Аннотация:The beneficial effects of humic acids (HA) have been numerously reported. According to a
modern view on biological activity of HA they can affect plant growth by different ways such as
increasing respiration, enhancing mineral nutrition, and/or stimulating hormonal activities
Although a large dataset of evidence indicates that HA can directly affect plant development in
several metabolic pathways, relatively little attention has been paid to uptake of HA by plants.
However, realization of the above mentioned mechanisms requires HA entering plants and
translocation from their roots to shoots. Therefore, uptake of HA by plants is a keystone in
understanding nature of HA activity. Recently it was demonstrated that endodermis possessing
hydrophobic character due to cell wall suberinization was seemingly the main control point for
HA transport in plants [1]. The objective of this work was to study distribution of HA in plants
lipid fraction using tritium labeled humics.
Tritium-labeled coal humic acids ([3H]HA) were prepared as described in [2]. Seedlings of
wheat Triticum aestivum L. were used for the experiments. Eight-day old plants were
transferred into the vials containing 15 mL of HA at concentration 50 mg⋅L–1 with specific
radioactivity ∼0.7 mCi L–1. After 24 h plants were taken out from the solutions and wheat shoots
were subjected to lipid extraction and separation by thin layer chromatography (TLC) procedure
followed by autoradiography of the chromatograms. Then the band where the highest
radioactivity was observed was subjected to GC-MS analyses.
Compounds of the [3H]HA band of plant lipid extract determined using CG-MS analyses
were found to be mainly hydrocarbons including normal and branched alkanes (about 73% of
total amount of compounds) and normal alkenes (about 19% of total amount of compounds). In
case with lipid fraction of humics, alkanes (normal and branched) and normal alkenes totally
accounted for about 54% of determined compounds. It could be therefore hypothesized that
compounds from HA (or at least part of them) must not be metabolized by plants before
assimilation but assimilated in crudo.
Alkanes can be usually found in plants in waxes which are associated with cuticle and
suberized tissues, and the determined composition of HA in lipid fraction might therefore reflect
their role as part of the waxes associated with suberized tissues. In most plants there are two
principal wax biosynthetic pathways: an acyl reduction pathway, which gives rise to primary
alcohols and wax esters, and a decarbonylation pathway, leading to the formation of aldehydes,
alkanes, secondary alcohols and ketones. It is the decarbonylation pathway providing principally
wax biosynthesis, and the principal step of the decarbonylation pathway is the hydroxylation of
alkanes to secondary alcohols. Therefore, HA-derived hydrocarbons could be hypothesized to
be involved in the wax biosynthesis as precursors for secondary alcohols.
References.
1. Kulikova NA, Abroskin DP, Beer AS, Badun GA, Chernysheva MG, Korobkov VI,
Perminova IV (2012) Endodermis is the major control point for radial transport of humic
substances into vascular system of plant. In: Functions of natural organic matter in changing
environment. Xu J., We J., He Y. (Eds.). Springer, Zhejiang Univ. Press, ISBN 978-7-308-
10271-1, pp. 491-492.
2. Badun GA, Chernysheva MG, Tyasto ZA, Kulikova NA, Kudryavtsev AV, Perminova IV
(2010) A new technique for tritium labeling of humic substances. Radiochim Acta 98: 161-166.