Sugar exudation rates from the rachis was greater than that of the petiole phloem between anthesis and berry maturity. The concentrations of the amino acids within the phloem and xylem sap of the rachis were highest just prior to or after midnight while the flow of sugar through the rachis phloem was greatest during the early afternoon. The amino acid concentrations within the xylem sap and phloem exudate derived from these structures were greatest during anthesis and fruit set, and a second peak occurred within the rachis phloem at the onset of ripening. Glutamine and glutamic acid were the predominant amino acids in the xylem sap of both grapevine rachises and petioles, while arginine and glycine were the principal amino acids of the phloem exudate. Xylem sap was extracted by the centrifugation of excised leaf petioles and rachises, while phloem exudate was collected by immersing these structures in an ethylenediaminetetraacetic acid (EDTA) buffer. The diurnal and seasonal dynamics of xylem and phloem amino acid composition in the leaf petiole and bunch rachis of field-grown Cabernet Sauvignon are described to better understand the critical periods for amino acid import into the berry. Gourieroux, Aude M Holzapfel, Bruno P Scollary, Geoffrey R McCully, Margaret E Canny, Martin J Rogiers, Suzy YĪmino acids are essential to grape berry and seed development and they are transferred to the reproductive structures through the phloem and xylem from various locations within the plant.
The amino acid distribution in rachis xylem sap and phloem exudate of Vitis vinifera 'Cabernet Sauvignon' bunches. Of the 9 fatty acids detected, only capric acid was significantly different among varieties.
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Nine free fatty acids were detected in all varieties. In the present study, the phloem sap of 12 citrus varieties with different degrees of tolerance to HLB were extracted with ethyl acetate and analyzed by GC-MS after derivatization with boron trifluoride, a fatty acid-specific reagent. Studies conducted on the composition of citrus phloem sap revealed the presence amino acids, organic acids and sugars and of low amounts of free fatty acids. It is transmitted by the Asian citrus psyllid, a phloem sap-feeding insect. Occurrence of free fatty acids in the phloem sap of different citrus varieties.Ĭandidatus Liberibacter asiaticus is a phloem restricted bacterium that causes citrus greening disease or huanglongbing (HLB), a major treat to commercial citrus production in Florida. Hexose translocation is to be regarded as a normal mode of carbohydrate transfer by the phloem equivalent to that of sucrose, raffinose-family sugars, or sugar alcohols. This study urges a rethink of the existing views on carbohydrate transport species in the phloem stream. The validity of the approach is further supported by the virtual absence of hexoses in exudates from species that were known as exclusive sucrose transporters. The rate of sucrose degradation is far too low to explain the large proportions of hexoses measured in phloem exudates nor did other factors tested seem to stimulate the occurrence of hexoses. Promoting effects of EDTA, activities of sucrose-degrading enzymes, and sugar uptake by micro-organisms on hexose contents of phloem exudates were checked. Representatives of other families also appear to translocate appreciable amounts of hexoses in the sieve tubes.
The Δ13C of phloem sap sugars was closely related to phloem sap sugar concentration (r = −0.90, P 80% of carbohydrates in the form of hexoses. globulus trees growing on opposite ends of a rainfall gradient in southwestern Australia. The hypothesis was tested with analyses of E. We expected Δ13C to decrease with decreasing plant water potential and phloem sap sugar concentration to increase, thereby maintaining turgor within sieve tubes. We hypothesized that correspondence between these two parameters results from covarying responses to plant water potential. Farquhar, Graham D.Ī strong correlation was previously observed between carbon isotope discrimination (Δ13C) of phloem sap sugars and phloem sap sugar concentration in the phloem-bleeding tree Eucalyptus globulus Labill. Water Relations Link Carbon and Oxygen Isotope Discrimination to Phloem Sap Sugar Concentration in Eucalyptus globulusĬernusak, Lucas A.
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