Furthermore, the existence of antirrhinoside in nectar could be based on passive secretion from the phloem.ĭirectory of Open Access Journals (Sweden)įull Text Available BACKGROUND: Floral nectar contains sugars and amino acids to attract pollinators. The concentration of several metabolites was lower in nectar than in phloem sap indicating selective retention of some metabolites. Otherwise, the composition of both aqueous solutions was not the same. The parallel analyses of nectar and phloem sap have shown that all metabolites which were found in nectar were also detectable in phloem sap with the exception of hexoses. High amounts of antirrhinoside were found in the phloem sap and lower amounts in the nectar of both plant species. erubescens synthesized the iridoid glycoside antirrhinoside.
Both members of the tribe Antirrhineae (Plantaginaceae) M. Nectar amino acid concentrations were negatively correlated with the nectar volumes per flower of the different plant species. The total concentration of amino acids was much lower in nectars than in phloem sap, indicating selective retention of nitrogenous solutes during nectar formation. One possible reason for this could be the activity of invertases in the nectaries. The nectar of all three plant species contained high amounts of sugars with different percentages of glucose, fructose, and sucrose, whereas phloem sap sugars consisted almost exclusively of sucrose. Nectar was collected with microcapillary tubes and phloem sap with the laser-aphid-stylet technique. Therefore, phloem sap and nectar from different plant species (Maurandya barclayana, Lophospermum erubescens, and Brassica napus) were compared. Does nectar composition reflect phloem composition, or is nectar synthesized and/or modified in nectaries? Studies where both, the nectar as well as the phloem sap taken from the same plant species were analyzed in parallel are rare. In addition, nectar also contains different secondary compounds, but little is understood about their origin or function. Results strongly support the contention that water relations form a mechanistic link between phloem sap sugar concentration and both instantaneous and integrated measures of theĬomparison of sugars, iridoid glycosides and amino acids in nectar and phloem sap of Maurandya barclayana, Lophospermum erubescens, and Brassica napus.įloral nectar contains sugars and amino acids to attract pollinators. A theoretical model suggested that the observed variation in stomatal conductance was sufficient to account for the variation observed in oxygen isotope discrimination across the study. Oxygen isotope discrimination in phloem sap sugars also correlated strongly with phloem sap sugar concentration. Accordingly, a strong, negative relationship was observed between instantaneous c 1 /c a and the phloem sap sugar concentration. The relationship between carbon isotope discrimination measured in phloem sap sugars collected from the stem and c 1 /c a measured instantaneously on subtending leaves was close to that theoretically predicted. Carbon isotope discrimination correlated positively with shoot water potential, whereas phloem sap sugar concentration correlated negatively with shoot water potential. A strong correlation was observed between the carbon isotope ratio in phloem sap sugars and phloem sap sugar concentration. The study comprised 40 individual Eucalyptus globulus trees growing in three plantations situated on opposing ends of a rainfall gradient in southwestern Australia.
Conversely, we expected the phloem sap sugar concentration to increase with decreasing plant water potential, thereby maintaining positive turgor pressure within the sieve tubes. Carbon isotope discrimination is expected to decrease with decreasing plant water potential due to the influence of stomatal conductance on the ratio of intercellular to ambient CO 2, concentrations (c 1 /c a ). We hypothesized that the correspondence between these two parameters results from co-linearity in their responses to variation in plant water potential. Arthur, D.J Pate, J.S.įull text: The carbon isotope ratio of phloem sap sugars has been previously observed to correlate strongly with the phloem sap sugar concentration in Eucalyptus globulus. International Nuclear Information System (INIS)Ĭernusak, L.A. Water relations link carbon and oxygen isotope discrimination to phloem sap sugar concentration in eucalyptus globulus
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