High Concentrations Of Kinetin Research Articles

Cytokinin Activation of Thiamine Biosynthesis in Tobacco Callus Cultures

Bioassays of tissue extracts show that high (500-1000 mug/liter) kinetin concentrations which permit growth of tobacco callus cultures on media without added thiamine activate the biosynthesis of this vitamin by the tissues. Although the tissue concentration of thiamine may fall appreciably, it is maintained at a level adequate for survival and slow growth of the cultures, and there is a large net increase in total thiamine content per culture with time. In the second and subsequent passages of tissue on a thiamine free medium, growth is obtained only when high kinetin concentrations are maintained. Effective inhibition of growth by antithiamines suggests that thiamine is utilized by the high-kinetin tissue.In the presence of low (30-100 mug/liter) kinetin concentrations, which would be optimal for growth in the presence of thiamine, growth only occurs early in the first passage of tissue from a medium with the vitamin to one without it. The thiamine concentration in the tissues falls to low levels, and no net biosynthesis is apparent. The tissues turn dark and die after 2 to 3 weeks. In contrast with this, in the absence of both added thiamine and kinetin no appreciable growth occurs, but the tissues keep their normal appearance, retain their thiamine content, and may stay alive for several weeks.

Thiamine requirement in relation to cytokinin in ?normal? and ?mutant? strains of tobacco callus

High concentrations of kinetin (400-2,000 μg/l) permit continuous growth of tobacco callus cultures (Nicotiana tabacum, var. Wisconsin No. 38) in the absence of exogenous thiamine. On the optimum concentration (1,000 μg/l) the tissue has been maintained through 21 bimonthly passages without change in vigor or other growth characteristics.The effect of kinetin is general, not "mutagenic", because tissue returned to low-kinetin, thiamine-free medium failed to grow.Kinetin-thiamine interactions in "cytokinin mutant" strains which were grown without cytokinin in light and darkness suggest that the endogenous content of cytokinins may markedly affect the requirement for thiamine and possibly the tissue content of this vitamin and other growth factors.The viability of tissue on low-kinetin media in enhanced by thiamine, but the addition of this vitamin does not eliminate the requirement for a cytokinin.The great divergence in minimum kinetin concentrations required for growth of the tissue in the presence and absence of thiamine indicates that the growth promoting action of cytokinin must be different in the two cases.

EFFECT OF PLANT HORMONES ON ULVA

1. Bacteria-free Ulva lactuca, in sea water media enriched with vitamins, grows as atypical, short, filamentous germlings which do not develop into a foliaceous thallus. These filaments reach a few millimeters, then bleach, leaving a few islands of intensely green cells which, upon transfer to new media, produce new germlings.2. The initiation of new germlings from these green islands and the length of the atypical filaments are increased by the combination of kinetin + indolacetic acid; adenine and indolacetic acid seem antagonistic. Conspicuous elongation of the filaments is promoted by the addition of gibberellins to the kinetin-indolacetic acid combination.3. A normal flat blade was obtained so far only with adenine + kinetin.4. The responses depend both on the interaction and concentrations of these morphogenetic agents: indolacetic acid is effective only in a very narrow range of concentrations and a blade is produced only with relatively high concentrations of kinetin.5. The rhizoids of Ulva and th...