Two peaks of ethylene production occur during the development of cotton fruits (Gossypium hirsutum L.). These periods precede the occurrence of young fruit shedding and mature fruit dehiscence, both of which are abscission phenomena and the latter is generally assumed to be part of the total ripening process. Detailed study of the dehiscence process revealed that ethylene production of individual, attached cotton (15,16). In these studies (15,16), a smaller peak of ethylene production was also noted near the time of maximum young fruit abscission.While fruit dehiscence is generally considered a component of the ripening process, where the regulatory role of ethylene is well established (3, 17), other considerations indicated the need for the present study. Fruit ripening has been studied most extensively in fleshy fruits which do not dehisce, and some fruits dehisce after they are dry while others open before appreciable weight loss occurs (13, 16). In some cases, for example pecans, dehiscence also involves detachment (abscission) of the seed from its vascular connections. Dehiscence as a physiological process has not received detailed attention, and yet it is a critical phase in the production of some crops where it is the dominant visible feature of the ripening process. Natural abscission of whole, ripe fruits of the species studied here is rare; seed dispersal can promptly follow dehiscence.Production of ethylene by flowers has been rather extensively studied, primarily in association with petal fading and abscission (3,17), and there is a presumptive association of ethylene with the natural separation of fruits from plants following ripening. All of this information was useful in our approach to the specific process of young fruit abscission.In the present investigation, a detailed monitoring of the seasonal pattern of ethylene production by intact cotton fruits was conducted, ethylene production by dehiscing cotton and pecan fruits was carefully detailed, and the capacity of physiological levels of exogenous ethylene to regulate dehiscence of detached fruits was determined.MATERIALS AND METHODS Pattern of Ethylene Production by Developing Cotton Fruits. In preliminary studies (15, 16) we observed ethylene production by detached cotton (Gossypium hirsutum L., cv. SP23) fruits from anthesis until the completion of fruit dehiscence. Triplicate samples of cotton fruits from a field on the Texas A&M University Farm, tagged on the same day at anthesis. were collected weekly, and enclosed in groups of three in a 500-ml Erlenmeyer flask on water-saturated filter paper. After 3 to 4 hr, the ethylene content of an air sample from each flask was measured gas chromatographically.Ethylene

In an earlier study we reported that detached cotton flowers produced sufficient ethylene before the period of natural abscission to suggest that ethylene might be a natural regulator of young fruit abscission. The present report explores this probability further.

No abstract

Fruits of the ages given in the figures were surface-sterilized with commercial grade sodium hypochloride (diluted 1: 4) and placed upright in Petri dishes containing a 2% glucose solution. Groups of 10 to 15 fruits were treated with CO2 in 54.5-liter Plexiglas chambers. Dishes of calcium carbonate were placed in the chambers to remove excess humidity. CO2 was applied at 0 (control treatment) and 13%. The experiments were conducted in a growth room with a 15-hr photoperiod and a constant temperature of 27 C. Dehiscence was recorded and each chamber was aired and refumigated daily until the completion of dehiscence.CO2-ethylene competition was tested by applying both CO2 and ethylene alone and in various combinations to field-grown, Tamcot SP37 cotton fruits as detailed in Figure 1. All other aspects of the experiment were identical with those described in the preceding paragraph.Reduced Pressure. The effect of reduced pressure on dehiscence of detached cotton, pecan, and okra fruits was observed. Handling, numbers, and ages of fruits were identical with those described for CO2 experiments. Fruits in the treatment were held at 200 mm Hg pressure under 12-liter bell jars. In this system the bell jars were placed between the vacuum source and a Matheson No. 49 vacuum regulator which maintained the desired pressure by allowing air to bleed into the system. In order to insure that accumulation of ethylene or depletion of available oxygen was not a factor in the experiments, air flow was maintained through both the vacuum and atmospheric pressure (control) systems. The flow of air passing over the fruits was regulated by a needle valve placed between the vacuum source and the bell jars; air flow was measured by a flow meter placed between the needle valve and the bell jars. The air flow in control chambers in most experiments was near 500 ml/min, providing air exchange each 12 min. In all experiments the chambers were opened daily and the number of fruit showing any opening of the separation zone due to slight pressure was recorded as dehisced.The effect of reduced pressure (200 mm Hg) on dehiscence of attached cotton fruits was studied by enclosing intact plants in 24-liter chambers made of two 12-liter bell jars placed end to end. Except for chamber size, this system was identical with the one used for detached fruits. Control plants were enclosed in chambers at atmospheric pressure. Two treatment and two control chambers, with one plant per chamber, were used. An observed air flow of about 1000 ml/min was maintained through all chambers providing air exchange in 24 min or less.

Over half of the ethylene produced by 1-day-old cotton flowers came from the combined stigma, style, and stamens. These tissues produced 0.0050 μl/flower·h compared to 0.0024 and 0.0010 μl/flower·h produced by the petals and ovary, respectively. Walls of dehiscing cotton fruits produced 0.052 μl ethylene/fruit·h. This was approximately 50% more than seeds plus fiber which produced 0.033 μl/fruit·h.