Vertical Profiles in Concentration of Potassium and Growth in Nicotiana tabacum. Effect of Potassium on Metabolic Proteins in Successive Leaves, and on the Direction of Translocation of (14)C-Photosynthate and its Allocation.

In intact vegetative plants of N. tabacum grown with progressively rising supplies of potassium, the increase in concentration of the cation is greater in the basal region, and growth is promoted in leaves approaching their final weight and subtending basal nodes while it is restricted in the apical leaves and internodes. The restrained growth changes to promotion after the leaves have attained 25 % and 51 % of their maximum weight in plants supplied with 3 and 9 meq K(+) dm(-3) respectively. The rate and duration of expansion as well as the final weight of the leaves were affected by K-supply, but not their emergence. Parallel with the changes in dry weight, the content of soluble proteins per gram as well as per leaf decreases in the emerging leaves and increases in nearly or fully mature leaves. The increase in the content of soluble proteins is consistent with the enhanced immobilization of (14)C-photosynthate, including a 58 % increase in its incorporation into soluble protein in 24 h in mature leaves when the concentration of K(+) is raised from 50 to 100 μeq g(-1) fresh weight. The available evidence suggests that the enhanced level of soluble proteins in a leaf may include a proportional increase in the activity of enzymes involved in the assimilation of CO(2) and NO(3), with corresponding increase in the availability of primary metabolites. The increased incorporation into protein and starch may be related to the enhanced growth of the leaves approaching their maximum area, and to the retention of protein in older leaves at higher concentrations of K(+). Distribution of the labelled metabolites from a mature source leaf 24 h after (14)CO(2)-assimilation is predominantly acropetal in plants with the concentration of K(+) in the axis increasing towards the apex. Likewise, supply in the basal direction is enhanced with the concentration of K(+) increasing in the successive internodes towards the base. The relatively large proportion of (14)C-metabolites, upto 60% in insoluble form in the meristematic tissues, the apex, basal internodes, and roots, increases with the concentration of K(+). Notwithstanding the enhanced utilization in the apex, the total (14)C-activity recovered rom it decreases. The diminished supply in the acropetal direction resulting from the diversion of photosynthates to basal sections of the shoot, and the enhanced polymerization in the lower internodes with high concentrations of K(+), could result in the estrained growth in the apical region and the concomitant enhanced growth in the basal section, observed in these plants.