Some exceptions to this are experiments concerned with problems of phytopathologyin which the influence of microorganisms on physiological or biochemicalparameters of plant cells or tissue is to be investigated. Other examples are coculturesof cell material of higher plants with Rhizobia to study symbiosis, or toimprove protection for micro-propagated plantlets to escape transient transplantstresses (Peiter et al. 2003; Waller et al. 2005).