Sorghum [Sorghum bicolor (L.) Moench] seed germination is sensitive to salinity, and seed priming is an effective method for alleviating the negative effects of salt stress on seed germination. However, few studies have compared the effects of different priming agents on sorghum germination under salt stress. In this study, we quantified the effects of priming with distilled water (HP), sodium chloride (NaCl), potassium chloride (KCl), calcium chloride (CaCl₂), and polyethylene glycol (PEG) on sorghum seed germination under 150 mM NaCl stress. The germination potential, germination rate, germination index, vigor index, root length, shoot length, root fresh weight, shoot fresh weight, root dry weight, and shoot dry weight were significantly reduced by salt stress. Different priming treatments alleviated the germination inhibition caused by salt stress to varying degrees, and 50 mM CaCl₂ was the most effective treatment. In addition, the mitigation effect of priming was stronger on root traits than on shoot traits. Mitigation efficacy was closely related to both the type of agent and the concentration of the solution. Principal component analysis showed that all concentrations of CaCl₂ had higher scores and were clearly distinguished from other treatments based on their positive effects on all germination traits. The effects of the other agents varied with concentration. The priming treatments were divided into three categories based on their priming efficacy, and the 50, 100, and 150 mM CaCl₂ treatments were placed in the first category. The 150 mM KCl, 10% PEG, HP, 150 mM NaCl, 30% PEG, and 50 mM KCl treatments were placed in the second category, and the 100 mM NaCl, 100 mM KCl, 20% PEG, and 50 mM NaCl treatments were least effective and were placed in the third category. Choosing appropriate priming agents and methods for future research and applications can ensure that crop seeds germinate healthily under saline conditions.

Waterlogging stress is one of the most important abiotic stresses limiting sorghum growth and development. Consequently, the responses of sorghum to waterlogging must be monitored and studied. This study investigated changes in the leaf water status, xylem exudation rate, leaf anatomical structure, leaf temperature and photosynthetic performance. Waterlogging-tolerant (Jinuoliang 01, abbreviated JN01) and waterlogging-sensitive (Jinza 31, abbreviated JZ31) sorghum cultivars were planted in pots. The experiment was carried out using a split block design with three replications. Waterlogging stress was imposed at the sorghum five-leaf stage. The leaf free water content (FWC) and relative water content (RWC) decreased under the waterlogged condition. The leaf thickness was thinner under the waterlogged condition, and the main changes occurred in the upper epidermal and mesophyll cells. Gas exchange parameters and the xylem exudation rate were also restrained by waterlogging; however, greater responses of these parameters were observed in JZ31. JZ31 had a higher leaf-air temperature difference (ΔT) than JN01. We found that changes in ΔT were always consistent with changes in the RWC and the gas exchange parameters. ΔT was significantly associated with the leaf RWC, photosynthetic rate (Pn) and transpiration rate (Tr). The results suggest that ΔT may be an indicator reflecting the water status in leaves and can be used to evaluate the tolerance of sorghum to waterlogging.

Seed germination is the sensitive period to salt stress. Calcium chloride (CaCl₂) has been proved as an effective priming agent which can promote the sorghum germination under salt stress. However, there are few reports on CaCl₂ priming to improve the salt tolerance during seed germination. The present study investigated the effects of CaCl₂ priming on sorghum germination, antioxidant metabolism, osmotic regulation and ion balance under salt stress (150 mM NaCl). The results revealed that the salt stress inhibited the elongation of mesocotyl and root and reduced the germination rate of sorghum. While CaCl₂ priming significantly promoted the elongation of mesocotyl and root, and increased the germination rate of sorghum under salt stress. CaCl₂ priming notably increased the content of osmotic substances in mesocotyl and root of sorghum under salt stress, and increased the relative water content in these tissues. CaCl₂ priming decreased Na⁺ content and increased K⁺, Ca²⁺ contents and the K⁺/ Na⁺ in mesocotyl and root, such effects might be induced by up-regulating the expression of NHX2, NHX4, SOS1, AKT1, AKT2, HKT1, HAK1, and KUP. CaCl₂ priming reduced the antioxidant enzymes activities and related gene expression compared with untreated sorghum seeds under salt stress. In short, CaCl₂ priming improved sorghum germination by enhancing osmotic regulation and ion balance instead of antioxidant enzyme activity. However, the molecular mechanisms of Ca²⁺ signaling induced by CaCl₂ priming in association with the enhanced germination in primed sorghum seeds under salt stress need to be addressed in future studies.

Root function plays a vital role in maintaining crop production. However, the role of deep roots in yield production and their effects on photosynthetic performance in sorghum remain unclear. This study aimed to provide theoretical supports for establishing highly efficient root systems of sorghum to achieve more yield under certain conditions. In this study, two sorghum (Sorghum bicolor L. Moench) cultivars, Jiza127 and Jiza305, were cultivated in soil columns as experimental materials. Three treatments (no roots removed, CK; roots removed at 30 cm underground, R30; roots removed at 60 cm underground, R60) were carried out under drought conditions during the filling stage. The root bleeding intensity, endogenous substances in the root bleeding sap, photosynthetic characteristics, dry matter accumulation, and yield were measured. The results showed that R30 and R60 significantly reduced yield in both sorghum cultivars, and the effect of R30 on yield was greater than that of R60. The contributions of roots below 30 cm to the yield of both sorghum hybrids were notably higher than those below 60 cm. R30 significantly reduced the dry matter weights (DMWs) of leaves, stems, sheaths, and panicles. R60 significantly reduced the DMW of panicles but had no significant effect on the DMWs of leaves and stems. R30 significantly reduced the photosynthetic level and PSII reaction center activity; however, the effect of R60 was not significant. Although both R30 and R60 significantly reduced root activity and the soluble sugar, amino acid, gibberellin (GA₃), and abscisic acid (ABA) contents of the root bleeding sap, some of the above indicators in R60 were significantly higher than those in R30 during the filling stage, indicating that the deeper roots (below 30 cm) had a critical regulatory effect on the physiological processes of the aerial parts in sorghum, which resulted in a stronger effect on yield, especially under drought conditions. In brief, the deep roots of sorghum played a key role in yield production, but the roots in different soil depths regulated yield production in different ways. Our results indicate that deep roots of sorghum deserve consideration as a potential trait for yield improvement especially under drought conditions.

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.