Discussion and Conclusions
The present results showed that the germination of Z. mays seeds was not influenced by the presence of Cu +2 and Zn+2 in the culture medium. The toxicity difference of the two metals was not evident at seed germination. The results of seed germination clearly indicated that the increasing concentrations of these
two metals did not influence the germination. The insignificant effect of metal toxicity on germination
suggests that seed uses its own reserves during germination process and this process is not influenced
by the presence of metal ions in the culture medium (Stefani et al. 1991). Therefore, the presence of small concentration of heavy metals in the culture medium cannot account for inhibition of germination in Z. mays. These results are consistent with other herbaceous species like Triticum vulgare and Avena sativa (Fiussello, 1973) and in arboreal gymnosperms Piceae rubens , and Abies balsamica (Scherbatskoy et al. 1987). The presence of heavy metals in the culture medium had a significant adverse effect on seedling growth and health. The study showed reduction in root and shoot length, and development of chlorotic and necrotic area. The highest concentration of Zn+2 prevented the shoot growth. The growth of root was arrested in the presence of 12 ppm of CuSO4. The presence of Cu+2 and Zn+2 affected the growth of Z. mays seedlings; the reduction in shoot growth was directly related to the heavy metal concentration (Table 1).Wa ll ey et al. (1974) reported similar effects in a number of other plant species.The presence of Cu +2 in the culture medium showed a stronger effect on root growth than shoot while the reverse was true for Zn +2.This suggests some preventive mechanism for the reduced translocation of Cu+2 from root to shoot (Nishizono et al. 1989). The distribution of the two metals was different between root and shoot as shown in Table2. Cu+2 seem to concentrate in the roots while Zn+2 appeared to be more diffusible than Cu+2. Stefani et al. (1991) similar pattern of distribution of heavy metals in Juncus acutus ]seedlings. All the concentrations of Zn+2 and Cu+2 caused the necrosis of shoot. However, actual toxicity of any of these metals was not ascertained. Nevertheless, the development of necrotic region depended on concentration. These findings agree with the observations of Chatterjee and Chatterjee (2000), who reported similar effects of cobalt, chromium and copper on cauliflower. The chlorosis caused by the presence Cu+2 was in a minor extent as compared to Zn+2. This may be explained by variable action of these metals on chloroplast. These assumptions are supported by independent studies by Becerril et al. (1988) and Barcelo et al.(1988). The accumulation of metals in roots and shoots varied greatly. The amount of Cu+2 accumulated increased with its availability in the medium. However, the extent of Zn+2 deposition was the maximum at 6 ppm. Therefore, Zn +2 uptake seems to be promoted by lower ionic concentration in the culture solution as reported by Sela et al., (1989).Early seedling development of Z. mays appeared to be prone to the presence of small amounts of metals in the culture medium. The data support the assumption that metal sensitivity is probably due to strong tendency of this variety to accumulate heavy metals. This justifies that the corn variety ‘Neelum’ is not suitable for the cultivation under situations where water and soil suffer from occasional and/or transitory metal pollution
อภิปรายและสรุปผลปรากฏพบว่าการงอกของเมล็ดไม่ได้รับ โดยของ Cu + 2 และ Zn + 2 ในสื่อวัฒนธรรม mays z ความแตกต่างความเป็นพิษของโลหะสองไม่ชัดในการงอกของเมล็ดพืช ผลของการงอกของเมล็ดพืชอย่างชัดเจนระบุที่ความเข้มข้นที่เพิ่มขึ้นเหล่านี้โลหะทั้งสองไม่ได้มีอิทธิพลต่อการงอกที่ ลักษณะสำคัญของความเป็นพิษของโลหะในการงอกแนะนำว่า ขณะใช้ระหว่างกระบวนการงอกเมล็ดสำรองของตัวเอง และไม่ได้มีอิทธิพลต่อกระบวนการนี้by the presence of metal ions in the culture medium (Stefani et al. 1991). Therefore, the presence of small concentration of heavy metals in the culture medium cannot account for inhibition of germination in Z. mays. These results are consistent with other herbaceous species like Triticum vulgare and Avena sativa (Fiussello, 1973) and in arboreal gymnosperms Piceae rubens , and Abies balsamica (Scherbatskoy et al. 1987). The presence of heavy metals in the culture medium had a significant adverse effect on seedling growth and health. The study showed reduction in root and shoot length, and development of chlorotic and necrotic area. The highest concentration of Zn+2 prevented the shoot growth. The growth of root was arrested in the presence of 12 ppm of CuSO4. The presence of Cu+2 and Zn+2 affected the growth of Z. mays seedlings; the reduction in shoot growth was directly related to the heavy metal concentration (Table 1).Wa ll ey et al. (1974) reported similar effects in a number of other plant species.The presence of Cu +2 in the culture medium showed a stronger effect on root growth than shoot while the reverse was true for Zn +2.This suggests some preventive mechanism for the reduced translocation of Cu+2 from root to shoot (Nishizono et al. 1989). The distribution of the two metals was different between root and shoot as shown in Table2. Cu+2 seem to concentrate in the roots while Zn+2 appeared to be more diffusible than Cu+2. Stefani et al. (1991) similar pattern of distribution of heavy metals in Juncus acutus ]seedlings. All the concentrations of Zn+2 and Cu+2 caused the necrosis of shoot. However, actual toxicity of any of these metals was not ascertained. Nevertheless, the development of necrotic region depended on concentration. These findings agree with the observations of Chatterjee and Chatterjee (2000), who reported similar effects of cobalt, chromium and copper on cauliflower. The chlorosis caused by the presence Cu+2 was in a minor extent as compared to Zn+2. This may be explained by variable action of these metals on chloroplast. These assumptions are supported by independent studies by Becerril et al. (1988) and Barcelo et al.(1988). The accumulation of metals in roots and shoots varied greatly. The amount of Cu+2 accumulated increased with its availability in the medium. However, the extent of Zn+2 deposition was the maximum at 6 ppm. Therefore, Zn +2 uptake seems to be promoted by lower ionic concentration in the culture solution as reported by Sela et al., (1989).Early seedling development of Z. mays appeared to be prone to the presence of small amounts of metals in the culture medium. The data support the assumption that metal sensitivity is probably due to strong tendency of this variety to accumulate heavy metals. This justifies that the corn variety ‘Neelum’ is not suitable for the cultivation under situations where water and soil suffer from occasional and/or transitory metal pollution
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