MSMA resistance studies

Area of Science:

• Agricultural Science
• Plant Biology
• Environmental Toxicology

Background:

• Monosodium methanearsonate (MSMA) is an herbicide used in agriculture.
• Understanding herbicide resistance mechanisms in plants like cocklebur and cotton is crucial for effective weed management.
• Arsenic metabolism and detoxification pathways in plants are not fully elucidated.

Purpose of the Study:

• To investigate the biochemical basis of MSMA resistance in common cocklebur (Xanthium strumarium L.) and cotton (Gossypium hirsutum L.).
• To analyze the effects of MSMA treatment on arsenic content, amino acid profiles, and glutathione metabolism in resistant and susceptible biotypes.
• To explore the potential role of glutathione synthetase and phytochelatins in MSMA tolerance.

Main Methods:

• MSMA-resistant and -susceptible biotypes of cocklebur and cotton were treated with MSMA.
• Analysis of plant parameters included glutathione synthetase activity, amino acid content (arginine, glutamic acid, alanine, citrulline, glutamine, glutathione), and arsenic content (MSMA, total arsenic, arsonate).
• No reduction of pentavalent arsenic to trivalent form was detected post-treatment.

Main Results:

• MSMA treatment increased arginine, glutamic acid, and glutamine content within three days.
• Glutathione levels initially decreased but were significantly elevated (8-20 times) in resistant cocklebur and cotton five days post-treatment.
• Glutathione synthetase activity was higher in cotton than cocklebur and unaffected by MSMA, though slightly higher in resistant biotypes.

Conclusions:

• Cotton's tolerance to MSMA may involve glutathione synthetase activity and phytochelatins.
• Elevated glutathione levels in resistant biotypes suggest a role for phytochelatins in the MSMA resistance mechanism.
• MSMA does not appear to undergo reduction to the toxic trivalent form within these plant species.