Effect of Low Levels of Calcium on Exudation of Sugars and Sugar Derivatives from Intact Peanut Roots under Axenic Conditions

Abstract

The effects of 10, 20, 35 and 50 mg of Ca2+ per liter on the qualitative and quantitative exudation of sugars from roots of 5-week-old peanut plants, Arachis hypogaea L., grown axenically in nutrient solutions, were measured. Nutrient solutions in which plants had been growing were collected at weekly intervals for 4 weeks, sugars in them were measured by gasliquid chromatography of the trimethylsilyl derivatives. Arabinose, ribose, xylose, fructose, mannose, glucose, galactose, mannitol, galacturonic acid, inositol, sucrose, and five unknowns were found. Qualitative and quantitative differences in exudates were correlated with age of the plants and calcium level. Four times more sugar was exuded at 10 mg than at 50 mg of Ca'+ per liter but no significant differences in growth were observed. Ion efflux measurements suggested that low levels of Ca"' increased root cell membrane permeability.Collection of organic root exudates should be carried out under axenic conditions to prevent losses and alterations by the microbial populations in the rhizosphere. By using the system reported by Hale (4), effects of various factors on qualitative and quantitative exudation of sugars from peanut roots and fruits have been studied (5,10,16). The release of these compounds into the region immediately surrounding roots in soil (rhizosphere) (12) The objectives of the present study were to determine the effect of various low levels of calcium on the root exudation of sugars from axenic peanut plants and to evaluate the possible relationship of exudation to changes in root cell membrane permeability. MATERIALS AND METHODSAseptic peanut seeds, Arachis hypogaea L. cv. Argentine, were obtained by removing the testa and surface sterilizing the remaining part of the seed for 5 min at 50 C in 20% solution of commercial sodium hypochlorite (4). Sterilized seeds were transferred aseptically to the surface of solidified nutrient medium in Petri dishes where they were allowed to germinate at 37 C in a humidified incubator. After 5 days, seedlings were transferred aseptically to sterile, screw-capped, glass jars in which they were transported to each of four sterile isolator chambers (4). The seedlings were transferred from the jars to transplanting tubes containing perlite saturated with Hoagland solution (4). After 4 weeks, 13 sterile (axenic) seedlings per isolator chamber were selected for uniformity and placed in separate 1-liter flasks containing nutrient solution. Random sterility checks of materials inside the chamber, of plant surfaces, and of the inner chamber surfaces were taken at weekly intervals by swabbing representative surfaces. Swabs were placed on potato dextrose agar, nutrient broth, Levine3 EMB agar, Sabouraud dextrose agar, brain heart infusion agar, and thioglycolate medium and incubated at room temperature or at 37 C. Plant sterility was checked before and after each experiment by removing an extra plant from the chamber and macerating samples of leaf, stem, and root tissue, placing them on media, and incubat...

Sugar exudation by roots of kallar grass [ Leptochloa fusca (L.) Kunth] is strongly affected by the nitrogen source

“…Aluminium is known to stimulate root exudation of organic acids, which plays a key role in the avoidance strategy of Al-tolerant cultivars of wheat (Delhaize et al 1993). Increased sugar exudation from peanut roots at low external Ca 2+ supply (0.25 mM Ca 2+ ) was attributed to increased root cell-membrane permeability (Shay and Hale 1973). On the other hand, Rovira (1959) did not find any consistent effect on the release of amino acids from roots of tomato, clover, and canary grass grown with Ca 2+ levels ranging from 0.5-50 mM.…”

Organization and regulation of the mannopine cyclase-associated opine catabolism genes in Agrobacterium tumefaciens 15955

“…The fact that opine catabolic genes are fairly resistant to catabolite repression in the absence of an inorganic nitrogen source gives Agrobacterium strains a great selective advantage. The cells still will be able to utilize the opines produced by crown galls, despite the presence of a wide range of other carbon sources found in root exudates (31,37,38).…”

The effect of soil pH on rhizosphere carbon flow of Lolium perenne

“…Levels of potassium (Kraffczyk et al, 1984), phosphorus (Rovira and Ridge, 1973;Bowen, 1969), nitrogen (Bowen, 1969), and calcium (Shay and Hale, 1973) in the nutrient solution in which plants were grown hydroponically affected the quantity and quality of exudates released from the plant roots. The presence of an active microflora also influences carbon loss from plants grown in solution culture (Kraffczyk et al, 1984;Lee and Gaskins, 1982) and in soil (Martin and Kemp, 1986;Martin, 1977).…”