The morphological and physiological properties of the genetic tumours from a Nicotiana interspecific hybrid.

Many plant tumours have been loosely referred to as genetic tumours when no obvious external cause was identifiable. In this study, the morphology of genetic tumours was detected by scanning electron microscopy (SEM) and the influence of exogenous phytohormones on genetic tumour growth was examined. Genetic tumours in Nicotiana hybrid were first observed in the hypocotyl area and later appeared from stems as a cluster complex. In vitro, genetic tumours were produced 5-6 days after explant treatment near each of the cut ends. The morphology of genetic tumours was investigated using SEM. Genetic tumours are mainly composed of epidermal cells surrounded by a well developed extracellular matrix (ECM), that is organized in a network linking surface cells. Globular structures containing several cells were formed from these clusters of epidermal cells. Vigorous tumourous growth from the leaf discs of the Nicotiana hybrid was obtained on medium supplemented with auxin and cytokinin at 0 to 10 muM, but 100 muM of auxin and cytokinin inhibited genetic tumour growth. Leaf discs treated with 10 muM cytokinin or auxin alone produced genetic tumours, but 10 muM cytokinin supplemented with 100 muM auxin stopped growth. Therefore genetic tumours are tissues that are, clearly, disturbed in endogenous hormone balance or have altered sensitivity to hormones and response to exogenous hormones.