Journal of Food, Agriculture & Environment, Vol.12 (3&4), July-October 2014 209 www.world-food.net Journal of Food, Agriculture & Environment Vol.12 (3&4): 209-212. 2014 WFL Publisher Science and Technology Meri-Rastilantie 3 B, FI-00980 Helsinki, Finland e-mail: info@world-food.net Received 10 March 2014, accepted 20 September 2014. Influence of the auxin-like activity of humic acid on bio and microbiometric parameters of Pisum sativum L. by in vitro cultures of pea plants Andrzej Gawlik 1 *, Danuta Kulpa 2 , Dorota Gołębiowska 1 and Romualda Bejger 1 1 Department of Physics and Agrophysics, West Pomeranian University of Technology in Szczecin, ul. Papieża Pawła VI No3, 71- 459 Szczecin, Poland. 2 Department of Plant Genetic, Breeding and Biotechnology, West Pomeranian University of Technology in Szczecin, ul. Papieża Pawła VI No3, 71-459 Szczecin, Poland. *e-mail: Andrzej.Gawlik@zut.edu.pl Abstract Humic acids (HA) can be found in all aquatic and land-based ecosystems. They may directly or indirectly influence the growth of plants. The aim of the study was to determine the influence of HA extracted from peloid on the growth and morphological features of pea plants by in vitro cultures. Sterilized pea seeds (Pisum sativum L.) of Ramdrod variety were placed on Murashige & Skoog (MS) medium with HA of the following concentration, expressed as content of HA carbon in dm 3 of medium: 0.005; 0.01 and 0.02 (gC HA ·dm -3 ). Control samples included those in which HA was not added to MS medium. After two weeks of the experiment, morphological features were determined in young pea plants and microbiometric features examined using the scanning electron microscope (SEM). Biometric measurements showed that HA added to the medium caused statistically significant increase in the height of the pea plant shoot, as well as longer roots in comparison with control samples. Additionally, growth of fresh weight of the shoot was observed, whereas in the case of the highest and the lowest concentration of HA a significant increase in fresh and dry weight of roots. Examination using the SEM showed that humic acids had positive influence on the length of internodal shoot and root cells. At the same time, a decrease in the number of stomas was observed. The experiment showed that HA activity is similar to auxins. No influence of HA on the green index and dry weight of shoots were recorded. Key words: Auxin-like activity of humic acid, biometric and microbiometric parameters of pea plants, Pisum sativum L., scanning electron microscope. Introduction At the moment, in both aquatic and land ecosystems, humic acid (HA) is the most important fraction of humic substances. Despite different origin and chemical composition, HA show a number of common features. The ‘core’ of macromolecules of HA has an aromatic structure containing a network of aromatic rings (chiefly derivatives of benzene) linked by various bridges and parts of aliphatic chains. The HA structure contains numerous functional groups, in particular COOH and OH, which contribute to its nature of polycarboxylic organic acids. Apart from C, O and H, some of basic elements present in the HA structure also includes nitrogen. HA is a reservoir of nitrogen for plants. It is released gradually. Durable forms of nitrogen in the HA structure are connected to a large extent with aromatic chains in the form of amines or heterocyclic structures. Due to its properties, HA plays a number of important functions in the environment. HAs may have an important influence on the structure and properties of soil and its water and air properties 1 . They are responsible for soil sorption capacity as well as they may directly modify life processes in plants 2-4 . Humic acids have the capacity of creating complexes with various metals 5, 6 . That way they may influence the concentration of free ions in the soil solution. Ions of iron and aluminium deserve special attention 7, 8 . Moreover, humic substances show capacity to bind heavy metals in soil and thus reducing their availability for plants 9 . The presence of sufficient quantity of humic substances in soil and formation of stable humus–enzyme complexes is the cause of fairly continuous enzymatic activity of soil 10 . In the early 20 th century, researchers recognised influence of humic substances on plants 11 . The influence on plant cells has been recently compared to the one exerted by auxins: indole-3 butyric acid (IBA), indole-3 acetic acid (IAA) or 2,4-dichloro- phenoxyacetic acid (2,4-D) 12-14 . Humus substances can be both stimulators and inhibitors for various processes in plants. Direct influence of humic substances on plants depends on a number of factors, such as type and dose of humic substances, manner of application, variety and development phase of a plant 15, 16 . Examining of humic acid influence on the growth of plants is frequently difficult due to interaction with other environmental factors. The use of in vitro cultures enables examining the influence of a given factor on the growth of plants in controlled conditions better than other methods. The research aimed at examining of the influence of various HA concentrations in soil on the growth and development of pea plants growing in in vitro cultures. Materials and Methods Humic acids: Humic acids (HA) originated from a peloid deposit in Kołobrzeg. They were extracted from peloid using Schnitzer method 17 . Samples of peloid of natural moisture content were extracted using 0.1 mol·dm -3 NaOH. Extracts were acidified with concentrated H 2 SO 4 to pH 1.5 to obtain HA sediment. HA sediment