Analele Universit ăţii din Oradea, Fascicula Biologie Tom. XX, Issue 2, 2013, pp. 71-79 71 GENOTOXIC EFFECTS OF SODIUM NITRATE IN ONION ROOTS Maria-Mihaela ANTOFIE * , Elena DOROFTEI ** * Faculty of Agricultural Sciences, Food Industry and Environmental Protection, University “Lucian Blaga”, Sibiu, Romania ** Faculty of Natural and Agricultural Science, „Ovidius” University, Constanţa, Romania Corresponding author Elena Doroftei, Faculty of Natural and Agricultural Science, “Ovidius” University, Constantza, Aleea Universitatii, no. 1, Corp B, 900470, Constanţa, Romania, Tel. +40722567008, email: edoroftei2000@yahoo.ca Abstract. The scope of this paper is to assess cyto- and genotoxic effects of sodium nitrate on Allium cepa root tips by using different concentrations (i.e. 0,1%; 1% and 5%) for treating uniform healthy onion bulbs for three different periods of time: 6, 24 and 72 hours. In the end of the experiment the harvested root tips were prepared according to Feulgen’s squash technique using Schiff reagent and the investigations were realized according to Allium test. The cytotoxic and genotoxic effects of nitrate were investigated by calculating the mitotic index and observing all chromosomes’ complement alterations during the mitosis. The phase rate of cells undergoing mitosis is also studied. For microscopy investigations a Novex Holland B microscope with digital camera included was used. The cytogenetic analysis of nitrate effects revealed a strong decrease in the mitotic index which is more intense with the concentration and time of exposure. Moreover, this effect is associated in case of the variant treated with 5% sodium nitrate acting for more than 24 hours, with the appearance of genotoxic effects such as chromosomal alterations, highly condensed chromatin expression easily identified during mitosis stages, sticky chromosomes and chromosomal bridges and laggards. Keywords: Allium cepa, mitosis, phase ratio, sodium nitrate, mitotic index. INTRODUCTION Nitrogen availability is often considered in agriculture as a limiting factor for plant growth and crops’ productivity and therefore it is generally considered that is a great need to add nitrogen based fertilizers. Still, nitrates and ammonium are considered as the most important forms of inorganic nitrogen sources supporting plant growth and development [23]. However, today it is well documented that such amendments to the soil can have negative human health, economic and environmental effects [20] and as a consequence nitrate became today a monitored polluter. Due to its negative effects on human health and environment, in 2008, in Romania it was officially adopted a list of 1963 localities proved to be vulnerable to nitrate pollution [19]. Starting with the same year it was officially adopted a national programme for monitoring the nitrate level in soils and in the ground and fresh waters. As an example in the fresh waters the nitrates pollution is ranging for 11 monitored rivers between 0.25 and 10 mg/l and for 6 lakes between 0.01 and 6 mg/l. From official point of view it is considered that the major cause for this high pollution is due primarily to agricultural sector [2]. Based on these serious environmental and healthy issues [18] it is obviously that in order to maintain the balance between nitrogen availability to crops and the need to supply soils with nitrate based fertilizers it is important to first evaluate risks to nitrate pollution. Moreover, in order to understand the relationship between the nitrogen sources into the soil and plant physiology a lot of scientific literature treated this subject after 1980. As it is well known the nitrate concentrations in soil considerably vary due to various factors such as microbial processes, mineralization and nitrification that are highly sensitive to any change into environmental conditions [18]. Measuring NO 3 - ions concentration by using isotopes ( 15 N and 18 O) in plants may provide today a unique insight into ecosystem availability and tolerance to nitrate dynamics creating a scientific base for applying the best solutions in ecological restoration [16]. Regarding the molecular mechanism of cellular up-take of nitrates it is well known that in order to cope with highly variable nitrate concentrations in soil, plants have developed h igh and l ow-a ffinity t ransport s ystems known as HATS and LATS [10]. Generally it is considered that when the external nitrate concentration is higher (>1 mM), LATS is preferentially used and when nitrate availability is limited, HATS is activated and takes over the nitrate uptake process [3, 6, 11, 15, 21]. Furthermore, once taken up into the root cytoplasm, nitrate is either translocated across the tonoplast followed by storage in vacuoles, either it is reduced to nitrite and then partitioned to plastids where it is further assimilated to organic nitrogen [19]. Based on recent hypothesis it is also possible that nitrate to be loaded into xylem vessels and subsequently unloaded (moved from the xylem sap into xylem parenchyma cells) in plant aerial tissues where it undergoes processes similar to those in roots [5, 16], an idea already developed more than ten years ago [18]. At higher concentrations in the soil solution, these compounds will accumulate and affect the cells, tissues and organs such as the roots – the primary entrance of such compounds into the crop body. Nitrate concentrations in soils generally range from very low levels (i.e. a few hundred μM to around 20 mM) up to 70 mM and the meristematic mitotic cells in the roots are appropriate indicator cells for the detection of clastogenicity of environmental pollutants, especially for water and soil contaminants monitoring [16]. Onion is recognized to contain the lowest level of nitrate among legumes and it is considered that shows a moderate tolerance to this compound [3]. Based on the peculiarities of onion such as small number of chromosomes which are easy to be studied it was considered that it can be used as a model in testing