Nutrients, ultrastructures, and Cd subcellular localization in the cottonseeds of three upland cotton cultivars under Cd stress

A pot experiment was performed to study the Cd-induced alterations in seed quality at maturity in two transgenic upland cotton cultivars, ZD-90 and SGK3, and the upland cotton standard line, TM-1. The results shown that Cd content in cotton kernels increased linearly with the elevation of Cd stress levels. SGK3 accumulated more Cd than others. Protein content in the kernels was increased under Cd stress generally, but those at 600 μM Cd level were lower than that under 400 μM Cd level. The changes in oil content were inversed to that of protein content. Significant ultra-structural changes in cottonseeds were induced by Cd stress, especially at higher Cd levels, which were more obvious in TM-1, followed by ZD-90 and SGK3. Plasmolytic shrinkage, disintegration of nucleus, cell wall thickening, and eventual cell collapse and disintegration were observed in the cells of cottonseeds under Cd stress. Transmission electron microscope (TEM) observation and energy dispersive X-ray analysis (EDAX) confirmed that Cd existed in the form of rings and crystals as well as electron dense granules, occurred in the intercellular space, the cytoplasm, and the cell wall. SGK3 was a tolerance cultivar to Cd stress with greater Cd accumulation and sequestration in cottonseeds.