Strigolactone enhance thermotolerance in carnation seedlings

High temperatures significantly hinder the cost-effective cultivation of carnation (Dianthus caryophyllus) by negatively affecting its growth and flowering quality. Strigolactones (SLs), plant hormones derived from carotenoids, are vital for plant development and responses to abiotic stresses. In this study, 15 μM was identified as the optimal concentration of the SL analog GR24 to alleviate heat damage (40/35 °C) in carnation seedlings, based on a thorough evaluation of morphological and physiological indicators after pretreatment with varying GR24 concentrations (5, 10, 15, 20 μM). Using 15 μM GR24 and the SL biosynthesis inhibitor TIS108, changes in phenotype, physiological traits, photosynthetic performance, root architecture, stomatal morphology, and expression of stress-related genes under heat stress (HT) were then examined. After 12 d of HT, GR24 pre-spraying significantly mitigated HT-induced reductions in plant height and leaf pair counts by 3.01% and 7.14%, respectively, while decreasing relative electrolyte leakage (REL), and malondialdehyde (MDA) content by 17.06% and 36.34%, compared to HT. Additionally, GR24 helped preserve photosynthetic efficiency by mitigating HT-related declines in parameters such as Fv/Fm and improving stomatal structure. It also supported root growth, increasing root length by 57.28% and root volume density by 30.74% relative to HT. Furthermore, qRT-PCR analysis revealed that GR24 modulated gene expression, promoting transcripts of DcbHLH062, DcHSP70s, DcMAX1, DcD14, DcMAX2, and DcSMXL8 under HT, while alleviating the suppression of DcGR and DcPSAK expression. Treatment with TIS108 provided reverse validation. These findings offer valuable insights into applying GR24 to enable energy-saving carnation cultivation under heat-stress conditions.