We have found that auxin (2, 4-D)-induced roots were further promoted by the addition of zinc in rice which is monocotyledonous plant. Therefore, we examined whether a similar phenomenon would occur in dicotyledonous plant such as pumpkin. Similarly, a change from root formation to callus induction was observed in pumpkin plant. However, the change to callus in pumpkin plant was induced at lower auxin concentration than that of the rice plant. The callus formation was also suppressed as that of rice plant with the addition of zinc. In rice, new roots were formed when callus formation was suppressed with zinc, but there was no new root formation in the pumpkin plant.

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In order to investigate the effect of OH-radicals on root system growth in two-year-old Japanese apricot (Prunus mume) seedlings, we exposed roots to solutions that produce OH radicals at Tanabe City, Wakayama Prefecture, in western Japan. Solutions containing OH radicals were used to simulate polluted dew water (HOOH with Fe(III) and oxalate ion). The concentrations used were regulated at 30, 90 and 270μM and the distilled water (0μM) was used as a control solution. In addition, no-treatment plants that were not treated with any solution were maintained outside experimental greenhouse house. Test solutions were surfaces of seedlings grown in experimental greenhouses in the early morning, three times a week from April to November 2002.
Upon completion of the exposure experiment in December, dry weights were measured for total root biomass, thick roots (>2mm in diameter) and fine roots (≤2mm in diameter). Similarly, the fine root: total root ratio was calculated using dry weight for root biomass.
Results revealed a significant difference among all treatments (P<0.05 and P<0.01 by ANOVA analysis) suggesting that exposing roots to OH radicals in solution had a negative impact on root growth in Japanese apricot seedlings.
Regression analysis of the concentrations of OH radical solutions against dry weight of fine root and fine root: total root ratio exhibited positive correlation (y=-0.122x+95.86; r=0.451 and y=-0.026x+ 26.1; r=0.510).

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