The property of progesterone to mitigate cold stress in maize is linked to a modulation of the mitochondrial respiratory pathway

Progesterone is associated with growth and development in plants as well as tolerance against environmental stress. However, the molecular mechanisms responsible for the effects of progesterone are not completely understood. In this study, the effects of progesterone on the mitochondrial respiratory pathway (MRP) were investigated in maize seedlings treated with cold stress. Cold stress significantly activated cytochrome pathway (CP) by 61 % and especially alternative respiratory pathway (AP) by 239 % compared with the control, ultimately resulting in an increase by 72 % in the total cellular respiratory rate (TCR). Progesterone alone enhanced CP by 15 %, AP by 59 % and TCR by 15 % compared with control seedlings, whereas the highest values for these parameters were recorded in seedlings subjected to cold plus progesterone. Alternative oxidase (AOX) is the terminal oxidase in the AP. An increase in the AOX gene transcript level was observed in response to cold stress and progesterone, mirroring the increase in AP rate. Meanwhile, AOX protein accumulation exhibited a positive correlation with the AOX gene transcript level. In accordance with the high AP activity, progesterone-treated seedlings exhibited low levels of reactive oxygen species (ROS), including superoxide and hydrogen peroxide, and oxidative damage parameters, including electrolyte leakage and lipid peroxidation levels. Our data demonstrate that the mitigating role of progesterone against the effects of cold stress seems to be linked to the modulation of MRP.