Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-deficient cucumber plants |
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Authors: | R Pinton S Cesco M De Nobili S Santi Z Varanini |
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Institution: | (1) Dipartimento di Produzione Vegetale e Tecnologie Agrarie, University of Udine, via delle Scienze 208, I-33100 Udine, Italy Tel: 0039(0)432-558641; Fax: 0039(0)432-558603, IT |
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Abstract: | The capacity of Fe-deficient cucumber plants to utilise water-extractable and pyrophosphate-extractable humic substances
as a source of Fe was investigated. Plants were grown for 13 days in nutrient solution in the presence or absence of Fe and
during the last 7 days water-extractable and pyrophosphate-extractable humic substances were added to the solution at a final
concentration of 5 μg organic C ml–1. The water-extractable humic fraction did not significantly modify leaf area and dry matter accumulation, leaf total Fe or
chlorophyll content of cucumber plants adequately supplied with Fe. In contrast, pyrophosphate-extractable humic substances
caused a slight but significant decrease of all the leaf parameters considered, with the exception of the chlorophyll content.
Root Fe content of Fe-sufficient plants was decreased by more than 50% in the presence of each humified fraction. Addition
of each humic fraction to Fe-deficient plants led to a partial disappearance of leaf chlorosis symptoms with a significant
increase in chlorophyll and leaf Fe content. Fe content of roots was also significantly increased in Fe-deficient plants by
the addition of humic substances to the nutrient solution. These results show that Fe-deficient cucumber plants can utilise
Fe contained in the two fractions of humified organic matter. However, by calculating the amount of total Fe accumulated per
plant in the presence of water-extractable or pyrophosphate-extractable humic substances, it could be seen that Fe contained
in the water-extractable humic fraction was almost totally used by Fe-deficient cucumber plants, while that present in the
pyrophosphate-extractable fraction could only be partially absorbed. The results strongly support a role of humified organic
matter in Fe nutrition of plants and are discussed in terms of a possible interaction between soil humic substances and the
biochemical mechanisms involved in the plant response to Fe deficiency.
Received: 6 November 1996 |
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Keywords: | Humic substances Cucumber Iron nutrition Iron deficiency Root acidification |
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