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Cadmium distribution in ratoon rice: OsNramp5 mutant reduces accumulation while physiological factors modulate
Qi Xiao1, Bingran Zhao2, Chanchan Du1
1National Key Laboratory of Crop Genetic Improvement, Hubei Hongshan Laboratory, MARA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of the Yangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, China.
OsNramp5 gene function significantly reduces cadmium accumulation in ratoon rice grains. Upper-node tillers are identified as major cadmium sinks, posing risks to food safety in rice ratooning systems.
Area of Science:
- Agricultural Science
- Environmental Science
- Plant Physiology
Background:
- Cadmium (Cd) accumulation in ratoon rice presents food safety concerns and hinders sustainable agriculture.
- Understanding Cd transport and accumulation is crucial for mitigating risks in rice ratooning.
Purpose of the Study:
- To investigate the physiological mechanisms of Cd accumulation in ratoon rice.
- To compare Cd accumulation patterns in two contrasting rice genotypes under controlled Cd exposure.
Main Methods:
- Comparative analysis of two rice genotypes with differing Cd accumulation.
- Controlled exposure to cadmium.
- Measurement of Cd content in grains and leaves.
- Analysis of gene expression related to metal transport (OsNramp1, OsHMA2, OsLCT1, OsCCX2).
- Assessment of transpiration and grain-filling rates.
Main Results:
- Loss-of-function of OsNramp5 reduced grain Cd by 39.5-51.2% in both main and ratoon seasons.
- OsNramp5 downregulation correlated with reduced OsNramp1 and OsHMA2 expression and increased leaf Cd chelation.
- Upper-node tillers accumulated significantly more grain Cd (30.8-59.5%) than lower-node tillers in the ratoon crop.
- Higher transpiration and grain-filling rates in upper-node tillers contributed to increased Cd accumulation.
- Lower-node tillers showed late-season Cd surges linked to OsLCT1/OsCCX2 upregulation and peak transpiration.
Conclusions:
- OsNramp5 loss-of-function is a viable genetic strategy to decrease grain Cd in ratoon rice.
- Upper-node tillers act as preferential Cd sinks in ratoon rice, increasing contamination risks.
- Physiological factors like transpiration and grain-filling rates significantly influence Cd distribution in ratoon rice.
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