Apple 1-Aminocyclopropane-1-Carboxylic Acid Synthase Genes, MdACS1 and MdACS3a, are Expressed in Different Systems of Ethylene Biosynthesis

1-Aminocyclopropane-1-carboxylic acid synthase (ACS) is one of the key regulatory enzymes involved in the synthesis of ethylene. Climacteric fruit ripening is accompanied by increased ethylene production, in which ethylene biosynthesis is changed from system 1 to system 2. In apple, at least four members of the ACS gene family have been identified, two of which, MdACS1 and MdACS3a, have been studied extensively due to their specific expression in fruit tissue. However, the regulatory role of MdACS1 and MdACS3a in the ethylene biosynthesis system is unknown. Here we addressed this issue by investigating ACS expression in ripening apple fruits. Expression analysis in ‘Golden Delicious’ and ‘Red Fuji’ fruits, in combination with treatments of 1-MCP (1-methylcyclopropene, an ethylene inhibitor) and Ethephon (an ethylene releaser) has demonstrated that MdACS3a and MdACS1operate in system 1 and system 2 ethylene biosynthesis, respectively.     

5-Aminolevulinic acid promotes anthocyanin accumulation in Fuji apples

5-Aminolevulinic acid (ALA) is an essential precursor of all tetrapyrrole compounds such as chlorophylls and heme in plants. It has also been suggested widely for applications to crops to enhance growth and production as a plant growth regulator. However, how successful ALA can be used in fruit production was rarely reported. We conducted a field experiment at eight locations in four provinces across eastern China; and the results showed that application of ALA solutions to ‘Fuji’ apple (Malus × domestica Borkh.) fruits 20 days prior to harvest significantly increased the anthocyanin content in the fruit skin. Also, ALA treatment increased the anthocyanin content of the detached apple skin in a growth chamber. Results from the semi-quantitive RT-PCR analysis showed that ALA induced gene expressions related to anthocyanin biosynthesis, including the structural genes Pal, Chs and Ufgt, and regulatory genes Myb, bHLH and Wd40. When levulinic acid (LA), an inhibitor of ALA dehydrase, was added, ALA promotion of anthocyanin accumulation and up-regulation of gene expressions were inhibited. Taken together, these results suggest that ALA promotion of anthocyanin accumulation in apples was facilitated by the up-regulation of gene expression, which might be related to the conversion of ALA to porphyrins.