INFLUENCE OF CADMIUM ON GROWTH AND BIOCHEMICAL CONTENTS OF TOMATO PLANTS

The increasing concentrations (10, 25, 50, 75 and 100 mg/kg) of soil cadmium on growth and biochemical contents in tomato plants were analysed on 30th sampling days. Control plants were maintained separately. Plants were grown in pots containing 3 kg of air dried sandy loam soil and treated with different concentrations (mg/kg) of cadmium (0, 10, 25, 50, 75 and 100). Treatments decreased the growth parameters such as root and shoot length and biochemical constituents such as protein, (except, proline and phenol content) contents in tomato plants compared to untreated plants. The shoot length of cadmium treated tomato plants was higher than the root length. proline and phenol content of root of tomato plants was higher than the shoot.


INTRODUCTION
Throughout the world the heavy metal pollution is causing great threat all organisms [1].Accumulation of heavy metals in plants may be a serious problem [2], since there are chances of entering to the potential food web [3].The contamination of food chain by plant accumulated heavy metals is current hot issue worldwide, as it causes serious health hazards, and identification and control should be taken care with serious actions [4][5].
The present study aimed to identify the extent of changes in growth parameters such as, root and shoot length and biochemical constituents such as, protein, proline and phenol contents in tomato plants due to cadmium toxicity.

MATERIALS AND METHODS
The certified seeds of tomato were obtained from Tamilnadu Agriculture University (TNAU), Agricultural Research Station, Aduthurai, Thanjavur district (TN), India.Seeds with uniform size, colour and weight were chosen for the experimental purpose.The soil used in the experiment was red soil 40%+sandy loam 60% in nature and pH of the soils was 7.2.It contains major nutrients of 118 kg available N, 88 kg P and 106 kg k/ha and micronutrients of 21.89 mg available Cu, 219.11 mg Fe, 168 mg Mn and 28.13 mg Zn/kg, cadmium was not available in this experimental soil.The cadmium chloride (Cd Cl2 ½ H2O) was used as cadmium source.
The pot culture experiments were conducted in Botanical Garden, Annamalai University.Tomato plants were grown in pots containing untreated soil (Control) and soil mixed with various levels of cadmium (viz., 10, 25, 50, 75 and 100 mg kg -1 ).The inner surfaces of pots were lined with a polythene sheet.Each pot contained 3 kg of air dried soil.Six seeds were sown in each pot.All pots were watered to field capacity daily.Plants were thinned to a maximum of three per pots, after a week of germination.Each treatment including the control was replicated three times.
The plant samples were collected on 30th days after sowing.Three plants from each replicates of pot were analyzed for the various growth parameters such as root and shoot length and biochemicals such as, protein, proline and phenol contents.Roots and shoots of treated and control plants were used for the estimation of protein contents as per Lowry et al. [6], proline as per Bates et al. [7] and total phenols as per Singleton and Rossi [8] methods.

RESULTS AND DISCUSSION
Physio-chemical properties of the soil are given in table-1.
The effect of cadmium on growth parameters such as root and shoot length of tomato plants are presented in Figure -1.All growth parameters of cadmium treated plants (10, 25, 50, 75 and 100 mg kg -1 ) gradually decreased when compared to untreated plants.The maximum root and shoot length were recorded in control plants on 30th sampling days.The minimum value of all growth parameters were found in 100 mg kg -1 of cadmium treated plants.Our results are in agreement with the findings of Juwarkar and Shende and Yi and Ching [9][10].Xu et al. [11] also suggested that the higher concentrations of cadmium can cause cell growth inhibition.Schutzendubel et al. [12] who reported that the cadmium also induced the generation of reactive oxygen species (ROS).The growth reduction also reported by Hagemeyer and Breckle [13] and Marcano et al. [14].

Protein content
Perusal of data in Figure -2, reveal that the plants raised in cadmium treated soils were poorer in protein contents as compared to control plants in 30th sampling days.Higher the cadmium contents lesser the values of protein in both root and shoots of tomato.The above results were in agreement with the findings of Costa and Spitz [15] in Lupinus albus, Costa and Morel [16] in lettuce, Satyakala [17] in Pistia stratiotes and Dinakar et al. [18] in Arachis hypogaea.The decrease in protein content can be compared with the work of Dietz et al. [19].Cadmium induced reduction of protein content was also reported by Jana [20].The inhibitory action of cadmium on amino acid and protein content may be due to binding of metals with sulphydryl group of protein, causing deleterious effect in the normal protein form [21].

Phenol content
Result indicated that increasing levels of cadmium treatment markedly increased the phenolic content of tomato roots and shoots (Figure -4).An enhancement of the amount of phenolic compounds can be observed under different environmental factors and stress conditions [27].Our results are in agreement with earlier reports [28,29].