Enhancement of Phloem Exudation from Cut Petioles by Chelating Agents

Abstract

The photosynthetic assimilates in leaves of Perilla crispa attached to the plant were labeled by treating the leaves with 4C02. When subsequently detached, these leaves exuded a negligible amount of radioactivity from the cut petiole into water. Ethylenediaminetetraacetate (EDTA), citric acid, and ethyleneglycol-bis(f8-aminoethyl ether) N,N'-tetraacetate greatly increased exudation of labeled assimilates into a solution bathing the petioles. The optimal concentration of EDTA was 20 mM, and maximal exudation took place between 2 and 4 hours after excision. Up to 22% of the radioactivity fixed in the leaf was exuded into an EDTA solution as compared to an export of 38% from attached leaves. The amount of radioactivity in the exudate was much reduced at low temperature.Presence of EDTA was required in the collecting solution for only 1 to 2 hours; upon transfer to water, exudation continued as in continuous presence of EDTA. Ca`+ completely inhibited the effect of EDTA.Anatomical studies indicated that callose formation on the sieve plates near the cut surface of the petioles was less in leaves on EDTA than on water.More than 95% of the radioactivity exuded by detached leaves was present in the sugars verbascose, stachyose, raffinose, and sucrose, which are translocated in the phloem of Perilla. Labeled glucose, fructose, and galactinol were detected in the leaf blade and petiole, but not in exudates.The addition of EDTA to a solution bathing the petiole of detached leaves of Chenopodium rubrum and Pharbitis nil also increased the exudation of labeled assimilates. In these two species, label appeared only in a compound that cochromatographed with sucrose.

Categories of Resistance to Greenbug (Homoptera: Aphididae) Biotype I in <B> <I>Aegilops tauschii</I> </B> Germplasm

“…Plants also deposit callose in sieve elements penetrated by stylets, thereby preventing the prolonged feeding of phloem-feeding insects. In plants, callose synthesis is Ca 2+ -dependent (King and Zeevaart, 1974). It has been shown that sieve tube occlusion upon wounding in legumes involves the dispersion of spindle like proteins (forisomes) with the aid of Ca 2+ influx to the injury site (Knoblauch et al, 2001;Thorpe et al, 2010).…”

Binding Properties of the N-Acetylglucosamine and High-Mannose N-Glycan PP2-A1 Phloem Lectin in Arabidopsis

“…Phloem sap was obtained by EDTA-facilitated exudation (King and Zeevaart, 1974). Four-to 6-week-old plants were grown in a greenhouse (16-h photoperiod).…”

“…Phloem sap was obtained from mature rosette leaves with an EDTA-facilitated exudation technique (King and Zeevaart, 1974) adapted for Arabidopsis. The quality of the sap was confirmed by the smaller proportions of Glc and hexose than of Suc ( Fig.…”

Myzus persicaeSulzer aphid contains oxylipins that originate from phloem sap

“…Phloem exudates were collected from plants grown in the same conditions without aphids according to a protocol adapted from King and Zeevaart (1974) that allows the collection of phloem exudates without major contaminations. The petioles of 10 g of V. faba freshly cut leaves were placed in 20 ml of a 20 mM Na 2 EDTA solution for 1 h in the dark under 90% of relative humidity.…”