Abscisic acid content in the root hemiparasite Melampyrum arvense L. before and after attachment to the host plant

Abstract

The content of abscisic acid (ABA) in abaxial leaf epidermis of the host (Capsella bursa pastoris) and the unattached hemiparasite Melampyrum arvense showed diurnal changes. ABA content increased during the light period and declined rapidly upon the darkening of leaves. In an attached hemiparasite the content of ABA in the epidermis was maintained at an almost constant level irrespective of the diurnal cycle. As compared with the maximum level in the host, at the end of the light phase the content of ABA in abaxial epidermis constituted about 70% and 164% in the unattached and attached hemiparasite, respectively. No significant changes in ABA content were recorded in adaxial epidermis. In all the samples abaxial/adaxial epidermis ABA content ratio was about 3.6:1 in light phase. In darkness this ratio decreased to about 1.1:1 in the host and the unattached hemiparasite and did not show significant change after attachment. ABA content ratio in mesophyll was 1:0.7:1.5 for the host, the unattached, and attached hemiparasite, respectively. In comparison with the host the concentration of ABA in xylem sap of the hemiparasite constituted about 31% and 152% for the unattached and attached M. arvense, respectively.