Salt Stress Induces Segmentation of Wheat Etioplasts but Only Mildly Affects Photosynthetic Activity in Chloroplasts

Owing to the projected rise in sea level, saltwater flooding and seawater infiltration are expected to affect coastal agricultural fields and young seedlings germinating in them more frequently. We therefore studied the effects of short-term salt shock treatment with 600 mM NaCl:KCl (1:1) and, in some cases, isosmotic polyethylene glycol 6000 (PEG) treatment on leaf segments of 8–11-day-old dark-grown, then greened or light-grown wheat (Triticum aestivum L. cv. Mv Béres) seedlings. Our transmission electron microscopic, flame photometric, infrared gas exchange analyses, fast chlorophyll a fluorescence induction (OJIP), pulse-amplitude modulated (PAM) fluorescence imaging and ultra-performance liquid chromatography (UPLC) measurements revealed moderate differences in photosynthesis-related parameters in salt-stressed light-grown and greened seedlings, with no important alterations in photosynthetic pigments with the exception of a significantly increased xanthophyll de-epoxidation ratio in stressed samples. The slightly lower Na+ and K+ contents of the dark-grown leaves exposed to the same salt stress did not correspond to the pronounced ultrastructural sensitivity of the dark-grown tissues, the observed peripheral segmentation and exclusion of stroma regions of etioplasts and photosynthetically inactive etio-chloroplasts under salt stress. This piecemeal degradation of the plastid indicates that seedlings germinating in the soil under no or limited autotrophy are the most sensitive to salt stress.