Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants |
| |
Authors: | Pinton R Cesco S Santi S Agnolon F Varanini Z |
| |
Institution: | (1) Dipartimento di Produzione Vegetale e Tecnologie Agrarie, University of Udine, via delle Scienze 208, I-33100 Udine, Italy E-mail |
| |
Abstract: | The ability of Fe-deficient cucumber plants to use iron complexed to a water-extractable humic substances fraction (WEHS),
was investigated. Seven-day-old Fe-deficient plants were transferred to a nutrient solution supplemented daily for 5 days
with 0.2 μM Fe as Fe-WEHS (5 μg org. C mL-1), Fe-EDTA, Fe-citrate or FeCl3. These treatments all allowed re-greening of the leaf tissue, and partial recovery of dry matter accumulation, chlorophyll
and iron contents. However, the recovery was faster in plants supplied with Fe-WEHS and was already evident 48 h after Fe
supply. The addition of 0.2 μM Fe to the nutrient solution caused also a partial recovery of the dry matter and iron accumulation
in roots of Fe-deficient cucumber plants, particularly in those supplied with Fe-WEHS. The addition of WEHS alone (5 μg org.
C mL-1, 0.04 μM Fe) to the nutrient solution slightly but significantly increased iron and chlorophyll contents in leaves of Fe-deficient
plants; in these plants, dry matter accumulation in leaves and roots was comparable or even higher than that measured in plants
treated with Fe-citrate or FeCl3. After addition of the different iron sources for 5 days to Fe-deficient roots, morphological modifications (proliferation
of lateral roots, increase in the diameter of the sub-apical zones and amplified root-hair formation) and physiological responses
(enhanced Fe(III)-chelate reductase and acidification of the nutrient solution) induced by Fe deficiency, were still evident,
particularly in plants treated with the humic molecules. The presence of WEHS caused also a further acidification of the nutrient
medium by Fe-deficient plants. The Fe-WEHS complex (1 μM Fe) could be reduced by intact cucumber roots, at rates of reduction
higher than those measured for Fe-EDTA at equimolar iron concentration. Plasma membrane vesicles, purified by two-phase partition
from root microsomes of Fe-deficient plants, were also able to reduce Fe-WEHS. Results show that Fe-deficient cucumber plants
can use iron complexed to water soluble humic substances, at least in part via reduction of complexed Fe(III) by the plasma
membrane Fe(III)-chelate reductase of root cells. In addition, the stimulating effect of humic substances on H+ release might be of relevance for the overall response of the plants to iron shortage.
This revised version was published online in June 2006 with corrections to the Cover Date. |
| |
Keywords: | Cucumis sativus Fe(III)-chelate reductase humic substances iron deficiency iron nutrition root acidification |
本文献已被 SpringerLink 等数据库收录! |
|