The translocation of the metals in xylem sap of barley

As indicated in 3.2, it is considered that the absorption of free PS by the root, without Fe, is a usual phenomenon. In addition, feeding with both synthetic and microbial chelators was conducted in section 4.5. Therefore, it was considered that the feeding effect of free chelators on the translocation of metal micronutrients in xylem tubes needs to be examined.

The chelators PS, FOB, and EDTA were dissolved in the hydroponic media (25 ^M) and supplied to the root of +Fe or -Fe barley plants for 3 hours in the afternoon. Xylem sap was collected for 3 hours after the supply of chelators (Alam et al., 2001a).

Table 14-3 shows the amount of metal micronutrients translocated in xylem sap. It was apparent that feeding with PS largely enhanced the amount (pmol plant-1 h 1) of Fe translocation in xylem tubes of -Fe barley. Feeding with FOB also enhanced Fe translocation slightly. Feeding with EDTA, however, repressed Fe translocation. Feeding with PS also enhanced the translocation of the other metals. It is speculated that absorbed free PS might chelate other metals in root cells and carry them into the xylem tubes.

It is known that the function of PS for carrying metals from rhizosphere to the cell is specific to Fe3+ (Ma et al., 1993) and Zn2+ in grasses (von Wiren et al., 1996, Zhang et al., 1991a). It is also known that externally fed PS can solubilize apoplastic Fe of the roots and be absorbed by the roots (Zhang et al., 1991b). However, how the free PS absorbed by the roots function in the root cell has not been discussed. The effect of free PS on the physiological form of the other metals in the root cell needs to be investigated.

Table 14-3. Amounts of phytosiderophores and metals translocated in xylem sap of Fe-deficient barley fed with or without various chelators._

Treatment

PS

Mn

Fe

Zn

Cu

Fe Chelator

p mol plant-1

h-1*

+ -

502±81

318±29

985±19

219±22

55±3.1

- -

4820±153

397±31

57±4.5

255±11

61±8.9

- PS

9871±588

645±38

392±18

392±23

91±11

- FOB

5561±704

410±44

94±11

253±18

59±9.2

- EDTA

1939±162

193±12

8.8±2.5

46±4.2

17±2.9

Values were compared with Fe-sufficient plants. This table is a corrected version of the one previously presented in Alam et al. (2001a). Values are mean ± SE of 2 replications. *Values previously presented were in nmol plant-1 h-1.

Values were compared with Fe-sufficient plants. This table is a corrected version of the one previously presented in Alam et al. (2001a). Values are mean ± SE of 2 replications. *Values previously presented were in nmol plant-1 h-1.

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