Concentration of iron in xylem sap of barley fed with ironIII and chelators

Takagi (1984) reported that PS could enhance Fe translocation to the shoot more rapidly than EDTA in rice fed with FeCl3 (20 ^M). It has been verified that PS are much more effective to enhance the absorption of Fe than the other natural or artificial chelators (Marschner et al., 1986; Romheld and Marschner, 1986). Our preliminary results (Kawai et al., 2001)

reported that PS enhanced Fe concentration in xylem sap more than the synthetic chelator EDTA.

Figure 14-7. Metal concentrations in xylem sap collected from barley grown hydroponically with different concentrations of EDTA-Fe (0, 1, 10, 100 ^M).

As a follow-up research, an experiment was conducted to examine whether PS could enhance Fe concentration in xylem sap more than other Fe chelators, when fed to the roots together with Fe3+. Roots of barley plants grown hydroponically under -Fe conditions were supplied with FeCl3 (30 ^M) and equimolar amounts of other Fe compounds, such as mugineic acid (PS), deferri-ferrioxamine B (FOB) (a microbial chelator) (van der Helm et al., 1987), EDTA, citrate, and malate from 13:00 to 16:00 p.m., when PS are not released from the roots. At 16:00 p.m., the plants were decapitated and xylem sap was collected for 3 hours.

The concentration of Fe in barley xylem sap was enhanced, with a factor of more than 10, in plants fed with PS and Fe3+ as compared to the control plants fed solely with Fe3+ (Figure 14-9). This result indicates that the PS-Fe complex was the most effective Fe source as compared with FOB, EDTA, citrate and malate. EDTA was not effective in enhancing Fe concentration in xylem sap, conversely to what was found in previous studies (Kawai et al., 2001).

Figure 14-8. Time course of the concentrations of Fe and phytosiderophores in xylem sap of Fe-deficient barley after being fed with FeCl3. Plant roots were fed with 30 ^M Fe3+ at 13:00 p.m. Plants were decapitated at 13:00, 16:00, 19:00, 22:00, 1:00, 4:00, 7:00, and 10:00 p.m. Xylem sap was collected for 3 hours from the stunts of the plants.

Figure 14-8. Time course of the concentrations of Fe and phytosiderophores in xylem sap of Fe-deficient barley after being fed with FeCl3. Plant roots were fed with 30 ^M Fe3+ at 13:00 p.m. Plants were decapitated at 13:00, 16:00, 19:00, 22:00, 1:00, 4:00, 7:00, and 10:00 p.m. Xylem sap was collected for 3 hours from the stunts of the plants.

Citrate was the second highest enhancer of the Fe concentration in xylem sap. Citrate has been used as an effective Fe source in nutrient solution by the pioneers of plant nutrition (Hewitt and Smith, 1975). It was also verified in this experiment that citrate-Fe is an adequate Fe source for the plant.

However, the question remains whether the PS-Fe3+ absorbed by the roots can be incorporated into the xylem without being dissociated into Fe3+ and PS in root cells. Further experiments using 59Fe and 14C isotopes will help us find the answer to this question.

Figure 14-9. Iron concentration of xylem sap collected from Fe deficient barley. Plant roots were treated with 30 ^M of various chelators together with an equimolar amount of FeCl3 for 3 hours in the nutrient solution (pH 6.5).
Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Post a comment