Regulation of the inward rectifying K+ channel MIRK and ion distribution in two melon cultivars (Cucumis melo L.) under NaCl salinity stress

Maintenance of a high K+/Na+ concentration ratio in plants by regulation of the expression of specific ion channels plays an important role in salt resistance. In this work, two melon cultivars differing in salt tolerance were used to evaluate melon inward rectifying K+ channel (MIRK) transcription, K+ and Na+ distribution, as well as stomata aperture under various salt treatments (0, 100 and 200 mM NaCl) for exploring the mechanism of salinity tolerance in melon. The salt-tolerant cultivar, cv. Bingxuecui (BXC), showed a smaller reduction in biomass due to salt treatments than the salt-sensitive cultivar, cv. Yulu (YL). Although the level of total Na+ in the whole plant was the same in both melon cultivars after salinity treatments, a lower Na+ level with higher K+/Na+ ratio was observed in the leaves of the BXC cultivar, which is likely to promote salt tolerance in melon. Salinity also resulted in down-regulation of MIRK transcription and stomata closure in the leaves of both varieties; however, compared to the YL cultivar, a lesser extent of MIRK transcription and stomata aperture reduction were observed in the BXC cultivar, both of which remained steadier at most sampling times. The high correlation observed between stomata aperture closure and MIRK transcription level suggests that the regulation of the MIRK channel in melon may be involved in modulation of the stomata apertures, subsequently balancing transpiration and CO2 exchange, which may ultimately contribute to a higher tolerance to salinity.