The timing of grain Cd accumulation in rice plants: the relative importance of remobilisation within the plant and root Cd uptake post-flowering

Abstract

The pathways by which Cd is accumulated in rice grain are not well understood, in particular the components attributable to direct transfer from the root, and to remobilisation of Cd previously accumulated in other plant parts. In order to observe the timing of Cd accumulation in rice plants and determine the major period for accumulation of Cd which can be translocated to the grain, Cd was supplied to the roots of rice plants grown under static hydroponic conditions at a non-toxic, environmentally relevant concentration (50 nM), according to three different timing regimes: (1) Pre-flowering Cd, (2) Post-flowering Cd, or (3) Continuous Cd. The rate of accumulation of Cd in the developing grain was monitored by harvesting immature rice panicles at four time points prior to a final harvest. Nearly all grain Cd was accumulated within 16 days of anthesis and the contribution of post-flowering Cd uptake was evident from 7 days after flowering. It was estimated that 60% of the final grain Cd content was remobilised from that accumulated by the plant prior to flowering and the other 40% came from uptake during grain maturation. This study shows that Cd uptake from the root to the grain in rice is indeed possible post-flowering and it is an important source of grain Cd.

Cadmium uptake and translocation in durum wheat varieties differing in grain-Cd accumulation

“…Similar to the findings of Rodda et al (2011) in rice, most Cd uptake occurred before heading. At this stage, plants of Creso contained 80% of final Cd with the supply of 1.5 and 3 mg Cd/kg, and 90% with 4.5 mg Cd/kg, while those of Svevo approximately 70%.…”

“…As a consequence, Cd partitioning to shoots was markedly higher at maturity than at heading in both varieties (Table 4). With increasing Cd supply, partitioning to shoot was significantly higher in Svevo, which is consistent with a direct transport of Cd from root to grain during post-heading growth (Rodda et al 2011). Since root is the primary sink for Cd, we suggest that high biomass partitioning to roots before heading could increase root to grain Cd remobilization (Chan and Hale 2004).…”

Impact of long-term cadmium exposure on mineral content of Solanum lycopersicum plants: Consequences on fruit production

“…This result is in agreement with those of Cieslieski et al (1996), who concluded that in durum wheat, the high accumulation of Cd in grain at maturity reflects redistribution of Cd via the phloem pathway. By contrast, Rodda et al (2011) found that the majority of Cd in rice grain was accumulated during the early period of grain development. This divergence may be due to differences on the mechanisms determining translocation of Cd to the edible plant tissues.…”

Heavy Metal Accumulation in Different Rice Cultivars as Influenced by Foliar Application of Nano-silicon

“…Si significantly reduced the transport of the apoplastic fluorescence tracer PTS (trisodium-8-hydroxy-1,3,6-pyrenesulfonate) from roots to shoots (Shi et al 2005), suggesting that the deposition of Si in the vicinity of the endodermis maybe partially blocked the apoplast bypass flow across the roots and restrained the apoplastic transport of Cd. Additionally, remobilization of Cd in leaf blades also contributes to grain Cd accumulation (Rodda et al 2011), and thus, Si sprayed onto leaves may enter leaves and increase Cd sequestration to cell wall and decrease the potential for further redistribution. Excess heavy metals generally cause the formation of reactive oxygen species that damage membrane permeability and function, while Si reduces membrane permeability and improves its structure and stability (Liang et al 2007), thus limiting the transport of heavy metals.…”