The Use of Hydroponics and Plant Tissue Culture Technologies for Dye Degradation

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The cultivation of plants and their further experiments with dye degradation can be carried out using hydroponic solutions. These solutions provide a nutrient status which is close to that of the soil in which the plant usually grows. Thus, such solutions are enriched with various macro and micro nutrients and can be used for the cultivation and/or maintenance of plants for phytoremediation. The use of hydroponics provides a cost effective method for phytoremediation of dyes. Aubert and Schwitzguebel carried out the screening of plant species (Rheum rabarbarum, Rumex acetosa, Rumex hydrolapatum and Apium graveolens), in hydroponic solutions for the removal of sulfonated anthraquinones. Many plant species have the capacity to absorb large quantities of water form hydroponic solutions. The water absorption capacity of a plant is a factor that should be taken into consideration while performing studies in hydroponic solutions because it reflects the overall health of a plant. Lower water absorption capacity for the plant Rumex acetosa in hydroponic solution indicated that the plant was not in optimum health under hydroponic conditions and thus the metabolism and transpiration was probably reduced as compared to soil grown plants. Though difficult, it is quite possible to grow adult terrestrial plants such as Rhubarb and common sorrel under hydroponic conditions (Aubert and Schwitzguebel, 2004). But, research that has been involving the cultivation and experimentation with plants in such systems also portrays some major disadvantages of these systems. Pege and Schwitzguebel found it impossible to collect leaves of the same age and same stage of growth and development in case of plants grown in hydroponics. It has been found that the level of enzymes like cytochrome P450 changes with the growth of the plants since they play a role in several physiological functions of the plant. The same is true with peroxidases. This methodology of work makes it difficult to exactly confirm the role of these enzymes in the detoxification of dyes (Pege and Schwitzguebel, 2009). Moreover, the enzyme activities of a plant may also be affected by conditions such as nutritional status, dark and shade requirements, effect of microbial contaminants etc. These factors make it very difficult to get reproducible results. To overcome these problems with wild plants grown in hydroponics or in wetlands, the importance of tissue culture based technologies has been stressed by a few researchers. Though tissue culture involves processes that require a high cost, the use of these technologies has been suggested for basic research which lays the foundation for the application of plant systems in wetland conditions. Our current ability to exploit phytoremediation technologies for the treatment of dyes is restricted by the fact that the knowledge regarding the basic mechanisms and pathways involving the decolorization of dyes is limited. The advantage of using tissue culture based technologies is that the plants can be grown in controlled conditions and once established, they can be propagated indefinitely and are available on demand as contrast to whole plants that have a limited life span. Moreover, in vitro culture techniques offer an environment that is totally free of microbial contamination and can be used to distinguish the responses and capabilities of plant cells from microbes present in the rhizhospheric regions in dye contaminated sites. They also offer conditions that are controlled in terms of nutrient levels, phytohormone level, light requirements etc. (Doran, 2009). Thus, Kagalkar et al have reported studies on the decolorization of various dyes using in vitro plants. These techniques have given reproducible results and have led the authors to analyze the role of different enzymes involved in the degradation of the dye DR5B and BBR (using the plants, Blumea malcolmii and Typhonium flagelliforme respectively), also predict the probable pathway behind the metabolism of these dyes (Kagalkar et al, 2009; Kagalkar et al, 2010). Tissue culture technologies also help to manipulate the plant in order to obtain callus cultures, suspension cultures and hairy roots. Hairy roots grow relatively quickly and do not require exogenous hormones in the medium (Doran, 2009). These advantages have led to the use of marigold hairy roots in the degradative analysis of the dye Reactive Red 198 (Patil et al, 2009). Experiments with separately cultured organs of a plant can evaluate the accumulation and/or biotransformation abilities thus minimizing the interference of translocation effect of dyes (Doran, 2009).

Though plant tissue culture technologies offer multiple advantages, their use is feasible only for studying the basic processes and not for the actual applications of dye degradation in the field. Moreover, the characteristic features of the plants that are demonstrated in hydroponics or in vitro culture conditions could be different than those observed in the soil because of the complexity of the soil environment which exposes the plant to different biotic (microorganisms) and abiotic (other contaminants) soil elements (Zabludowska et al, 2009). Hence such experiments should always be accompanied with field trials of the plant.

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