Drought priming promotes phloem loading-driven sucrose export to alleviate the photosynthetic limitations under low...

Reducing nitrogen (N) application can improve nitrogen use efficiency (NUE) and mitigate environmental pollution. However, this reduction often adversely affects photosynthesis and leads to inhibition of wheat growth. Thus, exploring effective agronomic measures to improve wheat's tolerance to low N is essential for balancing the conflict between N reduction and wheat growth. Drought priming has been proven to enhance plant stress tolerance, but its role and mechanisms in improving photosynthetic capacity under low N stress remain unclear. The effects of drought priming on wheat growth and photosynthesis were investigated under low N stress using hydroponic experiments with two wheat varieties, YM158 (low N-tolerant) and YM25 (low N-sensitive). The results showed that low N stress significantly inhibited biomass accumulation, whereas drought priming effectively alleviated this growth inhibition. Drought priming significantly increased the net photosynthetic rate (P _n) of both cultivars compared to non-primed treatments under low N stress, which was primarily associated with enhanced Rubisco maximum carboxylation rate (Vcmax) and activities of Rubisco and Rubisco activase (RCA). Furthermore, drought priming promoted triose phosphate (TP) utilization and upregulated the expression of sugar transporter genes, which reduced sucrose accumulation in leaves and consequently alleviated its feedback inhibition on photosynthesis. In summary, drought priming enhances phloem loading-driven sucrose transport, reduces leaf sucrose accumulation, and improves Rubisco activation, collectively alleviating photosynthetic feedback inhibition and sustaining stronger photosynthetic capacity under low N stress.