Effect of potassium on growth and the electrophoretic pattern of leaf proteins of sunflower supplied with ammonium or nitrate

Sunflower (Helianthus annuus L.) was grown on liquid medium containing either nitrate, ammonium or ammonium + nitrate, with or without potassium. The growth of plants supplied with nitrate or ammonium + nitrate in the presence of potassium (5 mmol/l) was comparable. Plants grown on ammonium‐N only showed significantly lower growth. Dry matter and organic nitrogen content in plants supplied with ammonium + nitrate (total nitrogen 10 mmol/1) in the presence of potassium (5 mmol/l) was higher than in nitrate grown plants. Leaf protein pattern on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS‐PAGE) was not affected by the nitrogen source provided in the medium.

Potassium deficiency led to reduced growth, necrotic spots on the leaves and specific alterations in leaf protein pattern, expressed by an increase or decrease in several polypeptides. This was common to all the nitrogen forms tested. A most pronounced change was the increased expression of polypeptides of molecular weight 60 and 62 kilodaltons.