Potentially Unlimited Growth of Excised Tomato Root Tips in a Liquid Medium

Abstract

IntroductoryIn the cultivation of isolated tissues, whether plant or animal, it is necessary to distinguish between growth at the expense of the culture medium and survival, in which the medium plays only an inert or, at most, a secondary role. In the first case the nutrient is itself the limiting factor in determining the degree and to some extent the character of the increment obtained. Given a satisfactory nutrient, adequate replacement of exhausted nutrient, and adequate removal of excretory products, growth should continue indefinitely. In the second case increment may also take place for a time at the expense of materials reabsorbed from the older portions of the original explant, the medium acting essentially as an inert substratum only. As these reabsorbed materials are exhausted, the culture will gradually succumb, no matter how often the medium is renewed. An extended period of growth ordinarily implies the maintenance of a high level of metabolism. Survival, on the other hand, is ordinarily dependent on minimal metabolic rates, and is hence prolonged by depressant conditions such, for example, as moderate cold, low oxygen supply, etc.

Studies on the Growth of Excised Roots

“…It has become traditional to meet the nitrogen requirement of excised roots by supplying nitrate (Bonner & Addicott, 1937;White, 1934), and the possibility that other nitrogens compounds, both organic and inorganic, might act as satisfactory nitrogen sources has not been explored in any detail despite the suitability of sterile cultures for such an investigation. White (1937) tested amino-acids as possible growth factors for excised tomato roots but noted that in most cases single amino-acids proved toxic, toxicity becoming evident at concentrations varying, according to the acid tested, from 0-5 to 50-0 mg./l.…”

The Growth and Metabolism of Excised Roots in Culture. I. The Measurement of Growth and the Role of Certain Vitamins

“…The early reports of ROBBINS (8) and WHITE (19) In 1938 ADDICOTT and BONNER (1) reported that growth of pea roots in thiamin-supplemented cultures was further enhanced by the addition of niacin. In 1939 ROBBINS and SCHMIDT (11) showed pyridoxine, vitaniin B6, to be a beneficial factor in tomato root growth.…”

VITAMIN B1 IN THE NUTRITION OF EXCISED TOMATO ROOTS

“…Besides the properties mentioned above, this material was shown to be stable to prolonged boiling in trichloroacetic acid, resistant to repeated drying, and resistant to moderately prolonged autoclaving such as was regularly employed in the preparation of nutrients (4). Further tests showed that its activity was completely destroyed by boiling for 2 hours in 1 N NaOH.…”