Instant salt stimulation poses a serious challenge to the survival of plant roots, which severely affects the membrane potential (MP) of ion currents and cortical cells. Previous studies in corn, barley, and Arabidopsis found that NaCl induced K ⁺ outflow and plasma membrane depolarization. In general, NaCl causes a rapid decline in cytoplasmic K ⁺ , and the ability to effectively maintain K ⁺ is an important feature of plant salt resistance . Salt-tolerant varieties can be screened by the flow rate of K ⁺ .

In order to further clarify the spatial and temporal results of early events and ion changes induced by NaCl in root ion and water transport, the ion fluxes of corn root cortex and middle column cells were studied using non-invasive micro-test techniques . After treatment with 100 mM NaCl for 1 min, the xylem of the root xylem decreased exponentially, the potential across the roots rapidly depolarized and the xylem K ⁺ activity (AK ⁺ ) decreased briefly. At this time, no large amount of Na ^{+ was} released into the xylem catheter. It was unexpectedly found that AK ⁺ decreased and Na ⁺ entered the middle column, causing rapid depolarization, resulting in K ⁺ outflow of the columnar structure . This depolarization is significantly different between the cortical and medial cells of the root. The cortical cells are first depolarized, resulting in K ⁺ outflow. At this time, K ⁺ enters the cortex from the middle column symplast. When Na ^{+ is} loaded into the xylem, the middle column cells are depolarized and AK ⁺ gradually recovers.

Through this study, it was found that the response of plant roots to NaCl has a temporal and spatial separation, from the cortex to the middle column, and then affects the reaction of the whole root to the salt, thereby making a defensive reaction against salt. The combination of non-invasive micro-test technology and other technologies, especially fluorescence imaging technology, clearly illustrates the fate of Na ⁺ and the response of plants to NaCl salt.

Key words: barley, maize, membrane potential, xylem loading, non-invasive micro-measurement

References: Wegner LH , et al . Plant, Cell and Environment, 2011, 34: 859 - 869.

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Legend: Kinetics of K ⁺ and H ⁺ flow rates for the reaction of 20 mM and 100 mM NaCl in the middle column of corn , negative values ​​indicate efflux.

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