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Effect of nitrate and humic substances of different molecular size on kinetic parameters of nitrate uptake in wheat seedlings
Author(s) -
Cacco Giovanni,
Attinà Emilio,
Gelsomino Antonio,
Sidari Maria
Publication year - 2000
Publication title -
journal of plant nutrition and soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 1436-8730
DOI - 10.1002/1522-2624(200006)163:3<313::aid-jpln313>3.0.co;2-u
Subject(s) - cmin , nitrate , chemistry , nitrate reductase , cycloheximide , nitrogen , environmental chemistry , horticulture , biochemistry , bioavailability , protein biosynthesis , biology , organic chemistry , bioinformatics , cmax
The kinetic parameters of nitrate uptake (I max , Km and C min ) were evaluated in young seedlings of Triticum durum L., cv. Appulo, exposed to nitrate and/or to soil‐extracted humic acids (HAs) of different molecular weight. The uptake was enhanced after induction at low levels of nitrate (50 μM KNO 3 ), while it was inhibited after induction at higher concentrations (2000 μM). The kinetic parameters of uptake were selectively influenced by pre‐treatment with HAs: total (TE) and, at a greater extent, low (LMS, < 3500 Da) molecular size humic fraction increased either the nitrate uptake rate (I max ) and the efficiency of the whole transport system (low Km and C min ), while an opposite result was evidenced in high molecular size (HMS, > 3500 Da)‐treated plants. An additive effect was shown when nitrate and humic substances were provided simultaneously: the uptake rate was enhanced in TE‐ and LMS‐treated plants, but was strongly delayed in HMS‐treated plants. Removal of nitrate and/or humic fractions de‐induced the system and NO 3 — uptake rate decreased. Exposure to HAs was not able to induce nitrate reductase activity in root and leaf tissues. Inhibitors of protein synthesis p‐fluorophenylalanine and cycloheximide reversed the positive effect of LMS fraction on nitrate uptake. This would support the hypothesis of a promoting effect of HAs on the molecular expression of proteins of the nitrate transport system.