Effects of chitosan and calcium chloride treatments on malic acid-metabolizing enzymes and the related gene expression in post-harvest pear cv. ‘Huang guan’

Abstract Malic acid in the ‘Huang guan’ pear ( Pyrus pyrifolia Nakai) is the predominant organic acid associated with taste, flavor and juice quality. The effects of different treatments on malic acid-metabolizing enzymes and the related genes expression during storage have been studied. Malic acid content was higher in the peel than in the pulp. NAD-dependent malate dehydrogenase (NAD-MDH) and NADP-dependent malic enzyme (NADP-ME) correlated with gene expression during cold storage. NAD-MDH promoted malic acid synthesis, whereas NADP-ME promoted malic acid degradation. Chitosan treatment had a significantly positive effect on the activities of NAD-MDH and a negative effect on the activities of NADP-ME both in pulp and peel, and CaCl 2 just significantly affected those in peel. The gene expressions of Mdh were not significantly impacted under both treatments, in addition to the gene expression of Me under CaCl 2 treatment. An expression analysis of the proton pump gene revealed that vVAtp1 significantly negatively regulated the malic acid content, and there was a significant negative correlation between the vVpp gene and the accumulation of malic acid in the peel. Different treatments inhibited the gene expression of vVAtp2 , as well as promoted gene expression of vVAtp1 . Overall, both treatments attenuated enzyme activity and malic degradation of pear fruit during storage period.