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Melatonin mediates multiple physiological processes in plants and is involved in many reactions related to the protection of plants from abiotic stress. In this paper, the effect of melatonin on the antioxidant capacity of rice under salt stress was studied. Melatonin alleviated the inhibition of salt stress on the growth of rice seedlings, mainly by increasing the dry weight and fresh weight of shoots and roots. Melatonin alleviated the membrane damage caused by salt stress, which was mainly manifested by the decrease of TBARS content and the decrease of leaf and root damage. During the whole salt stress period, rice after melatonin pretreatment showed lower ROS (H 2 O 2 , O 2 •−,OH−) accumulation. In the early stage (1–3 d) of stress, the rice after melatonin pretreatment showed a strong increase in antioxidant enzyme activity, while in the later stage (5,7 d), it showed a strong increase in antioxidant content. During the whole period of salt stress, melatonin had a weak regulatory effect on AsA-GSH cycle. Through the above regulation process, the decreasing effect of melatonin on ROS content of rice under salt stress did not decrease with prolonged stress time in a short time (1-7 d). In conclusion, melatonin improved the antioxidant capacity of rice under continuous salt stress, and rice showed variable antioxidant strategies after melatonin pretreatment. • Salt stress resulted in continuous accumulation of ROS, and MT pretreatment alleviated the oxidative damage of rice. • MT regulates antioxidant strategy in response to continuous salt stress. • MT pretreatment improves salt tolerance of rice. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) plays a key role in rice germination. The small molecule drug, A-769662, activates AMP-activated protein kinase, a mammalian homolog of SnRK1. However, it is unknown whether A-769662 activates SnRK1, thereby affecting germination. SnRK1 in desalted extracts from germinating rice seeds was strongly activated by adding A-769662 in vitro. Applying 50 or 100 μM A-769662 accelerated germination and increased the root length, shoot length, and seedling fresh weight. 50 μM A-769662 treatment increased the catalytic activity and phosphorylation of SnRK1 during germination. Transcriptome analysis and biochemical validation were performed to investigate the mechanism whereby A-769662 treatment promoted rice germination. A-769662 treatment promoted starch hydrolysis by increasing the expression and activity of amylase and inhibited starch biosynthesis by decreasing the expression of OsAGPL2 , OsAGPS2a , Wx , and SSIIa. The abscisic acid (ABA) level and gene expression of ABA-induced transcription factors, including OsNF-YC9 , OsNF-YC12 , OsWRKY24 , OsPYL8 , OsMKKK62 , and OsMKKK63 , which reduced the inhibition of germination by ABA were decreased under 50 μM A-769662 treatment. The increased expression of the OsACO3 and OsACO5 genes and increased ethylene levels under A-769662 treatment, which counteracted the inhibition of ABA on germination and, thus, promoted germination. These results demonstrate the activation of A-769662 on SnRK1 and further reveal the regulatory mechanism of A-769662 in rice seed germination and nutrient remobilization. • AMPK activator, A-769662, strongly increases SnRK1 activity in vitro. • A-769662 treatment accelerates germination by affecting amylase gene expression, ABA pathway and ethylene biosynthesis. • SnRK1 may alter T6P level by regulating expression of TPP genes. [ABSTRACT FROM AUTHOR]

Melatonin (MT), an important antioxidant existing in plants and animals, has been widely reported to participate in the process of plants coping with stress. In this study, we demonstrated the mechanism of MT enhancing photosynthesis in rice under salt stress. The results showed that MT treatment increased relative water content, sucrose and starch content of rice under salt stress. This was mainly owing to the fact that MT enhanced the net photosynthetic rate and enhanced the absorption and transmission of light energy. The effect of MT on photosynthesis of rice under salt stress conditions was mainly due to the regulation of three processes: maintaining low ROS status by improving the total antioxidant capacity, promoting the xanthophyll cycle and increasing the xanthophyll pool size to dissipate excess light energy, increasing the activities of key photosynthetic enzymes. Taken together, these results provide a mechanism for MT to improve the photosynthetic capacity of rice under salt stress. • MT improved plant growth and photosynthetic products accumulation under salt stress. • MT increased the net photosynthetic rate and electron transport of rice under salt stress. • MT increased the xanthophyll cycle and activities of key photosynthetic enzymes, decreased the accumulation of ROS. [ABSTRACT FROM AUTHOR]

The redistribution of nonstructural carbohydrates (NSCs) in rice (Oryza sativa) sheaths contributes greatly to grain filling. Sucrose nonfermenting-1-related protein kinase 1 (SnRK1) regulates sheath-to-panicle transport of NSCs during rice grain filling; however, it is unknown whether elevated activity of SnRK1 in sheaths improves NSC transport and grain filling. Expression of OsSnRK1a is mainly responsible for regulating SnRK1 activity in rice sheaths. Analysis of transgenic rice plants containing the OsSnRK1a promoter::GUS construct indicated that OsSnRK1a is widely expressed in rice. Notably, OsSnRK1a is highly expressed in mesophyll cells of sheaths. Therefore, a green tissue promoter specifically expressed in sheaths and leaf parenchyma cells and phloem tissue was used to over-express OsSnRK1a in japonica rice. The transgenic lines exhibited increased SnRK1a expression and SnRK1 activity in sheaths. The NSC and starch in the transgenic lines and WT all showed accumulation before heading and during the early-filling stage, and declining at the peak filling stage. But the starch and NSC content in transgenic lines was lower than that of WT. Moreover, the transgenic lines showed lower sucrose contents and higher sucrose efflux rates. The accelerated sheath NSC transport improved grain filling, and stimulated panicle development in transgenic lines. SnRK1a expression and SnRK1 activity were also increased in the leaves of transgenic lines, which improved leaf photosynthetic activity and contributed to optimal grain filling and panicle development. These results verify the promotion of high SnRK1 activity in sheath NSC transport, and also provide a new approach to improving sheath NSC transport and rice yield. • OsSnRK1a is highly expressed in mesophyll cells of sheaths. • The PP promoter was used increased SnRK1a expression and SnRK1 activity in sheaths of transgenic lines. • Elevated SnRK1 activity in sheaths accelerated NSC transport in transgenic lines, thereby improving grain filling and final yield. • SnRK1 activity and the photosynthetic rate were also increased in leaves of the transgenic lines. [ABSTRACT FROM AUTHOR]

Rice glutelin is sensitive to temperature and nitrogen, however, the regulatory mechanism of glutelin response to temperature and nitrogen is unclear. In this study, we conducted the open field warming experiment by the Free-air temperature enhancement facility and application of nitrogen during grain filling. In three-year field warming experiments, glutelin relative content was significantly increased under elevated temperature and application of nitrogen. Temperature and nitrogen and their interaction increased the glutelin accumulation rate in the early and middle grain filling stages (10-25d after flowering), but decreased the glutelin accumulation rate in the middle and late grain filling stages (25-45d after flowering). Elevated temperature promoted pro-glutelin levels whereas application of nitrogen under warming increased the amount of α-glutelin. At the transcriptional level, the expression levels of the glutelin-encoding genes and protein disulphide isomerase-like enzyme (PDIL1-1), glutelin precursor accumulation 4 (GPA4), glutelin precursor mutant 6 (GPA2), glutelin precursor accumulation 3 (GPA3) and vacuolar processing enzyme (OsVPE1) of glutelin folding, transport and accumulation-related genes were up-regulated by nitrogen under natural temperature as early as 5d after flowering. However, elevated temperature up-regulated glutelin-encoding genes before 20d after flowering, and the expression of endoplasmic reticulum chaperone (OsBip1), OsPDIL1-1 , small GTPase gene (GPA1), GPA2-GPA4 and OsVPE1 were significantly increased post 20d after flowering under warming. In addition, the increase in glutelin content worsened grain quality, particularly chalkiness and eating quality. Overall, the results were helpful to understand glutelin accumulation and provide a theoretical basis for further study the relationship between rice quality and glutelin under global warming. • Elevated temperature and additional nitrogen and their interaction significantly increased the glutelin relative content. • Temperature and nitrogen and their interaction increased the glutelin accumulation rate in the early and mid-filling periods. • Elevated temperature promoted the level of pro-glutelin whereas further additional nitrogen improved the level of α-glutelin. • Glutelin synthesis and maturity were regulated by elevated temperature at 5-20d and 20-30d after flowering, respectively. [ABSTRACT FROM AUTHOR]