Guttation fluid peroxidases from Helianthus annuus

Abstract

The isoperoxidases (EC 1.11.1.7) in guttation fluid of Helianthus annuus appeared as two bands, G1 (slower moving) and G2 (slightly faster), following disc gel electrophoresis and again as two bands, SG1 ( M r 39 000) and SG2 ( M r 36 000) on SDS gels. These were electrophoretically indistinguishable from the corresponding isoperoxidases R1 and R2 (on non-SDS gels) and SR1 and SR2 (on SDS gels) found in bleed taken from just above the root (root bleed). In addition, what appeared to be SR1 and SR2 were also found in root apoplast washes. The total peroxidase activity of root bleed was very similar to that of bleed taken from higher up the hypocotyl, indicating that no additional peroxidase activity entered the sap above the root. These observations suggest that the root is the main, if not the sole, source of the peroxidases in guttation fluid. R1, but not G1, showed a slight but consistent increase in electrophoretic mobility on non-SDS gels following treatment with commercial acid phosphatase. Similarly the mobility on SDS gels of SR1, but not of SG1, increased after incubation with acid phosphatase. This indicates that R1 and G1 are not identical in all respects and that, after release from the root into the xylem sap, R1 becomes modified in vivo before appearing in the guttation fluid as G1.