In vitro-cultured wheat spikes provide a simplified alternative for studies of cadmium uptake in developing grains

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 ^-1 L-glutamine, supplemented with 0, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20 or 25 mg L ^-1 cadmium chloride (CdCl ₂). Grains were collected at maturity and their Cd accumulation was determined using inductively coupled plasma mass spectrometry (ICP-MS). Results: Cd accumulation at CdCl ₂ 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 CdCl ₂ concentrations above 15 mg L ^-1. Starch concentration in grains increased slightly at 3 and 4 mg L ^-1 CdCl ₂. 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 CdCl ₂ at 5 days post-anthesis showed that TaGR and PCS expression in bread wheat was up-regulated at 5 mg L ^-1 CdCl ₂ but down-regulated at other CdCl ₂ 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 CdCl ₂ concentrations of 2 mg L ^-1 and above.