Temperature Effects on Growth and Manganese Tolerance in Tobacco¹

Abstract

Symptoms of Mn toxicity in tobacco (Nicotiana tabacum L.) are often observed in the mountain region of North Carolina at soil acidity and soil test levels of Mn which do not produce toxicity in the piedmont. Although genotypic differences between tobacco types grown in the regions may contribute to the differential response, variations in temperature between the regions may also be involved. To investigate the effects of temperature on plant growth and Mn tolerance, tobacco plants of a prevalent cultivar (‘Coker 347’) for the piedmont region were grown in sand culture at day/night temperatures of 22/18, 26/22, and 30/26 C. Manganese was applied daily at rates of 10, 20, 40, 80, and 120 mg/liter in a complete nutrient solution. Plants were sampled weekly during a 6‐week growth period and evaluated for visual toxicity symptoms, dry weight. Mn concentration, relative growth rate (RGR), and relative accumulation rate (RAR) of Mn. Plant tolerance to high rates of applied Mn increased with increasing temperature despite significantly greater tissue concentrations of Mn during early growth. Tissue levels of Mn in leaves associated with the appearance of visual toxicity symptoms were 700 to 1,200 mg/kg dry wt at 22/18 C, 2,000 to 3,500 mg/kg at 26/22 C, and 5,000 to 8,000 mg/kg at 30/26 C. Mn toxicity symptoms were more severe in immature leaves and often decreased as the leaves matured even though the concentration of Mn in the leaves increased. The RGR of leaves during the exponential growth phase increased with increasing temperatures at each Mn rate, but the RAR of Mn was unaffected by either temperature or applied Mn rate. It is proposed that the increased tolerance to high levels of tissue Mn by plants grown in warm temperatures is associated with more rapid rates of leaf expansion accompanied by increased vaculor capacity for disposal of accumulated Mn.

Surface Chemical Properties of Purified Root Cell Walls from Two Tobacco Genotypes Exhibiting Different Tolerance to Manganese Toxicity

“…pH < 5.5 (14,19,20) and trichomes (3). The Mn trapped in plant vacuoles has been speculated to be complexed with organic acids (14).…”

“…Various mechanisms have been proposed to explain Mn tolerance. One of those is a compartmentalization mechanism that suggests that excess Mn ions are deposited into less metabolically active cell compartments such as vacuoles (14,19,20) and trichomes (3). The Mn trapped in plant vacuoles has been speculated to be complexed with organic acids (14).…”

Light and Excess Manganese

“…However, the response of plants to excess Mn is affected by leaf age (Horst, 1988), temperature (Heenan and Carter, 1977;Rufty et al, 1979), soil nutrient balance, soil pH, genotype, and light intensity. The effect of light intensity on Mn-toxicity symptoms was first reported in 1935, when McCool (1935) found that plants grown in low light displayed fewer symptoms of Mn toxicity than those grown in high light.…”

INTERACTION OF TEMPERATURE AND CO2 ENRICHMENT ON SOYBEAN: GROWTH AND DRY MATTER PARTITIONING

“…Increase in atmospheric CO, will also affect growth rates and behavior of plants (Strain 1985 Sionit 1983;Jones et al 1984), to produce greater leaf area (Jones et al 1984;Peet 1984), and to have higher yields (Kimball 1983) when grown in a COr-enriched atmosphere. Plants also have low COt assimilation and growth rates when grown at low temperature regimes (Markhart et al 1980;Raper and Kramer 1980 (Rufty et al 1979). …”