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Xylem sap proteins.

C L Biles¹, F B Abeles

¹U.S. Department of Agriculture, Agricultural Research Service, Appalachian Fruit Research Station, 45 Wiltshire Road, Kearneysville, West Virginia, 25430.

Plant Physiology

|June 1, 1991

Summary

Plant roots secrete acidic peroxidases into xylem sap, which may help seal damaged vascular tissue. Ethylene exposure increases this peroxidase activity and reduces sap flow.

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Area of Science:

Plant physiology
Biochemistry
Molecular biology

Background:

Xylem sap contains various proteins, including acidic peroxidases.
Peroxidases are enzymes involved in various plant processes.

Purpose of the Study:

To investigate the origin and function of peroxidases in xylem sap.
To determine the effect of ethylene on xylem sap peroxidase activity.

Main Methods:

Xylem sap was collected from apple, peach, pear, strawberry, tomato, and cucumber plants using pressure extrusion, stem exudates, and guttation fluid.
Isoelectric focusing was used to analyze peroxidase isozymes.
Cucumber seedlings were treated with ethylene to assess its impact on exudate and peroxidase activity.

Main Results:

Two main peroxidase isozymes (pI 9 and pI 4.6) were identified in initial stem exudates.
The pI 4.6 peroxidase isozyme was found in root tissue and guttation fluid, suggesting root origin.
Ethylene treatment increased peroxidase activity and reduced exudate volume in cucumber seedlings.

Conclusions:

Roots likely produce and secrete the pI 4.6 peroxidase into xylem sap.
Xylem sap peroxidases may play a role in plugging damaged vascular tissue.
Ethylene influences xylem sap peroxidase activity and exudation.

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