2013 Annual Report
1a.Objectives (from AD-416):
(1) Establish baseline metabolic profiles of commercial citrus products through the use of H1-Nuclear Magnetic Resonance (NMR).
(2) Determine the influence of cultivar variety, environment and plant health on the metabolite composition by comparing the profiles obtained for these samples to those obtained for other citrus products.
(3) Ddentify diagnostically significant metabolites.
1b.Approach (from AD-416):
Citrus fruits harvested by a commercial source will be processed into juice and provided for analysis. Juice samples will be prepared for analysis by H1-NMR and analyzed. Initial data analysis and the subsequent statistical analysis will be conducted at the UC Davis in conjunction with the ARS Scientists at the Western Regional Research Center, Albany, CA. Additional samples for analysis may be obtained from commercial citrus growers or from citrus variety collections. It is expected that the total number of samples to analyze will range from 100 to 150 samples.
This project was one component of a multi-prong approach to identify naturally occurring metabolites found in Citrus fruits that could be used diagnostically to distinguish healthy trees from those suffering from Citrus Greening disease (HBL). Through H1-NMR analysis, more than thirty different metabolites, including amino acids, organic acids, sugars and other metabolites were quantified in over 100 samples. Analysis of these resulting metabolite profiles revealed distinct metabolite differences between fruits harvested from healthy trees (healthy) and fruits showing symptoms of HLB that were harvested from infected trees (symptomatic fruit). The analysis of asymptomatic fruits taken from infected trees was also conducted. Unlike the profiles resulting from healthy fruits and symptomatic fruits which were clearly distinguishable, profiles from asymptomatic fruits as a group were less uniform and the lack of uniformity prevented them from being classified into their own group. In fact, the profiles of some asymptomatic samples were very similar to profiles found for healthy samples, whereas the metabolic profiles of other asymptomatic samples were closer to the profiles found for symptomatic samples. These results suggest that asymptomatic samples represent a continuum between healthy and symptomatic profiles and that a tree’s response to HLB is based upon a complex mixture of environmental factors. In order to better distinguish between asymptomatic fruits, additional work will need to be done with sample sets in which these factors, including the extent of infection and time since infection, are better understood.
This project was initiated in support of 5325-41430-011-02T and addresses objectives 1: "Develop new or improve existing methods to detect, identify, and characterize N-containing plant metabolites", 2: "Screen specialty crops for their metabolimic profiles with a particular empasis on nitrogen-containing metabolites. Initial efforts will focus on the fruits and leaves from citrus, grapes, tomatoes, peaches, nectarines, and plums", & 3: "Isolate and characterize a SAM-dependent N-methyltransferase in order to increase our knowledge about this class of enzymes in plants and their relationship tp nitrogen metabolism."