GROWTH IN VITRO OF EXCISED TOBACCO AND SUNFLOWER TISSUE WITH DIFFERENT TEMPERATURES, HYDROGEN‐ION CONCENTRATIONS AND AMOUNTS OF SUGAR

Abstract

FACTORS RESPONSIBLE for the initiation and continuation of pathological growth have been studied with plant materials because they offer certain opportunities for research (Riker, 1939) not provided by animal materials. Some advantages of plant materials include (a) large numbers, (b) low cost, (c) ease of experimental use, (d) physiological variability, (e) genetic purity, and (f) the possibilitv of tissue culture on a medium of known composition (Riker, 1942). Among the plant materials the crown gall disease caused by Phytomonas tumefaciens (Smith and Town.) Bergey et al. has received special attention because of certain similarities between this pathological growth in plants and cancer of higher animals (e.g., Smith, 1922; Levine, 1936; White and Braun, 1912). The early literature on crown gall was reviewed by Riker and Berge (1935). The anatomy of the host tissue and physiology of the bacteria have been extensively studied by various investigators. The physiology of the host tissue, however, has remained relatively obscure because of certain technical difficulties, some of which mav be overcome by cultivation of tissue on a synthetic medium in vitro. Plant tissue culture has been accomplislhed only recently. The idea was probably first suggested by Haberlandt (1902). Limited growth of excised root tips was reported by Kotte (1922) and by Robbins (1922), while unlimited growth was reported by White (1934) with tomato roots. Since root tips contain several kinds of tissue, their cultivation may be considered organ culture. True tissue cultures capable of unlimited growth were first reported by White (1939) with tobacco callus and by Gautheret (1939) and Nobecourt (1939) with carrot callus. Recently, White and Braun (1941) have cultivated tissue from secondary crown galls on sunflower. The extensive history and applications of plant tissue culture have been reviewed by White (1943). In tissue culture simple, somatic cells may be isolated from the influence of neighboring cells, tissues, and organs and may be studied under controlled conditions on a synthetic medium containing only ingredients whose chemical formulae can be written. Such a technique offers a tool for the study of critical vital processes of tissue metabolisn. While many basic requirements of excised root tips in vitro have been determined by various investi-