Nitric Oxide Improved Growth and Yield in Soybean ( Glycine max ) by Mediating Physiological, Anatomical, and Transcriptional Modifications

This study investigated the physiological, molecular, and anatomical responses of soybean to the long-time utilization of nitric oxide (NO; 0 and 25 µM) under two application methods (foliar application or supplementation of nutrient solution). The NO application increased shoot biomass (mean = 49.7%), root dry mass (mean = 38.9%), number of leaves (mean = 28.5%), leaf fresh mass (mean = 29.2%), and number of pods (mean = 59.5%). NO enhanced K (14.5%), Fe (25.2%), and Zn (27%) in both leaves and seeds. Either foliar or soil application of NO upregulated bHLH (mean = 3.3-fold) and EREB (mean = sevenfold) genes at the transcription level. The NO treatments induced expression of HSF34 , R2R3MYB , WRKY1 , and MAPK1 genes by averages of 14, 8.2, 4.5, and 5.6 folds, respectively. Similarly, the histone deacetylase (HDA) gene was upregulated in response to either foliar (3.2-fold) or soil supplementation (2.6-fold) of NO, indicating that NO can lead to epigenetic modification. The NO treatments also led to the upregulation in the CAT1 gene by an average of 9.2-fold. The applied supplement enhanced photosynthetic pigments, including the concentrations of Chla, Chlb, and carotenoids. Significant upward trends in the activities of nitrate reductase (37%), catalase (39%), peroxidase (52%), and phenylalanine ammonia-lyase (28.3%) enzymes were found in response to NO. The NO treatments increased soluble phenols and proline concentration in leaves by 52.5% and 32%, respectively. NO utilization also reinforced the differentiation of metaxylem tissue, a clear illustration of how NO can improve nutritional status. Overall, this study makes a significant contribution to the NO-responsive genes, especially transcription factors.