In constant environment studies, root applications of 10^-6, 10^-5, 10^-4, 10^-3, or l0^-2 M maleic hydrazide (MH) to tobacco (Nicotiana tabacum L.) seedlings in the cotyledonary stage of growth showed 10^-5, M MH to be the marginal concentration above which root growth was inhibited. The 10^-6 M concentration showed a slight stimulatory effect, but this effect was not statistically significant. In greenhouse studies foliar applications of 10, 40, 70, and 100 milligrams of MH on mature tobacco plants, grown in nutrient culture, indicated significant reductions in the growth of individual roots as compared to the control. No significant differences of the degrees of inhibition among the 40, 70, and 100-milligram treatments were observed. The degree of sucker control was negligible with the 10-milligram treatment and moderate with the 40-milligram treatment. Good control was obtained with the 70 and 100-milligram treatments. Roots on treated plants showed lateral branching. This fact may indicate why percent nicotine is not significantly different in many studies where cured leaf from MH-treated and hand suckered plants is compared. Less than one per cent of the MH applied to the leaves was found in the root systems. Oxygen uptake studies of tobacco root tissue indicated that Qo₂ is increased with an increase in the pH value of the phthlate-phosphate buffer over the range of 4.0 to 6.0. Oxygen uptake studies showed significant reduction in the Qo₂ at pH 6.0 with root tissue from plants treated with MH via the leaves or roots 48 or 24 hours, respectively, after treatment.

(Full article published with kind permission from "Tobacco International")