in vitro system was used to sample the volatile components produced by weed seeds. Inhibition of seed germination was accompanied by decreased 02 levels and production of volatile metabolites identified as acetaldehyde, ethanol, and acetone. The effectiveness of these compounds in reducing germination was dependent on 02 levels.

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Ethylene and 2.4-dichlorophenoxyacetic acid (2.4-D) inhibited the growth of etiolated soybean (Glycine max cv. "Hawkeye") seedlings causing tissue swelling and an increase in RNA, DNA and protein content in the subapical hypocotyl tissue. 2.4-D increased ethylene evolution from soybean seedlings and it was found that some of the effect of this herbicide on soybeans was due to the increased ethylene production.Ethylene is responsible in part for the inhibition of elongation and of increase in weight that occurs at supraoptimal concentrations of 2.4-D applied to excised hypocotyl sections. Abscisic acid inhibits 2.4-D-induced tissue swelling and ethylene production in the excised, elongating section. The cotyledons of the soybean seedlings appear to regulate the 2.4-D-induced production of ethylene and the roots are necessary for the 2.4-D-induced tissue swelling.

In this paper we will show that the stimulation of RNA synthesis and protein synthesis is analogous to that reported for other hormone systems. Materials and MethodsMethods utsed to grow and prepare explants and to measure ethylene in the surrounding gas phase have been described earlier (3,17).Preparation of RNA. The perchloric acid method of RNA extraction was modified after Key and Shannon (13). One and one-half grams of tissue (10-15 explants) were homogenized in 2 ml 0.01 M Tris buffer, pH 7.5, in a ground glass homogenizing flask with a ground glass pestle for 1 to 2 minutes. The sides of the homogenizing flask were washed down with 3 ml of 0.01 M Tris buffer and the resultant suspension was filtered through glass wool. Samples (3.5 or 4.0 ml) were taken immediately after filtration throtugh glass wool, made to 0.2 xN with respect to HClO4, thorotighly mixed, and centriffuged at 1000 X 9 for 10 minutes. The pellets wNere then suspenlded and washed twice with 0.2 N HC104 and centrifulged at 1000 X g for 10 minutes. The resiilting pellets were then suLspended and washed twice in methanol containing 0.05 _Ni formic acid and centrifuged at 2000 X g for 10 minutes. All above steps, including centrifugation, were carried ouit at 2°to 4°. The washed pellets were twice extracted at 370 for 30 minutes in a 2: 2: 1 mixture of ethanol: ether: chloroform to remove lipids and centrifuiged at 3000 X g for 10 minutes. RNA was hydrolyzed in 0.3 N KOH for 18 hoturs at 31-0. After chilling, HClO, was added to a final concentration of about 0.3 N, followed by centrifugation at 2000 X g for 10 minutes to remove the KClO4 precipitate, protein, and DANA. Absorbance of samples of RNA was measured at 260 and 290 mju with a spectrophotometer. After determining the RNA, each sample was neutralized with KOH to pH 4.5 to 5.

Soybean seedlings treated with ethylene exhibited small increases in ribonucleic acid content in the elongating section of the hypocotyl. Chromatin isolated from the elongating section of ethylene-treated seedlings showed a 35 to 60% increase in the capacity for RNA synthesis. The ethylene-induced response was saturated at 1 microliter/liter of ethylene and was fully expressed after 3 hours. Auxin caused marked accumulation of RNA and DNA in the elongating and basal tissue of the hypocotyl. Chromatin isolated from these auxin-treated tissues showed an 8-to 10-fold increase in RNA synthetic capacity as measured in vitro. Ethylene added with auxin reduced the auxin enhancement of nucleic acid synthesis in the elongating and basal tissues. Both ethylene and auxin treatment of the seedlings inhibited nucleic acid accumulation and chromatin activity in the apical tissue. Ethylene did not appear to mediate the auxin effects on nucleic acid synthesis in soybean hypocotyl with the possible exception of inhibition in the apical tissue.The RNA which was synthesized by chromatin isolated from control and auxin-and ethylene-treated tissues was characterized by nearest neighbor analyses. gested that auxin enhances the production of chromatin-associated RNA polymerase. Auxin treatment of soybean seedlings results in a higher rate of ethylene evolution (3). Ethylene enhances the accumulation of RNA, DNA, and protein in the hypocotyl of soybean seedlings (3), as has been shown for auxin (5). Since ethylene and auxin cause similar morphological aberrations and total nucleic acid changes in soybean seedlings, it was suggested that ethylene mediated some of the auxin-enhanced nucleic acid accumulation (3). In view of the chromatin data of O'Brien et al. (8, 9) with auxin-treated soybean seedlings, it seemed pertinent to investigate the chromatin response of soybean tissue treated with ethylene to determine whether ethylene is responsible, at least in part, for the auxin-induced increase in chromatin activity. The relationship of ethylene to the auxin enhancement of total RNA synthesis was further investigated. MATERIALS AND METHODSSoybean seeds (Glycine max var. Hawkeye 63) were germinated in moist vermiculite in the dark for 212 days at 300. The seedlings were rinsed under tap water to remove the seed coats and vermiculite. The intact seedlings were marked with ink 0.5 and 1.5 cm below the cotyledons. The zone between the cotyledons and the original 0.5 cm mark is referred to as the apical section, and the zone between the original 0.5 and 1.5 cm mark, the elongating section. The zone between the original 1.5 cm mark and the root is referred to as the basal section. The seedlings were inserted root first through the holes of a desiccator plate supported in a 10-liter desiccator. Each desiccator usually contained 160 seedlings. Spray treatments of 2,4-D were applied with an atomizer to the etiolated seedlings in the desiccator (about 10 ml of 110 ,ug/ml of the potassium salt at pH 6.0 per desiccator). Ethylene was added to...