Dominant amino acids, organic acids and sugars in water-soluble root exudates of C₄ plants: a mini-review

Abstract

VRANOVÁ, V., KAŇOVÁ, H., REJŠEK, K., FORMÁNEK, P.: Dominant amino acids, organic acids and sugars in water-soluble root exudates of C 4 plants: a mini-review. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 5, pp. 441-446 The aim of this mini-review was to identify the dominant carbohydrates, organic acids and amino acids in water-soluble root exudates of plants which represent dominant compounds there. The study is focused on plants of C 4 -type of metabolism taking into account available literature. From group of carbohydrates, those dominant are represented glucose, fructose, arabinose and sucrose. Between dominant amino acids occurring in root exudates of C 4 -metabolism plants are alanine, se rine, arginine, glutamine, glutamic and aspartic acid, glycine, proline, cystine, lysine and -aminobutyric acid. Citric, malic, tartaric, succinic, trans-aconitic represent the dominant organic acids. This knowledge may be useful for planning analyses of these compounds in root exudates of C 4 plants. Except ), amino acids, amides, sugars, aliphatic acids, aromatic acids, volatile aromatic compounds, gases such as ethylene, vitamins, peptides, proteins, enzymes, plant hormones, alcohols, ketones, olefi ns, urea, phytoalexins (Curl and Truelove, 1986;Vančura, 1988;Grayston et al., 1996;Paynel et al., 2001;Uren, 2007;Neumann and Römheld, 2007). Oxidative enzymes assessed in root exudates were e.g. haem-containing peroxidases, unspecifi c coper-containing oxida ses, monooxygenases-hydroxylating and aromatic-ring cleavage dioxygenases (Gramss and Rudeschko, 1998). In total, 200 diff erent carbon containing molecules are present in root exudates (Curl and Truelove, 1986), and up to 40 % of the net carbon fi xed during photosynthesis can be released into the rhizosphere Lynch, 1983, 1990). Root exudates can be sectioned according to their chemical character, properties and molecular weight (Rovira, 1956;1969). Commonly, root exudates are divided into high molecular weight waterinsoluble materials such as cell walls, sloughed-off material, other root debris and mucilage, and low molecular weight compounds denoted as water-solu ble exudates such as sugars, amino acids, organic acids, hormones and vitamins (Rovira et al., 1979;Cheng et al., 1993; Traoré et al., 2000). Of the low molecular weight root exudates, sugars, organic acids and amino acids form the dominant components (Aulakh et al., 2001). Sugars, organic acids and amino acids effl ux from roots is thought to occur by passive diff usion (Jones and Darrah, 1994; Shepher and Davies, 1994;Rroço et al., 2002;Uren, 2007;Neumann and Römheld, 2007). With age of plants, the amount of organic acids in root exudates increased and the proportion of sugars and amino 442 V. Vranová, H. Kaňová, K. Rejšek, P. Formánek acids decreased, expressed per weight unit of root dry weight (Smith, 1970;Aulakh et al., 2001;Gransee and Wittenmayer, 2000;Uren, 2007). The intensity of exudation related to unit of root biomass was found to decrease with age of plant...

Natural Occurrence of Enantiomers of Organic Compounds Versus Phytoremediations: Should Research on Phytoremediations Be Revisited? A Mini‐review

“…The effect of individual compounds occurring in root exudates (especially malic or tartaric acid) on heavy metals or organic pollutants (especially PAHs and pesticides) availability has been tested . Malic, tartaric, succinic, citric, oxalic, and acetic and propionic acid are dominant organic acids of plant root exudates . Lactic acid can also be dominant when plants are stressed by heavy metals (e.g., Cd) .…”