Effects Of Potassium On Nicotinoid Substances Accumulation And Their Biosynthesis-related Gene Expression

Potassium is one kind of macroelements essential for plants, and play a vital role in the growth and development of tobacco plants, nicotinoid synthesis and quality formation of tobacco leaf. Potassium is so called "a quality element". In this test, flue-cured tobacco K326 was applied as material. By setting different concentrations of potassium nutrient solution, and potassium nutrition recovery after low potassium stress, as well as addition of exogenous putrescine and spermidine biosynthesis inhibitor cyclohexylamine(CHA), effects of potassium supply levels on nicotine and nornicotine accumulation were studied in tobacco using sand culture. Expression of nicotine biosynthesis genes such as putrescine N-methyltransferase(PMT), quinolinic acid phosphoribosyltransferases(QPT) and nicotine N-demethylase(NND) gene was also detected. The results showed that:(1)The vegetative growth of tobacco plants was significantly affected by potassium supply levels. Low concentration of potassium stress could inhibit the growth of the aerial and underground parts(root system) of plants, thus weakened the vegetative growth of tobacco plants. While 5 time concentrations of high potassium also showed the same inhibitory effect on tobacco vegetative growth. Supply recovery of potassium after low potassium stress could partly eliminate the inhibitory effect of low potassium on the vegetative growth.(2)Nicotine content increased gradually with the growth of tobacco plants. The supply of lower potassium ion in the nutrient solution would also significantly increase nicotine content. Interestingly, higher level of potassium supply(5K) had obviously inhibitory effect on nicotine accumulation. Supply recovery of potassium after low potassium(K/50) stress for 10 d could reduce nicotine accumulation caused by the low potassium. Addition of exogenous putrescine to the nutrient solution could lead to increased nicotine content, and application of spermine biosynthesis inhibitor- CHA had the same effect as putrescine.Unlike change in nicotine accumulation, in the early growth stage of 8 leaf 1 heart, nornicotine content was quite low, but increased gradually with the growth of tobacco plants. Low potassium stresses(K/10 and K/50) for 10 d had no obvious effects on nornicotine that was still remained at lower levels, and higher level of potassium ions(5K) also had less effect on nornicotine accumulation. Whereas low potassium stress(K/50) for 20 d could remarkably promote the accumulation of nornicotine which could be slowed by potassium supply again. Moreover, Addition of either exogenous putrescine or spermidine biosynthesis inhibitor-CHA to the nutrient solution could also enhance nornicotine accumulation in leaf.(3) In the early period of treatment, tobacco plants possessed higher levels of PMT gene expression that increased with the growth of tobacco plants. Its expression was found to be promoted by low stress of potassium, but inhibited by 5 time higher potassium concentration. It was also observed that potassium supply recovery after low potassium(K/50) stress could obviously reduce the promoting effect of low potassium on PMT gene expression. Both exogenous putrescine and CHA could also increase the expression of the PMT gene.In the early stage of stresses, NND gene expression was weak unlike PMT, low and high potassium stresses had no significant influence on its expression. NND gene expression gradually strengthened with tobacco growth, and was promoted by low potassium treatment(K/50), that could be greatly weakened by potassium recovery. Exogenous putrescine or CHA treatment could also enhance the NND gene expression.Compared with the PMT gene expression, QPT gene expression was small, and displayed a decrease trend with the growth of tobacco plants. Both lower potassium supply and 5 time high potassium appeared to reduce the amount of QPT gene expression, and both exogenous putrescine and CHA also showed some inhibitory properties in QPT gene expression.This study once more supported that supply levels of potassium are associated with accumulation of nicotine and nornicotine, namely low potassium could promote accumulation of nicotine, and nornicotine in later period of potassium stress in tobacco plants, while high potassium concentration had a negative effect on nicotine accumulation. Potassium may affect the accumulation of nicotine and nornicotine by changing Put supply levels required for nicotinoid biosynthesis, or by regulating gene expression of PMT, NND in tobacco plants.