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Protocol

Investigation of plant hydraulic characteristics (water transport pathway through aquaporins/apoplast and root hydraulic conductivity) can be done on plants grown in hydroponics system. The advantage of the hydroponic system is that we have complete access to the root without interference of soil particles, and then a number of plant treatment can easily be applied to the root system. The hydroponic system has to be established with proper aeration (oil free compressor) facility.

To raise the crop for hydroponic system seeds should be treated with fungicide (to avoid fungal contamination) and sowing is done into sand saturated with nutrient solution. Rhizobium inoculum (Strain No: IC 2002) should be added to ensure proper root nodulation in legume crops. Around a week later seedlings are attached to the perforated thermocol sheet and laid over a plastic tub with hydroponic solution (cereals) or alternatively seedlings can be directly transfer to 250ml Erlenmeyer conical flask (legumes) containing nutrient solution (modified Hoagland’s solution). In the case of cereal crops seedlings from plastic tubs are transferred to 300ml Erlenmeyer conical flask containing nutrient solution optimally after 4th leaf stage. Seedlings should be transferred into the flasks carefully through the hole of a rubber stopper that fits tightly to the flask aperture and the hypocotyle is fixed with cotton to avoid the seedling from slipping through. Ideally, the glass flasks should be painted in two layers; first black to ensure darkness in the rooting medium and prevent the algae growth followed by a second layer of white paint to reflect the excess of sun rays and avoid over-heating of roots. Aeration needs to be continuously supplied to roots to avoid water-logging symptoms. Water needs to be refilled daily to compensate the losses of nutrient solution from the flasks through transpiration and the whole solution should be changed every few days.

Data Analysis

The composition of the modified Hoagland’s solution for the legume crops (chickpea, groundnut, pigeon pea) is: MgSO4 (1mM), K2SO4 (0.92mM), CaCl2.2H2O (0.75mM), KH2PO4 (0.25mM), Fe-EDTA (0.04mM), Urea (5mM) and micronutrients [H3BO3 (2.4µM), MnSO4 (0.9µM), ZnSO4 (0.6µM), CuSO4 (0.62µM), Na2MoO4 (0.6µM)]. The composition of the solution for the cereal crops (pearl millet, sorghum, maize) is: MgSO4 (2.05mM), K2SO4 (1.25mM), CaCl2.2H2O (3.3mM), KH2PO4 (0.5mM), Fe-EDTA (0.04mM), Urea (5mM) and micronutrients [H3BO3 (4µM), MnSO4 (6.6µM), ZnSO4 (1.55µM), CuSO4 (1.55µM), CoSO4(0.12 µM) and Na2MoO4 (0.12µM)]. The pH of the nutrient solution has to be maintained between 6.0 and 6.2 (in the case of legumes, hydroponic solution can be buffered with a pinch of Ca2CO3 every time the nutrient solution is changed, in order to maintain pH at a neutral level).

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