Cadmium-Induced Structure Change of Pigment Glands and the Reduction of the Gossypol Content in Cottonseed Kernels

The risk of cotton production on arable land contaminated with heavy metals has increased in recent years. Cotton shows stronger and more extensive resistance to heavy metals, such as cadmium (Cd) than that of other major crops. Here, a potted plant experiment was performed to study Cd-induced alterations in the cottonseed kernel gossypol content and pigment gland structure at maturity in two transgenic cotton cultivars (ZD-90 and SGK3) and an upland cotton standard genotype (TM-1). The results showed that Cd accumulation in cottonseed kernels increased with increasing Cd levels in the soil. The seed kernel Cd content in plants grown on Cd-treated soils was 10-20 times greater than the amount in the corresponding controls. There was a significant difference in Cd accumulation in cottonseed kernels at the 400 and 600 mu M Cd levels. Cd accumulation was higher in SGK3 and ZD-90 than in TM-1. However, the gossypol content in cottonseed kernels was lower in SGK3 and ZD-90 than in TM-1. There was a negative correlation (r = 0.550) between Cd accumulation and the gossypol content in cottonseed kernels. The density of cottonseed kernel pigment glands decreased under Cd stress. This is consistent with the change in gossypol content, which decreased under Cd stress. The damage of the cultivars ZD-90 and SGK3 from Cd poisoning was relatively low under Cd stress, while TM-1 was seriously affected and exhibited Cd sensitivity. Further studies are necessary to understand the cause of the reduced gossypol content in cotton seeds under Cd stress.