Strigolactone and Ethylene Inhibitor Suppressing Dark-induced Leaf Senescence in Perennial Ryegrass Involving Transcriptional Downregulation of Chlorophyll Degradation

Abstract

Accelerated or premature leaf senescence induced by dark conditions could be associated with chlorophyll degradation and regulated by hormones. To study the effects of strigolactone (SL) on dark-induced leaf senescence and to examine the interaction effects of SL and ethylene on regulating dark-induced leaf senescence, plants of perennial ryegrass (Lolium perenne) exposed to darkness for 8 days were treated with a synthetic SL analogue (GR24), aminoethoxyvinyl glycine [AVG (an ethylene biosynthesis inhibitor)], or SL and AVG by foliar spray. Chlorophyll content, photochemical efficiency, electrolyte leakage, and ethylene production were measured. Expressions of genes associated with leaf senescence, SL biosynthesis and signaling, ethylene biosynthesis and signaling, and chlorophyll biosynthesis and degradation were determined. Foliar application of GR24 promoted leaf senescence in perennial ryegrass grown in darkness, and the intensity of action increased with the GR24 concentration. SL-accelerated leaf senescence was associated with the downregulation of four chlorophyll biosynthesis-associated genes and upregulation of four chlorophyll degradation-associated genes. AVG had functions counteractive to SL, suppressing dark-induced leaf senescence by downregulating chlorophyll degradation genes and SL synthesis genes. Our results suggested that SL and ethylene interactively regulated leaf senescence, mainly by controlling chlorophyll degradation induced by darkness in perennial ryegrass.