Do cyanogenic glucosides help sorghum manage a fluctuating nitrogen supply?

Area of Science:

• Agricultural Science
• Plant Physiology
• Biochemistry

Background:

• Sorghum (Sorghum bicolor [L.] Moench) is a vital forage crop containing dhurrin, a cyanogenic glucoside.
• Dhurrin releases toxic hydrogen cyanide upon tissue damage, posing a poisoning risk.
• The acyanogenic sorghum line tcd1 was developed to mitigate cyanide risks in forage.

Purpose of the Study:

• To investigate if dhurrin provides a growth advantage in cyanogenic sorghum (BTx623) compared to acyanogenic sorghum (tcd1) under limited and variable nitrogen conditions.
• To understand the role of dhurrin in nitrogen metabolism and storage in sorghum.

Main Methods:

• Cultivating BTx623 and tcd1 sorghum lines under two distinct nitrogen regimes: 'surge' (high dose, low frequency) and 'pulse' (low dose, high frequency).
• Monitoring plant growth, dhurrin concentrations, and nitrogen accumulation (nitrate, amino acids) over 42 days.
• Analyzing gene expression related to dhurrin biosynthesis and recycling.

Main Results:

• BTx623 showed no significant growth advantage or disadvantage compared to tcd1 under either nitrogen treatment.
• Young BTx623 plants utilized dhurrin for defense and rapidly recycled it during nitrogen deficiency under the surge treatment.
• Sorghum plants accumulated nitrogen in nitrate and amino acids, but not dhurrin, at later stages under the surge treatment.
• Evidence suggests gene expression changes promoting dhurrin biosynthesis and reduced recycling under surge nitrogen application.

Conclusions:

• Dhurrin plays a dual role in sorghum, serving in both plant defense and nitrogen storage/metabolism.
• The acyanogenic sorghum line tcd1 demonstrates potential as a safe and effective forage option, comparable to cyanogenic lines.
• Understanding dhurrin's role in nitrogen metabolism provides insights into sorghum cultivation and forage safety.