COMPARISON OF DAYLENGTH AND TEMPERATURE RESPONSES IN NICOTIANA AND ITS TAXONOMIC SECTIONS

Steinberg , Robert A. (U.S.D.A., Beltsville, Md.) Comparison of daylength and temperature responses in Nicotiana and its taxonomic sections. Amer. Jour. Bot. 46(4): 261–268. Illus. 1959.—Fifty-seven of the sixty species of Nicotiana were grown in the greenhouse under long- and short-day regimes. Supplemental tungsten light of about 30 ft.-c. (bench) was used to extend natural illumination to 16 hr. daily. Short-day controls received natural illumination for 9.5–12 hr. daily from about September to March. Two temperature levels were also employed—one with temperature held uniformly at about 25°C. and the other with a day temperature of about 20°C. and a night temperature of about 10°C. Daylength behavior of the species ranged from long-day to day-neutral to short-day. All species were brought into flower and all, except N. acaulis and N. ameghinoi, formed viable seed in at least 1 of the 4 environments. A modified classification of photoperiodic flowering responses based on rapidity and not ability to flower was adopted to permit quantitative comparison of species responses to both daylength and temperature. Very few species flowered equally rapidly (day-neutral) in both the 10- and 16-hr. day-lengths. Temperature level caused modifications in response from long-day to day-neutral and vice versa, and from short-day to day-neutral and vice versa. Data for N. glauca and some other species would indicate that a greater spread between temperature levels could possibly lead to opposite classifications at upper and lower temperatures. Excellent agreement was found between daylength responses of the species and the 14 taxonomic sections of Goodspeed for the genus Nicotiana. Only 2 of the sections (Paniculatae and Undulatae) were heterogeneous in that both included short- and long-day species in the same section. The native habitat of all short-day species was South America. Certain of the species gave a compensatory response to variations in light duration and low temperature similar to that given by sugarbeets and other biennials. This phenomenon may therefore be of general occurrence. Use of a quantitative expression for photoperiodic flowering responses is proposed to avoid ambiguity. It is the quotient of days from sowing to first blossom on short-days divided by that on long-days. The value 0.6₂₀°C. (9–12) would read short-day at 20°C. with 9–12 hr. daylengths. Close agreement was found in daylength flowering ratios in successive tests in the greenhouse. The ratios alter under cold treatment with species susceptible to low-temperature stimulation or inhibition of blossoming.     

Synthesis of ribonucleic acid in normal bone in vitro

1. The incorporation of [2-(14)C]uridine into nucleic acids of bone cells was studied in rat and pig trabecular-bone fragments surviving in vitro. 2. The rapid uptake of uridine into trichloroacetic acid-soluble material, and its subsequent incorporation into a crude nucleic acid fraction of bone or purified RNA extracted from isolated bone cells, was proportional to uridine concentration in the incubation medium over a range 0.5-20.0mum. 3. During continued exposure to radioactive uridine, bulk RNA became labelled in a curvilinear fashion. Radioactivity rapidly entered nuclear RNA, which approached its maximum specific activity by 2hr. of incubation; cytoplasmic RNA, and particularly microsomal RNA, was more slowly labelled. The kinetics of labelling and rapid decline of the nuclear/microsomal specific activity ratio were consistent with a precursor-product relationship. 4. Bulk RNA preparations were resolved by zonal centrifugation in sucrose density gradients into components with approximate sedimentation coefficients 28s, 18s and 4s. 5. Rapidly labelled RNA, predominantly nuclear in location, demonstrated a polydisperse sedimentation pattern that did not conform to the major types of stable cellular RNA. Material of highest specific activity, sedimenting in the 4-18s region and insoluble in 10% (w/v) sodium chloride, rapidly achieved its maximum activity during continued exposure to radioactive precursor and decayed equally rapidly during ;chase' incubation, exhibiting an average half-life of 4.3hr. 6. Ribosomal 28s and 18s RNA were of lower specific activity, which increased linearly for at least 6hr. in the continued presence of radioactive uridine. There was persistent but variable incorporation into ribosomal RNA during ;chase' incubation despite rapid decline in total radioactivity of the acid-soluble pool containing RNA precursors.     

Metabolism of histones in malignant tissues and liver of the rat and mouse

1. The relative amounts of incorporation in vivo of l-lysine, and in one experiment l-arginine, into different histone fractions from Krebs ascites and a lymphoma ascites cells of mice and a `solid' tumour and liver of rats have been determined. 2. No marked differences in the incorporations of the amino acids into the fractions F1, F2a, F2b and F3 from the tumours were generally observed, although in some experiments there was a greater incorporation into fraction F2b, which could be decreased by further purification. 3. In the tumours the incorporations into all cell protein fractions obtained were approximately the same, indicating that the amount of incorporation was that required for the increase of cell mass. 4. In rat liver, the incorporations into fractions F1, F2a and F3 were not greatly different. That into fraction F2b was variable. The incorporation into the histone fractions was much less than that into the acid-insoluble nuclear residue, indicating that considerable turnover of amino acids in the latter occurs. 5. The decrease in radioactivity of labelled histone and acid-insoluble nuclear protein in vivo during several days confirmed the relatively small turnover of the histone fraction. The time taken for liver whole histone to lose half its radioactivity was about 1 week. A histone fraction of slower metabolism was also detected. 6. It is concluded that no appreciable turnover of protein occurs in any one histone fraction, the somewhat higher values obtained in certain cases being associated with acidic impurities. The apparently high rate of incorporation into histone of resting liver is discussed in relation to recent evidence on DNA metabolism of resting liver.