Amino-acid influx at the soil-root interface of Zea mays L. and its implications in the rhizosphere

Abstract

The aim of the study was to investigate the ability of intact Zea mays. L. roots to regulate the amount of free amino-acids present in the rhizosphere. Using metabolic inhibitors it was demonstrated that the release of aminoacids from the root occurred by passive diffusion, whilst free amino-acids outside the root could be re-captured by an active transport mechanism. The influx of amino-acids into the root was shown to be relatively independent of spatial location along the root and was little affected by the presence of other organic compounds in solution. It was deduced from root concentration gradients that the main site of amino-acid exudation was at root tips. Amino-acid uptake by the root was shown to be independent of both inorganic-N concentration and the presence of other organic solutes in solution. A computer simulation model was constructed to assess the contribution of organic-N uptake (acidic, basic and neutral amino-acids) to the plant's N budget, in comparison to the inorganic solutes NO3 and NH4. Simulations of N uptake from a 0.5 mm radius rhizosphere indicated that when inorganic-N concentrations in soil were limiting (~< 0.1 pmoles cm -3 soil), the uptake of amino-N accounted for up to 90% the total N taken up by the roots. In situations where fertilizer inputs are high, and levels of organic matter in soil are low, the contribution of amino-N might still be expected to form < 30 % of the total N taken up by the root system. It was concluded that the uptake of amino-acids from the rhizosphere may be important in both N nutrition and in the minimization of root C and N losses to the soil. Consequently this may be important in governing the size of the rhizosphere microbial population.Abbreviations: CCCP -Carbonyl cyanide m-chlorophenyl-hydrazone, PCMBS -p-chloromercuri-phenylsulfonic acid, NEM -N-Ethyl-maleimide. All inhibitors obtained from

Characterization of Siderophore Producing Rhizobacteria and Its Effect on Growth Performance of Different Vegetables

“…Plant growth promoting rhizobacteria increased the synthesis of gibberellins, which would have triggered the activity of specific enzymes including amylase to promote early germination, which have brought an increase in availability of starch assimilation (Bharathi et al, 2004). It is a well-established fact that overall plant growth and root development influenced by improved phosphorous nutrition (Jones et al, 1994). A large number of evidence suggests that PGPR enhance the growth, seed emergence and crop yield (Herman et al, 2008).…”

Wheat roots efflux a diverse array of organic N compounds and are highly proficient at their recapture

“…amino acids: Schobert and Komor 1987;Jämtgård et al 2008). In this context it is worth noting that past studies showing simultaneous efflux and re-capture of amino acids supplied amino acids at arbitrary concentrations of 1 10 & 20 μM (Lesuffleur et al 2007; Lesuffleur and Cliquet 2010) or 2.5 μM (Phillips et al 2004(Phillips et al , 2006 or 100 μM (Jones and Darrah 1994). In general these concentrations are larger and bear little semblance to concentrations that occur in exudates.…”

Absorção e assimilação de uréia pela bromélia epífita com tanque Vriesea gigantea

“…This is in agreement with the large number of amino acid transporters that have been identified in many plant species, some of them related to root carrier systems [29,30]. Thus, the large amount of amino acids found in soils, the presence of amino acid transporters in root systems and the high ability of these plants to take up amino acids make organic N sources of great importance for the plant nutrition in alpine, boreal and arctic ecosystems.…”

“…Many transporters of organic N sources have been found in plants, many of them in root tissues [29,30], so there is a physical precondition for its utilization. In fact, some agricultural plant species have been shown to absorb organic nitrogen.…”