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RESEARCH PRODUCT

Heavy metal-hormone interactions in rice plants: Effects on growth, net photosynthesis, and carbohydrate distribution

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The effect of external applications of gibberellins (GA3) and abscisic acid (ABA) on the growth, carbohydrate content, and net photosynthesis of heavy metal-stressed rice plants (Oryza sativa cv. Bahia) was investigated. Treatment with cadmium (0.1 mm) and nickel (0.5 mm) inhibited rice growth and stimulated carbohydrate accumulation, especially in seeds from which seedlings were developing, stems, and first leaves. The addition of GA3 (14 μm) to the rice culture solution together with Cd or Ni partially reversed the effects of heavy metals, stimulating growth as well as mobilization of carbohydrate reserves in seeds from which seedlings had developed. GA3 increased the sugar content in roots and second and third leaves and also modified the carbohydrate distribution pattern compared with heavy metal-treated plants. In contrast to GA3, ABA (19 μm) supplied to rice cultures potentiated the effect of heavy metals, inhibiting the growth of young leaves and the translocation of storage products from source to sink organs. In addition, sugars were accumulated in roots and second leaf but not in the third leaf, the extension in length of which was also inhibited by the treatment. Net photosynthesis rates recovered transitorily in Cd-treated plants after the addition of hormones. The possible relationship between growth and carbohydrate distribution, as well as the involvement of hormones, in the response of plant to heavy metal stress is discussed.