Diurnal variations of amino acids and organic acids in xylem fluid from Lagerstroemia indica: an endogenous circadian rhythm

Abstract

Diurnal variations in the concentrations of major organic compounds occurred in xylem fluid extracted from Lagerstroemia indica L. The concentration of amino acids and the N/C ratio was at a maximum and that of organic acids was at a minimum between 1230 and 2030 h. Since the concentrations of total organic nitrogen, total amino acids and most individual amino acids (but not organic acids or sugars) were also proportional to xylem tension two experiments were performed to discern whether variations in chemistry were a consequence of diurnal changes in moisture stress. In the first experiment, L. indica, exposed to variable levels of moisture stress during midday, manifested an increase in organic acids and a reduction in the N/C ratio. In the second experiment, chemical profiles of xylem fluid were collected and compared for plants exposed to a natural photoperiod, constant darkness or continuous light at noon and midnight. After 1 day amino acids increased in concentration during midday for all treatments; the variation was greatest (10‐fold) for plants in constant darkness where xylem tension varied from 0.20 to 0.25 MPa. Only plants exposed to continuous light lost a diurnal rhythm after 3 days. Thus, the circadian rhythm was endogenous, terminated in continuous light and was not mediated by changes in moisture stress. Glutamine accounted for most of the diurnal variation in total amino acids, organic nitrogen and the N/C ratio in xylem fluid.

Dynamics of concentrations and nutrient fluxes in the xylem of Ricinus communis– diurnal course, impact of nutrient availability and nutrient uptake

“…The dynamic nature of nutrient transport in the xylem has been demonstrated previously by both techniques that allow sampling of xylem sap from intact, transpiring plants [root pressure chamber:, e.g. Schurr & Schulze (1995); xylem‐tapping insects: Andersen & Brodbeck (1989), Andersen, Brodbeck & Mizell (1993), (1995)]. A number of processes has been suggested that cause the diurnal variation of xylem sap composition (Schurr 1998b), that range from variation of nutrient availability at the root system, nutrient uptake, variable dilution by the transpiration rate to lateral exchange along the xylem with parenchyma and/or phloem.…”

Alternation of host plants as a survival mechanism of leafhoppers Dilobopterus costalimai and Oncometopia facialis (Hemiptera: Cicadellidae), vectors of the Citrus Variegated Chlorosis (CVC)

“…The free amino acids found in the sap of plants are the base diet of the leafhoppers feeding on the xylem or plant phloem, which determines the selection of the primary host plants and dispersion of leafhoppers in different habitats and times of the year (Russel et al 1987, Andersen et al 1993. For species Homalodisca coagulata the selection of host plants and the adult population were verified to be positively correlated with the concentration of a few amino acids found in standard plants regarding feeding, and the nymphs failed to develop successfully on the hosts preferred by the adults due to the fact that they cannot assimilate as efficiently as the adults the essential nutrients in nutritionally unbalanced plants (Brodbeck et al 1990;1995).…”

Geostatistical characterization of the spatial distribution of Xylella fastidiosa sharpshooter vectors on citrus

“…Adults of the glassywinged sharpshooter, Homalodisca coagulata (Say) for example, tend to select host plants with higher concentrations of certain nutrients in the xylem sap (Brodbeck et al 1990). The nutritional quality of xylem sap can vary considerably in plants depending on several environmental factors, such as soil fertility and humidity, shade, plant age and location, etc (Andersen et al 1993, Andersen & Brodbeck 1991. This behavior could explain the aggregated pattern observed for Acrogonia sp.…”