Objectives In order to understand the mechanism of high efficient absorption of potassium in tobacco, and to provide reference for selecting potassium-enriched flue-cured tobacco, the potassium metabolism characteristics of flue-cured tobacco varieties at the maturity were studied.
Methods The potassium-enriched flue-cured tobacco cultivar ND202 and conventional cultivars, K326 and NC89, were selected, and a pot experiment was carried out. Changes of soil available potassium contents in non-rhizosphere and rhizosphere, physiological characteristics of roots, potassium accumulation in different parts of tobacco, and potassium channel and transporter gene expression at the mature stage were analyzed.
Results The potassium accumulation of ND202 mature leaves was significantly higher than those of K326 and NC89, but the differences among the cultivars were not significant in roots and stems. The potassium accumulation of whole plant of ND202 was the highest, reaching to 10.18 g/plant and was 109.90% and 90.28% higher than those of NC89 and K326, respectively (P < 0.05). At the mature stage, the average root fresh weight and root volume of ND202 were significantly higher than those of K326, and root vigor was significantly higher than that of NC89. The rhizosphere soil available potassium content of ND202 at the rosette and vigorous growing stages was significantly lower than those of NC89 and K326 respectively, and significantly lower than those of NC89 and K326 at the maturity stage. The non-rhizosphere soil available potassium of ND202 was significantly higher than those of NC89 and K326 at the mature stage. The relative expression levels of inner flow potassium channel gene NKT1 and NtKC1 varied among cultivars and parts at the mature stage. The expression of NKT1 in the upper leaves of ND202 was significantly higher than that in K326 and NC89, the relative expression of NtKC1 in roots, upper and middle leaves was significantly higher than that of NC89 and K326, and the relative expression of potassium channel gene NtTPK1 was significantly higher than NC89 and K326 in the root and middle leaves, which was beneficial to the absorption of potassium ions. The relative expression of efflux potassium channel gene NTORK1 of ND202 in the lower leaves was significantly lower than that of NC89 and K326, and the less potassium efflux was favorable to the increase of potassium content. The relative expression levels of potassium transporter gene NtHAK1 and NtKT12 in different parts and different cultivars were different. The relative expression of NtHAK1 in roots and upper leaves and middle leaves, and the relative expression of NtKT12 in roots and upper leaves of ND202 were significantly higher than those of K326 and NC89, which was beneficial to potassium translocation and accumulation.
Conclusions Potassium-enriched flue-cured tobacco ND202 has characteristics of developed root system, higher root absorption ability, higher relative expression of potassium ion channel and transporter gene, and larger amount of potassium accumulation in leaves at the mature stage.
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