The Effect of Indole-3-acetic Acid and Other Growth Regulators on the Ripening of Avocado Fruits

Abstract

Observations were made of the effects of several plant regulators, indole-3-acetic acid, kinetin, abscisic acid, and gibberellic acid, as well as of extracts prepared from leaves and fruit stalks on the respiration pattern, ethylene production, and the number of days to ripen of avocado fruits (Persea americana Mill.).These substances were vacuum infiltrated to insure good penetration and distribution. Kinetin, abscisic acid, gibberellic acid, and the extracts had no effect on either ripening time or on the respiration pattern and ethylene production of the fruits. Indoleacetic acid, however, had a marked effect on ripening. At high concentrations (100 and 1000 aM), indoleacetic acid stimulated respiration and induced preclimacteric ethylene production, resulting in accelerated ripening of the fruits. At the low concentrations (1 and 10 gM), it delayed ripening of fruits and suppressed the climacteric respiration and ethylene production. The results reinforce several previous observations with other fruits that auxins may largely constitute 'resistance to ripening' and may be responsible for the lack of ripening shown by unpicked fruits.The inability of some fruits, notably the avocado, to ripen on the tree (3,7,8), coupled with the lack of response by freshly harvested fruits to ethylene treatment (16,20,23), have prompted several workers to propose the existence of a ripening inhibitor in attached fruits (3,7,8). This inhibitor is presumed to be formed in leaves of the parent tree and translocated to the fruit while still attached (3,7,8). Following harvest, the inhibitor is inactivated during the preclimacteric period and ripening is initiated by endogenously produced ethylene (14,16,20,23). Plant hormones have been shown to affect some aspects of fruit ripening. For example, indoleacetic acid has been reported to delay the onset of the climacteric in bananas (30) and pears (14), and both gibberellins and cytokinins have been shown to delay the degradation of Chl in ripening tomatoes (1) and orange peel (12).A growing body of information indicates that the ripening inhibitor may be an auxin (14,15,27 (14) with slight modifications. Pressure over the fruits was reduced to 260 mm Hg for 6 min and infiltration time was reduced to 5 min to minimize the development of anaerobic conditions. When intact fruits were used, the peduncle was removed to improve penetration of the infiltrated substances. Infiltrated fruit was compared with water-infiltrated as well as uninfiltrated fruit. In some experinents, fruits were cut in half; one half being infiltrated with a solution of the test substance and the other with water. On the average, an increase in weight of about 3 % was obtained from infiltration.Determination of CO2 and Ethylene. Fruits were placed singly in 1.8-liter jars at 20 C. Humidified air was passed at 70 ml/min and respiration followed with a Beckman infrared gas analyzer (Model 215A). Ethylene production was monitored automatically every 3 hr on an Aerograph HY-FI Model 600-D gas chromatograph us...

The effect of phytohormones on the growth, cellulose production and pellicle properties of Gluconacetobacter xylinus ATCC 53582

“…We observed that when G. xylinus was grown in the presence of IAA, pellicles were thin ( Figure 2A) and of low cellulose content ( Figure 2C). This result can be explained in context of a plantmicrobe interaction: elevated auxin levels in the plant delay ripening and senescence, 28,[48][49][50] as a result, the sugars available for bacterial cellulose synthesis will be lower compared to ripened fruit. Exogenous IAA impedes G. xylinus cellulose synthesis yet stimulates growth rate so that cellular density is at a peak when the fruit ripens and glucose becomes more readily available.…”

Treatment of Grape Berries, a Nonclimacteric Fruit with a Synthetic Auxin, Retards Ripening and Alters the Expression of Developmentally Regulated Genes

“…Experiments in which tomato fruit (climacteric) were used in culture (Cohen, 1996) have given further credence to earlier observations that elevated auxin levels can delay ripening. Auxins have also been shown to affect the ripening of a number of nonclimacteric fruit, including avocado (Tingwa and Young, 1975), bananas (Vendrell, 1969), pear (Frenkel and Dyck, 1973), and strawberry (Fruguriu anunussa L.; Given et al, 1988). Strawberries, in particular, provide a useful experimental system because the achenes, which are the source of the auxins involved in ripening, can be removed.…”

Factors associated with postharvest ripening heterogeneity of ‘Hass’ avocados (Persea americanaMill)

“…In addition to C 7 sugars as ripening inhibitors of the fruit while on the tree, endogenous levels of auxins in the fruit have been reported during the early seventies as the resistant factor in ripening of avocado [53,54]. The application of exogenous auxins to the fruit stimulated ethylene production and accelerated ripening, but if auxins are infused into the fruit tissue by the vascular system, ethylene levels are limited and ripening is inhibited.…”

“…Ripening processes are highly dependent on continuous protein synthesis to provide substrates/intermediates to key metabolic pathways such as ethylene biosynthesis and respiration [37]. The ripening process can be affected by many factors including: water movement, phytohormones, mineral nutrition, carbohydrates and ripening enzymes [38][39][40][41][42]. As a climacteric fruit, avocado ripening is characterized by an increase in the respiration rate accompanied by an increase in ethylene production.…”