To observe the effect of earthworms in Cd-polluted soils, a pot experiment was conducted. The seeds were washed with Tween 20 and surface sterilized before sowing. The pots were filled with soil and cattle dung (partially decomposed) in the ratio of 2:1. The pots were inoculated with earthworms (5 earthworms Kg -1 soil) 7 days prior to sowing, and seeds were then uniformly sown in pots. Plants were allowed to grow under natural conditions and then harvested after 30 and 60 days after sowing (DAS).Different concentrations of Cd (0.50, 0.75, 1.00 and 1.25 mM) were prepared using CdCl₂ (anhydrous) obtained from HiMedia. The various concentrations were prepared by dissolving CdCl₂ in double-distilled water. The soil was spiked with the different concentrations of Cd and analysed for Cd concentration before experimental set-up using atomic absorption spectrophotometer (AAS). The Cd content was found to be approximately 56 mg (0.5 mM Cd), 84 mg (0.75 mM Cd), 112 mg (1.00 mM Cd) and 140 mg (1.25 mM) in respective concentrations per kilogram of soil. All metal-treated soils were supplemented with fixed number of earthworms. Two sets were maintained which included one without earthworms (WTE) and other supplemented with earthworms (WE).

Earthworms help to mitigate the toxic effects produced by Cd on plant growth and photosynthetic efficiency along with enhanced phytoremediation capacity when co-inoculated with Cd in soil.

In the present study, the expression of genes CHLASE, PSY, CHS and PAL was enhanced in plants grown in Cd-treated soils supplemented with earthworms. Significant differences in expression of CHLASE, PSY, CHS and PAL were observed after the analysis of data using two-way ANOVA and Tukey's HSD test. The expression of gene CHLASE was enhanced by 1.56-fold in Cd-treated plants which was further enhanced to 3.63-fold when earthworms were co-inoculated along with Cd-treated soils. In comparison to control plants, the expression of PSY and CHS was significantly enhanced by 1.43-fold and 2.07-fold when plants were grown in 1.25 mM Cd treatment. The expression was further enhanced to 3.32-fold (PSY) and 3.37-fold (CHS) when earthworms were supplemented along with Cd treatment (1.25 mM). Similarly, significant increase in the expression of PAL was also observed in Cd-treated plants by 1.64-fold in Cd-treated soil which was enhanced to 2.74-fold in the presence of earthworms.

Solanum lycopersicum cv.Micro-Tom tomato seeds were sterilized with a series of washes: 3 min in 70% ethanol, to which 3-4 drops of tween 20 were added, 13 min in a 5% bleach solution and 3 washes of 10 min each in sterile water. The seeds were then placed in a 0.6% agar medium (5 seeds per petri dish). The petri dishes were kept for 5 days in the dark, followed by 4 days in the light. The germinating seedlings were then transferred to pots with sterile quartz sand. For mycorrhization, the fungus Glomus mosseae Gerd. & Trappe (BEG 12) was purchased from Biorize (Dijon, France). A mixture of sand (70%) and fungal inoculum (30%) was used. The mycorrhizal and control plants were grown in a growth chamber under a 14 h light (24&#8451)/10 h dark (20&#8451) regime, and watered, 125 ml/plant twice a week with water, and once a week with a modified Long-Ashton solution containing a low phosphorus concentration (3.2 µM Na₂HPO₄.12H₂O). The fruit was collected when it reached the required ripening stage i.e. turning.

Mycorrhization accelerated the flowering and fruit development and increased the fruit yield. Eleven transcripts were differentially regulated in the fruit upon mycorrhization, and the mycorrhiza-responsive genes resulted to be involved in nitrogen and carbohydrate metabolism as well as in regulation and signal transduction. Mycorrhization has increased the amino acid abundance in the fruit from mycorrhizal plants, with glutamine and asparagine being the most responsive amino acids.