Cold Shock for Cold Tolerance: Phytohormone Dynamics in Sorghum Provides Insights

The loss of yield due to cold stress during the early reproductive phase poses challenges to the expansion of sorghum cultivation into temperate regions. A better understanding of the physiological mechanisms is crucial for rapid progress in breeding cold-tolerant sorghum varieties. To identify the floral phytohormones responsible for reproductive cold tolerance, a cold-tolerant and a cold-sensitive genotype were subjected to cold stress at various developmental stages during the early reproductive phase. In addition to abscisic acid and its derivatives, including abscisic acid glucose ester, dihydrophaseic acid, and phaseic acid, various gibberellins as well as jasmonic acid and its bioactive form jasmonic acid isoleucine were examined. We found that cold-tolerant sorghum is capable of downregulating abscisic acid concentration under cold stress. While existing literature primarily attributes increased abscisic acid concentration, combined with an insufficient pool of bioactive gibberellins, in sensitive plants as a result of abnormal pollen development, this study shows that this is not the case in sorghum. Additionally, an antagonistic interaction between gibberellins and jasmonic acid was observed regardless of genotype and environmental conditions. These findings contribute to a better understanding of the physiological mechanisms behind cold tolerance in sorghum and could provide important insights for future breeding efforts aiming to accelerate the expansion of cold-tolerant sorghum varieties into temperate climates.