Saturday, 15 July 2006

Zinc Uptake in Phaseolus Vulgaris (CV. Borlotto ).

Marco Sciortino1, Tanja Mimmo1, Andrea Simoni1, Claudio Marzadori1, and Giorgio Gianquinto2. (1) Dept of Agroenvironmental Sciences and Technologies, Alma Mater Studiorum – Univ of Bologna, Viale Fanin 40, Bologna, 40127, Italy, (2) Dipartimento di Agronomia Ambientale e Produzioni Vegetali, Univ degli Studi di Padova, Viale dell'Università, 16, Legnaro (Pd), 35020, Italy

High levels of available phosphorus (P) in soil or high application rates of phosphate may induce zinc deficiency in plants grown on soils, especially on soils with low concentrations of available zinc. The interaction of phosphorus and zinc (Zn), the so-called phosphorus-induced zinc deficiency, has been observed in many crop species such as bean, wheat, tomato, cotton, flax and soybean. High rate of P fertilizers applied to soil with Zn contents lower than the average background levels of Italian soils (10 to 150 mg/kg) can reduce Zn concentrations in bean shoots. This is particularly evident in summer crops, when high light intensity promotes growth and induces Zn dilution in plant shoots: the higher the light intensity, the more severe the Zn deficiency. The objective of the present work was to investigate the effect of different zinc levels on the growth of Phaseolus Vulgaris (cv. Borlotto). The hydroponic experiments were carried out during the spring season in a greenhouse under controlled climatic conditions using a floating system: pregerminated bean plants were transplanted on a floating platform using perlite as substrate and organized in a randomized block design. Plants were grown in a Hoagland solution adding different concentrations of Zn: 0.16, 0.23, 0.31, 0.38 mg/L (Zn0, Zn1, Zn2, Zn3). Twice a week, pH and electric conductivity (EC) of the solution and water consumption were measured. After 3 weeks the dwarf beans (Phaseolus Vulgaris cv. Borlotto) were harvested, divided into stems, leaves and roots. After microwave-mineralization each sample was analyzed by ICP-OES (Inductive Coupled Plasma – Optic Emission Spectroscopy) to determine the total Zn concentration. Results showed that pH decreased significantly only in the treatments without Zn supply indicating that Zn prevented an acidification of the rhizosphere. On the other hand, electric conductivity increased in almost all treatments. The plants treated at low zinc concentration (Zn1 and Zn0) did not show any symptoms of zinc deficiency and grew vigorously. Instead the plants treated with the higher Zn concentration (Zn2 and Zn3) showed symptoms of zinc toxicity: stunted growth, shortening of internodes and decrease in leaf size. In addition, the plants treated with Zn3 showed leaf penalty, interveinal chlorosis and necrosis. The chemical analysis revealed that there were no significant differences in zinc concentration in the plant organs between Zn1 and Zn0 (Duncan Test at a=0.05), whereas significant differences have been detected in the treatments Zn2 and Zn3; the concentration in the roots was extremely high (5260 and 4267 mg/kg dw, respectively), in the leaves (2280 and 1209 mg/kg dw, respectively) and in stem (3170 and 1472 mg/kg dw, respectively). In conclusion, our results suggest that the dwarf beans are able to manage efficiently very low Zn concentrations when Phosphorus does not affect the plant Zn uptake. However, when there are no limiting factors, plants take up very high concentrations of zinc translocating the metal to the leaves where toxicity symptoms are visibly evident.

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