Gibberellin-sensitive Suspension Cultures.

Suspension cultures were incubated in the presence and absence of gibberellic acid (GA(3)) in an attempt to define a new experimental system for study of the molecular action of gibberellins upon growth. Unlike many suspension cultures, an auxin-independent green clone from spinach (Spinacia oleracea L.) and an auxin-dependent line of "Paul's Scarlet" rose (Rosa sp.) were promoted in expansion growth by GA(3) at 10(-11) to 10(-6) molar. In Rosa the cells also elongated upon GA(3) treatment whereas in Spinacia they remained isodiametric.Attempts were made to intensify the response. The effect of GA(3) in Spinacia was stronger when gas exchange between the culture and the laboratory air was facilitated. The response of Rosa was dependent on the presence of a cytokinin, although this culture did not require exogenous cytokinin for serial subculture. GA(3) antagonized the growth retardant AMO-1618 in Rosa but not in Spinacia. In general, conditions that enhanced growth also rendered GA(3) a more effective promoter; conversely, GA(3) tended to become inhibitory under conditions that permitted only slow growth.

The role of the gas phase in the greening and growth of illuminated cell suspension cultures of spinach (Spinacia oleracea, L.).

The gas phase developed above spinach suspension cultures critically affected their growth and greening. Ethylene accumulation inhibited greening; this effect of ethylene was antagonised when the culture gas phase was enriched with carbon dioxide. Greening was enhanced by reducing the partial pressure of oxygen below the air level; this effect was observed when oxygen supply did not restrict growth.

Carbon Dioxide as an Essential Requirement for Cultured Sycamore Cells.

Carbon dioxide (optimum concentration c. 1.0%) is essential to the initiation of the growth in suspension culture or on agar plates of cultured sycamore cells. By effective flushing of the cultures with CO2 -free air it is possible to demonstrate this requirement with initial cell densities up to 50 × 103 cells ml-1 . This growth-promoting activity of carbon dioxide is not related to any effect it may have on the pH of the culture medium. The cells fix applied carbon dioxide into organic and amino acids but attempts to replace the carbon dioxide requirement by non-toxic levels of organic or amino acids have not been successful.

Kinetic aspects of synchrony in suspension cultures of Acer pseudoplatanus L.

Synchronous divisions have been induced in cell suspension cultures of sycamore (Acer pseudoplatanus L.) initiated at low density from stationary phase, nitrate-starved cells. The pattern of division and DNA replication synchrony is unusual in that it does not show progressive decay but rather a sharp transition to asynchrony. Feulgen densitometry data indicate that in terms of an S-phase synchrony index, DNA replication becomes more highly synchronized as cell density rises and interphase duration is reduced. In comparison with asynchronous cultures the duration of mitosis appears to be reduced during synchronous growth. The persistence of division and S-phase synchrony and the apparent shortening of interphase and mitosis in these sycamore cultures suggests the operation of intercellular entrainment. The departure from synchrony during the interphase which precedes initiation of asynchronous division remains unexplained.

Metabolic events in synchronised cell cultures of Acer pseudoplatanus L.

Cell division was synchronised in 4-litre batch cultures of Acer pseudoplatanus L. by starvation and regrowth. Up to five consecutive cell cycles were observed in each culture. Mitosis and cytokinesis were synchronised within 0.2 cell cycles. Accumulation of extractable DNA was discontinuous and separate from cytokinesis. Correction for the degree of synchrony in the population gave: G1=13-37 h, S=15 h, G2=14-19 h and M=0.9-1.3 h. Thymidine kinase activity and [(14)C]thymidine incorporation were highest during S-phase. A peak of activity of aspartate transcarbamoylase occurred during G2. Peaks in succinate dehydrogenase activity and respiration rate were observed at the initiation of DNA synthesis and just prior to mitosis. The activity of glucose-6-phosphate dehydrogenase doubled in one step during the cell cycle. Total RNA and protein accumulated continuously through the cell cycle; the final rate being twice that observed initially.

The development of haploid embryoids from anther cultures of Atropa belladonna L.

Development of haploid embryoids from the microspores of Atropa belladonna occurs with relatively high frequency when anthers are excised from buds in which the petals are shorter than the sepals (at this stage microspores are predominantly uninucleate) and cultured on a medium containing iron as the ferric salt of ethylenediamine-di-O-hydroxyphenylacetic acid (FeEDDHA). Additions of combinations of kinetin, auxin and casamino-acids to the culture medium induce callusing in both haploid and diploid tissues, lead to the origin of embryoids from somatic tissues of the anther and should be avoided. Simple techniques for the maintenance of haploid clones are described.Stages in early embryogenesis in the pollen grains have been observed and these indicate that embryogenesis is most frequently initiated by an equal division in the uninucleate spore. The frequency of grains showing embryoid formation is very low and it is estimated that plantlets are formed from up to 50% of these grains.