MIFE technique-based screening for mesophyll K+ retention for crop breeding for salinity tolerance

Potassium is known as a rate-limiting factor for crop yield and plays an important role in plants response under abiotic stresses. Recently, cytosolic K⁺ retention ability in leaf mesophyll has emerged as an important component of plant salt tolerance mechanism (Wu <em>et al.</em>, 2013; Wu <em>et al.</em>, 2014; Wu <em>et al.</em>, 2015). In this protocol, the procedure for screening leaf mesophyll for K⁺ retention by the MIFE (microelectrode ion flux estimation) technique is described in detail using wheat as an example. By measuring NaCl-induced K⁺ efflux in leaf mesophyll, a large number of plant accessions can be screened and categorised according to their salinity stress tolerance. The method provides a rapid and reliable tool that targets the activity of specific membrane transporters directly contributing to salinity tolerance trait and, because of this, has a competitive advantage over traditional whole-plant phenotyping. While the focus of this protocol is on wheat, the suggested method may be adopted for screening K⁺ retention in leaf mesophyll in any other crop species.