Free Amino Acid Composition of Leaf Exudates and Phloem Sap

Abstract

Comparisons were made between the free amino acid composition in leaf exudates and that in pure phloem sap, using twin samples taken from a single leaf of two oat (Avena sativa L.) and three barley (Hordeum vulgare L.) varieties. Leaf exudate was collected in a 5 mm EDTA-solution (pH 7.0) from cut leaf blades and phloem sap was obtained through excised aphid (Rhopalosiphum padi L.) stylets. Fluorescent derivatives of amino acids were obtained using 9-fluorenylmethyl chloroformate and were separated by means of high performance liquid chromatography. The total concentration of free amino acids varied considerably in the exudate samples. There was no correlation between the total amino acid content in the exudate samples and that of the corresponding phloem sap samples, but the amino acid composition of the corresponding samples was highly correlated (median R2-value 0.848). There was only limited between-plant variation in phloem sap amino acid composition. Nevertheless, in comparisons involving all samples, many of the amino acids showed significant correlations between their relative amounts in exudate and phloem sap. The results presented here indicate that the exudate technique holds great promise as an interesting alternative to the laborious and time-consuming stylet-cutting technique of obtaining samples for comparative studies of phloem sap.parts of large aphids (4) but as most aphids are small, mechanical excision of their stylets is very difficult. Despite recent technological advances, including the adoption of high frequency microcautery (9) and ruby lasers (1, 3) for cutting the mouthparts, the aphid stylet technique remains laborious and time-consuming and, usually, only small quantities of phloem sap are obtained.The exudation technique involves collection of the sap exuding from cut plant parts. King and Zeevaart (5)

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

“…However, our data indicate higher Ser and Gly and lower amounts of Leu/Ile and Asn than were reported previously. The amino acid profile we obtained is also similar to those reported previously for barley (Winter et al, 1992), oat (Weibull et al, 1990), rice (Hayashi and Chino, 1990), and maize (Faria et al, 2007). Moreover, despite the lower total ST amino acid concentration in Arabidopsis (Hunt et al, 2006), the amino acid profile was similar to our results for wheat, with the exception that Arabidopsis had higher Asn and lower Ser concentrations.…”

“…For example, 15-to 60-nL samples were used for sugar beet (Beta vulgaris) analysis (Lohaus et al, 1994), 30-to 100-nL samples were collected by stylectomy for the Mexican sunflower (Tithonia diversifolia; Bernays and Klein, 2002), while only samples above 50 nL were used for a study of alfalfa (Medicago sativa; Girousse et al, 1996). A mean volume of 34 nL was reported in studies of oat (Avena sativa) and barley (Weibull et al, 1990), and 250 to 500 nL was used in a study of British grasses (Hale et al, 2003). Work on Arabidopsis employed sap volumes between 10 and 50 nL (Hunt et al, 2006).…”

“…Limitations in the sensitivity of the HPLC technique, however, meant that analysis could only be performed where enough phloem sap was obtained. In the literature, volumes between 15 and 500 nL were used to determine directly the ST solute concentrations in various species using HPLC (Weibull et al, 1990;Lohaus et al, 1994;Girousse et al, 1996;Bernays and Klein, 2002;Hale et al, 2003), while lower collected volumes could not be analyzed directly. Since severed stylets exude at a range of rates, limitations of analytic techniques have previously restricted study to those stylets with a high exudation rate, thus producing larger sample volumes and leading to potentially unrepresentative data in the literature.…”

S-Methylmethionine Plays a Major Role in Phloem Sulfur Transport and Is Synthesized by a Novel Type of Methyltransferase

“…EDTA chelates the Ca 2 ϩ required for callose formation and thereby blocks the sealing of cut sieve tubes (King and Zeevaart, 1974). The sap obtained by the EDTA technique is comparable in composition to that from severed stylets (Weibull et al, 1990;Valle et al, 1998). A tracer dose of 35 S-Met was applied to the tips of leaves from species representing five diverse families, and the corresponding phloem exudates were analyzed for 35 S-SMM ( Figure 4A).…”

Amino acids through developmental stages of sunflower leaves

“…The relative levels of the two nitrogen-rich essential protein-bound amino acids, diamino acids, lysine and arginine, increased from young leaf to mature leaf and then decreased in senescent leaf. This decrease indicates the reduction of nutritive quality in senescent leaves (WEIBULL et al 1990), since these two amino acids are target sites for proteolysis by trypsin which is a common protease of insect gut (BROADWAY and DUFFEY 1988). The high level of free amino acids in young and mature leaves, especially of free glutamic acid (and its amides), reflect the active metabolism of growing tissues (WEIBULL 1987).…”