Changes in contents of starch and protein, and activities of enzymes involved in starch synthesis were studied during tubcrization of stolon tips of Solanum tuberosum L. cv. Irish Cobbler. Starch content and activities of phosphorylase and granule‐bound starch synthctase based on fresh weight increased rapidly in the early phase (stage I, the stolon tips just before swelling; stage 2, the swelling tips; stage 3, young tubers of 0.2–0.5 cm diameter), and they all remained nearly unchanged in the later phase (stage 3 to stage 6, young tubers of 3.5 cm diameter). The content of soluble protein based on fresh weight remained unchanged. Activities of soluble starch snythetase and ADP‐glucose pyrophosphorylase were not detected at stage 1 and 2, but increased at later stages.
Endogenous levels of auxin, cytokinin and gibberellin were assayed for the materials at the corresponding developmental stages. Auxin content was high at stages 1 and 2, and lowered at later stages. Cytokinin content increased abruptly at stage 6. Gibberellin content was low at all stages.
The internal conditions for starch deposition and tuberization in potato were discussed in regard to regulation of enzyme activities by growth regulators.
Uptake and metabolism of [U‐14C]‐mannitol by suspension cultures of Damns carota L. cv. Kirodagosun and Nicotiana tabacum L. cv. Wisconsin 38, and by cotyledon cultures of Pinus radiata D. Don have been studied. Uptake of label ranged from 138 to 906 nmol (g FW)−1 h−1, resulting in absorption of 3 to 22% of the mannitol supplied to the cultures, over a 14 h incubation period. Of the absorbed mannitol 33 to 75% was metabolized, with label appearing in lipid, insoluble, acidic, basic, neutral and CO, fractions. No adaptation to culture with mannitol prior to the experiments was observed, but tobacco showed a decreased ability to metabolize the compound after 8 days in its presence. Because of the rates of uptake observed, and the metabolism of this compound, it is concluded that mannitol is not an ideal osmoticum for long‐term studies with any of these species, though its use in the short‐term remains valid.
Excised cotyledons of radiata pine (Pinus radiata D. Don), cultured under shootforming (plus cytokinin) and elongating (minus cytokinin) conditions, were incubated in 14C‐glucose, 14C‐acetate or 14C‐bicarbonate at different stages of growth and differentiation. 14CO2 was produced when the cotyledons were fed 14C‐glucose and 14C‐acetate (no measurement was made for 14C‐bicarbonate feeding). Label from these precursors was incorporated into ethanol‐soluble and ‐insoluble fractions. The largest percentage of radioactivity was associated with the ethanol‐soluble portion, which was further fractionated into lipids, amino acids, organic acids and sugars. The amount of label and the pattern of labelling associated with each of the above classes of metabolites varied with time in culture and morphogenetic behaviour of the cotyledons. In general, there was a tendency towards a high rate of incorporation of label in elongating cotyledons during the period of rapid elongation. On the other hand, a high rate of incorporation of label in shoot‐forming cotyledons coincided with the period of meristematic tissue formation. The data obtained support the hypothesis that organized development in vitro involves a shift in metabolism, which precedes and is coincident with the initiation of the process.
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