Methods for quantitative determination of ethylene in aqueous solutions for biological studies

Abstract. In many plant physiological studies, quantitative determination of ethylene in aqueous solutions is necessary. We describe two methods for such measurements based on vacuum extraction, or on stripping ethylene from solution with the carrier gas of a gas chromatograph. The gas-stripping technique is limited by the small sample volumes that can be used, whereas the vacuum extraction technique can accommodate much larger volumes and is useful when the ethylene concentration in the solution is very low. The use of these techniques will facilitate the treatment of submerged plant tissues with known amounts of ethylene, and also the quantitative determination of ethylene from tissues grown in either static or continuous flow liquid cultures.     

Translation of Two Messenger RNAs from Lens in a Cell Free System from Krebs II Ascites Cells

SPECIALIZED tissues which synthesize only a small number of different proteins offer obvious advantages as sources of specific and pure messenger RNAs (mRNAs). Presumptive mRNAs have been isolated and partially characterized from reticulocytes^1,2, muscle³, myelomas⁴ and eye lens⁵. The messenger role of 9S RNA from reticulocytes has been established by its ability to direct the synthesis of haemoglobin in cell-free systems from reticulocytes² and Krebs 11 ascites tumour cells⁶ and in Xenopus oocytes⁷. We show here that 10S and 14S RNA fractions from calf lens direct the synthesis of different polypeptide components of lens crystallin in the ascites cell-free system. These results complement and extend the demonstration, in the accompanying article⁸, that 14S lens RNA is translated in the reticulocyte lysate.     

Properties of Mitochondria Prepared by Two Different Isolation Procedures From the Cotyledons of Germinating Bean Seedlings

Mitochondria from 1-day-old bean cotyledons were isolated bya ‘slow’ isolation procedure involving a wash andby a ‘rapid’ procedure. The mitochondria isolatedby the ‘rapid’ procedure were more tightly coupledthan those isolated by the ‘slow’ procedure. Anexogenous supply of cytochrome c or NAD was shown to improvethe activity of mitochondria isolated by the ‘slow’procedure, but not those isolated by the ‘rapid’procedure. The phosphorylative abilities of the latter weremuch greater than the former and were retained for longer periods.It was found that there was a leakage of NAD out of the mitochondria.     

The Relationship between Stimulus Intensity and Oriented Phototactic Response (Topotaxis) in Chlamydomonas

Two techniques have been used to study the quantitative relationship between stimulus intensity and oriented phototactic response (topotaxis) in Chlamydomonas. The net response of a cell population was monitored photometrically and was recorded continuously against time. The responses of individual cells were observed through a microscope and their swimming tracks were recorded on film. The net response of the population is positive at low stimulus intensity and negative at high intensity. The direction of response can be reversed within two seconds by raising or lowering the intensity. The intensity-response curve for phototaxis is similar to the dose-response curve for phototropism. The net response has no distinct threshold; it increases linearly with log intensity; then it decreases and finally becomes negative. The individual-cell studies reveal that the intensity-dependent increase in net topotactic response is due primarily to an increase in the number of cells responding and in the directness of their swimming path. As stimulus intensity is raised, the swimming path becomes increasingly well-aligned with the stimulus beam, whether net response is positive throughout the intensity range tested, negative throughout that range, or changing from positive to negative. Changes in swimming rate do not contribute significantly to the intensity-dependent changes in net response. Swimming rate shows virtually no change throughout the intensity range of positive topotaxis and shows only a small increase in the negative range. However, a transient decrease in swimming rate (stop response) is often observed at the onset of stimulation. The implications of these results for the orientation mechanism are discussed.     

Fat Metabolism in Germinating Citrullus vulgaris

A column chromatographic technique, enabling identificationand quantitative estimation of fatty acids, has been employedto study fat metabolism in Citrullus during germination in thelight. This plant is characterized by an unusually rapid disappearanceof storage fat as the cotyledons expand and turn green. In spiteof the high catabolic activity there is no evidence for accumulationof free fatty acids or short-chain fatty acids at this stage.Information on this point derived from acid value or saponificationvalue of the oil is shown to be untrustworthy. Citrullus seed fat contains the following percentages of acids:linoleic 70·6, oleic 7·2, palmitic 10·1,stearic 11·2, and arachidic 0·6, and careful analysishas also revealed small amounts of octadecatrienoic acids, bothconjugated and non-conjugated. All the major acids are brokendown at rates proportionate to the quantities originally present,with the exception of oleic acid which is metabolized somewhatmore rapidly. ‘Linolenic’ acid is synthesized in the expandinggreen cotyledons and the fatty acid composition of the latter,in the late germination stages, resembles that of a green leafand is very different from that of the seed. The results suggest a rapid removal of storage fat from thecotyledons and concomitant formation in small quantity of atypial leaf fat as the new photo-synthetic function develops.     

STUDIES ON PLANT GROWTH-REGULATING SUBSTANCES: CHLORO-SUBSTITUTED PHENYLACETIC ACIDS

The plant growth-regulating activity of all the mono- and di- chloro-substituted phenylacetic acids, together with the 2:3:6-trichloro- derivative, has been determined in the wheat cylinder, pea segment and pea curvature tests. Each of these compounds showed activity, the 2:3-dichloro- and the 2:3:6-trichloro- derivatives being extremely active. The 3:5-dichloro- acid was inactive in the wheat test but showed moderate activity in the pea tests.
All these findings are discussed in relation to the plant growth-regulating activity of corresponding benzoic and phenoxyacetic acids.     

FURTHER OBSERVATIONS ON THE BIOLOGY OF THE CABBAGE ROOT FLY, ERIOISCHIA BRASSJCAE BCHÉ

In 1951, eggs of Erioischia brassicae were first found in the field on 2 May, and the peak period of egg-laying occurred 19–31 May. This was up to a month later than in the period 1948-50.
The periodic removal and examination of the surface soil showed that eggs of E. brassicae were continuously present on the host plants from mid-June to early November. Plants under observation during this period showed an average of 285 eggs per plant and other plants exposed to attack from July to November showed an average of 162 eggs per plant. Peak periods of egg-laying, as indicated by numbers of eggs per plant per day, occurred in late June and early July, in mid-August and, to a less extent, in the first half of October. The plants showed no increase in the rate of infestation as the season advanced, although E. brassicae has a reproductive capacity of about 100 eggs per female and three to four generations a year.
The difference between the observed egg populations and pupal populations indicated that E. brassicae had a heavy mortality rate in its immature stages. The condition of puparia showed that the species was subject to a high degree of natural control, a fact for consideration when direct control measures are formulated.
Pupal diapause extending from October 1949 to May 1951 was observed in one specimen of E. brassicae and from October 1949 to August 1951 in one specimen of its Hymenopterous parasite, Trybliographa rapae Westw.
Tests with tar-oil winter wash showed that at a concentration of 1 1/4% it killed eggs of Erioischia brassicae and repelled gravid females for approximately a week. Laboratory tests with BHC indicated that it had no adverse effects on the eggs but was larvicidal.     

Nutrient Dilution by Starch in CO2-enriched Chrysanthemum

Increasing growth irradiance and CO₂ generally decreases foliarnutrient concentration on a dry weight basis and increases foliarstarch concentration. However, the extent to which starch concentrations‘dilute’ foliar nutrient concentrations when thelatter are expressed on a dry weight basis is not known. Todetermine the importance of differential starch accumulationin calculating nutrient concentrations on a dry weight basis,leaf nutrient and starch concentrations were measured in Chrysanthemum? morifolium ‘Fiesta’ (Ramat.) cuttings grown atthree irradiance levels and two CO₂ levels for eight weeks inboth winter and spring. On a dry weight basis, foliar concentrationsof most nutrients were lower in both seasons as a result ofthe elevated CO₂ and irradiance levels, and total dry weightswere higher. Per cent starch was greater at the high CO₂ levelin both seasons but was only greater at higher irradiances inthe winter experiment. When starch was subtracted from the leafdry weights, the differences between CO₂ and irradiance treatmentsdisappeared with respect to N, P, K, Ca, Mg, S, and B but notfor Fe, Mn, Zn, and Cu. Key words: CO₂ enrichment, starch, nutrients, irradiance     

Influence of Photoperiod, Daylength, and Feeding Schedule on Tadpole Growth and Development

The metamorphic rate of Rana pipiens tadpoles was studied under different photoperiods, daylengths, and feeding schedules. Tail resorption and hindlimb growth and development induced by immersion in 30 μg/l thyroxine (T₄) were accelerated under longer photoperiods and continuous light when 6L: 18D, 12L: 12D, 18L: 6D, and 24L regimes were compared. Constant light exposure did not produce faster development than an 18 hr photoperiod, and initially was less effective. The rate of spontaneous and T₄-induced metamorphosis was greater the shorter the day on 9L:9D, 12L: 12D, or 15L: 15D cycles, although all groups received the same overall amount of light, but in different dosages. When feeding schedule but not the LD cycle was varied, groups of tadpoles fed on 18, 24, or 30 hr regimes showed no differences in growth and development rate on 19L: 5D, and only random variations under continuous light. Differences in metamorphic rate on 18, 24, or 30 hr days are not due to the feeding schedules, but to the LD cycles. From these experiments we conclude that illumination, particularly the length and frequency of the photoperiod, affects the utilization of T₄. Development rates independent of the total amount of illumination, but related to daylength and light schedule, suggest interaction of light with an endogenous timing mechanism.