Boron's Role in Diminishing Cadmium Concentrations in Rice (Oryza sativa L.): Insights into Absorption Inhibition and...

Area of Science:

• Agricultural Science
• Environmental Science
• Plant Physiology

Background:

• Cadmium (Cd) contamination in paddy soils poses a significant food safety risk.
• Boron (B) is essential for plant growth and has shown potential in mitigating heavy metal absorption.
• Mechanisms of boron's effect on Cd accumulation in rice grains and plant physiology are not fully understood.

Purpose of the Study:

• To investigate the role of boron in reducing cadmium accumulation in rice grains.
• To elucidate the physiological and molecular mechanisms underlying boron's effects on cadmium transport and rice maturation.
• To assess the efficacy of boron application as an agronomic strategy for mitigating cadmium contamination in rice.

Main Methods:

• Pot and hydroponic experiments were conducted to evaluate boron's impact on rice seedlings.
• Measurements included root Cd influx, transport factors, and gene expression analysis (OsNramp5, OsIRT1, OsHMA2).
• Enzyme activities and gene expression related to sugar metabolism were analyzed to understand maturation effects. A field experiment was performed to validate findings under practical conditions.

Main Results:

• Basal boron application (1.5 mg kg^-1) reduced grain Cd concentration by 61.1% in pot experiments.
• Boron mitigated root Cd²⁺ influx by 32.4% and transport factors by 36.0-47.3% through downregulation of key transporter genes.
• Boron application enhanced sugar metabolism, shortened the rice growth period from 132 to 120 days, and decreased grain Cd by 47.7% in field trials.

Conclusions:

• Boron effectively reduces cadmium accumulation in rice grains by inhibiting Cd uptake and transport, and promoting earlier maturation.
• Downregulation of OsNramp5, OsIRT1, and OsHMA2 expression is a key mechanism for boron-induced reduction in Cd transport.
• Boron application presents a viable agronomic strategy to enhance food safety in rice cultivation on cadmium-contaminated soils.