Exogenous dopamine delays the senescence of detached Malus hupehensis leaves by reducing phytohormone signalling and sugar degradation

Leaf senescence is the ultimate stage in leaf development, accompanied by the degradation and redistribution of nutrients and biological macromolecules. Dopamine (DA), a type of catecholamine, plays a role in responding to various plant stresses through its strong antioxidant capacity. However, the relationship between DA and leaf senescence is poorly understood. Thus, leaves isolated from Malus hupehensis were treated with DA, and a dark -induced senescence experiment was conducted. We first found that 100 mu mol L-1 DA was the optimal treatment for delaying leaf senescence. The leaves treated with 100 mu mol L-1 DA showed higher chlorophyll content and Fv/Fm, and lower relative electrolyte leakage and malondialdehyde content during dark-induced senescence. DA was able to markedly decrease the expression of senescence associated genes (MdSAG12, MdSAG13, and MdSAG29) and a chlorophyll degradation gene (MdPAO). Compared with untreated leaves, the activity of antioxidant enzymes of leaves under DA treatment was significantly higher, and the level of reactive oxygen species (ROS) was significantly lower. Moreover, DA significantly reduced the content of phytohormones (1-aminocyclopropane-1-carboxylate acid, abscisic acid, salicylic acid, and jasmonic acid) that accelerate senes-cence during dark treatment and changed the expression of genes involved in phytohormone pathways to inhibit the transmission of signals. In addition, DA treatment significantly reduced the expression of genes related to the degradation of soluble sugar (fructose, glucose, sucrose, and sorbitol), thus significantly increasing the soluble sugar content relative to untreated leaves. Overall, our findings revealed that exogenous dopamine could decrease the expression of SAGs, improve the activity of antioxidant enzymes, reduce ROS levels, and the content of phytohormones that accelerate senescence and their signalling pathways, and decrease the degradation rate of soluble sugar to delay the senescence of apple leaves.

Automated summary

Through experiments on Malus hupehensis leaves, it was found that exogenous dopamine can delay leaf senescence by increasing chlorophyll content and photosynthetic efficiency, reducing electrolyte leakage and malondialdehyde content, suppressing the expression of senescence-related genes and chlorophyll degradation genes, enhancing antioxidant enzyme activity, reducing reactive oxygen species levels, decreasing the content of senescence-promoting phytohormones and their signaling pathways, and inhibiting the degradation of soluble sugars.