PROTEIN, METHIONINE, AND CYSTEINE UPREGULATION IN <i>PHASEOLUS VULGARIS</i> ‘BLACK TURTLE BEAN’ SEEDS THROUGH SULFUR FERTILIZATION AT V2 AND R2 STAGES OF GROWTH

The purpose of this research was to increase protein, methionine, and cysteine content in Phaseolus vulgaris L., common bean in relation to the inhibitory compound tannin. Previous research has shown that sulfur fertilization increases total protein, methionine and cysteine content in various crops, but always in tandem with inhibitory compound increases. If successful, the resulting bean seed will have a better nutrient profile for malnourished populations around the world.

Granular gypsum was applied at 0 kg S ha^-1 [kilograms of sulfur per hectare], 10 kg S ha^-1, 20 kg S ha^-1, 40 kg S ha^-1, 60 kg S ha^-1, and 80 kg S ha^-1 in two experiments. The main difference between experiments was timing of application (V2 and R2 stage of growth application respectively). Soluble protein, crude protein, methionine, cysteine, and tannin content were compared to controls. Ratios of soluble protein: tannin, crude protein: tannin, methionine: tannin, and cysteine: tannin were also compared.

Yield depression occurred at 20 kg S ha^-1 for both application timings. Fertilization at the V2 stage of growth decreased soluble protein at 10 kg S ha^-1 compared to controls. Crude protein increased at 10 and 40 kg S ha^-1 compared to 80 kg S ha^-1; drought may have influenced this outcome. For V2 application, methionine peaked at 20 kg S ha^-1 while cysteine peaked at 80 kg S ha^-1. For R2 application, crude protein decreased at 10 kg S ha^-1, 40 kg S ha^-1, and 80 kg S ha^-1, and cysteine was lower at 60 kg S ha^-1 compared to controls. Tannin contents were higher at 80 kg S ha^-1. These results may suggest nutrient imbalance in the soil.

Sulfur application at the V2 stage of growth produced the highest protein to tannin ratios compared to R2 application, though amino acid to tannin ratios were similar for both fertilization timings. We conclude that sulfur fertilization at V2 stage of growth gives the most improvement in nutritional quality compared to R2 application, with 20 kg S ha^-1 giving the best overall quality increases in Phaseolus vulgaris bean seeds.