Culture solutions

Various assay methods have been used to detect the presence of inhibitory substances. These include some of the classical tests used by investigators of growth-promoting substances—i.e., the various Avena coleoptile assays which utilize intact, decapitated, or isolated cylinders and the split pea stem test. Effects on seed germination and seedling shoot or root growth and development have also been measured in addition to other visible expressions of inhibition. Details of many of these tests have been compiled by Mitchell et al. (99). Tests have been carried out in Petri dishes, with various solution culture techniques, and by sand and soil culture. Effects so measured may or may not be similar to those obtained under field situations— i.e., the establishment of inhibition under controlled conditions pro-... 

Many of the problems arise out of the extrapolation of what happens in solution cultures to soils. Although. solution cultures have served and continue to serve very useful functions in basic research of plant science, they differ from soils in several important ways. The surface area available in soils for processes such as sorption is much greater than in solution cultures, solution cultures are mixed continuously, the microbial ecology differs greatly between the two media, and the status of water and O2 in the two systems is usually quite different. 

Reabsorption of the ligand plus its metal partner is a necessary requirement of processes like Fe acquisition by phytosiderophores (32). However, whether or not reabsorption of diffusates, which undoubtedly occurs in solution cultures (45), has a significant role to play is uncertain, largely because in soil most diffusates (sugars, amino acids, and other organic acids) are readily utilized by microorganisms or adsorbed by soil colloids. 

The role of the secretion from the root apex of organic acids such as citric and malic in the resistance of maize and wheat, respectively, to Al toxicity (81,82) has emerged recently as one with plausibility (83). These studies have been carried out in solution cultures, but how does the suggestion hold up in soil The first and probably greatest difficulty is that the toxic species of Al, probably hydrated Al ", must diffuse to some site in the root apex and stimulate the produc-... 

Very few root. secretions can be expected to be effective unless the right set of circumstances arises sufficiently often. Further, research involving soil-grown plants is required to establish whether the right set of circumstances, as discussed above, does make a real contribution to the well-being of field-grown plants. Similarly, close scrutiny of all research must be made, particularly when results obtained in solution cultures and other contrived situations are believed to be relevant for plants growing in soil. 

A. Wallace, Effect of chelating agents on uptake of trace metals when chelating agents are supplied to soil in contrast to when they are applied to solution culture. J. Plant Niitr. 2 171 (1980). 

M. C. T. Trought and M. C. Drew, The development of waterlogging damage in young wheat plants in anaerobic solution culture. Journal of Experimental Botany 57 1573 (1980). 

Traditionally, nutrient uptake from solution culture was taken to depend on the concentration of the external mineral nutrient, C , the amount of nutrientabsorbing surface, and the kinetics of uptake per unit surface area or unit length of root (22). The flux of nutrients into the roots, J, is described by one of two functionally equivalent equations. ... 

Experiments to examine rhizodeposition can vary markedly in scale and complexity depending on the information required, the equipment available, and the plants concerned. In general, experiments to study exudates and other material lost from young roots are the simplest and are carried out in the laboratory under controlled conditions. Plants are grown in nutrient solution culture, sometimes with sand or other solid support systems, and compounds released into the culture solution are collected and analyzed chemically. The experiments are mainly short-term and the roots can be kept sterile if required. Techniques are also available to label plants growing in these systems with C and to monitor the presence of the isotopes in the rhizodeposits. 

Rhizodeposition in nutrient solution culture is relatively easy to measure and readily altered. It may not reflect what happens in vivo due to the absence of a solid substratum for root growth. Simply including glass beads in nutrient solution can significantly increase rhizodeposition in maize (16), and such an effect must be considered when estimating rhizodeposition in relation to the natural environment. Consequently, a range of systems using various solid supports have been developed. Rhizodeposition in soil is considered in Sect. II.C. 

The in vitro procedure was tested in "critical" experiments designed to make direct comparisons of in vivo and in vitro estimates of exchangeability and potential bioavailability and to test the use of in vitro exchangeability values in in vivo experiments. (8). Three foods which were expected to show different levels of calcium solubility and exchangeability, collards, soybeans and spinach, were intrinsically labeled with 45Ca in nutrient solution culture. They were used together with 47 Ca as an extrinsic label in both in vitro and in vivo experiments. 

Smolders, E., and Shaw, G., 1995,. Changes in radiocaesium uptake and distribution in wheat during plant development a solution culture study. Plant Soil 176 1-6. 

Mackowiak CL, Grossl PR. 1999. lodate and iodide effects on iodine uptake and partitioning in rice (Oryza sativa L.) grown in solution culture. Plant and Soil 212 135-143. 

Hill SA, Miyasaka SC, Taro responses to excess copper in solution culture, Hort Science 55A65— 67, 2000. 

Figure 17.6 Callus development around the lenticels of a tuber (cv. Norland) grown in media that was too wet. Similar responses were noted with submerged tubers grown in solution cultures or aeroponic cultures with continuous misting (source Tibbitts et al., 1994).

Richard, J. and Labuza, T.P. 1990. Rapid determination of the water activity of some reference solutions, culture media and cheese using a new dew point apparatus. Sci. Aliments. 10 57-64. 

In the first research reports on atrazine, McWhorter and Holstun (1961) found that in solution cultures used to provide maximum differentiation and the most rigorous test for selectivity of 29 triazine compounds, the chloro-derivatives were highly selective. These included atrazine, simazine, and propazine. 

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