IDENTIFICATION OF AN AGAR CONSTITUENT RESPONSIBLE FOR HYDRIC CONTROL IN MICROPROPAGATION OF RADIATA PINE

Tissue cultured Pinus radiata grown on media containing agar as the ge lling agent display toxic symptoms and poor long-term shoot survival, however it does have the attribute of hydric control, through a mechan ism which, until now, has not been elucidated. Gelrite as an alternati ve gelling agent is clearly non-toxic but results in hyperhydric (vitr ified) tissues. In an effort to overcome these problems, the controlli ng mechanism found in agar was examined. Hydric control was shown to b e effected by a non-gelling, cold-water soluble constituent of a comme rcial agar, rather than by physical properties of the gel. It could be separated from low molecular weight components of the agar responsibl e for the toxic symptoms by dialysis. It was identified as being an ag aroid-type xylogalactan bearing pyruvate and sulphate substituents. Im proved management of gelling agents in culture medium has contributed substantially to a thirty fold increase in propagation rates.