The understanding of the effects of boron (B) toxicity and deficiency on the growth and nutrients accumulation of crop seedlings in the field is required to substantiate the need of adequate dosage for their survival and optimal production. In this study, the susceptibility of Zea mays to excess and deficiency of B was obtained by feeding the seedlings with varied concentrations of B in standard nutrient solution. B was applied as Boric acid (H3BO3) and at the rate of 0.33ppm (FN/B-optimal dosage) which served as control, 0 ppm (-B) served as B-deficient level, 1.65, 3.30 and 6.60ppm (×5B, ×10B and ×20B respectively) served as toxic levels. Results showed that the number of leaves, leaf area, leaf area ratio, shoot fresh and dry weights, root fresh weight and biomass, chlorophyll a, b and total chlorophyll, calcium (Ca), Magnesium (Mg), nitrogen (N), and protein accumulation were significantly reduced by the application of 3.30 ppm (×10B) and 6.60 ppm (×20B) B dosage. The retardation effects of the ×20B level was not significantly different from ×10B level at P<.05 indicating 3.30 ppm (×10B) as the critical level of toxicity for maize seedlings growth and development. The data also showed that toxicity of B was more harmful to juvenile maize than its deficiency since B deficiency diminished just few parameters such as the shoot dry weights, chlorophyll b and total chlorophyll at P<.05. Moreover, the study suggested three different optimal concentrations; 0.33, 1.65 and > 3.30 ppm respectively for general growth, chlorophyll and carotenoids synthesis in maize seedlings. Lastly, the study emphasized the accumulation of carotenoids and potassium (K) as possible adaptive mechanisms evolved by the maize seedlings to B-stress tolerance and suggested an under-play physiological role for B in the formation and development of the seedlings leaf.