Regulation of Ethylene Evolution and Leaf Abscission by Auxin.

Many physiological processes have shown art,.lowith a neck to accommodate a 25 mm diameter Sgous responses to both auxin and ethylene. These rubber vaccine cap. The gas collection bottles were processes include root initiation, intumescence formathen sealed and incubated at 21'; etiolated tissue was tion, epinasty (9), fruit ripening (3, 12), floral placed in the dark and green tissue in 150 ft-c coninitiation in the pineapple (8, 19), breaking of bud tinuous light. dormancy (2,4), stimulation of guttation (21,22), For abscission tests, explants were isolatd conand leaf abscission (1,23). sisting of the primary leaf abscission zone with 5 mm Auxin applications can also stimulate ethylene of tissue at the distal side and 5 mm of petiole at the evolution. Zimmerman and Wilcoxon (24) first proximal side. Six ml of agar were poured into noticed this phenomenon when tomato plants treated the gas collection bottles and 10 explants were inwith IAA in lanolin produced an emanation which serted into the agar so that 3 mm of the proximal caused an epinastic response when confined with ends were submerged. When desired, auxin was apChenopodium albumn and marigold. Later 2,4-diplied proximally by incorporation into the agar. chlorophenoxyacetic acid (2,4-D) was found to stimTwo-milliliter gas samples were subsequ ntly with"ulate ethylene evolution from pears (12) and cotton drawn from the bottles with a syringe that' could be (15), and recently Morgan and Hall (16) have resealed with a petcock placed between the syriftge barported that ethylene production from cotton was stimrel and the needle. These samples were injected into ulated by IAA. a F and M Scientific Corporation Model 720 gas Because ethylene and auxin have so many effects chromatograph equipped with a Model 1609 flame in common and since auxin has been found to stimionization detector. Helium at 110 nil/minute flowed ulate ethylene evolution, "... some of the effects thr9 ugh a quarter inch, 60 cm activated alumina attributed to so-called growth substances might be due column. With the oven temperature at 450, the indirectly to the unsaturated hydrocarbon gas proanalysis time wvas 1 minute. Authenticity of the duced in the tissues" (24). This suggestion has been ethylene peak was determined by cochromatography recently readvanced b3 others (15,16). with standards (obtained from Olin MIathieson Before an auxin-ethylene relationship can be estabCompany) and by use of mercuric perchlor'aite and lished, however, it is necessary to show that auxin NaCI as specific reagents for the absorption and reenhanced ethylene evolution occurs in a variety of lease of ethylene (7). plant material, and 'hat ethylene evolution can be conAbscission data are expressed as mi% ethylene trolled by endogenous as well as ex.genous levels of evolved per explant but can be converted approxiauxin. We will also demonstrate the importance of mately to parts per million by dividing by 3.4 or auxin regulated ethylene evolution on a physiological expressed as mpl/mg dry weight by dividing by 3.1 process, by investigating the abscission of bean petiole and then making the appropriate changes of units. explants. The area of the ethylene peak was determined by a disc chart integrator. Sensitivity of the chromatogMaterials and Methods raph permitted the determination of 0.05 mpl ethylene per ml and the ethylene content of each s..,nple could Plant material for the majority of the experiments be determined with a precision of 5 %. consisted of Phascolus vilgaris L. var. Red Kidney IAA, ,l-(indole-3)-propionic acid (IYA), ,which was grown in soil in 10-cm pots. Etiolated (indole-3)-n-butyric acid (IBA), a-naphtlialereacetic plants were grown in the dark at 24 -L 20 and green acid (NAA), and gibberellic acid K salt (GA) were seedlings were grown under identical temperatures with 1200 ft-c of fluorescent light given for 14 hours obtained frim Calbiochenm Chlporation; 11.8 % 2per day. chloroethyltrimethylamnonium chloride (CCC) from Ethylene evolved from experimental material was Cyanamid International Company; 5 % N-dimethy)'a' collected by placing the tissue sections in 43 1 2 ml amine succinamic acid (B995) from U. S bb., bottles (5 cm in diameter and 2.5 cm high) fitted Company, Naugatuck Chemical Di ' SReceived March 16, 1964. phon), from Vrii aoia•• •o'•a r••\ Receved ,%lrch 6, 164.dichlorobenzyltributylphosphonium -C