Kiwifruit is one of the most commercially available fruits packed with various nutrients. Over the last decade, the cultivation of kiwifruit has been plagued by a severe epidemic caused by Pseudomonas syringae pv. actinidiae (Psa).

Copper (Cu) -based fertilizers and pesticides are widely used to fight against Psa, which in turn increases the accumulation of Cu in kiwifruit, threatening food safety and human health.

Researchers from the Wuhan Botanical Garden of the Chinese Academy of Sciences have revealed that ascorbic acid (AsA) could enhance the Cu tolerance and mitigate Cu toxicity in kiwifruit.

Ascorbic acid (AsA), commonly known as vitamin C, has a range of functions involving the detoxification of reactive oxygen species and maintaining plant growth and human health.

The study was published in Journal of Hazardous Materials on Aug. 23.

In the study, the researchers assessed the Cu content of 108 kiwifruit samples of 27 cultivars worldwide. They found that the average Cu content of kiwifruit with red- or yellow-fleshed was significantly higher than that of green-fleshed, and the Cu content level in fruit flesh and cores was significantly lower than that in fruit skin and seeds.

High concentration of Cu resulted in obvious damage in the kiwifruit plants, which was mitigated when the kiwifruit plants were feeding with exogenous AsA.

The researchers found that Cu treatment for 12 h increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3′,5′-epimerase (GME).

Overexpressing GGP3 in transgenic kiwifruit increased the endogenous AsA content of kiwifruit. Increased AsA content in transgenic lines could mitigate Cu toxicity, result in mitigated Cu stress inhibition of photosynthesis, scavenge excess ROS, and alter stress-related gene expression of kiwifruit under Cu treatment. The transgenic kiwifruit had higher AsA content (8.4- to 12.2-fold) than that of wild-type.

Copper concentrations in major kiwifruit cultivars around the world (Image by LIU Xiaoying)