Flow and perfusion studies

Butch studies of samples requiring contact with liquid media 

A means of measuring plant cell culture activities in liquid media by unstirred batch calorimetry was demonstrated by Fontana et al. [47]. Cells were floated on liquid media supplemented with an inert, high density preparation of Percoll. Other additives could also be used to increase media density. Cells at the air-media interface were able to obtain adequate supplies of both O2 and nutrients for rapid metabolism without diffusion rate limitations. 

Pressurization of specially constructed calorimetry ampules using common bottled gases is relatively simple [39]. Pressurizable ampules can be constructed that are suitable for both scanning and isothermal determinations with selected gases or gas mixtures. This allows direct determination of pressure effects on metabolic rates as a function of temperature. However, few high pressure calorimetry studies have been done on plants. 

Non-calorimetric studies of effects of hydrostatic high pressure on plant sources are more common. In general, pressure effects on plant metabolic rates are small, but some distinct changes have been noted in growth, photosynthesis, temperature responses, and plant structure [48]. Interpretation of the role of pressure on plant metabolism remains uncertain. Hypotheses that have been framed to explain pressure effects are generally written in terms of volume changes and structural transitions in chloroplasts and in lipid membranes, but there are equally tenable alternative explanations such as pressure effects on equilibria. 

A scanning calorimetry study of tomato cells at elevated pressures by Criddle et al. [39 was able to identify important elements related to high temperature inactivation. Metabolic heat rate measurements were conducted at temperatures from 25 to 60 C and at pressures from ambient to 12 MPa. Elevated pressure increased the inactivation temperature for the tomato cells. The combined calorimetry and pressure results thus show that a reaction with a positive volume change is associated with high-temperature inactivation of tomato cells. 

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