d by HPLC. The m/z 191 (Figure 2), m/z 179, 225, 277, 311, 339, 431, 471, 540, and 702 (Figure 3), and m/z 327, 481, and 655 (Figure 4) in fragmentation patterns for water extract of lettuces cultivated in EPCS was significantly different from those in CCS, indicating that production of specific metabolites may change with variation of soil conditions induced by electric pulse or directly influenced by the electric pulse.


Biogeochemical condition of culture soil for growth of each lettuce may not be very different but may be changed by electric pulse based on the weight difference of lettuces cultivated in CCS and EPCS. Twenty percent increase of crop weight in EPCS may be caused by improvement of nutritional soil condition for lettuce growth or physiological activation of lettuces by the electric pulse. Ammonium and nitrate are commonly absorbable nutrient ions by plants but nitrite is not [21,22]. However, nitrite can be chemically and biochemically oxidized to nitrate and biochemically reduced to ammonium [23-25]. Electrochemical redox reactions induced by the electric pulse may activate oxidation of nitrite to nitrate [26]. Total nitrogen contents may thus be useful to estimate nutritional soil condition for lettuce growth. The total nitrogen content in EPCS was more than double that in CCS, reciprocally proportional to weight of lettuces. Inorganic nitrogen may be more effectively generated from soils composed of organic and inorganic nitrogen compounds by biochemical and chemical reaction in EPCS than CCS. Phosphate has a strong tendency to be adsorbed onto soil particles and readily becomes a waterinsoluble salt. However, phosphate may be desorbed by

Figure 3. Fragmentation patterns for water-extracted compounds of lettuce detected at retention time from 8.77 to 15.97 min (Figure 1, box II) in HPLC.

Figure 4. Fragmentation patterns for water-extracted compounds of lettuce detected at retention time from 20.87 to 23.61 min (Figure 1, box III) in HPLC.

biological weathering induced by bacterial metabolites and exudate secreted by roots of plants [27-29]. Higher phosphate in EPCS than CCS may be caused by additional weathering induced by the electric pulse [30]. Minerals also may be dissolved in watered soil by the biochemical weathering induced by microbial metabolism, roots of plants [31] and chemical weathering induced by electric pulse [32]. Nutrient salts and minerals are essential factors for plant growth, which may be more effectively balanced or increased for lettuce growth in EPCS than CCS [33].

Nutritional soil conditions were improved by the electric pulse. However, the improvement of nutritional soil condition may not have increased lettuce growth based on the difference of HPLC and mass spectrometry pattern for water extract of lettuces cultivated in CCS and EPCS. Difference of peak patterns in HPLC and fragmentation patterns in mass spectrometry for lettuces cultivated in CCS and EPCS are an indicator that some organic compounds produced by lettuces are directly influenced by the electric pulse or indirectly by variation of nutritional soil condition induced by the electric pulse. Metabolites produced by growing lettuces may be sugars, organic acids, amino acids, nucleic acids, and fatty acids. Practically, most of the metabolites produced in cells of lettuces grown for 21 days may be converted to structural polymers. Metabolite concentrations may be difficult to measure without separate purification. However, the differences of metabolites of hormones produced by lettuces grown in CCS and EPCS can be compared using patterns of HPLC and mass spectrometry. Hormones produced by lettuces can be identified using the fragmentation (m/z) pattern of precursor ions and product ions generated by electrospray ionization of standard hormones. The m/z patterns of organic compounds contained in lettuce extract were compared with the mass spectrometric database obtained using the standard hormones [19,20]. The m/z patterns obtained in mass spectrometry for the lettuce extract were not identified with the m/z pattern for the standard hormone (Table 4 and Figures 2-4). Variation and difference of m/z pattern in the mass spectrometry for lettuce extract can be an indicator to clearly show difference of metabolites produced by lettuces grown in CCS and EPCS. The difference of peak height and m/z pattern in the mass spectrometry for the lettuce extract does not predict whether the electric pulse charged to lettuce culture soil directly or indirectly activates lettuce growth by improvement of nutritional soil condition. Conclusively, the low intensity electric pulse charged to the culture soil for lettuce cultivation influenced improvement of nutritional soil condition for the water-soluble nutrient salts and minerals and increase of some organic compounds contained in lettuce extract. The relatively higher content of water-soluble organic compounds, of which molecular weight is possible to be minimally 133 (Figure 2) and maximally 711 (Figure 3) based on the m/z measured by the mass spectrometry, may be a clue that building blocks for biosynthesis of structural compounds may be more actively produced.


This work was supported by the New & Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea governmental Ministry of Knowledge Economy (2010T1001100334).


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