The Role of Potassium and Ascorbic acid on Some Growth and Physiological Responses in Catharanthus roseus

Different concentrations (1.5, 3.16, 15, and 30 mM) and forms (K2SO4 and KNO3) of potassium were applied through Hoagland’s nutrient solution. Ascorbic acid, 750 and 1500 mg L^-1, was sprayed twice on seedlings (age 68 and 78 days). Wet and dry weight, plant height, photosynthetic pigments, sodium, and potassium contents were measured at the end of the growing season. Also, total free amino acids was measured by HPLC. The excess of potassium increased the total wet (62%) and dry weight (54%), leaf area (31%), shoot and root height (49% and 15%, respectively), total chlorophyll (44%), and K+/Na+ ratio (100%) while the total free amino acids (2 times) and sodium content (28%) decreased. Ascorbic acid showed an almost similar trend under potassium in the mentioned traits, but it did not affect the root height and total sodium and potassium contents. There was a positive interaction between the potassium and ascorbic acid on the plant weight and height, leaf area, photosynthetic pigments, and K+/Na+ ratio. Regarding the positive effect of potassium and ascorbic acid on the growth parameters along with the similar changes on the photosynthetic pigments and the K+/Na+ ratio with the reduction of total free amino acids, it may be argued that both treatments improved plant growth through plant stability, increased photosynthetic rate, and production of more protein and other metabolites in Catharanthus roseus. Due to the importance of chemical compounds in Catharanthus roseus, any increase in the growth parameters leading to an increase in the yield of the plant can be very valuable.