High voltage electrostatic field alters soluble sugar accumulation and promotes melon fruit growth

A few studies have revealed the potential and applications of high voltage electric field (HVEF) within the food industry. However, whether or how the growth, development, and quality of vegetables and fruits are affected by HVEF remains largely unknown. To comprehensively understand the responses of soluble sugar accumulation to HVEF, soluble sugar contents, activity of enzymes, and expression of genes related to sugar metabolism and transport in melon fruit were investigated. Results indicate that HVEF with a field strength of 35 kV m^-1 (2 h on and 1 h off) can significantly increase photosynthetic rate, plant height, root growth, and single fruit weight. The sucrose concentration was significantly higher, while the concentration of fructose and glucose was lower in melon fruit exposed to the HVEF. In addition, the activities of sucrose synthesizing enzyme (sucrose phosphate synthase (SPS, EC 2.4.1.14)), sucrose degradation enzyme (sucrose synthase, SUSY, (EC 2.4.1.13); neutral invertase, NINV, (EC 3.2.1.26)) and hexose degradation enzyme (fructokinase, FRK, (EC 2.7.1.4); hexokinase, HK, (EC 2.7.1.1)) were enhanced in melon fruit exposed to HVEF. The qRT-PCR results demonstrated that genes linked to sugar metabolism and transport, including CmSPS1/3, CmHK2/3, and CmFRK4/7, exhibited varied regulation when exposed to HVEF. Our results indicate that HVEF increased sugar metabolism and utilization capability, eventually leading to higher sink strength and faster fruit growth. These results also help promote the practical application of HVEF in facility agriculture.