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Auxin Distribution in Fruits and Its Significance in Fruit

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Auxin Distribution in Fruits and Its Significance in Fruit Apr., 19391 GUSTAFSON-AUXIN IN FRUITS 189 outside and at many stages during the developmen­ the cessation of division in successive tissues; and tal period from very small ovary primordia to ma­ (c) greater cell expansion after cell division ceases. ture fruit. Differences in fruit size are therefore usually due In each tissue growth takes place at first chiefly to differences in both cell number and cell size, by cell multiplication, though cell size slowly in­ though either factor may alone be responsible in cer­ creases also, After a specific cell size is reached, di­ tain cases. vision ceases, and all further growth of this tissue is Specific differences in development between Cu­ hy cell expansion. curbiia and the three other genera are described. The innermost tissues, as compared with the suc­ Possible factors responsible for the differences in cessively outer ones, show (a) more rapid increase cell division and in cell expansion between the vari­ in cell size during the period of cell division, (b) ous tissues and in the various races are discussed. earlier cessation of division, and (c) greater cell The problem of the size relation of cell to organ size at the time when division ceases. is part of the more general problem of the factors In Cucurbita Pepo, large-fruited races as com­ determining growth and differentiation. The first pared with small-fruited ones typically show (a) no step in the solution of this problem is a thorough difference in cell size during early development; (b) descriptive analysis in quantitative terms. a more extended period of cell division, due to less DEPART~IENT or BOTANY, rapid increase in cell size, greater cell size at the COLUMDlA UNIVERSITY, time of last division, and a greater interval between NEW YORK CITY LITERATURE CITED .:bIELUNG, E. 1893. t;ber mittlere Zellengrossen. Flora MACARTHUR, J. W., AND L. BUTI.ER. 1938. Size inherit­ 77: 176-207. ance and geometric growth processes in the tomato HrXLEY, J., AND G. TEIssn:R. 1936. Terminology of rela­ fruit. Genetics 23: 253-268. tive g-rowth. Nature 137: 780. SACHS, J. 1893. t;ber einige Beziehungen der specifischen Grs'rAFsoN, F. G. 1939. Auxin distribution in fruits. Grosse der Pflanzen zu ihrer Organisation. Flora Amer. Jour. Bot. 26: 189-194. 77: 49-81. HOUGHTALING, HELEN B. 1935. A developmental analysis SINNO'lvr, E. 'V. 1930. The morphogenetic relationships of size and shape in tomato fruits. Bull. Torrey Bot. between cell and organ in the petiole of A eel'. Bull. Club 62: 243-252. Torrey Bot. Club 57: 1-20. AUXIN DISTRIBUTION IN FRUITS AND ITS SIGNIFICANCE IN FRUIT DEVELOPMENT 1 Fclix G. Gustafson GnoWTH SUBSTANCES or auxins, as they will be in many plants. In this paper it was shown that the called in this paper (Went and Thimann, 1937), are auxin content is actually much higher in the ovaries now generally considered to be factors in vegetative of those plants that produce fruits parthenocarpi­ growth of plants. Recent investigations on artificial cally than in similar varieties requiring fertilization parthenocarpy produced by chemicals (Gustafson, for fruit production. 19:36; Hagemann, 1937; Gardner and Marth, 1937) Before it is possible to proceed very far with this have shown that auxin under artificial conditions matter, it is first necessary to investigate the auxin can also cause fruit development without fertiliza­ distribution in fruits. In 1936 Dollfus published tion. This coupled with the fact that auxin has been some experiments which tended to show that auxin shown to be widely distributed in the vegetative is produced in the developing seeds. He used the parts of plants leads one to assume that auxin is diffusion method. In these experiments he found also concerned with normal fruit growth. Gustafson that a substance diffused from the ovules into the ( 1939) has proposed the theory that a high auxin agar which caused Avena coleoptiles to curve, but content in the ovary in the flower bud stage is re­ no such substance diffused out of the outer part of sponsible for natural parthenocarpy, which is found the ovary. Meyer (1936) has also found auxin in 1 Received for publication December 15, 1938. fruits. He extracted the auxin with alcohol in a Paper from the Department of Botany of the Univer­ reflux condenser for two hours and mixed the ex­ sity of Michigan, No. 682. tract from 10 grams of fresh material with 1 gram The writer wishes to express his thanks and apprecia­ tion to F. W. 'Vent, E. G. Anderson, J. Van Overbeek, of lanolin, which was applied to one side of intact and William S. Stewart, of the California Institute of Avena coleoptiles. While this method is perhaps not 'I'echnology, and to William Hertrich of the Huntington so good as the method in which agar containing the Gardens, San Marino, California, for various aids ex­ auxin is applied to decapitated etiolated Avena tended during the course of this investigation and to the Directors of the Horace H. Rackham Trust Fund of the coleoptiles, nevertheless it is fairly accurate. In University of Michigan for financial aid. these experiments Meyer used a number of species 190 AMERICAN JOURNAL OF BOTANY [Vol. 26. of plants, and in the fruits of all these species he was A few experiments were performed in which the able to demonstrate the presence of auxin. He did plant material was placed on the agar blocks as in not do much with the distribution within the fruits, Went's original experiments. In most instances such but in the few determinations he made, seed material blocks when placed on Avena coleoptiles caused no gave a greater Avena coleoptile curvature than the curvatures. It had been hoped that this method could other parts of the fruit. be used, but as so few plants gave any results, it was The present work was undertaken to investigate abandoned for the extraction method. This brings further the auxin distribution in fruits. Fruits from up a question which is in the minds of many­ many plants, in different stages of development and namely: Is extracted auxin the same as that which during different seasons, were used. diffuses into the agar block, and if so, is the con­ PROCEDURE.-The work here reported was done centration in the plants that give negative results so at the William G. Kerckhoff Laboratories at the low that only by using a large quantity of material California Institute of Technology. Part of the ex­ can a test be obtained; or is the auxin which is ob­ perimental material was grown especially either in tained by extraction released from a combined form, the greenhouse or in the field, while some of it, as with low diffusibility, by the extraction treatment? the Yucca Whipplei, Agave Brundigii, Pittosporum Those experiments in which, by daily extraction, ac­ undulatum, and Clivia sp., was obtained from the tive material continued to be obtained for a period Huntington Gardens at San Marino. The auxin con­ of 10 days certainly suggest an affirmative answer to tent and distribution was determined hv the Avena the latter alternative. method, the technique of which has be~n discussed In these experiments the fruits were separated in detail by Went and Thimann (1937). into an interior and exterior part, or, as in the to­ Auxin was extracted with freshly distilled ether mato and summer squash, further subdivisions were according to Van Overbeck's (1938) modification made. When a fruit was divided into only two parts, of other methods. Th~dried residue was thoroughly the interior part included the central axis, the pla­ mixed with a known amount (usually .4 to .8 cc.) of centae, the ovules and all the cells in between and 1.5 per cent agar and after standing 90 minutes was immediately surrounding the ovules, and the exte­ poured into a nickel plated brass mold 1.5 X 8.0 X rior part usually included only the ovary wall, as in 10.5 mm, in size. After the agar had been cut level the peppers, tomatoes, beans, and Yucca. In the sec­ with the surface of the mold, the large block was cut ond experiment with peppers, listed in table 1, the into 12 equal pieces. The material was now ready beans and Yucca, only the ovules and seeds were in­ for the test. Great care was taken to have freshly cluded in the interior part. The extraction method prepared extracts. Usually the extract was pre­ varied considerably in these experiments. All mate­ pared the same day that it was used, but if the ex­ rial was cut into rather small pieces to begin with, tract could not be used the same day that it was but in some experiments these pieces were frozen made, it was always stored in a refrigerator in dried with liquid air, and while they were in the frozen condition. Fleshy material was repeatedly extracted condition, attempts at maceration were made. These until the Avena test plants showed no curvatures differences in treatment of the material should in no when treated with the agar-extract. In some experi­ way influence the results, as all material experi­ ments such material as tomato and squash was first mented with at anv one time was alwavs treated in frozen with liquid air then ground in a mortar and the same way, anl extractions were co~tinued until the ether added. The extraction was always carried no further reaction was obtained with the Avena out in the dark and usually, though not always, at a coleoptiles. low temperature. The investigation was divided into two parts. Control experiments in which Avena plants were Part one dealt with the auxin distribution in non­ treated with a known concentration of indole acetic parthenocarpic fruits, and the second part with a acid (usually 21.5 gamma per liter) were run with comparison of auxin concentration in artificial par­ every experiment.
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