The Hormonal Regulation of Growth of Suspension Cultures of Acer pseudoulatanus L. cells
The auxin economy of cell suspension cultures of Acer pseudo­platanus L. has been investigated using physiological and physico­chemical techniques. Experiments on the intra- and extra-cellular concentrations of auxins in an auxin-dependent line (OS) of sycamore cells have suggested that endogenous IAA may be a major regulatory factor during a large part of a culture passage. Further experiments with two auxin-prototrophic cell lines (HK and EHM) have revealed that auxin-prototrophy cannot be explained simply in terms of the achievement of higher endogenous IAA levels than are found in auxotrophic lines. This has led to the view that the auxin-requirement of sycamore cells is an initiation-dependency rather than a continuous-dependency on exogenous auxins. This phenomenon has many features in common with current views on the development of tumours in plants. The mechanism which most appropriately accounts for these observations involves an autocatalytic cycle in which endogenous auxins may be both the cause and the effect of certain growth processes. In the whole plant one such process which has been linked to autocatalysis is xylogenesis. Autocatalysis has been implicated in the cell-death hypothesis (Sheldrake, 1973) and requires tha.t IAA is produced as a result of high tryptophan concen­trations deriving from the hydrolysed proteins of lysed cells. Studies have been performed on the changes in tryptophan levels in these cells. These indicate that the cell-death hypothesis is inapplicable to this system. This has led to a critical re­evaluation of the original evidence in favour of the cell-death hypothesis. It has been the view of certain workers that cell suspension cultures provide an excellent system for the study of growth regulation by phytohormones. This view is based upon the unique properties of suspension cultures which provide an aseptic, homo­geneous plant material freed from the more correlative influences found in the whole plant. Advantage has been taken of these features when growth of the cell suspension cultures was analysed mathematic­ally. The cultures were found to provide data with an accuracy and a reproduceability not normally available with whole plants. The relevance of hormonal control of tissue culture growth to whole plants is discussed with particular reference to cambial initiation and differentiation.
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