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Pakistan Journal of Biological Sciences

Year: 2005 | Volume: 8 | Issue: 11 | Page No.: 1599-1609
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Authors

R. Hajiboland

H. Boniadi

Keywords

Research Article

Accumulation of Cu in Root Apoplasm and Re-translocation to Young Leaves in Rice, Maize and Sunflower with Different Toxicity Tolerance

R. Hajiboland and H. Boniadi
The influence of Cu toxicity on growth and accumulation of Cu in three crop species including rice (Oryza sativa L. cv. T. Hashemi), maize (Zea mays L. cv. SC 704) and sunflower (Helianthus annuus L. cv. Mehr) was investigated in hydroponic culture media under environmentally controlled conditions. As indicated by the growth parameters, the tolerance of studied species to Cu toxicity effect was in order of rice>maize>sunflower. However, the accumulation of Cu in roots and shoots was rather adversely related to the tolerance of plants. The copper accumulation in root apoplasm in rice and sunflower was much higher than that in maize. It was likely the cause of high copper translocation into shoots in the former plants. Root length was the most sensitive parameter to Cu toxicity and could be considered as an indicator of responses of studied species to excess Cu. Root respiration increased in rice and maize, but decreased in sunflower plants in response to Cu toxicity. In rice, leakage of K+ from roots, in contrast to other two species, was not affected significantly by excess Cu. Supplemental Ca ameliorated toxicity effect of Cu depends on species, however, this effect was not necessarily associated with the reduction of uptake and transport of Cu. Growth of plants under high light intensity compared to low light conditions results in an alleviation of toxicity because of dilution effect and likely higher antioxidant pool of tissues. Re-translocation of Cu in plants loaded with toxic levels of Cu indicated that, firstly a substantial portion of Cu was remobilized and translocated from mature to young leaves. Secondly, the extent of retranslocation was species dependent, the highest and lowest amounts were observed in maize and rice respectively. Results suggested that different redistribution of Cu among leaves of different growth status in association with different tolerance at tissue levels could substantially contribute in growth responses of species to excess Cu.
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