Updated January 30, 2023:
View uploaded report 
Using methanolic leaf extracts from two different cultivars of soybeans, we were able to examine at the level of metabolites some of the differences between a drought-susceptible cultivar, Pana, vs. a drought-tolerant cultivar, PI 567731. Leaf extracts from the two cultivars grown under control conditions share 60 ionic formulas which are matched to the SoyCyc database. Prominent amongst these are mono- and diacylglycerols, pheophytin a and chlorophyll a, monosaccharides, disaccharides, xanthins, and vicenin-2 (a flavonoid diglucosylation product). Notable also is the simultaneous presence of plastaquinone, detected with products echinone and plastoquinol, essential components of photosynthetic electron transfer.
More interesting, however, are the metabolites which are detected in only one of the two cultivars. There are several carboxylic acid molecules present in Pana that were not detected in PI 567731; these are essential precursors to lipids. Carlactone is an oxidation product of cartenal, possibly indicating oxidative stress in Pana even in the control which has not experienced drought. This is further supported by the presence of glutathione disulfide, the oxidized dimer of glutathione. Galactopinitols are required substrates and products of galactosylcyclitol biosynthesis. The compound 15-cis-phytoene is needed for production of plastoquinol and carotenes. Likewise, the substance menoquinol-8 is a polyprenyl quinone required for electron transport. A richer more diverse complement of pheophytins and chlorophylls are detected in Pana in comparison to PI 567731 (e.g., chlorophyll b was only detected in Pana). However, our earlier work showed that PI 567731 maintains greater levels of pheophytins and chlorophylls during drought itself.
There are five metabolites uniquely detected in PI 567731 leaf extracts. First is3-ß-D-galactosyl-sn-glycerol, formed from the degradation of diacyl glycerols. Soyasapogenol B is a key precursor in the formation of its glucuronide. There are many possible structures for the trisaccharides, so anabolism of more complex saccharides from mono- and disaccharides might explain the appearance of trisaccharides here. Plastoquinones are electron carriers that are necessary building blocks for plastoquinol, and are found in chloroplasts, thus playing a central role in the photosynthetic electron transport chain. Moreover, for the metabolites unique to PI 567731, several key biosynthetic pathways are identified: saponin, glycherretinate, B series fagopyritols, starch, and stachyose. Degradation pathways include those for glycerodiphosphoesters and stachyose. One transport pathway—acquisition of phosphate—is also apparent in a metabolite specific to PI 567731. Although less chemically diverse, the metabolites identified uniquely in PI 567731 tend to be building blocks of complex sugars as well as phosphate acquisition. It may be that PI 567731 has a larger reservoir of energy storage molecules than Pana, which may enable it to adapt better to conditions of drought.