Starch, a substance stored in seeds, is the main source of energy for germination in sorghum seeds. However, as the seeds age, the catabolism of seed starch is affected, thereby seriously damaging germination ability. In this study, we aimed to understand how exogenous spermidine promoted germination in aged sorghum seed. Our phenotypic analysis indicated that exogenous spermidine not only significantly improved the germination rate, germination potential, germination index, and vigor index of aged seeds, but also increased the root and shoot length after germination. Further, physiological analysis showed that exogenous spermidine increased the content of soluble sugar by upregulating the activity of amylase and sucrose invertase. Exogenous spermidine also improved the activities of key enzymes in glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway of aged sorghum seeds. Interestingly, exogenous spermidine protected the mitochondrial structure of aged seeds, which was consistent with the increase in the respiration rate and ATP content during seed germination. Moreover, qRT-PCR analysis revealed that exogenous spermidine induced the expression of key genes related to starch and sugar metabolism in aged sorghum seeds. In conclusion, our study demonstrated that exogenous spermidine promoted aged sorghum seed germination by regulating starch and sugar metabolism.

The length of sorghum mesocotyl plays a vital role in seed emergence from the soil, which is the foundation of healthy growth. In this study, we aimed to understand how exogenous auxin (IAA) promoted mesocotyl elongation of sorghum and its physiology mechanism. The results presented that exogenous IAA significantly promoted mesocotyl elongation in MS24B (short mesocotyl inbred line) by increasing the cell length, while with extra exogenous NPA (IAA inhibitor) application, the mesocotyl length presented a significant short phenotype. In Z210 (long mesocotyl inbred line), exogenous IAA had a slight effect on mesocotyl length elongation, while the NPA treatment decreased the mesocotyl length considerably. In MS24B, IAA treatment increased the activity of amylase to degrade starch to soluble sugar, and the activity of hexokinase was improved to consume the increased soluble sugar to offer more energy. The energy will help to increase the activity of PM H⁺-ATPase and the expression of expansin-related genes, which ultimately will promote the acidification of the plasma membrane in MS24B for cell elongation. Overall, the exogenous IAA functioned on the activation of energy metabolism, which in turn, inducted the acidification of the plasma membrane for mesocotyl elongation.

Sorghum faces significant production challenges due to drought stress. Melatonin has been demonstrated to play a crucial role in coping with stresses in plants. This study investigated the effect of exogenous melatonin on the sorghum seedling growth, photosynthetic capacity, and antioxidant system under drought stress. The results indicated that drought stress inhibited the growth of sorghum seedlings by a marked reduction in leaf relative water content, along with a significant increase in both malondialdehyde and hydrogen peroxide content. The drought stress also led to a significant diminution in chlorophyll contents, thereby curtailing the capacity for light energy capture. Furthermore, the efficiency of the photosynthetic electron transport chain was adversely impacted. However, the application of exogenous melatonin notably mitigated the adverse effects on sorghum seedlings under the drought stress. Additionally, it stimulated an elevation in the photosynthetic rate and a decrease in non-photochemical quenching. The exogenous melatonin also facilitated the preservation of the chloroplast ultra-structure and boosted the activity of antioxidant enzymes and the content of non-enzymatic antioxidants. Cluster heat maps and principal component analysis further revealed significant correlations among various parameters under different treatment conditions. These results highlight melatonin’s role in improving sorghum’s drought tolerance, which is beneficial for agricultural management.

Seed aging has adverse effects on agricultural production, mainly because seed vigor is inhibited. Spermidine can improve seed vitality and germination ability to a certain extent and is essential for plant growth and plant response to stress. This study explored how spermidine counteracted aging effects on sorghum seed germination through antioxidant metabolism regulation. Aged seeds showed decreased vigor due to heightened reactive oxygen species (ROS) and diminished antioxidants. Applying spermidine notably enhanced aged seeds’ germination and vigor by boosting antioxidant enzyme activity and curbing ROS. Integrated transcriptomic, proteomic, and metabolomic analyses demonstrated that the majority of differentially expressed genes following exogenous spermidine treatment in aged sorghum seeds were significantly enriched in pathways related to glutathione metabolism, phenylpropanoid, and flavonoid biosynthesis, resulting in increased expression of genes encoding peroxidase, chalcone synthase, and glutathione s-transferase. Exogenous spermidine facilitated the synthesis of peroxidases and glutathione transferases. Analysis of flavonoid pathway intermediates showed a notable increase in antioxidant metabolites like isoquercitrin, underscoring their role in oxidative stress resistance. This multi-omics strategy underscores Spd’s role in boosting aged seeds’ antioxidants, highlighting the molecular basis of seed aging and Spd’s rejuvenating impact.

Sorghum (Sorghum bicolor L. Moench), renowned for its resilience in marginal environments, frequently encounters productivity limitations due to insufficient nitrogen (N) availability. This investigation employed transcriptomic and metabolomic approaches to elucidate the mechanisms underlying nitrogen use efficiency (NUE) in two sorghum genotypes, 398B and CS3541, exhibiting contrasting NUE responses to low-N stress. N deficiency significantly diminished plant height, root dry weight, and leaf dry weight in both genotypes, while markedly increasing root length. Notably, 398B demonstrated a pronounced increase in root length and exhibited higher nitrogen uptake efficiency (NUpE) and utilization efficiency (NUtE) compared to CS3541. Transcriptomic analyses revealed that starch and sucrose metabolism, as well as phenylpropanoid biosynthesis pathways, were significantly enriched in both genotypes, indicative of enhanced carbon (C) and N metabolism. Notably, two low-affinity nitrate transporter genes (Sobic.001G302800.v3.2, NRT1/PTR6.3 and Sobic.004G193000.v3.2, NRT1/PTR6.4) were upregulated in 398B roots under N deficiency, suggesting a crucial role in facilitating N uptake. Metabolomic profiling of sorghum leaves under low-N conditions highlighted an accumulation of phenolic acids, flavonoids, flavanols, and saccharides in 398B, suggesting improved N utilization and assimilation. Overall, integrated transcriptome and metabolome analyses identified key genes and metabolites associated with NUE. Our findings provide novel insights into the genetic and molecular basis of NUE in sorghum, particularly emphasizing the role of root structural adaptations and the regulation of specific transporter genes in enhancing NUpE. Additionally, our study underscored the importance of metabolic adjustments in leaves for improving NUtE. These results contribute to the development of sorghum genotypes with enhanced NUE, offering the potential for sustainable agricultural practices in low-N environments.

Sorghum northern anthracnose is a leaf disease affecting sorghum, which results in plant death and substantial yield loss. This study aimed to effectively understand the disease, clarify its biological characteristics, and evaluate the resistance of germplasm resources. A field sample was collected to isolate and purify the pathogen. The pathogen, identified as Kabatiella zeae Narita et Hiratsuka using both morphological and molecular techniques, was further confirmed as the causative agent of northern anthracnose of sorghum following Robert Koch’s principles. The results revealed the optimal culture temperature to be 25 °C, preferred dark culture conditions, and the best growth on potato glucose agar medium with sucrose and L-leucine as the optimal carbon and nitrogen sources, respectively. A total of 138 sorghum germplasm resources were inoculated and evaluated using the isolated pathogen, with 20 lines (14.49%) exhibiting high resistance, 18 lines (13.04%) showing disease resistance, 27 lines (19.57%) demonstrating medium resistance, 37 lines (26.81%) being susceptible, and 36 lines (26.09%) classified as highly susceptible. The indoor fungicide screening was conducted through pathogen medium application, and enilconazole, pyraclostrobin, methylthiophanate, and flusilazole were screened for the best fungicide inhibition with a 100% inhibition rate compared with the control. This study provides reference for field pharmaceutical control in sorghum production.