Effects of Some Rare Elements on Nicotine Content of the Tobacco Plant

Abstract

Fifty-four rare elements were tested for their effects on the nicotine level of tobacco (Nicotiana tabacum L.) plants grown in solution culture. Be, Cu, Pd, Pt, and Sm definitely increased nicotine yield (over 25%), Tobacco (Nicotiana tabacumn L.) is one of the most widely used plant materials for nutrient studies. The presence and possible function of various elements in tobacco have frequently been studied and reviewed (4). Much interest is centered on the effect of certain elements on the nicotine content of tobacco plants. Available information in this area, however, is based on experiments conducted under varying conditions of growth or topping (decapitation) and, therefore, are not comparable. This paper describes experiments examining the effects of 54 elements, most of them rare ones, on the nicotine content of tobacco plants. Nicotiana tabacuin cv. Connecticut Broad-leaf plants were grown in solution culture (McMurtrey's nutrient formula [2]) in the greenhouse. The culture solution contained in mg/l: 225 N, 65 P, 125 K, 245 Ca, 30 Mg, 20 S, 50 Cl, and small quantities of B, Mn, and Fe. A 10-liter glass tank was used for each plant. Plants were started in sand culture and transferred to solution culture when they reached 13 to 15 cm in height. After 2 to 3 weeks, when the tobacco plant was established in the culture solution, 10 mg of a test element of spectroscopically pure grade was added to the culture solution for each plant, so that the final concentration of each test element was 1 mg/l. Five weeks later, the plants were topped according to usual production practices. The plants were harvested 2 weeks later. Nicotine determinations were made by procedures described previously (1). Each experiment was repeated several times, depending on the availability of the element involved. Some tests were repeated as many as 12 times. Two to four control plants were included in each test. Fresh weight and nicotine content were expressed relative to controls within the same replication. Based on changes in fresh weight and in nicotine concentration (fresh weight basis), the effect of each element on average nicotine yield per plant was calculated, relative to control, and mean values are listed in Table I. From results in Table I, based on 5 % confidence limit, the 54 elements may be classified in the following five categories. (a) Definite increase of nicotine yield (statistically significant increase of 25% or more per plant) Be, Cu, Pd, Pt, and Sm. (b) Possible increase of nicotine yield (statistically significant increase of less than 25% per plant) Cs, Er, Li, Rh, Ru, Se, Sr, Ti, and Yb. (c) Definite decrease of nicotine yield (statisti-cally significant decrease of 25% or more per plant) Bi, Co, Ho, Pb, Ni, Rb, Ag, TI, Sn, U, V, and Zr. (d) Possible decrease of nicotine yield (statistically significant decrease of less than 25% per plant) As, Ce, Cr, Dy, Gd, I, Mo, Nd, Re, Ta, and Th. (e) No statistically significant effects on nicotine yield. Among the elements in this group which varied less than 5% were Hf. In, Lu, Pr, Te, W, and Zn; those exceeding 5% were Al, Ge, Au, Ir, La, Hg, Os, Sc, Tb, and Tm. The influence of each element on the growth and development of a tobacco plant is an important factor affecting nicotine yield. Certain compounds such as tin chloride, thallium nitrate, zirconium chloride, and lead nitrate caused a drastic decrease in both fresh weight and nicotine concentration; whereas other compounds, such as aluminum chloride, erbium nitrate, germanic acid, holmium phosphate, indium chloride, mercuric chloride, osmic acid, palladium chloride, platinum chloride, samarium chloride, and silver nitrate increased the fresh weight and decreased nicotine concentration, or vice versa. Cupric chloride, however, caused rather significant increase in both fresh weight and nicotine concentration. Many of these elements tested have been reported to be present in leaf tobacco, including Al, As, Be, Cs (3, 4). The lack of information on other elements does not necessarily mean their absence in tobacco. It should also be noted that the presence of certain elements does not necessarily mean that they are essential for tobacco plant growth and metabolism. Among the elements that increased nicotine levels in tobacco , Be has been shown to occur in the range of 0.015 to 0.075 mg/kg (dry weight) and Cu 15 to 21 mg/kg. Among those that inhibit nicotine production, Co ranges from 0.9 to 1.54 mg/kg, Pb from 0 to 200 mg/kg (possibly due to lead-805