Amino acids in orange juice may reveal the way in which citrus greening (HLB) is able to attack.
Studies of these amino acids by U.S. Department of Agriculture (USDA) chemist Andrew P. Breksa III and University of California, Davis, professor Carolyn M. Slupsky may lead to an effective approach to treating the disease.
For a 2012 study in the Journal of Proteome Research, the scientists used nuclear magnetic resonance spectroscopy to study the amino acid composition of juice from oranges grown on HLB-positive or HLB-negative trees.
The investigation is the first in which this technology is used for that purpose.
The study yielded distinctive profiles of the kinds and amounts of 11 different amino acids in three types of oranges: fruit from healthy trees; symptom-free fruit from HLB-positive trees; and fruit with HLB symptoms from HLB-positive trees.
With further research, the profiles may prove to be a reliable, rapid and early indicator of the presence of the HLB pathogen in an orchard, according to Breksa.
Breksa also noted that the profiles may reveal clues to mechanisms underlying the microbe's mostly unknown mode of attack. For instance, if the HLB pathogen were causing havoc with the trees' ability to create, use and recycle amino acids, scientists might be able to use that information as a starting point for a counterattack strategy.
Phenylalanine may be a case in point. An orange tree can convert this amino acid into cinnamic acid, a precursor to compounds thought to be important to the tree's defense system. But the researchers found that juice squeezed from oranges of HLB-positive trees had significantly higher concentrations of phenylalanine, which suggests that the HLB pathogen may have interfered with the tree's conversion of phenylalanine to cinnamic acid.