Effects of exogenous calcium and calcium chelant on cold tolerance of postharvest loquat fruit

The effect of calcium chloride (CaCl2) and calcium chelant-ethylene glycol bis (2-aminoethyl ether) tetraacetic acid (EGTA) on chilling injury (CI) of postharvest loquat fruit (Eriobotrya japonica L. cv. 'Changhong') during cold storage was investigated. The results showed that CaCl2 treatment significantly prevented CI and maintained the membrane integrity resulting in the reduction of ion leakage and malondialdehyde (MDA) content. The exogenous calcium increased energy charge (EC) and the content of adenosine triphosphate (ATP), adenosine diphosphate (ADP). Meanwhile, CaCl2 treatment effectively enhanced the enzyme activities associated with energy metabolism including H--adenosine triphosphatase (H+ -ATPaese), Ca2+-adenosine triphosphatase (Ca2+-APTase), succinic dehydrogenase (SDH), cytochrome c oxidase (CCO). Furthermore, the activities of Delta(1)-pyrroline-5-carboxylic acid synthase (P5CS), ornithin-(sic)-aminotransferase (OAT), glutamic acid decarboxylase (GAD), diamine oxidase (DAO) and polyamine oxidase (PAO) were enhanced by CaCl2 treatment, which contributed to the accumulation of osmotic substances gamma-aminobutyric acid (GABA), proline and polyamines (PAs). However, EGTA treatment significantly promoted CI index, increased MDA content and ion leakage. Moreover, low level of EC and GABA were also found in EGTA-treated loquat fruit. These results suggested that exogenous calcium could effectively enhance the chilling tolerance due to the high energy level and promoted accumulation of endogenous osmotic substances proline, GABA and PAs in loquat fruit.