Differential Effects of Ammonium (NH(4)(+)) and Potassium (K(+)) Nutrition on Photoassimilate Partitioning and Growth of Tobacco Seedlings

Plants utilize carbohydrates as the main energy source, but much focus has been on the impact of N and K on plant growth. Less is known about the combined impact of NH(4)(+) and K(+) nutrition on photoassimilate distribution among plant organs, and the resultant effect of such distribution on growth of tobacco seedlings, hence this study. Here, we investigated the synergetic effect of NH(4)(+) and K(+) nutrition on photoassimilate distribution, and their resultant effect on growth of tobacco seedlings. Soluble sugar and starch content peaks under moderate NH(4)(+) and moderate K(+) (2-2 mM), leading to improved plant growth, as evidenced by the increase in tobacco weight and root activity. Whereas, a drastic reduction in the above indicators was observed in plants under high NH(4)(+) and low K(+) (20-0.2 mM), due to low carbohydrate synthesis and poor photoassimilate distribution. A strong positive linear relationship also exists between carbohydrate (soluble sugar and starch) and the activities of these enzymes but not for invertase. Our findings demonstrated that NH(4)(+) and K(+)-induced ion imbalance influences plant growth and is critical for photoassimilate distribution among organs of tobacco seedlings.