Abstract
Helianthus annuus L. is an important oilseed crop, which exhibits moderate salt tolerance and can be cultivated in areas affected by salinity. Using patch-clamp electrophysiology, we have characterized Na(+) influx and K(+) efflux conductances in protoplasts of salt-tolerant H. annuus L. hybrid KBSH-53 under high salinity. This work demonstrates that the plasma membrane of sunflower root cells has a classic set of ionic conductances dominated by K(+) outwardly rectifying channels (KORs) and non-selective cation channels (NSCCs). KORs in sunflower show extreme Na(+) sensitivity at high extracellular [Ca(2+)] that can potentially have a positive adaptive effect under salt stress (decreasing K(+) loss). Na(+) influx currents in sunflower roots demonstrate voltage-independent activation, lack time-dependent component, and are sensitive to Gd(3+). Sunflower Na(+)-permeable NSCCs mediate a much weaker Na(+) influx currents on the background of physiological levels of Ca(2+) as compared to other species. This suggests that sunflower NSCCs have greater Ca(2+) sensitivity. The responses of Na(+) influx to Ca(2+) correlates well with protection of sunflower growth by external Ca(2+) in seedlings treated with NaCl. It can be, thus, hypothesized that NaCl tolerance in sunflower seedling roots is programmed at the ion channel level via their sensitivity to Ca(2+) and Na(+).