Mango is a highly perishable fruit with a short post-harvest time due to the intense metabolic activity after harvesting. In attempt to evaluate the effects of chitosan in mango fruits, it was treated with 0%, 1%, 2% or 3% of chitosan solutions, placed into plastic trays, and stored at room temperature. Changes in physical and chemical parameters were evaluated. Chitosan delayed the climacteric peak, water loss and firmness. Further, few changes in soluble solid content, titratable acidity, pH of the pulp as well as in sugar content and decreased starch degradation were observed. Altogether, our results suggest chitosan edible coating effectively prolongs the quality attributes, affecting basic mitochondrial respiration and starch degradation rate.

Guava is a typically tropical fruit highly perishable with a short shelf-life due to intense metabolic activity after harvested. In attempt to minimize the problems related to the postharvest, we evaluated the physiochemical characteristics and antioxidant system in guava fruits under chitosan coating at concentrations of 1%, 2%, and 3% stored at 25°C during 96h. The chitosan suppressed the respiratory rate, fresh weight loss, firmness and skin color with delay in the degradation of chlorophyll. In the treatment with 2% and 3% of chitosan in the solid soluble content and ascorbic acid were reduced; retarded the loss of titratable acidity during 96h after treatment. These treatment induced significant decreases in the phenylalanine ammonia-lyase activity and significantly increases of peroxidase Activity. Our results suggest that chitosan effectively prolongs the quality attributes in guava fruits after harvesting due to increases in the antioxidant processes, delaying the ripening during room temperature of storage.

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The molecule vitamin C, in the chemical form of ascorbic acid (AsA), is known to be essential for the metabolism of humans and animals. Humans do not produce AsA, so they depend on plants as a source of vitamin C for their food. The AsA synthesis pathway occurs partially in the cytosol, but the last oxidation step is physically linked to the respiratory chain of plant mitochondria. This oxidation step is catalyzed by l-galactono-1,4-lactone dehydrogenase (l-GalLDH). This enzyme is not considered a limiting step for AsA production; however, it presents a distinguishing characteristic: the l-GalLDH can introduce electrons directly into the respiratory chain through cytochrome c (Cytc) and therefore can be considered an extramitochondrial electron source that bypasses the phosphorylating Complex III. The use of Cytc as electron acceptor has been debated in terms of its need for AsA synthesis, but little has been said in relation to its impact on the functioning of the respiratory chain. This work seeks to offer a new view about the possible changes that result of the link between AsA synthesis and the mitochondrial respiration. We hypothesized that some physiological alterations related to low AsA may be not only explained by the deficiency of this molecule but also by the changes in the respiratory function. We discussed some findings showing that respiratory mutants contained changes in AsA synthesis. Besides, recent works that also indicate that the excessive electron transport vial-GalLDH enzyme may affect other respiratory pathways. We proposed that Cytc reduction by l-GalLDH may be part of an alternative respiratory pathway that is active during AsA synthesis. Also, it is proposed that possible links of this pathway with other pathways of alternative electron transport in plant mitochondria may exist. The review suggests potential implications of this relationship, particularly for situations of stress. We hypothesized that this pathway of alternative electron input would serve as a strategy for adaptation of plant respiration to changing conditions.

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31Attempts to improve the ascorbate (AsA) content of plants are still dealing with the limited 32 understanding of why exists a wide variability of this powerful anti-oxidant molecule in different 33 plant sources, species and environmental situations. In plant mitochondria, the last step of AsA 34 synthesis is catalyzed by the enzyme L-galactone-1,4-lactone dehydrogenase (L-GalLDH). By using 35GalLDH-RNAi silencing plant lines, biochemical and proteomic approaches, we here discovered 36 that, in addition to accumulate this antioxidant, mitochondria synthesize AsA to down-regulate the 37 respiratory activity and the cellular energy provision. The work reveals that the AsA synthesis 38 pathway within mitochondria is a branched electron transfer process that channels electrons 39 towards the alternative oxidase, interfering with conventional electron transport. It was 40 unexpectedly found that significant hydrogen peroxide is generated during AsA synthesis, which 41 affects the AsA level. The induced AsA synthesis shows proteomic alterations of mitochondrial 42 and extra-mitochondrial proteins related to oxidative and energetic metabolism. The most 43 identified proteins were known components of plant responses to high light acclimation, 44 programmed cell death, oxidative stress, senescence, cell expansion, iron and phosphorus 45 starvation, different abiotic stress/pathogen attack responses and others. We propose that 46 changing the electron flux associated with AsA synthesis might be part of a new mechanism by 47 which the L-GalLDH enzyme would adapt plant mitochondria to fluctuating energy demands and 48 redox status occurring under different physiological contexts. 49 50 to mETC but via flavin dinucleotide (FAD) (Sweetlove et al., 2010). These oxidation reactions are all 60 coupled to reduction of the ubiquinone (UQ) to ubiquinol (UQH 2 ) (Schertl and Braun, 2014). 61

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