¹⁴C‐Metabolism in cultured cotyledon explants of radiata pine

Abstract

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.

Comparative studies on pyrimidine metabolism in excised cotyledons of Pinus radiata during shoot formation in vitro

“…2). This series of events, also documented in previous studies (Yeung et al, 1981;Villalobos et al, 1984a, b), is not observed in NSF cotyledons, which rapidly elongate and develop in culture like intact cotyledons, as well as in (OLD) cotyledons, which are less responsive to BA (Obata-Sasamoto et al, 1984;Aitken-Christie et al, 1985).…”

“…The higher uptake values observed for uridine, uracil, and thymidine at day 3 (Table 1), may be the result of a wounding effect. Increasing ability to take up label during the initial days in culture was also reported in SF and NSF cotyledons fed with [ 14 C]-aspartic acid (Konschuh and Thorpe, 1997), and [ 14 C]-glucose, [ 14 C]-acetate, and [ 14 C]-bicarbonate (Obata-Sasamoto et al, 1984). An active de novo synthesis of pyrimidine nucleotides, as denoted by the incorporation of 14 C-labeled orotic acid into nucleotides (UMP+UD-P+UTP) and nucleic acids (RNA+DNA), was observed under both SF and NSF conditions.…”

Alternative and cytochrome pathway respiration during shoot bud formation in cultured Pinus radiata cotyledons

“…In contrast, in the absence of BA,, cultured cotyledons rapidly elongate and develop similar in many respects to intact cotyledons (Obata-Sasamoto et al 1984), By day 10, the cotyledons have reached their maximum length and are several times longer than those cultured in the presence of BA. Joy and Thorpe (1990) reported rapid increases in metabolism caused by the initial excisioo of radiata pine cotyledons and the introduction to light and cytokinin.…”

Activities of Ribulose Bisphosphate Carboxylase and Phosphoenolpyruvate Carboxylase and 14C-Bicarbonate Fixation during in Vitro Culture of Pinus radiata Cotyledons

“…However, the ratio of "'C in the malate plus aspartate fraction to the total "'C fixed is still about 4 times higher in the SF than in the NSF cotyledons, similar to the labeling pattern observed on d 5. An earlier study (20) with P. radiata cotyledons cultured for 3, 10, and 21 d also had indicated that incorporation of 14C into the ethanol soluble fractions (including organic acids and soluble amino acids (of extracts from NSF cotyledons is at least 2 to 3 times higher than in the extracts of SF cotyledons after a 3 h incubation with NaH'4CO3. An increased synthesis of PEPC protein with increased activity during cell division in tobacco cell cultures (18) and significantly higher labeling of malate in dividing cells as opposed to cells from stationary phase cultures of Chenopodium rubrum have been reported (1 1).…”