Changes in the plastid ultrastructure duringSedum rotundifolium leaf development

Abstract

The ultrastructure of plastids was investigated in succulent leaves of Sedum rotundifolium to examine their changes during development. Leaves were categorized as etiolated, immature, young, and mature, based on their developmental stage and size. Of particular interest were the features of the tubular inclusion bodies (TIBs) and starch grains. These, along with vacuole size, showed remarkable changes over time. Etioplasts of unexposed leaves had prolamellar bodies, abundant starch grains, large TIB, few plastoglobuli, and thylakoid systems. Membranes of the thylakoids were still continuous with those of the prolamellar body. The plastids were often influenced by the presence and profile of inclusion bodies and starch grains throughout the early stages. Morphology was highly variable in the etioplasts but consistently hemispherical or ovoid in mature chloroplasts. T|B was most abundant in the etiolated leaves, but disappeared completely with development. Starch grains also became significantly reduced in size. Both young and mature mesophyll cells exhibited a normal chloroplast ultrastructure and huge central vacuoles, with an extremely thin peripheral cytoplasm. Grana were extensive and comprised a large portion of the chloroplasts. Traces of peripheral reticulum were also discovered in the chloroplasts of expanded leaves. The implications of these ultrastructural changes in the tubular inclusions and starch grains are discussed with relevance to Crassulacean acid metabolism (CAM).

Oxidative stress protection and stomatal patterning as components of salinity tolerance mechanism in quinoa (Chenopodium quinoa)

“…Given the fact that the sensitivity of key cytosolic enzymes to Na + appears to be similar for both glycophytes and halophytes (Flowers and Colmer 2008), and a lack of any detrimental effects of salinity on chlorophyll content (data not shown), it is reasonable to suggest that all accumulated Na + was safely sequestered in vacuoles, regardless of the leaf position. At the same time, a degree of vacuolation of young developing leaves is much lower compared with fully developed leaves (Kim 2006). This limits the amount of Na + that can be sequestered in young leaves and calls for a need for the larger pool of organic osmolytes.…”