Studies on potassium nutrition of plants IV.—Effect of potassium nutrition on the composition of leaves of cabbage seedlings (Brassica oleracea capitata)

Abstract

The effect of potassium concentration in the nutrient medium on the composition of leaves of cabbage seedlings has been investigated. The plants were grown in sand culture with seven treatments ranging from extreme deficiency to relatively high potassium concentration. The total amounts of the mineral components were not influenced by the level of potassium nutrition. Similarly, proteins, amino acids and other organic nitrogen components, taken as a whole, did not vary appreciably as shown by the constancy of the Kjeldahl nitrogen values.Sugar (reducing sugars + sucrose) content rose with increasing potassium concentration in the medium to a maximum (11 .OX) at 2.5 meauiv./l and fell slightly at the highest K+ concentration. Starch content varied in a similar manner but vdues were, in general, less than half those of the corresponding sugar contents. Total organic acids content was at a maximum (18.6%) when K+ concentration ip the medium was 0.1 mequiv./l and fell to a minimum (7.7%) at a K+ concentration of 2.5 mequiv./l. Other carbohydrates' (the difference between content of 70 % [by vol.] alcohol-insoluble residue and Kjeldahl nitrogen x 6.25) also contributed to the balance of percentage composition; the content rose to a maximum (35.2%) at a K+ concentration of 2.5 mequiv./l and fell off both at higher and lower K+ concentrations. Within the limits of experimental error, the totals of the leaf components determined were constant over the range of potassium concentrations of 0.1-5.0 mequiv./l in the medium and, on average, 90.7% of the dried leaf was accounted for.Similar differences in mineral composition and 'protein', sugars and starch contents were found in plant fractions of different leaf ages in potassium deficiency. The differences were related to differences in potassium content which decreased with increasing leaf age. IntroductionSeveral authorsl-7 have described how potassium deficiency influenced the total quantities of organic acids in leaves and the relative proportions of certain acids. In the cases of broad bean ( Vicia faba),2 Bryophyllum diagremontianum Berger,3 tomato,4 orchard grass,5 and cabbage, red beet and potato leaves,7 potassium deficiency resulted in large increases of total organic acids. It follows that there must be a corresponding decrease in the content of some other component or components to maintain the balance of leaf composition. The object of the present work was to determine how the balance of percentage dry weight composition was main-

The effect of potassium nutrition on pest and disease resistance in plants

“…Nevertheless, in some studies no or even the opposite effect of K on sugar contents was found [e.g. no effect in tobacco (Nageswara and Kameswara 2004), decrease in sugars at low K in cabbage (Freeman and Mossadeghi 1970)]. A positive correlation between K and nitrate uptake has been shown, which is mirrored by higher NR activity in leaves of K‐supplied plants (Blevins et al 1978, Rufty et al 1981).…”