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Dark pericarp disease (DPD), a physiological disorder induced by excess Manganese (Mn) in litchi, severely impacts the appearance and its economic value. To elucidate the underlying mechanisms of DPD, this study investigated the variations of phenolic compound, antioxidant defense system, subcellular structure, and transcriptome profiles in both normal fruit and dark pericarp fruit (DPF) at three developmental stages (green, turning, and maturity) of 'Guiwei' litchi. The results reveal that excess Mn in DPF pericarp resulted in a significant increase in reactive oxygen species, especially H 2 O 2, and subsequent alterations in antioxidant enzyme activities. Notably, SOD (EC 1.15.1.1) activity at the green stage, along with POD (EC 1.11.1.7) and APX (EC 1.11.1.11) activities at the turning and the maturity stages, and GST (EC 2.5.1.18) activity during fruit development, were markedly higher in DPF. Cell injury was observed in pericarp, facilitating the formation of dark materials in DPF. Transcriptome profiling further reveals that genes involved in flavonoid and anthocyanin synthesis were up-regulated during the green stage but down-regulated during the turning and maturity stages. In contrast, PAL (EC 4.3.1.24), C4H (EC 1.14.14.91), 4CL (EC 6.2.1.12), CAD (EC 1.1.1.195), and particularly POD, were up-regulated, leading to reduced flavonoid and anthocyanin accumulation and increased lignin content in DPF pericarp. The above suggests that the antioxidant system and phenolic metabolism jointly resisted the oxidative stress induced by Mn stress. We speculate that phenols, terpenes, or their complexes might be the substrates of the dark substances in DPF pericarp, but more investigations are needed to identify them. [Display omitted] • Mn toxicity induces dark pericarp disease (DPD) in litchi. • Excess Mn triggers ROS breakout and antioxidant system defence in pericarp. • Mn stress disrupts the structure of pericarp cell. • DPD alters the synthesis/accumulation of flavonoid and lignin in pericarp. • Phenols and lignin might be the substrates of dark materials in dark pericarp fruit. [ABSTRACT FROM AUTHOR]

Roxarsone (ROX), a widely used feed additive, occurs as itself and its metabolites in animal manure. Rice is prone to accumulate As than other staple food. Four diets with 0, 40, 80 and 120 mg ROX kg − 1 were fed in chickens, and four chicken manures (CMs) were collected to fertilize rice plants in a soil culture experiment. Linear regression analysis shows that the slopes of As species including 4-hydroxy-phenylarsonic acid, As(V), As(III), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in CM versus dietary ROX were 0.033, 0.314, 0.033, 0.054 and 0.138, respectively. Both As(III) and DMA were determined in all rice grains, and As(III), As(V), MMA and DMA in rice hull, but detectable As forms in rice straws and soils increased with increasing ROX dose. Grain As(III) was unrelated to ROX dose but exceeded the Chinese rice As limit (0.15 mg As(III) kg − 1 ). Dietary ROX enhanced straw As(III) mostly, with the slope of 0.020, followed by hull DMA (0.006) and grain DMA (0.002). The slopes of soil As(V) and As(III) were 0.003 and 0.001. This is the first report illustrating the quantitative delivery of ROX via food chain, which helps to evaluate health and environmental risks caused by ROX use in animal production. [ABSTRACT FROM AUTHOR]