Impact of Seawater Salinity on Ultrastructure of Chloroplasts and Oleosomes in Relation to Fat Metabolism in Flag Leaf of Two Wheat Cultivars During Grain-filling

Abstract

Salt stress enhances generation of Reactive Oxygen Species (ROS) which are usually produced within chloroplast and mitochondria because of sustained flow of electrons in these organelles, so that chloroplasts are one of the most sensitive systems to various stress factors. Effect of seawater salinity (10% and 25%) on ultrastructure of chloroplasts and oleosomes as well as oleosomes volume in relation to fat metabolism in flag leaf of two wheat cultivars, Gemmieza-9 (salt sensitive cultivar) and Sids-1 (salt tolerant cultivar) during grain-filling was investigated. Irrigation of wheat plants with 25% seawater induced dramatic changes in chloroplasts and oleosomes particularly after 21 days post-anthesis. The results showed that there were slight differences between the two cultivars in response to seawater at 10% and 14 days post-anthesis in terms of chloroplasts ultrastructure. Moreover, disorganized membrane system was identified with swollen thylakoids and many plastoglobuli were recognized in the chloroplasts in comparison to control plants. Changes in membrane structure are mainly due to the rapid oxidative damage evaluated as malondialdehyde, membrane leakage and membrane stability index. Numerous spherical oleosomes were observed as free in the vacuole of flag leaf cells of both untreated and seawater treated plants. Oleosomes appeared to have a sharply-defined osmiophilic interface and apparently lack a limiting membrane. Seawater irrigation induced a progressive increase in lipase activity and glycerol content in flag leaf of both cultivars during grain-filling. Sids-1 accumulated more glycerol and total saturated fatty acids percentage as well as more reduction in total unsaturated fatty acids percentage, mono-unsaturated fatty acids percentage and poly-unsaturated fatty acids percentage than sensitive one under salt-stress.