Ionic, not the osmotic component, is responsible for the salinity-induced inhibition of greening in etiolated wheat (Triticum aestivum L. cv. Mv Béres) leaves : a comparative study

Main conclusion Greening was partially (in 300 mM NaCl, $CaCl_{2}$, 600 mM $KNO_{3}$ or KCl) or fully inhibited (in 600 mM NaCl, $NaNO_{3}$ or NaCl:KCl) by the ionic and not the osmotic component of salinity. Abstract Although high soil salinity is an increasing global problem, not much is known about how direct exposure to salinity affects etiolated leaves of seedlings germinating in the soil and then reaching the surface. We investigated the effect of various salt treatments on the greening process of leaves in 8- to 11-day-old etiolated wheat (Triticum aestivum L. Mv. Béres) seedlings. Etiolated leaf segments pre-treated on different salt (600 mM NaCl:KCl 1:1, 600 mM NaCl, 600 mM KCl, 600 mM $NaNO_{3}$, 600 mM KNO3, 300 mM KCl, 300 mM NaCl or 300 mM $CaCl_{2}$) or isosmotic polyethylene glycol 6000 (PEG) solutions for 1.5 h in the dark and then greened for 16 h on the same solutions were studied. Leaf segments greened on PEG (osmotic stress) or on 300 mM KCl had similar chloroplasts compared to control samples greened on Hoagland solution. Slightly slower development of chloroplast structure and function (photosynthetic activity) was observed in segments greened on 300 mM NaCl or $CaCl_{2}$, 600 mM KNO3 or KCl. However, etioplast-to-chloroplast transformation and chlorophyll accumulation were fully inhibited and peculiar prothylakoid swelling occurred in segments greened on 600 mM NaCl, $NaNO_{3}$ or NaCl:KCl (1:1) solutions. The data indicate that not the high osmolarity of the used salt solution, but its ions, especially $Na^{+}$, had the strongest negative impact on these processes.