Spermidine enhances chilling tolerance of kale seeds by modulating ROS and phytohormone metabolism.

Chilling stress is an important constraint for kale seed germination and seedlings establishment. It is vital to develop an effective approach to enhance kale seed germination ability under chilling stress. The present study reported that spermidine (Spd) could improve seed chilling tolerance in two kale cultivars 'Nagoya' (MGW) and 'Pigeon' (BB) during germination. The results showed that MGW was cold tolerant with a 90.67% germination percentage (GP) under chilling stress, while BB was cold sensitive with a 70.67% GP under chilling stress. Spd content in MGW and BB seeds during seed germination were up-regulated and down-regulated by chilling stress, respectively. Besides, chilling stress apparently decreased the gibberellin (GA) and ethylene (ET) contents, while increased the levels of abscisic acid (ABA) and reactive oxygen species (ROS) in MGW and BB seeds during germination. Exogenous Spd application increased GA, ET contents and decreased ABA content through regulating the gene expressions of metabolic-related enzymes, thus effectively alleviating the low temperature damage on kale seed germination. Besides, Spd significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD), and reduced the levels of hydrogen peroxide (H2O2) and superoxide anion (O2·-). The present study demonstrated that endogenous Spd metabolism plays an important role in kale seed germination under chilling stress. The effect of exogenous Spd on the metabolism of endogenous Spd, GA, ABA, ET and antioxidant enzymes might be the important reason for promoting the kale seed vigor at low temperature.

High Drying Temperature Accelerates Sunflower Seed Deterioration by Regulating the Fatty Acid Metabolism, Glycometabolism, and Abscisic Acid/Gibberellin Balance.

Sunflower seed storage is accompanied by the loss of seed vigor. Seed drying is a key link between seed harvest and seed storage; however, to date, the effect of seed drying on sunflower seed deterioration during storage remains unclear. The present study performed hot air drying for sunflower seeds with an initial moisture content of 30% to examine the manner in which drying temperature (35, 40, 45, 50, and 55°C) affects the drying performance and seed vigor following storage process (6 and 12 months). A drying temperature of 40°C was evidently safe for sunflower seeds, whereas the high drying temperatures (HTD, 45, 50, and 55°C) significantly lowered sunflower seed vigor by regulating the fatty acid metabolism, glycometabolism, and abscisic acid (ABA)/gibberellin (GA) balance. HDT significantly increased the seed damage rate and accelerated sunflower seed deterioration during natural and artificial aging process. Further biochemical analysis indicated that HDT significantly increased lipoxygenase and dioxygenase activities, leading to malonaldehyde and reactive oxygen species over-accumulation during storage. During early seed germination, HDT significantly inhibited fatty acid hydrolysis and glycometabolism by decreasing triacylglycerol lipase, CoA-SH oxidase, and invertase activities. Moreover, HDT remarkably increased ABA levels but reduced GA levels by regulating gene expressions and metabolic enzyme activities during early imbibitions. Cumulatively, the seed drying effect on sunflower seed vigor deterioration during the storage process may be strongly related to fatty acid oxidation and hydrolysis metabolism, toxic substance accumulation, and ABA/GA balance.

Drying temperature regulates vigor of high moisture rice seeds via involvement in phytohormone, ROS, and relevant gene expression.

BACKGROUND: Rice is an important food crop in China. Seed drying is an important step in the production of rice seeds. However, the regulatory mechanism of the effect of drying temperature on vigor of rice seeds with high initial moisture content (IMC) has not been examined. RESULTS: This study presents hot-air drying of rice seeds with high IMC (>30%) to assess the effect of drying temperature (35, 41, and 47 °C) on drying performance and seed vigor in terms of germination capacity. The results show a significant positive correlation between the drying rate, seed temperature, and drying temperature. High-temperature drying tends to cause a large accumulation of reactive oxygen species (ROS) and increases the activity of antioxidant enzymes in rice seeds. High-temperature drying also significantly increased abscisic acid (ABA) content and decreased gibberellin (GA) content through the regulation of the activity of metabolism related-enzymes. Moreover, changes in GA and ABA metabolism during early seed germination might be an important reason for the decrease in seed vigor with high-temperature drying. High-temperature drying also significantly inhibited the activity of α-amylase during early seed germination. CONCLUSION: A drying temperature of 35 °C was safe for rice seeds with high IMC, whereas higher drying temperatures (41 and 47 °C) reduced rice seed vigor remarkably. The metabolism of ROS, antioxidant enzymes, GA, ABA, and α-amylase might be closely involved in the regulation of the effect of drying temperature on the seed vigor of rice seeds with high IMC. The results of this study, therefore, provide a theoretical basis and technical guidance for mechanical drying of rice seeds. © 2020 Society of Chemical Industry.