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

Abstract

This study investigated the physiological, molecular, and anatomical responses of soybean to the long-time utilization of nitric oxide (NO; 0 and 25\xa0µM) under two application methods (foliar application or supplementation of nutrient solution). The NO application increased shoot biomass (mean\u2009=\u200949.7%), root dry mass (mean\u2009=\u200938.9%), number of leaves (mean\u2009=\u200928.5%), leaf fresh mass (mean\u2009=\u200929.2%), and number of pods (mean\u2009=\u200959.5%). 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\u2009=\u20093.3-fold) and EREB (mean\u2009=\u2009sevenfold) 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.