Exogenous Methylglyoxal Ameliorates Source Strength and Retrieves Yield Loss Under Drought Stress During Grain Filling in Maize

In maize ( Zea mays L.) production, grain-filling stage is a pivotal phase that drought occurring would irreversibly cause leaf senescence and yield loss. Meanwhile, drought induces the disequilibrium of carbohydrates that inevitably produces the toxic substance methylglyoxal (MG) that plays dual roles including cytotoxic metabolite or signaling molecule in plants. However, how exogenous MG influences maize yield formation in response to drought during grain filling remains unknown. In this study, maize plants were exposed to moderate and severe drought conditions from 15 to 28 days after pollination with foliar spraying of MG (0, 15, 25, and 35 mM). Notably, MG application significantly increased kernel number and retrieved yield loss by 14–48% under drought, demonstrating an increased resistance of the plants. Interestingly, high (25–35 mM) and low concentrations (15–25 mM) of MG application under moderate and severe drought performed the highest yield output, respectively. To investigate the mechanisms by which MG enhanced drought resistance, we confirmed that MG application postponed leaf senescence under both drought conditions and significantly improved photosynthesis under severe drought during filling stage. Specifically, MG application escalated the levels of soluble sugar and sucrose while suppressing endogenous MG accumulation by activating glyoxalase system in leaf during the early phase of drought stress and well-watered condition. Collectively, these results demonstrate that exogenous MG application enhances drought tolerance during maize grain filling, possibly through regulation on the homeostasis of endogenous MG and sugars. These findings provide a new approach to secure yield against drought stress in maize production.