Effect of Potassium Supply on the Transport of Photosynthates to the Fruits of Tomatoes (Lycopersicon esculentum)

Abstract

AbstractIn experiments with intact tomato plants the effect of potassium on the translocation of photosynthates was studied. Four series of plants were grown in nutrient solutions with two different potassium levels (K1 and K2 treatments). When the fruits of the first truss had developed the plants were treated with labelled CO2 for 2 h in a glove box. The plants were then divided in roots, stems, fruits and leaves, which were prepared for chemical analysis.In all experimental series the plants with the higher K supply grew better and therefore assimilated higher amounts of labelled CO2 (cpm/plant). The assimilation rates per g fresh material, however, were not increased in each experimental set by the K2 treatment. The absolute quantities of labelled photosynthates transported from leaves and stems to the fruits were also greater in the plant with the higher potassium supply. In all experimental series the proportion of labelled material found in the fruits was higher in the plants of the K2 treatment (total label of the plant=100%) than in the plants of the K1 treatment. This beneficial effect of potassium was also observed in cases, where potassium had not affected the CO2 assimilation rate. Expressing the distribution of labelled material in relative terms (percentage proportions) means that the effect of CO2 assimilation on the transport of photosynthates was excluded to a high extent. The higher percentage proportions of labelled material found in fruits and roots of the K2 as compared to the K1 treatment is, therefore, predominantly dependent on a specific effect of potassium on the translocation of assimilates.The labelled material found in the soluble fraction of the stems consisted of about 90% sugars, nearly half of which was sucrose, the rest being mainly glucose and fructose. This finding suggests that sucrose is the most important transport form of carbohydrates in tomatoes.