Sugars exudation

Gum arable comes from various species of Acacia. The gum exudes through cracks, injuries, and incisions in the bark and is collected by hand as dried tears. Gum arable is unique among gums because of its high solubiUty and the low viscosity and Newtonian flow of its solutions. While other gums form highly viscous solutions at 1—2% concentration, 20% solutions of gum arable resemble a thin sugar symp in body and flow properties. 

Root exudates Diffusates Sugars, organic acids, amino acids,... 

Only limited information is available on effects of potassium (K) supply on root exudation. Increa.sed exudation of sugars, organic acids, and amino acids has... 

Despite increased citrate accumulation in roots of Zn-deficient rice plants, root exudation of citrate was not enhanced. However, in distinct adapted rice cultivars, enhanced release of citrate could be observed in the presence of high bicarbonate concentrations in the rooting medium, a stress factor, which is frequently associated with Fe and Zn deficiency in calcareous soils (235) (Hajibo-huid, unpublished). This bicarbonate-induced citrate exudation has been related to improved Zn acquisition in bicarbonate-tolerant and Zn-efficient rice genotypes (Fig. 9) (23S). Increased exudation of sugars, amino acids, and phenolic compounds in response to Zn deficiency has been reported for various dicotyledonous and monocotyledonous plant species and seems to be related to increased... 

Diffusion-mediated release of root exudates is likely to be affected by root zone temperature due to temperature-dependent changes in the speed of diffusion processes and modifications of membrane permeability (259,260). This might explain the stimulation of root exudation in tomato and clover at high temperatures, reported by Rovira (261), and also the increase in exudation of. sugars and amino acids in maize, cucumber, and strawberry exposed to low-temperature treatments (5-10°C), which was mainly attributed to a disturbance in membrane permeability (259,262). A decrease of exudation rates at low temperatures may be predicted for exudation processes that depend on metabolic energy. This assumption is supported by the continuous decrease of phytosiderophore release in Fe-deficient barley by decreasing the temperature from 30 to 5°C (67). 

Materials deposited by roots into the rhizosphere can be divided roughly into two main groups first, water-soluble exudates such as sugars, amino acids, or-... 

More recently, it was realized that rhizosphere cartton dynamics are more complex than these early models envisaged. Jones and Darrah (51-53) showed lhal roots actively scavenge their root exudates and that the re-uptake of exudates was selective. In most situations, sugars and amino acids were. scavenged by roots, while organic acid exudates were not (54). The authors also found that exudation losses were largely passive. This active involvement of the root essen-... 

A variety of chemicals may be leached from the aerial portions of plants by rainwater or by fog-drip (16) including organic acids, sugars, amino acids, pectic substances, gibberellic acids, terpenoids, alkaloids, and phenolic compounds. Colton and Einhellig (17) suggested that leaf leachates of velvetleaf (Abutilon theophrasti) may be inhibitory to soybean (Glycine maxT We have recently discovered specialized hairs on the stems of velvetleaf plants which exude toxic chemicals. 

Root exudates A wide variety of chemicals, such as sugars, amino acids, and aromatics, is excreted by roots of plants. Very little information is available on the allelopathic interaction of root exudates with the higher plants, except for the identification of a few products in isolated cases (46). 

Various plant species, ex. extracts, exudates, sugar- inhib d. Nitrosomonas, Nitrobacter 123-1 ... 

Fig. 1.—John Davidson s specimen of Pseudotsuga Douglasii, with exudation of sugar from water-pores at tips of leaves. ...

Miiller R, Morant M, Jarmer H, Nilsson L, Nielsen TH (2007) Genome-wide analysis of the ara-bidopsis leaf transcriptome reveals interaction of phosphate and sugar metabolism. Plant Physiol 143 156-171. doi http //www.plantphysiol.org/cgi/content/abstract/143/l/156 Neumann G, Romheld V (1999) Root exudation of carboxylic acids and protons in phosphorus-deficient plants. Plant Soil 211 121-130... 

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