Carbohydrate and amino acid composition in phloem sap of Lolium perenne L. before and after defoliation

Abstract

Carbohydrate and amino acid composition of phloem sap was studied in the grass Lolium perenne L., before and after defoliation. Leaf exudate was collected in a 5 mmol·L–1 EDTA solution from cut leaf blades or stubble, and phloem sap was obtained through excised aphid (Rhopalosiphum padi L.) stylets. Results indicate that leaf exudates obtained from leaves devoid of petiole might not be relevant predictors of carbohydrate content of pure phloem sap. Sucrose was the dominating carbohydrate, accounting for 93% of the total soluble sugars in the phloem sap. Myo-inositol, glucose, and fructose were present in trace amounts, while fructans, raffinose, and loliose have never been detected. Predominant amino acid in the phloem sap was glutamine followed by glutamate, aspartate, and serine. Phloem sap component concentration declined during the first hours following defoliation. Sucrose was the main sugar transported in the phloem sap of Lolium perenne, despite the fact that the product of fructan degradation was fructose and not sucrose. The results are discussed in relation with the physiological mechanisms that contribute to plant recovery after defoliation.Key words: fructan, sucrose, loliose, defoliation, phloem sap, amino acids.

Relationship between Fruit Soluble Solid Content and the Sucrose Concentration of the Phloem Sap at Different Leaf to Fruit Ratios in Tomato

“…In addition, sucrose was collected in neutral buffer, which inhibits sucrose hydrolysis by acid invertase, which may be released from the wounded cells (Amiard et al, 2004). Sucrose concentration of the phloem sap ranged from 3 to 7% in 'House Momotaro' and 1 to 10% in 'Saturn', depending on the treatments.…”

An Appraisal on the Source-to-Sink Relationship in Plants: an Application of Desorption Electrospray Ionization Mass Spectrometry Imaging

“…The main amino acids found in the phloem are aspartate, glutamate, asparagine, and glutamine, whereas the major ureides are allantoin and allantoic acid. 1,3,8,35 Young leaves contain from two to four fold more nitrogen than mature leaves and this content decreases as the leaves age. That is because growing leaves demand a huge amount of protein for growing.…”

Optimal concentration for sugar transport in plants

“…Both bleeding and stylectomy have advantages and disadvantages as techniques for sampling phloem sap. Bleeding techniques are relatively simple to use but they are destructive and susceptible to contamination by apoplastic material and intracellular contents of neighbouring cells [31,42]. Samples produced by bleeding are also subject to dilution over time by water that is osmotically attracted to the incision [43], and may thus only provide a lower limit on the actual phloem concentration.…”