by 6-BA or AVG treatment corresponded with the upregulation of LpWRKY69 and LpWRKY70. The LpWRKY69 and LpWRKY70 promoters were predicted to share conserved cis-elements potentially recognized by TFs in the CK or ethylene pathways. These results indicate that LpWRKY69 and LpWRKY70 may negatively regulate heat-induced leaf senescence through CK or ethylene pathways, conferring heat tolerance in perennial ryegrass.
热应激是温带植物物种的主要非生物胁迫因素，其特征症状为过早的叶片衰老。本研究的目的是评估细胞分裂素（CK）和乙烯抑制剂氨基乙氧基乙烯基甘氨酸（AVG）对温带多年生草种多年生黑麦草（Lolium perenne）热诱导叶片衰老的生理影响，并研究 WRKY 转录因子（TFs）是否与 CK 或乙烯介导的热诱导叶片衰老调控有关，通过向多年生黑麦草外施 CK 或 AVG。用 6-苄基氨基嘌呤（6-BA）和 AVG 叶面喷雾的多年生黑麦草植株在热胁迫（35/30°C）下表现出延长的绿叶保持表型和较小程度的叶片衰老，表现为电解质渗漏、丙二醛含量、过氧化氢和超氧自由基含量下降，叶绿素（Chl）含量增加，同时 Chl 降解酶（脱镁叶绿素酶和叶绿素酶）活性降低，Chl 合成酶（卟啉原脱氨酶）活性升高，这归因于 6-BA 或 AVG 的应用。6-BA 或 AVG 处理对热诱导叶片衰老的抑制作用与 LpWRKY69 和 LpWRKY70 的上调相对应。LpWRKY69 和 LpWRKY70 启动子被预测具有保守的顺式元件，这些元件可能被 CK 或乙烯途径中的 TFs 识别。这些结果表明，LpWRKY69 和 LpWRKY70 可能通过 CK 或乙烯途径负调控热诱导叶片衰老，从而赋予多年生黑麦草耐热性。
