Amino Acids in Agricultural Soil and their Uptake by Plants

Barley plants in a solution uptake study

Therefore, in the investigations this thesis is based upon, key aspects of the uptake of amino acids by agricultural plants were explored in field studies (to ensure ecological relevance) and laboratory analyses (to ensure precision). Small tension lysimeters were used to collect soil solution from several agricultural soils with minimal disturbance. Concentrations of free amino acids were found to be low (0-12.7 ìM). However, they may be continuously replenished from bound amino acid pools and were found to be sufficiently high (generally) for uptake by hydroponically grown barley, Hordeum vulgare L., and Arabidopsis, Arabidopsis thaliana L. Hence, the effective minimum concentrations for uptake by these species do not seem to exceed most of the field-measured concentrations.

The uptake affinity in both barley and Arabidopsis was found to be comparable to reported
values for nitrate at corresponding concentrations and for uptake of amino acids by soil micro-organisms. The amino acid transporters lysine histidine transporter 1 (LHT1) and amino acid permease 5 (AAP5) were found to be largely responsible for amino acid uptake in Arabidopsis at these concentrations. These transporters have complementary affinities for amino acids with differing properties; LHT1 transporting acidic and neutral amino acids, and AAP5 basic amino acids.
Furthermore, the gene expression of LHT1 and AAP5 clearly increased after roots were exposed to amino acids, even in the presence of inorganic nitrogen, resulting in up to 15-fold increases in the rate of amino acid uptake. The induced amino acid uptake rates were up to 10-fold higher than nitrate uptake rates in Arabidopsis. According to standard textbooks, nitrate and ammonium are the major nitrogen sources for plants. However, the results of these studies indicate that plants have the capacity to take up amino acids at field concentrations in presence of nitrate and ammonium. This capacity requires gene expression, synthesis and regulation of amino acid transporters, and the ability of plants to sense and respond to amino acid concentrations at ambient concentrations. There is, therefore, little doubt that plants can take up amino acids in their natural environment. Thus, it is time to reconsider traditional views of the nitrogen compounds used by agricultural plants.

Ref. Sandra Jämtgård. 2010. The Occurrence of Amino Acids in Agricultural Soil and their Uptake by Plants. Doctoral Thesis Swedish University of Agricultural Sciences Umeå.

Uptake of Multiple Amino Acids by Wheat

Schematic representation of the experimental setup, showing roots of wheat seedlings penetrating the glass media and the sampling procedure using 2 ml syringe.

Recent research has proven that higher plants can utilize amino acids as nitrogen (N) and carbon (C) sources. Most studies have focused on single amino acids with or without inorganicN, but a range of amino acids may be expected under conditions where the main N input derives from turnover of organic N sources. This study investigated the uptake of multiple amino acids by plant roots and further the active versus passive uptake was determined. Under minimum microbial activity conditions, seedlings of wheat (Triticum aestivum L. cv. ‘Baldus’) were exposed to a series of different concentrations of seven mixed amino acids solutions. Samples of the depleted solutions were periodically collected over a period of ten hours to measure the concentration of amino acids. For all tested amino acids passive uptake was a minor contribution compared to the total uptake. The uptake rates of the amino acids were well described by single Michaelis- Menten kinetic equations with R2 ranging from 0.87 to 0.96. All of the tested amino acids showed a similar uptake pattern.Wheat plants had the highest affinity (lowest Km values) for glutamine followed by tryptophan, alanine, arginine, glycine, and serine. The Vmax values for amino acids uptake by wheat ranged from 2.26 for tryptophan to 16.6 ìmol g.1 root FW h.1 in case of serine.

This study reports, for the first time the simultaneous uptake of multiple amino acids in important agricultural crops. The simultaneous uptake of the six mixed amino acids was dependent on the outer concentration and not on the amino acid type .  The uptake kinetics for the six amino acids showed similar trends, a results that agrees with the conclusion of Fischer et al. (1998) that plants contain multiple sets of amino acid transport proteins and that there are also a large number of general amino acid transporters, which can transport many different amino acids. The finding of multiple amino acids uptake also agrees with the expectations of Okumoto et al. (2002) that multiple transporters with differing kinetic characteristics are responsible for import of amino acids into seeds since this action could allow the growing seed to adapt to varying N-supply and alteration in amino acids available.

Ref: A. El-Naggar, A. de Neergaard, A. El-Araby & H. Hogh-Jensen (2009): Simultaneous Uptake of Multiple Amino Acids by Wheat, Journal of Plant Nutrition, 32:5, 725-740

Mengumpulkan bangkai-bangkai

Oleh: Nasih Widya Yuwono

Bangkai yang berserakan di atas lahan tentu menimbulkan pemandangan yang tidak sedap, aroma bau busuk yang menyengat, kerumunan lalat dan melahirkan belatung2 yang rakus mengoyak. Yang paling mengerikan, bangkai menjadi sarang pembiakan  mikrobia pathogen. Upaya menyingkirkan bangkai dari lingkungan secara sistematik dalam tempoh yang sesingkat-singkatnya diperlukan untuk mencegah ancaman terhadap kesehatan tersebut. Demikianlah cara pandang kebanyakan kita atas bangkai.

Warga dan prajurit membakar sapi yang mati akibat awan panas Gunung Merapi (Foto: okezon.com)

Saya ingin menunjukkan cara berpikir yang lain. Tahukah anda sisa hewan tersebut dapat dimanfaatkan sebagai bahan pupuk organik ?

Dengan menguraikan bangkai menjadi asam amino atau unsur hara terlarut, maka kita dapatkan pupuk organik hewani. Bangkai tersusun sebagian besar berupa air dan senyawa protein. Jika terurai, maka dihasilkan bahan yang kaya dengan unsur N (nitrogen). Unsur nitrogen inilah yang paling banyak diserap tanaman untuk pertumbuhannya.

Proses penguraian bangkai dapat dikerjakan secara mekanik (fisik), mikrobiologi, atau kimia.

Uptake of organic nitrogen by plants

Plant uptake of organic N has been studied for more than a century and has also been covered by several recent and older reviews.

In spite of the numerous studies showing the capacities of plants to absorb organic N compounds through roots, and demonstrations of how plants acquire such compounds also in field settings, the issue is still a matter of intense debate.

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