BACKGROUND: An immature wheat spike culture system was used to monitor cadmium (Cd) accumulation in grains, hulls and awns of bread wheat and durum wheat. Immature spikes were cultured prior to anthesis in a medium containing 50 g L−1 sucrose and 0.4 g L−1L-glutamine, supplemented with 0, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20 or 25 mg L−1 cadmium chloride (CdCl2). Grains were collected at maturity and their Cd accumulation was determined using inductively coupled plasma mass spectrometry (ICP-MS).
RESULTS: Cd accumulation at CdCl2 concentrations of 3 mg L−1 and above was higher in grains of durum wheat compared with bread wheat. In hulls a similar trend was observed at CdCl2 concentrations above 15 mg L−1. Starch concentration in grains increased slightly at 3 and 4 mg L−1 CdCl2. Cd accumulation negatively affected grain protein concentration. Expression patterns of Cd-related genes glutathione reductase (TaGR), metallothionein (MT) and phytochelatin synthase (PCS) in spikes cultured in media containing 0, 5, 10, 15 and 25 mg L−1 CdCl2 at 5 days post-anthesis showed that TaGR and PCS expression in bread wheat was up-regulated at 5 mg L−1 CdCl2 but down-regulated at other CdCl2 concentrations. However, in durum wheat, expression of all three genes was down-regulated or remained unchanged.
CONCLUSION: This study demonstrates that immature spike culture can be used to study Cd accumulation in grains and can delineate hyper-accumulating durum wheat from bread wheat at CdCl2 concentrations of 2 mg L−1 and above. Copyright © 2011 Society of Chemical Industry