Effect of nitrogen and sulphur nutrition on storage protein quality in soybean [Glycine max (L.) Merrill]

The relative availabilities of nitrogen and sulphur can modulate seed storage protein composition in grain legumes and cereals. Soybean contains two major seed storage proteins, glycinins and I²-conglycinins that account for approximately 70% of total protein and their composition is affected by nitrogen and sulphur supplies. The present study demonstrated the effect of sulphur (Gypsum @ 20 kg S ha-1 ) and recommended a dose of nitrogen (Urea @ 31.25 kg N ha-1 ) alone or in combination on accumulation patterns of various protein fractions and protein quality in soybean seeds under agro-climatic conditions of Punjab. Application of nitrogen or sulphur alone decreased the relative proportion of I²-subunit of purified I²-conglycinin fraction than control. The acidic polypeptides of glycinin fraction of globulin and 11S/7S ratio were increased in all the treatments in comparison to control, and the maximum increase was reported in the combined application of gypsum with the recommended dose of urea. The lower proportion of total 7S, increased acidic polypeptides and improved 11S:7S ratio by combined treatment of nitrogen and sulphur suggests that gypsum @ 20 kg S ha-1 can be beneficial when applied along the recommended nitrogen dose to improve soybean protein quality.