Treatment with gibberellic acid, at concentrations as low as 10(-7)M, of intact tomato fruits, or of pieces in tissue culture, markedly retarded ripening in terms of development of redness. Ethylene stimulations of color development were prevented by treatment with gibberellic acid, but ethylene stimulations of respiration were not. Gibberellin can delay the progress of some components of the ripening of fruit, preventing some of the changes triggered by ethylene.

Continuous application of propylene to 40 to 80% mature fruits of normal tomato strains (Lycopersicon esculentum Mill.) advanced ripening in fruits of all ages by at least 50%. Although preclimacteric respiration was stimulated by propylene treatment, there was no concomitant increase in ethylene production. Once ripening commenced, the rates of endogenous ethylene production were similar in both propylene-treated and untreated fruits. Continuous exposure to propylene also stimulated respiration in inimature fruits of rin, a nonripening mutant. Although respiration reached rates similar to those during the climacteric of comparable normal fruits there was no change in endogenous ethylene production which remained at a low level. Internal ethylene concentrations in attached 45 to 75% mature fruits of rin and a normal strain were similar. It is suggested that the onset of ripening in normal tomato fruit is not controlled by endogenous ethylene, although increased ethylene production is probably an integral part of the ripening processes.In commercial practice, tomato fruits are harvested at the mature green stage to facilitate shipment. Satisfactory nondestructive indices of maturity are not available for tomatoes, and commercial consignments usually comprise fruits of a wide range of physiological ages. In other immature climacteric fruits, e.g., bananas and melons, uniform ripening can be achieved by treating the fruit with ethylene (8). However, treatment of immature tomato fruits with ethylene even at high concentrations, does not result in uniform ripening. although ripening in individual fruits is advanced. Lyons and Pratt (5) showed that continuous treatment with 1000 -dl/l ethylene in air reduced the time to ripen by about one-half in fruit picked at from 64 to 93 of the total growth period.At 20 C, the commencement of natural ripening in tomato fruits is indicated by a simultaneous increase in respiration and ethylene production. Red or orange pigments usually appear '

No abstract

Two mutants, rin and nor, which grow normally but produce nonripening fruits have also been reported (7,8). Physiological studies with rin have shown that developing fruits contain low levels of ethylene similar to those in a normal strain and eventually turn yellow on the plant or following detachment (3, 5). Even when stored for long periods at temperatures suitable for normal ripening, rin fruits do not undergo the respiratory climacteric and the associated large increase in ethylene production found during ripening in normal tomato fruits (3).

Since ethylene application did not induce ripening in detached fruits of the nonripening mutant rin we initiated studies to determine possible involvement of other hormones. We proposed that the lack of ripening in mutant rin tomato fruit may result from a lack of abscisic acid or from excessive endogenous levels of cytokinin. Application of abscisic acid (3 X cultivar. These same investigators were able to alter the morphology of this mutant to a normal appearance of ABA application (4).This study was conducted to determine whether ABA applications would enhance ripening of normal fruit, and to ascertain whether ABA application might induce a normal ripening pattern in fruit ofthe rin mutant. Secondarily, we wanted to know whether the application of cytokinins might result in inhibition of the ripening pattern of normal tomato fruit, according to the suggestion of Varga and Bruinsma (11). MATERIALS AND METHODSUniform populations of fruits of Rutgers (Lycopersicon esculentum Mill.) and of a partially isogenic strain of rin were produced in a greenhouse as described previously (2, 6). Fruits were harvested at 80% of development. The upper layers of tissue of each stem scar were carefuly removed with a scalpel. The fruits were then transferred to a jar in which 1 ml of solution per 100 g fresh weight of fruit was infiltrated under a vacuum of about 160 mm Hg.A racemic mixture of cis , tratis-and trans, trans-ABA (Burdick Laboratories, Muskegon, Mich.) was applied at 3 x 10-s M and 10-1 M in 0.1 % (v/v) aqueous methanol. The control solution was 0.1 %lo aqueous methanol.BA at 4.44 X 10-4 M was prepared by autoclaving in distilled H20. Concentrations of 1.8 x 10-4 M, 4.44 X 10-M and 4.44 X 10-6 M BA were applied to the fruit. Autoclaved distilled H20 was used as a control.Each treatment was replicated five times. CO2 and ethylene evolution rates were measured daily (7). The time of first red color appearance was also noted for each fruit.Leaf senescence was measured as the rate of Chl breakdown in 7-mm diameter leaf disks taken from the tip leaflet of the newest fully expanded leaf. All procedures were carried out under sterile conditions. Each treatment contained 12 disks which were incubated in the dark at 22 C. Chl was extracted at 6 days after detachment by placing 2 disks into 5 ml of dimethylformamide. Each extraction was replicated 6 times. RESULTSABA at 3 x 10-5 and 10-s M reduced the time to initiate ripening in Rutgers fruit by about 50%7 as indicated by the onset of the respiratory climacteric and the associated rise in ethylene production and the development of red color (Fig. 1). Treatment with ABA also tended to increase the maximum rates of CO2 and ethylene production during ripening but these noted differences were not significant. Treatment of rin fruits with ABA did not significantly alter the rates of either CO2 or ethylene production or cause any changes in color (Fig. 2). BA treatment did not effect any significant changes in the time to the onset of ripening or the rates of CO2 and et...