Search

The physiological age of mother tubers (Solanum tuberosum L. cv. Kennebec) used as a source of material influenced kinetin-induced in vitro tuberisation. Tuberisation significantly increased with physiological age. Kinetin- or ancymidol-induced tuberisation, plantlet and microtuber dry weight decreased with increasing number of subcultures. Single-node segments obtained from tubers stored for more than 9.5 months at 4 °C showed increased kinetin-induced tuberisation rates and earlier tuberisation than those obtained from younger tubers. For any physiological age, material may be safely multiplied using node propagation until the third subculture and bioassayed for tuberisation without variation in the response.

Histidine-tagged human cardiotrophin-1 (hCT-1), a recently discovered cytokine with excellent therapeutic potential, was expressed in tobacco chloroplasts under the transcriptional and translational control of two different promoters (rrn and psbA) and 5'-untranslated regions (5'-UTRs) (psbA and phage T7 gene 10). The psbA 5'-UTR promotes recombinant hCT-1 (rhCT-1) accumulation in chloroplasts at higher levels (eight-fold) than those obtained for the phage T7 gene 10 5'-UTR, regardless of the promoter used, indicating that the correct choice of translational control element is most important for protein production in chloroplasts. The maximum level of rhCT-1 achieved was 1.14 mg/g fresh weight (equivalent to 5% of total soluble protein) with the psbA promoter and 5'-UTR in young leaves harvested after 32 h of continuous light, although the bioactivity was significantly lower (approximately 35%) than that of commercial hCT-1. However, harvesting in the dark or after 12 h of light did not result in a significant decrease in the bioactivity of rhCT-1, suggesting that 32 h of over-lighting affects the biological activity of rhCT-1. Because high levels of rhCT-1 accumulation took place mainly in young leaves, it is proposed that seedlings should be used in a 'closed system' unit, yielding up to 3.2 kg per year of rhCT-1. This amount would be sufficient to meet the estimated annual worldwide needs of hCT-1 for liver transplantation surgery in a cost-effective manner. Furthermore, our strategy is an environmentally friendly method for the production of plant-based biopharmaceuticals.

The gelling agent Phytagel™ was compared with Difco Bacto-agar forin vitro tuberization of six potato cultivars (Jaerla, Blanka, Claustar, Kennebec, Desiree, and Baraka). On a culture medium with 6% sucrose but lacking growth regulators, tuberization was higher when Phytagel™ was used rather than Difco Bacto-agar, regardless of the photoperiodic regime used. Chemical analyses of the gelling agents revealed a higher mineral content and organic impurities in Bacto-agar than in Phytagel™, which is therefore recommended for microtuber production. The same gelling agent should be used in all treatments of microtuberization experiments in order to draw meaningful physiological conclusions.

SummaryThe maturity of a new potato clone can be determined from physiological measurements in field trials that involve considerable time, space and work. To improve the procedure, an in vitro bioassay based on tuberization behaviour of potato cultivars of different maturity classes was established. Twenty-six sets of temperature, photoperiod and photosynthetic photon flux values were assayed on the eight potato cultivars Jaerla, Zorba, Spunta, Kennebec, Turia, Desiree, Baraka and Fenix. In vitro tuberization was influenced by cultivar, photoperiod and temperature. The environmental condition defined by 12 h photoperiod, 34 μmol m–2 s–1 of photosynthetic photon flux and 25°C temperature produced statistical differences in tuberization among maturity classes. Both the earliness of tuberization and the “degree of tuberization” (based on the type of microtubers developed) permitted assigning a cultivar to a maturity class. Early cultivars showed higher readiness to tuberize and higher values of “degree of t...

Summary A significant increase in the number of tubers was obtained in the presence of either kinetin (11.6·10 -3 mM), paclobutrazol (8.5·10 -3 mM) or acetate (5.4 mM) for in vitro stolons in darkness, and both single-node sections and intact 3-cm long sprouts were produced after long photoperiod (16 h) subculture. Longitudinal growth decreased whenever tuberization was promoted, especially in the presence of paclobutrazol. Calcium chloride (6 mM) slightly induced tuberization in the dark. Putrescine (0.15 mM) favoured vegetative development in all explants.

Are short-day (SD) conditions inductive or permissive for potato tuberization? This question was addressed using anin vitro culture system. Kinetin induction ofin vitro tuberization in potato stolons cultured in the dark can be partially inhibited by light treatments. Photoperiod required for a major inhibition varied with cultivars: 8 hours for cv. Red Pontiac and 16 hours for cv. Kennebec. Short photoperiods decreased kinetininduced tuberization for all cultivars. Stolons cultured on kinetin-free medium generally did not tuberize, regardless of light treatment. Effects of kinetin and photoperiod on stolon and tuber development are observed. Relationships among kinetin, photoperiod and tuber-inducing stimulus produced under short days are discussed.

Amyloplast division was studied in an in vitro potato (Solanum tuberosum L. cv. Kennebec) stolon tuberizing system which was triggered by the presence of added kinetin. Amyloplast division proceeded by binayr fission of dumbbell shaped amyloplasts. A visible tubular coiled structure from the amylobody appeared to be associated with amyloplast division. Possible ways of daughter amyloplast separation are discussed.

The aim of the study was to assess the potential in vitro effects of jasmonic acid and kinetin on tuberization of potato (Solanum tuberosum). Of the two, the former was by far the stronger in vitro promoter of stolon tuberization. Number of tubers induced per stolon, tuberization rate, and final tuber weight were higher by factors of 2.8, 2.3, and 6.4, respectively. Bioassay sensitivity of jasmonic acid, measured in terms of the point at which the concentration for inducing tuberization was saturating, was more than 20 times greater than that of kinetin. Tuberization in both cases was associated with a decrease in rooting ability. Jasmonic acid also triggered a general state of induction throughout the stolon.

Carbon dioxide stimulates tuberization of isolated potato (Solanum tuberosum L.) stolons cultured in vitro. The stimulatory effect is inhibited by C2H4 which is by itself also inhibitory of tuberization. Furthermore, C2H4 inhibits kinetin-induced tuber initiation. Both the formation and elongation of roots are inhibited by C2H4. The antagonistic actions of CO2 and C2H4 on tuberization are discussed.

Phytagel™ allowed the production of longer internodes, faster in vitro tuberization, and larger tubers in Solanum tuberosum L. cv. Baraka as compared to Difco Bacto-agar during both an 8-h photoperiod or in darkness. It also allowed a higher tuberization percentage in the dark. Only a 0.2% (wt/vol) Phytagel allowed optimal micropropagation and microtuberization under the photoperiod regime used. Water availability does not account for the observed differences in growth and tuberization between media containing the above gelling agents. In consequence, Phytagel appears as an advantageous alternative to agar for micropropagation and microtuberization.