- Title
- Influences of root iron plaque formation and rice variety on cadmium accumulation in rice
- Creator
- Siddique, Abu Bakkar
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Rice is the most important food crop of the developing world and the dominant staple food of more than half of the world’s population. Cadmium (Cd) is considered one of the most perilous elements, and its existence in crop fields is of great environmental concern due to its high harmfulness, persistence, and severe extent of bioaccumulation. Rice consumption is a major dietary source of Cd and poses a potential threat to human health. In this present research, hydroponic and soil experiments under glasshouse conditions were carried out to investigate firstly, variation of Cd accumulation by different rice cultivar under root plaque formation using iron (Fe) amendment: and secondly, variation of Cd loading in different rice parts as well as human health risk estimation from rice consumption. The hydroponic study was employed three levels of Fe (0, 50 and 100 mg L-1) and Cd (0, 0.5 and 1.0 mg L-1) to investigate the varietal variation of Fe plaque formation on Cd accumulation in rice plants. Reddish-brown colored Fe plaque gradually deposited on the root surfaces after Fe treatment and plaque formation capacities varied among the rice cultivars. The addition of Fe and Cd significantly affected the Cd concentration in the citrate-bicarbonate-dithionite (CBD) extracts of roots and the shoots and roots of rice seedlings. Quest variety demonstrated the highest capacity of Fe plaque formation compared to the other varieties. The results demonstrated that enhanced Fe plaque formation could minimize the detrimental effects of Cd on rice shoot growth to some extent. A pot experiment was carried out to study the impact of soil type and rice cultivars on variations in the iron plaque formation, Cd sequestration in Fe plaques and Cd bioaccumulation in different parts of the rice plant at both seedling stage and harvesting stage of rice plant. This pot study utilized three different Cd-graded paddy soils (0, 1.0 and 3.0mg/kg, respectively) using two Australian rice cultivars at glasshouse conditions under three levels of Fe (0, 1.0 and 2.0g/kg) application. The results of the seedling stage indicated that the biomass yield decreased with Cd addition and increased with Fe application and a significant difference was observed between the two rice cultivars grown in both soil types. The results revealed that shoot biomass decreased by 12.2–23.2% in Quest and 12.8–30.8% in Langi in the Cd1.0 and Cd3.0 treatments, while shoot biomass increased by 11.2–19.5% in Quest and 26–43.3% in Langi in Fe1.0 and Fe2.0 as compared to the Fe control. The different levels of Cd and Fe, soil type and rice cultivar significantly affected the Cd and Fe contents in iron plaque and in the roots and shoots of rice seedlings. The Cd concentration in the roots and shoots of rice seedlings were in the order of Langi cultivar > Quest cultivar, but the Fe concentration in rice tissues showed the reverse order. Fe plaque formations were promoted by Fe application, which was 7.8 and 10.4 times higher at 1 and 2 g kg-1 Fe applications compared to the control Fe treatment. The Quest cultivar exhibited 13% higher iron plaque formation capacity compared to the Langi cultivar in both soil types. Results of the harvesting stage showed that yield and yield-related components declined as Cd toxicity increased, and the Quest cultivar showed less sensitivity to Cd toxic effects than the Langi cultivar. The concentrations of Cd in rice plant cultivated were 1.09mg/kg and 1.37mg/kg in Soil 1 while those in rice plant grown were 0.38mg/kg and 0.52mg/kg in Soil-2, respectively, under addition of 1.0mg/kg and 3.0mg/kg Cd. The Cd bioaccumulation in different segments of rice plants was significantly affected by soil pH. For example, grain Cd concentration was 0.87 mg/kg in Soil 1 (pH 4.6) whereas in Soil 2, grain Cd concentration was 0.31 mg/kg. Soil pore water Cd dynamics was declined over time and enhanced with Cd application but reduced with Fe addition. The pore water Cd in Soil 1 reached 90.5 µg L-1 by 10 days after transplanting (DAT) of rice seedlings and gradually declined to 32.43 µg L-1 over time (110 DAT), and Soil 2 exhibited around 50 % less Cd in pore water as compated Soil 1. Translocation factors (TFs) from root to straw (TFroot-straw) or straw to husk (TFstraw-husk) were higher than root to grain (TFroot-grain) or straw to grain (TFstraw-grain). The Cd concentration in rice plants was observed in the order of: root>stem>leaf>husk>grain. The Quest cultivar had a higher ability to produce Fe plaques and a 1.3- and 1.4-times higher Cd concentration compared with the Langi cultivar in Soils 1 and 2, respectively. Average daily intake (ADI) of Cd exceeded the permissible limit (5.8×10-3 mg -1kg-1 bw per week) when rice plants were subjected 1 and 3 mg kg-1 Cd stress with or without Fe application. Results also indicated that ADI value was lower in Quest genotype as compared to Langi rice cultivar. Estimation of human health risks revealed that the non-carcinogenic risks (HQ>1) and carcinogenic risks (CR>1.0×10-4) were increased with increasing Cd levels in soil. The application of Fe decreased the human health risks from rice consumption which was more pronounced in Fe 2.0 than in Fe1.0 treatments. These results also indicate that enhanced iron plaque formation on the root surface was crucial to reducing Cd concentration in rice plants, which could be an effective strategy to regulate grain Cd accumulation of rice plants.
- Subject
- cadmium accumulation; rice; root plaque; rice consumption; health risks
- Identifier
- http://hdl.handle.net/1959.13/1508197
- Identifier
- uon:56103
- Rights
- Copyright 2022 Abu Bakkar Siddique
- Language
- eng
- Full Text
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