Lead (Pb) is one of the most abundant toxic heavy metals, which have a serious impact on the growth and yield of crop plants. Nitric oxide (NO) is a natural signaling molecule that regulates the growth and productivity of plants. Here, exogenous NO was found to enhance Pb tolerance in watermelon, which resulted in more Pb restriction in roots and less up-translocated Pb to aerial parts. Pb stress, however, led to an increase in shoot dry weight, root biomass, root relative water content, leaf malondialdehyde (MDA) content, and the total soluble protein content in leaves and roots. By contrast, shoot height and fresh weight, leaf biomass, and root MDA content were decreased under Pb stress. NO treatments alleviated Pb toxicity by decreasing Pb translocation, enhancing root growth (elongation and biomass), inducing antioxidant enzymes activities, and reducing root MDA contents in watermelon seedlings. In conclusion, our results provide useful insights into the mechanism of Pb tolerance in cucurbit crops and information for the cultivation management of watermelon in the presence of this heavy metal (Pb).

铅（Pb）是最丰富的有毒重金属之一，对农作物的生长和产量产生严重影响。一氧化氮（NO）是调节植物生长和生产力的天然信号分子。在这里，发现外源NO增强了西瓜对Pb的耐受性，这导致根部更多的Pb限制和较少的Pb向上移位到地上部分。然而，铅胁迫导致茎干重量，根生物量，根相对水含量，叶丙二醛（MDA）含量以及叶和根中总可溶性蛋白质含量增加。相比之下，在铅胁迫下，苗高和鲜重，叶片生物量和根系MDA含量均降低。NO处理可通过减少Pb的转运，增强根的生长（伸长和生物量），诱导抗氧化酶的活性来减轻Pb的毒性，并降低西瓜幼苗的根MDA含量。总之，我们的结果为了解葫芦科作物对铅的耐受性机理提供了有用的见识，并为在这种重金属（Pb）存在下西瓜的栽培管理提供了信息。