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Samples of polystyrene and poly(methyl methacrylate) have been prepared by bulk polymerization under conditions previously investigated in the literature. The molecular weight distributions were determined for early-conversion samples by gel permeation chromatography, and the experimental distribution curves were compared with calculated curves based on kinetic data. The agreement between the experimental and calculated curves was such as to indicate the utility of gel permeation chromatography in the investigation of polymer reaction kinetics and mechanisms.

A method for fluoride determination has been developed in which a level of 0.0–2.5 μg fluoride was determined quantitatively from several milligram samples of biological material. This technique allows the drying, ashing, and diffusion of small samples without transfer. The SPADNS-zirconium lake is a sensitive and convenient color reagent. Recoveries of 96 to 102% were obtained.

Methods are described for the isolation and characterization of the nucleic acids of Oenothera organensis pollen. Alkaline hydrolysis, followed by paper chromatography served to characterize the ribonucleic acid. However, the low concentration of deoxyribonucleic acid and the large amounts of interfering polysaccharide material required application of special techniques and column chromatographic methods. In addition, a method is described for the isolation of “native” deoxyribonucleic acid from root tips of Zea mays and Oenothera .

In many previous studies developing barley embryos have been shown to be highly radiosensitive. With acute irradiations, many of the responses exhibited are dependent in great measure upon the specific embryonic stage irradiated. The present study was undertaken to determine to what extent nucleic acid metabolism in barley embryos might be altered following acute irradiation, and whether here, too, embryonic stage would play a decisive role. Embryos developing within the ovaries of the parent plants were irradiated with 450 r acute X-radiation at one of four specific stages: early proembryo, late proembryo, mid-differentiation, or late differentiation. Fractional analyses of the individual bases of DNA and RNA were carried out at embryonic “maturity”. Because of the presence of interfering substances within the embryos, modification of previously published methods was necessary, the procedures developed being described herein. The DNA of control embryos is of the A-T type with the ratio between guanine and cytosine being unity and that between adenine and thymine being only 0·68. The total nucleic acid content of irradiated embryos showed residual depressions of 30–36 per cent, most of this being due to an effect upon RNA which makes up about 85 per cent of the total nucleic acid at embryonic maturity. Overall depression of RNA amounted to as much as 39 per cent but with a maximum difference among irradiated groups of only 5 per cent. This low variability in RNA content indicates that neither difference in embryonic stage nor post-irradiation time are important factors. In contrast, DNA depression ranged from 7 to 33 per cent among irradiated groups, the degree of depression being inversely correlated with the embryonic stage irradiated. With the exception of the oldest embryo group, residual DNA depression was independent of post-irradiation time. Of the RNA bases, guanine and cytosine showed proportionately less alteration than adenine (which was the least radiosensitive) or uracil (which was the most labile). Changes in DNA base components were generally more complex with wide fluctuations in the amount of cytosine and guanine depression. Effects on adenine were less pronounced. Of the DNA bases, thymine was characteristically the most labile, being the only DNA base to be significantly depressed in all four irradiated groups and the only one to be so affected in two of the groups. Embryos irradiated early in proembryo development or late in differentiation showed greater degrees of residual DNA depression at embryonic maturity but with little alteration in DNA base ratios. Irradiation during late proembryo development, in contrast, produced little lasting effect on DNA content, but marked changes in DNA base ratios primarily because of a decrease in thymine. When compared with results from other studies the present data suggest that a relationship exists between alteration of DNA base ratios and the occurrence of organ abnormalities during embryonic development. Metabolic disturbance as an expression of intra- or inter-tissue incompatibility mediated through radiation-induced genetic heterogeneity is considered as a possible cause.

Investigation was made for the effect of fluoride on plant growth, acid soluble nucleotides, and RNA in germinating corn seedling roots. Fluoride suppresses root growth as measured by changes in fresh weight. Column chromatographic analyses demonstrated that fluoride modifies ratios of acid soluble nucleotide species. The relative amount of nucleotides is altered mainly due to triphosphate nucleotides of which ATP is most accumulated. Paper chromatographic analyses showed that fluoride induces changes of RNA structure. The RNA is characterized by lowered relative content of cytosine and by increased ratio of cytosine to guanine. Adenine is depressed significantly only in the root tissue treated by the highest fluoride concentration.

A study was made of the relationship between the level of r RNA and the rate of growth in pinto bean plants treated with 0·35 ppm ozone for 20–40 min. Cytoplasmic ribosomes and a fraction containing both cytoplasmic and chloroplast ribosomes were initially isolated from primary leaves. The r RNA components of 25S, 23S, and 16S were extracted from these fractions and analysed by sucrose density gradient. The levels of cytoplasmic r RNA components, 25S and 16S, are not significantly affected by ozone. In contrast, ozone specifically decreases the relative level of 23S of chloroplast r RNA, as the rate of growth is inhibited.

A study was made of cytoplasmic and chloroplast ribosomes in the primary leaves of pinto bean plants exposed to ozone. The isolated ribosomes were analysed by sucrose density gradient. Ozone at the levels of 0·35 ppm for 20–35 min does not change the concentrations of various sedimenting particles of the cytoplasmic ribosomes. Ozone at similar levels, however, specifically decreases the population of chloroplast ribosomes per unit fresh weight of leaves. The distribution pattern of these chloroplast ribosomes is characterized by the low concentration of the fast-sedimenting polysome particles concomitant with the low magnitude of other slow-sedimenting components. The kinetics of ribosome populations during leaf growth demonstrates that ozone does not influence the daily levels of different ribosomal components of cytoplasmic ribosomes. However, ozone prematurely decreases the concentrations of polysomes and other components of chloroplast ribosomes below control level at the early stage of leaf development. These findings are discussed to explain initiation of the premature senescence caused by ozone.

A study was made of ribosomes and ribonuclease in the roots of corn seedlings aged by fluoride. Fluoride induced a reduction of ribosome content in which a decrease in polysome level was accompanied by an increase in number and concentration of monosomes and subunits combined. Fluoride increased the specific activity of ribonuclease, probably associated with ribosomal protein. This enhanced activity was likely due to enzyme activation caused by fluoride. Sucrose density gradient analyses demonstrated that ribosome fractions contained a mixture of heterogeneous RNA components.

Growth inhibition caused by fluoride was further studied by analyzing free and bound ribosomes, and the ribosomal components in corn roots. Ribosomes were isolated by differential centrifugation. Ribosomal components were analyzed by column chromatography and electrophoresis. Fluoride reduces the amounts of both free and bound ribosomes. Fluoride also modifies the RNA to protein ratio of bound ribosomes more than that of free ribosomes. Fluoride does not affect base ratios of the ribosomal RNA, but reduces its content and changes the structure of the ribosomal protein moiety.

Summary Chloroplast ribosomes and cytoplasmic ribosomes were isolated from the primary leaves of control and ozone-treated pinto bean plants. On the basis of a unit of ribosomal protein, the levels of ribosomal sulfhydryl groups and their kinetic responses to 5,5′-dithiobis(2-nitrobenzoic acid) were assayed by Ellman's procedure in the presence of sodium dodecyl sulfate. The sedimentation profile of ribosomes was determined by sucrose density gradient. Ozone, 0.30 ppm for 20 to 50 min, decrease the levels of sulfhydryl groups in chloroplast ribosomes far more than in cytoplasmic ribosomes. Both ozone and p-chloromercuribenzoate directly dissociate polysomes and monosomes of isolated chloroplast ribosomes into smaller particles in vitro. The levels of sulfhydryl groups which react with 5,5′-dithiobis(2-nitrobenzoic acid) are higher in chloroplast ribosomes than in cytoplasmic ribosomes. The reaction with 5,5′-dithiobis(2-nitrobenzoic acid) of this higher level of sulfhydryl groups in chloroplast ribosomes goes to completion much faster than the reaction of the lower level of sulfhydryl groups in cytoplasmic ribosomes. With these data, the mechanism which is directly involved in the previous finding, ozone's preferential influence on the disintegration of chloroplast ribosomes in bean leaves is discussed.

Spinach plants were treated with 0.35 ppm ozone and the photochemical activity of photosystem II determined after separation from the isolated chloroplasts using digitonin. Ozone impaired the activity of the system and also reduced the amount of β-carotene in the chloroplasts.

The rates of incorporation of P/sup 32/ into RNA and DNA were stadied by autoradiography in different embryonic stages of barley. The total amount of incorporated P/sup 32/ increased during the embryonic development. The P/sup 32/ incorporation rate in DNA decreased gradually as the growth rate slowed down. The results indicate that RNA turnover in slow or nongrowing tissue is still relatively large. (D.L.C.)

Fluoride-polluted navel orange leaves, Citrus sinensis (Linn.) Osbeck, were fractionated into the subcellular components in hexane/carbon tetrachloride mixtures having various densities. Fluoride was determined at each fraction. Analyses were also made for the subcellular distribution of chlorophyll, nitrogen, and DNA to assess the extent of cross-contamination of each component. The fraction containing cell wall, nuclei, and partly broken cells apparently contained a major amount of fluoride. However, if allowance was made for the cross-contamination of chloroplasts and chloroplast fragments, the fraction of chloroplasts was found to be the site of the highest fluoride accumulation. When each particulate component was washed with water after drying, the combined washings contained more than 50% of the total fluoride of the isolated fractions. The usual method of subcellular fractionation with aqueous solvent shifted the major site of fluoride accumulation from the fraction of chloroplasts to that of the supernatant.

Little attention has been given to the occurrence of exocellular hydrolytic enzymes associated with the roots of higher plants. Such enzymes, if present, could solubilize macromolecular constituents of organic soils, permitting uptake and utilization by the plant of the resultant low molecular weight organic compounds. The present work supports this concept by demonstrating that several exocellular hydrolytic enzymes are associated with the roots of intact corn seedlings. Distinction has been made between exocellular enzymes released into the culture media and enzymes apparently bound to the root surface. A previous paper from this laboratory (17) reviewed earlier studies and presented evidence for the occurrence of exocellular enzymes associated with the primary cell wall of corn coleoptiles. Of particular relevance to the present work is a report (36) of the secretion of peroxidase, acid phosphatase, indolylacetic acid oxidase, and amylase into the culture media bathing plant *tissue cultures. In addition, reports have appeared (2, 6, 14) of the occurrence of an exocellular invertase, possibly involved in sucrose metabolism by roots. In the present work it is reported that invertase, cellobiase, adenosine triphosphatase, pyrophosphatase, and nuclease activity is observed when appropriate substrates are added to nutrient solution bathing the roots of intact seedling corn plants. In addition, inveritase and nuclease are detected as soluble enzymes in the nutrient solution.

Fluoride-polluted navel orange leaves, Citrus sinensis (Linn.) Osbeck, were fractionated into the subcellular components in hexane/carbon tetrachloride mixtures having various densities. Fluoride was determined at each fraction. Analyses were also made for the subcellular distribution of chlorophyll, nitrogen, and DNA to assess the extent of cross-contamination of each component. The fraction containing cell wall, nuclei, and partly broken cells apparently contained a major amount of fluoride. However, if allowance was made for the cross-contamination of chloroplasts and chloroplast fragments, the fraction of chloroplasts was found to be the site of the highest fluoride accumulation. When each particulate component was washed with water after drying, the combined washings contained more than 50% of the total fluoride of the isolated fractions. The usual method of subcellular fractionation with aqueous solvent shifted the major site of fluoride accumulation from the fraction of chloroplasts to that of the supernatant.

POLLEN-STYLE compatibility in Oenothera organensis is determined by a series of allelic genes designated S1S2, S3S4, etc.1. S1 or S2 pollen on an S1S2 stigma germinates but penetrates the style only a few millimetres. S3, S4… Sn pollen on S1S2 grows through the entire length of the style (about 150 mm), reaching the ovary in a 12-h period. (Plants derived from the original Emerson1 collections have retained their high degree of self-incompatibility. These collections were made in 1937 at a time when the population of O. organensis in this type location (Dripping Springs, Organ Mountains, New Mexico) was estimated to be more than 100 plants. A subsequent collection made in 1959 by Drs. S. Emerson and R. S. Bandurski has proved to have a much higher degree of self-fertility. At the time this later collection was made, the number of individuals in the type locality had been reduced to about 8 plants. It thus appears that the population became at least partially self-fertile as the plant neared extinction.)