Study of a factor produced by suspension-cultured Pinus radiata cells which enhances cell growth at low inoculum densities

Abstract

Pinus radiata cells in suspension culture abruptly lose their growth capacity when diluted below a critical inoculum density. This threshold density can be lowered by adding the supernatant (conditioned medium) from healthy cultures which have been grown separately at high densities. Fresh medium is conditioned rapidly indicating that the factor responsible is either potent or produced rapidly. Activity-response curves increase progressively with concentration indicating that still greater effect may be obtained if the factor can be concentrated following separation from other medium components. The effect is not mimicked by a number of candidate compounds (including auxins, cytokinins, polyamines and vitamins). Partial characterisation studies indicate that the factor is relatively small (<1 000 dalton) and possibly an oligosaccharide. It is considered that the factor is an essential structural component of the walls of expanding cells where it is reversibly-bound.