Crystalline abscisin II, with a tentative molecular formula of C(15)H(20)O(4), has been isolated from young cotton fruit. It accelerates abscission when applied in amounts as low as 0.01 microg per abscission zone. It inhibits indoleacetic acid-induced straight growth of Avena coleoptiles but has no gibberellin activity on dwarf maize.

No abstract

It is a common observation that a leaf stalk usually abscises shortly after the removal of its blade. LA RUE (2) delayed this abscission of debladed leaf stalks by the application of indoleacetic acid to the stalk. Compounds related to indoleacetic acid also have delayed the premature abscission of leaves and fruits (1, 3). These observations suggest that the auxin normally present in an organ is an important factor in delaying its abscission, and that a decrease in this auxin precedes or accompanies abscission. To test these ideas, determinations were made of the auxin content of bean leaves of various ages. This paper presents the results of the auxin determinations and a discussion of their significance.The first trifoliate leaves of Black Valentine beans, grown in the greenhouse, were used in this investigation. In beans an abscission zone lies between the blade of each leaflet and the leaf stalk. Thus blades differ from stalks in relation to the leaflet abscission zone; tissues of the blade are distal to the zone and tissues of the stalk are proximal to the zone. Samples of blades and stalks were taken from the plants at each age studied, 15, 30, 40, 60, and 70 days after planting. At 15 days the leaves were immature, the blades only partially expanded. At 30 days the leaves were fully expanded. At 70 days the blades were turning yellow and showing other signs of approaching abscission.Each sample was treated in the following manner: Immediately after cutting it was weighed, put into a container, and frozen at -150 C. As soon as convenient it was dried in a lyophilizer. The dried material was ground through a 40-mesh screen in a Wiley Mill, and weighed. Each sample was put into a separate 250-ml. Erlenmeyer flask containing 100-ml. of freshly distilled cold ethyl ether, and the flask kept for two hours in a refrigerator at 00 C. The material was then filtered through No. 1 qualitative paper and the residue washed with three 2-to 3-ml. portions of fresh ether. The ether extract thus obtained was evaporated to a few milliliters and with a pipette transferred to a small test tube where it was evaporated to dryness.A measured amount of lj% agar was added to this dried extract, the mixture shaken vigorously for a few minutes, poured into a 10.8 x 8 x 1 mm. brass mold, and cut into 12 blocks. These blocks were placed on Avena

Abscisic acid was measured in developing cotton fruit (Gossypiuln hirsutunt) by means of gas-liquid chromatography.High levels of abscisic acid occurred in correlation with abortion and abscission of young fruit, with low germination of immature seed, and with senescence and dehiscence of mature fruit. Declining or low levels of abscisic acid occurred in correlation with the period of most rapid fruit growth and with high germination of immature and mature seed. Abscisic acid was isolated and identified from the young fruit of cotton (12,13) and was demonstrated to be an abscission-accelerating hormone of young cotton fruit (3). It occurs in the fruits of a wide variety of plants (see 4, 10); however, knowledge of the occurrence of ABA in correlation with the development and/or abscission of fruits is still quite limited. Van Steveninck (22) found that the occurrence of an inhibitor, now known to be ABA (14), was correlated with the abscission of young lupin fruit. Rudnicki and colleagues found ABA to increase with ripening of strawberry fruits (16) and of pears (17) and during the development of apple fruits (18).In bioassays for ABA the interference of other hormones has been a serious hazard. However, the recent development of chemical assays with a high degree of specificity (6, 8) enables measurement of ABA independently of the other hormones. The research reported in this paper was undertaken with two objectives: (a) to confirm and extend with quantitative data the occurrence of ABA in correlation with young fruit abscission in cotton, and (b) to obtain similar data over the entire life-span of the cotton fruit and correlate that information with the events that take place in the course of the development and maturation of seed, fiber, and walls of the cotton fruit. MATERIALS AND METHODSThe cotton used in these experiments was Gossypium hirsutum L., cultivars Acala 4-42 and Acala SJ-1, grown at the 'Present address: Alina Farms Corporation, McFarland, California 93250.United States Cotton Research Station, Shafter, California, in the summer of 1967. The plants were grown in rows 101.6 cm (40 inches) apart and thinned to one plant every 30.4 cm (12 inches). The cultural practices of irrigation and cultivation were the standard ones of the Station. Flowers at anthesis were tagged on two dates: 6 July (early) and 8 August (late). Only one flower per plant was tagged. On the early date the tagged flowers were either the first or second on the plant; on the late date the plants had numerous flower buds, flowers, and fruits in various stages of development. Fruits were collected at anthesis (day 0) and at 2. 4,6,8,10,15,20, 30, 40, and 50 days after anthesis.Collected fruits were frozen on solid CO2 and stored at -20 C until 5 min before extraction. Fifteen fruits 0 and 2 days old, 10 fruits 4, 6. and 8 days old, and five fruits each in the samples of 10 days and older were extracted. Before extraction bracts and pedicels were removed from the fruits, and fruits 15 days and older were separated into (a) ...

Slatis has raised a single valid point. The chromosome-per-cell distributions displayed in our put numbers on our observations. We do recognize the implications of such damage in our experimental cell populations, if the observations were significantly elevated above control values. We cannot say that they were, or that they were not.We feel that Slatis' attempt to show chromosome damage by pointing to differences which are the result of random sampling error is not a matter of a one-tailed or a two-tailed test.We agree that the pertinent statistical tests, at least for data in our Table 2, should be one-tailed. In fact, our conclusions were based on one-tailed ttests, the full results of which were not tabulated. The confidence limits given with our data were for the convenience of readers who wished to inform themselves of the magnitude of random sampling errors associated with the percentages in the Abscisic Acid: A New Name for Abscisin II (Dormin) Abscisin II was the name given to the second of two abscission-accelerating substances isolated (1) from cotton fruit. The same substance was subsequently isolated (2) from sycamore leaves as the result of a search for a "dormin" [an endogenous substance inducing dormancy (3)]. Since then, the substance has been identified in a large number of higher plants. The structure of abscisin II has been determined and confirmed by synthesis (4); structure and correct absolute configuration (5) are shown by the insert.

No abstract

No abstract

No abstract