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Introduction: Folic acid (FA) is a critical metabolite in all living organisms and an important nutritional component of broccoli. Few studies have been conducted on the impact of an exogenous application of FA on the postharvest physiology of fruits and vegetables during storage. In this regard, the mechanism by which an exogenous application of FA extends the postharvest quality of broccoli is unclear. Objective: This study utilized a multicomponent analysis to investigate how an exogenous application of FA effects the postharvest quality of broccoli. Methods: Broccoli was soaked in 5 mg/L FA for 10 min and the effect of the treatment on the appearance and nutritional quality of broccoli was evaluated. These data were combined with transcriptomic, metabolomic, and DNA methylation data to provide insight into the potential mechanism by which FA delays senescence. Results: The FA treatment inhibited the yellowing of broccoli during storage. CHH methylation was identified as the main type of methylation that occurs in broccoli and the FA treatment was found to inhibit DNA methylation, promote the accumulation of endogenous FA and chlorophyl, and inhibit ethylene biosynthesis in stored broccoli. The FA treatment also prevented the formation of off-odors by inhibiting the degradation of glucosinolate. Conclusions: FA treatment inhibited the loss of nutrients during the storage of broccoli, delayed its yellowing, and inhibited the generation of off-odors. Our study provides deeper insight into the mechanism by which the postharvest application of FA delays postharvest senescence in broccoli and provides the foundation for further studies of postharvest metabolism in broccoli.

Leaf curling is an essential prerequisite for the formation of leafy heads in Chinese cabbage. However, the part or tissue that determines leaf curvature remains largely unclear. In this study, we first introduced the auxin-responsive marker DR5::GUS into the Chinese cabbage genome and visualized its expression during the farming season. We demonstrated that auxin response is adaxially/abaxially distributed in leaf veins. Together with the fact that leaf veins occupy considerable proportions of the Chinese cabbage leaf, we propose that leaf veins play a crucial supporting role as a framework for heading. Then, by combining analyses of QTL mapping and a time-course transcriptome from heading Chinese cabbage and non-heading pak choi during the farming season, we identified the auxin-related gene BrPIN5 as a strong candidate for leafy head formation. PIN5 displays an adaxial/abaxial expression pattern in leaf veins, similar to that of DR5::GUS, revealing an involvement of BrPIN5 in leafy head development. The association of BrPIN5 function with heading was further confirmed by its haplo-specificity to heading individuals in both a natural population and two segregating populations. We thus conclude that the adaxial/abaxial patterning of auxin and auxin genes in leaf veins functions in the formation of the leafy head in Chinese cabbage.

Foodborne illnesses present a major threat to public health and are frequently attributed to foodborne pathogens present on fresh produce. Some opportunistic pathogens of broccoli are also responsible for causing head rot. Three different light treatments, UV-C, red LED (50 μml/m2/s), and UV-C + LED were used to treat broccoli prior to or during storage. Following the light treatments, microorganisms present in eluates obtained from the surface of broccoli heads were characterized using a metagenomic approach. Metagenomic DNA libraries were subjected to high-throughput sequencing on an Illumina Hiseq platform. Results indicated that the combined treatment of LED red light and UV-C provided the best sensory preservation of broccoli, followed by LED red light and then UV-C. The bacterial communities in the eluates obtained from the surface of broccoli heads in all three light treatments were primarily represented at the phylum level by Proteobacteria and Firmicutes, while fungal communities were primarily represented by Ascomycota and Basidiomycota. Further analysis indicated that the all three light treatments reduced the presence of foodborne pathogens and bacterial taxa responsible for broccoli spoilage. While UV-C had a significant inhibitory effect on Botrytis cinerea, the light treatments increased the relative abundance of Pseudomonas fluorescens. Results indicate that a metagenomic approach can be used to detect pathogenic bacteria and fungi on fresh vegetables and assess the impact of management practices, such as light treatments, designed to maintain postharvest quality, on the composition of the microbiome present on the surface of harvested produce.

The effect of palmitic acid (PA) on stem browning was investigated in freshly harvested mini-Chinese cabbage (Brassica pekinensis). Results indicated that concentrations of PA ranging from 0.03 g L−1 to 0.05 g L−1 inhibited stem browning and decreased the rate of respiration, electrolyte leakage, and weight loss, as well as the level of malondialdehyde (MDA) in freshly harvested mini-Chinese cabbage stored at 25 °C for 5 d. The PA treatment enhanced the activity of antioxidant enzymes (ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), 4-coumarate:CoA ligase (4CL) and phenylalamine ammonia lyase (PAL)), and inhibited the activity of polyphenol oxidase (PPO). The PA treatment also increased the level of several phenolics (chlorogenic acid, gallic acid, catechin, p-coumaric acid, ferulic acid, p-hydroxybenzoic acid, and cinnamic acid) and flavonoids (quercetin, luteolin, kaempferol, and isorhamnetin). In summary, results indicate that treatment of mini-Chinese cabbage with PA represents an effective method for delaying stem browning and maintaining the physiological quality of freshly harvested mini-Chinese cabbage due to the ability of PA to enhance antioxidant enzyme activity and the level of phenolics and flavonoids during 5 d.

The MOB1 proteins are highly conserved in yeasts, animals, and plants. Previously, we showed that the Arabidopsis (Arabidopsis thaliana) MOB1A gene (AtMOB1A/NCP1) plays critical roles in auxin-mediated plant development. Here, we report that AtMOB1A and AtMOB1B redundantly and negatively regulate jasmonate (JA) accumulation and function in Arabidopsis development. The two MOB1 genes exhibited similar expression patterns, and the MOB1 proteins displayed similar subcellular localizations and physically interacted in vivo. Furthermore, the atmob1a atmob1b (mob1a/1b) double mutant displayed severe developmental defects, which were much stronger than those of either single mutant. Interestingly, many JA-related genes were up-regulated in mob1a/1b, suggesting that AtMOB1A and AtMOB1B negatively regulate the JA pathways. mob1a/1b plants accumulated more JA and were hypersensitive to exogenous JA treatments. Disruption of MYC2, a key gene in JA signaling, in the mob1a/1b background partially alleviated the root defects and JA hypersensitivity observed in mob1a/1b. Moreover, the expression levels of the MYC2-repressed genes PLT1 and PLT2 were significantly decreased in the mob1a/1b double mutant. Our results showed that MOB1A/1B genetically interact with SIK1 and antagonistically modulate JA-related gene expression. Taken together, our findings indicate that AtMOB1A and AtMOB1B play important roles in regulating JA accumulation and Arabidopsis development. [ABSTRACT FROM AUTHOR]

Ultraviolet B (UV-B) radiation is an important environmental signal for plant growth and development, but its signal transduction mechanism is unclear. UV-B is known to induce stomatal closure via hydrogen peroxide (H2O2), and to affect ethylene biosynthesis. As ethylene is also known to induce stomatal closure via H2O2 generation, the possibility of UV-B-induced stomatal closure via ethylene-mediated H2O2 generation was investigated in Vicia faba by epidermal strip bioassay, laser-scanning confocal microscopy, and assays of ethylene production. It was found that H2O2 production in guard cells and subsequent stomatal closure induced by UV-B radiation were inhibited by interfering with ethylene biosynthesis as well as ethylene signalling, suggesting that ethylene is epistatic to UV-B radiation in stomatal movement. Ethylene production preceded H2O2 production upon UV-B radiation, while exogenous ethylene induced H2O2 production in guard cells and subsequent stomatal closure, further supporting the conclusion. Inhibitors for peroxidase but not for NADPH oxidase abolished H2O2 production upon UV-B radiation in guard cells, suggesting that peroxidase is the source of UV-B-induced H2O2 production. Taken together, our results strongly support the idea that ethylene mediates UV-B-induced stomatal closure via peroxidase-dependent H2O2 generation. [ABSTRACT FROM PUBLISHER]