Genotypic difference of maize lateral roots in response to local nitrate supply

Lateral roots are primary organs for plant to take up and utilize soil nutrients. Their development is controlled by the internal genetic factors and mineral nutrient levels in the growth environment. In this paper, two maize (Zea mays L.) inbred lines, 478 and Wu312, were used to study the effect of local supplied nitrate (NO3-) with different concentrations on lateral roots' growth with an agar culture system. The results showed that a localized supply of 0.5 (mmol/L) nitrate could stimulate lateral roots' length of corresponding place for both maize inbred lines, with a stronger effect on 478 than Wu312. The elongation of lateral roots of 478 had an increase by 41.3% in comparison of control group, whereas in Wu312, it only has an increase by 21.7%. When 0.5 (mmol/L) nitrate was supplied in two segments locally along the radical, elongation of lateral roots in both segments had a increase in 478, whereas in Wu312, only lateral roots in the upper segment increased. External nitrate concentration being 1 (mmol/L) was optimum for the lateral roots growth. When external nitrate concentrations were lower than 1 (mmol/L), they could stimulate lateral roots growth. However, when external nitrate concentrations were higher than 1 (mmol/L), the effect of stimulation reduced. Local supplied nitrate that ranged from 0.5 to 25(mmol/L) displayed a promotion action on 478. Under these conditions the stimulation effect of local nitrate was higher than uniform nitrate. In Wu312, however, the stimulation effect was only displayed as long as (local) nitrate supply was lower than 5(mmol/L). At low nitrate concentration, localized supply of nitrate had no significant influence on the number of lateral roots. When localized nitrate supply was higher than 5(mmol/L), lateral root number of Wu312 decreased sharply. For 478, lateral root number decreased when local nitrate was higher than 15(mmol/L). Comparing the response to local nitrate stimulation, the lateral root of 478 was more responsive than that of Wu312. However, the mechanism involved needs to be further investigated.