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Autophagy, an evolutionally conserved cellular degradation process, plays critical roles in plant development and stress response. Despite the wealth of information on the vital role of autophagy in responses to environmental stresses, little is known about the regulation of autophagy. In this study, we demonstrated that spermidine (Spd), a kind of polyamine, was involved in the regulation of salt tolerance through activating the expression of ATG (autophagy-related) genes and the formation of autophagosomes in cucumber under salt stress. Furthermore, NADPH oxidase-derived apoplastic H2O2-mediated Spd-induced salt tolerance and autophagy. Exogenous Spd significantly increased the tolerance to salt stress and inhibited the accumulation and ubiquitination of insoluble proteins. Foliar application of Spd promoted the transcript levels of ATG genes and autophagosomes formation. Besides, Spd induced the expression of RBOH (respiratory burst oxidase homolog), and the accumulation of H2O2 both in leaves and roots. However, either pretreatment with dimethylthiourea (DMTU, an H2O2 scavenger) or diphenyleneiodonium chloride (DPI, an inhibitor of NADPH oxidase) reduced Spd-induced accumulation of apoplastic H2O2. Importantly, Spd-induced salt tolerance and autophagy were compromised when plants were pretreated with DMTU or DPI. Furthermore, the silencing of ATG4 and ATG7 reduced Spd-induced salt tolerance and autophagosomes formation. Taken together, these results revealed that RBOH-dependent H2O2 mediated the Spd-induced autophagy and salt tolerance in cucumber. Abbreviations: Asat: light-saturated rate of CO2 assimilation; ATG: autophagy-related; DCF-DA: 2, 7-dichlorofluorescein diacetate; DMTU: dimethylthiourea; DPI: diphenyleneiodonium chloride; DW: dry weight; EL: electrolyte leakage; FW: fresh weight; Fv/Fm: the maximum quantum yield of photosystem II; GFP: green fluorescent protein; MDC: monodansylcadaverine; PDS: phytoene desaturase; PE: phosphatidylethanolamine; PLD: phospholipase D; RBOH: respiratory burst oxidase homolog; ROS: reactive oxygen species; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SIN1: salt induced NAC1; Spd: spermidine; TOR: target of rapamycin; VIGS: virus-induced gene silencing. [ABSTRACT FROM AUTHOR]

There is a growing interest in the impact of light intensity and temperature on vegetable growth and dietary quality characteristics. Lettuce (Lactuca sativa L.), as one of the model vegetables in plant factories, was grown under two light levels (G1: 160 µmol m–2 s–1, G2: 200 µmol m–2 s–1) with different day/night temperatures (T1: 20 ± 1°C/15 ± 1°C, T2: 24 ± 1°C/19 ± 1°C) to investigate mutual effects of light intensity and temperature on its growth and quality properties. The results revealed that the T2G2 treatment showed higher plant height, biomass and net photosynthetic rate, while T1G2 resulted in decreased leaf area and lower maximum photochemical efficiency of photosystem II (Fv/Fm) compared to T1G1. Simultaneous increases in light intensity and temperature based on T1G1 significantly increased the contents of anthocyanin, vitamin C (Vc) and soluble protein by 58%, 21% and 172%, respectively. The higher light intensity promoted the nutritional values of lettuce, characterised by lower nitrate level and soluble protein contents. Principal component analysis showed a negative collinearity between the nitrate content and soluble protein and Vc contents. In conclusion, light intensity and temperature co-regulated the lettuce's growth and development, and their simultaneous increases better for growth and nutritional values of lettuce. These results provide a better understanding of the cultivation of plants in an artificial plant factory while maintaining yield and quality. [ABSTRACT FROM AUTHOR]