Assessment of seed storage protein quality of some quantitative and qualitative rice cultivars (Oryza sativa L.)

Rice is a good source of energy and has the highest protein efficiency among plant proteins. However, its protein content is relatively low compared to other cereals. Seed storage protein in rice classified into four groups: albumin and globulin in aleurone layer, and prolamine and glutelin in endosperm. Therefore, during the bleaching process of rice grains, albumin proteins and part of globulin are removed by its bran. Since the protein content of the grain and its amount will be directly related to its nutritional quality and due to the importance of rice grain in diet, seed storage proteins quality in a quantitative and qualitative breeding population of rice such as two new mutant cultivars, Roshan and Shahriar, with their parents (Nemat and Amol3 respectively) as well as qualitative varieties, Sang-tarom, along with two different varieties of brown and black rice was studied.

Qualitative properties of grain proteins were evaluated based on their solubility as well as the seed storage proteins For albumin, globulin, prolamine and glutelin proteins. Quantification of stored proteins was performed by Bradford reagent and quantification of their subunits by densitometric analysis.

The results showed that there is a significant difference for the amount of seed storage proteins of different rice genotypes. So that Sang-tarom and Roshan cultivars had the highest amount of albumin protein (19.53 and 22.40 mg/g respectively). This was while the brown grain variety with the lowest amount of albumin and globulin protein and the highest amount of glutelin and prolamine proteins has the highest amount of total protein (1640.43 mg/g). Evaluation of the banding pattern of stored storage proteins also showed that this banding pattern was the same in different genotypes except in Roshan (60 kDa) and Shahriar (13 kDa) mutant cultivars. Densitometric analysis of protein subunits also showed that the highest amount of glutelin subunits was present in Sang-tarom cultivar and the lowest in Shahriar cultivar and brown grain variety. Also, the highest amount of prolamine subunits was observed in Sang-tarom cultivar and brown grain variety and the lowest in Shahriar cultivar. As Shahriar cultivar was able to have the highest amount of glutelin to prolamine protein.

Although the profiles of seed storage proteins in different varieties of rice are the same, but this pattern is different in the two cultivars of mutant Roshan and Shahriyar. So that, the absent of the 60kDa subunit of proglutelin and the 13kDa subunit of prolamine can be used as protein markers in both Roshan and Shahriar, respectively. Our study demonstrated that although there is a significant relationship between protein subunits and the amount of stored proteins, but there was no significant relationship between stored proteins with different quantitative and qualitative rice cultivars. Therefore it seems that improving the seed storage protein quality will probably not limit the improvement of new rice cultivars with desirable quantitative and qualitative characteristics.