Chlorophyll Accumulation, Protochlorophyllide Formation and Prolamellar Body Conversion are Held Back in Wheat Leaves Exposed to High Salt Stress

Abstract

When exposed to salt stress, leaves from dark-grown wheat seedlings (Triticum aestivum, cv. Giza 168) showed reduced accumulation of chlorophyll during irradiation. Plastids from salt-treated leaves had highly swollen prothylakoids (PTs) whereas the prolamellar bodies (PLBs) were regular. The long-wavelength Pchlide form emitting at 656 nm was intact and the phototransformation of Pchlide to Chlide was not affected. Newly formed thylakoids in the salt-stressed leaves were also swollen and showed traversing stromal strands. Dispersal of PLBs was partly inhibited and remnants of the PLBs formed an electron-dense structure. Newly formed Chlide had a delayed blue-shift (Shibata shift) both after irradiation with flashes and with continuous light. The reformation of Pchlide in darkness after a flash irradiation or after a period of 3 h irradiation was retarded in the salt-treated leaves. The main chlorophyll form in salt-stressed leaves had a fluorescence emission maximum at shorter wavelength (681 nm) than the chlorophyll in control leaves (683 nm) indicating a restrained formation of the photosynthetic apparatus during irradiation. The increase in the low temperature fluorescence emission spectrum at 735 nm, which occurred gradually during several hours of irradiation with continuous light in control leaves, was completely suppressed in salt-treated leaves.