Naturally-Occurring and Ethylene-Induced Phenolic Compounds in the Carrot Root.

Area of Science:

• Plant Physiology
• Biochemistry
• Food Science

Background:

• Carrot roots can develop off-flavors and discoloration during storage due to phenol accumulation.
• Understanding the physiological triggers for these changes is crucial for improving storage quality.

Purpose of the Study:

• To investigate the effect of ethylene on carrot root metabolism.
• To identify the compounds synthesized under ethylene influence.
• To elucidate the metabolic pathways involved in ethylene-induced changes.

Main Methods:

• Carrot root slices were exposed to varying concentrations of ethylene.
• Phenol content and new compound formation were analyzed.
• Metabolic pathways were studied using radiolabeled precursors ([1-¹⁴C]acetate, [2-¹⁴C]malonate, [3-¹⁴C]acetoacetate, and labeled glucose).
• Enzyme activity was assessed using inhibitors like cycloheximide.

Main Results:

• Ethylene (100 ppm) increased total phenol content, particularly isochlorogenic acid.
• Higher ethylene levels induced the synthesis of isocoumarin, eugenin, and other compounds.
• These compounds are likely synthesized via the acetate pathway.
• Ethylene stimulated O₂ uptake and CO₂ evolution, preferentially activating the Embden-Meyerhof-Parnas (EMP) pathway over the Pentose Phosphate (PP) pathway.
• Isocoumarin synthesis was also induced by dinitrophenol and methylene blue.
• Cycloheximide suggested de novo protein synthesis is required for ethylene-induced isocoumarin formation.

Conclusions:

• Ethylene significantly alters carrot root metabolism during storage.
• Ethylene triggers the de novo synthesis of
• stress-metabolites
• including isocoumarin and eugenin.
• These metabolic shifts are linked to glucose metabolism and may involve new enzyme synthesis.