Adela A. Fraschina

Ripening-related changes in ethylene production, respiration rate and cell-wall enzyme activity in goldenberry (Physalis peruviana L.), a solanaceous species

Abstract The ripening of goldenberry (Physalis peruviana) is associated with a conspicuous climacteric rise in carbon dioxide and ethylene production. Its respiration rate and ethylene biosynthesis can be classified as extremely high. Ethylene yields between 7 and 24 nmol h−1 per g in the ripe/overripe stages thus compare favorably with production rates previously reported for tomato fruit. As the fruit color turns from green (chlorophyll) to yellowish orange (carotenoids) and a progressive softening occurs, several cell-wall enzyme changes arise. Pectinmethylesterase and α- and β-galactosidase reach activity levels similar to those in tomato fruit. Pectinmethylesterase and α-galactosidase increase toward the ripe stage. α-Arabinofuranosidase and β-glucosidase show lower activities but with an increasing pattern during ripening. On the other hand, polygalacturonase and α-glucosidase activities are hardly noticeable.

Effect of a high-temperature stress on endo-β-mannanase and α- and β-galactosidase activities during tomato fruit ripening

Abstract Tomato fruit show physiological disorders when exposed to temperatures at or above 30 °C. It has been suggested that the α- and β-galactosidases (α- and β-Gal), as well as the endo-β-mannanase could play roles during fruit ripening. Their pattern of activities was followed in detached tomato fruit, and the degree of inhibition of the activity at high temperatures was evaluated. The potential resumption of the enzyme activity when fruits were transferred to a room-temperature environment was also studied. Mature-green fruits were incubated at: (a) 36 °C for 2 days, (b) 40 °C for 2 days, or (c) 40 °C for 2 days +36 °C for another 2 days. After heat treatments, fruits were transferred to a 21 °C dark environment. Control fruit were stored at 21 °C. In the control fruit, activity was higher for α-Gal than for β-Gal and revealed slightly increasing patterns toward the red-ripe stage. Endo-β-mannanase activity was not detected in mature-green tomatoes but appeared at the breaker stage and rose rapidly, reaching constant values at the red-ripe stage. The firmness and enzymatic activities of fruits initially treated at 36 °C for 2 days were similar to those of the control group. Galactosidase activity decreased in tomatoes incubated at 40 °C for 2 days; and in those whose heat treatment was extended another 2 days at 36 °C the α-and β-Gal reached a minimum of 1 5 and 1 25 , respectively, of the initial activity on the fourth day. The activity of the endo-β-mannanase could be detected only 6 days after the fruit had been transferred to a 21 °C environment and increased slowly up to 24% of that attained by the control group. α-Gal showed a low rate of recovery but β-Gal activity recovered after 16 days at 21 °C. Results could be associated with an active role of these enzymes on the fruit softening process.

Delayed ripening of ‘Bartlett’ pears treated with nitric oxide

Summary Preclimacteric European pears (Pyrus communis L. ‘Bartlett’) were either untreated or treated with 10 μl l–1 nitric oxide (NO) at 20°C for 2 h and then kept at 20°C. Other lots were treated with 0, 10 or 50 μl l–1 NO for 12 h. In pears treated with 10 μl l–1 NO for 2 h the ethylene climacteric was delayed 4 d, maximum ethylene production decreased by 28% and firmness and colour changes had a 2 d delay. An additional treatment with 10 μl l–1 NO after 4 d decreased ethylene production even further (48%). In contrast, pears treated with 50 μl l–1 NO for 12 h displayed a 719-fold increase in ethylene biosynthesis 1 d following treatment. This sharp increase in ethylene emission, characteristic of a stress response, did not accelerate the normal progress of ripening-related events. In fruit treated with 10 and 50 μl l–1 NO for 12 h, yellowing was delayed 2 d in comparison with control fruit while the softening rate was almost unaffected. Thus, different ripening processes are not influenced in the same fashion by NO treatments. Results suggest a time × concentration effect when NO is applied.

Controlled-atmosphere storage of tomato fruit: low oxygen or elevated carbon dioxide levels alter galactosidase activity and inhibit exogenous ethylene action

The effects of 3% O2 and 20% CO2, both alone and together with 100 µg g−1 C2H4, on ethylene production, chlorophyll degradation, carotenoid biosynthesis and α- and β-galactosidase activity in breaker tomato (Lycopersicon esculentum Mill) fruit were investigated. The low O2 and high CO2 atmospheres prevented the rise in ethylene production, total carotenoid and lycopene biosynthesis and α- and β-galactosidase activity and slowed down chlorophyll degradation and loss of firmness (P < 0.05). These suppressive effects were not reversed, or only in part – in the case of chlorophyll breakdown – by addition of 100 µg g−1 C2H4 to said controlled atmospheres. After transfer from the various atmospheres to air, flesh firmness decreased and ethylene production, total carotenoids, lycopene and β-galactosidase II activity increased but these parameters were, in all cases, still significantly different from those of fruit held in air. Keeping tomatoes in controlled atmospheres, even in the presence of ethylene, had marked residual effects. Results suggest an antagonism between elevated CO2/low O2 and exogenous ethylene which could determine most of the ripening parameter behaviour under controlled-atmosphere storage, though a direct regulatory mechanism by O2 and/or CO2 should not be discarded. © 1999 Society of Chemical Industry

Ethylene and Glycosidase Promotion in GA3- and IAA-treated Tomato Fruit (Lycopersicon esculentum Mill.)

Transient (1 h) treatment of breaker tomatoes (Lycopersicon esculentum Mill, cv. Bonanza) with exogenous GA 3 or IAA at a high concentration (20 mM) resulted in a two- to four-fold increase compared with the control in ethylene biosynthesis during a 9-day experiment. This sharp increase in ethylene emission is characteristic of a stress response. Both phytohormones promoted the activity of 1-aminocyclopropane-I-carboxylate synthase that probably accounts for most of the enhanced ethylene synthesis. GA 3 and IAA also stimulated total α- and (3-galactosidase and α-L-arabinofuranosidase activity but showed some potential to delay ripening parameters, among them, fruit softening, chlorophyll loss, and total carotenoid synthesis. GA 3 - or IAA-treated fruit did not respond to exogenous 100 ppm C 2 H 4 with an increase of autocatalytic ethylene production. Moreover, GA 3 or IAA applied alone showed a faster increase in ethylene biosynthesis than that achieved by exogenous C 2 H 4 . The combination of GA 3 and C 2 H 4 -supplemented atmosphere did not result in synergistic effects on glycosidase activity except for a few cases. IAA-treated fruit exposed to C 2 H 4 -supplemented atmosphere did not promote additional glycosidase activity but rather seemed to have antagonistic effects on β-galactosidase during the first few days of the experiment. Glycosidase response to GA 3 and IAA treatments did not correlate with changes in tomato pericarp firmness, thus suggesting that some isoforms may have no role in tomato fruit softening.

The Free Proline Content of Water Stressed Maize Roots

Summary The relation of accumulation of free proline to different stress conditions was investigated in root tips of young plantules of Zea mays . The level of proline was found to increase as a consequence of drought treatments, and decrease to normal values when the seedlings were rewatered, and root growth reassumed. The accumulation of proline occurred in light or darkness, and even with restricted sugar supply. Other stress conditions, salinity, low temperature and abscisic acid treatment, also determined the accumulation of proline. The response of the two cultivars under study, differed when exposed to stress, and was not related to the degree of reduction in growth rate.

Assessment of different treatments for the concentration of three tomato fruit glycosidases from crude extracts

Ultrafiltration, (NH4)2SO4 addition to 80% saturation and lyophilization after desalting, were assessed as different methods for the concentration of tomato fruit α- and β-galactosidases and α-L-arabinofuranosidase. Lyophilization was the most effective giving 95%, 82% and 75% recovery of enzyme activities, respectively. These enzymes are stable when preserved after lyophilization or in concentrated crude extracts at −20 or −50°C even after extended storage, either in the presence or absence of trehalose.

Distribution of Some Nitrogen Compounds in Seedlings of Maize and Sunflower in Relation to Water Stress

Seedlings exposed to drought exhibit (1) an increase in free proline commonly associated with a decrease in growth and (2) a relative increase in soluble protein on a dry-weight basis. During stress, root growth is reduced, but not as completely as in the shoot. On recovery, the maize plumule initiates growth rapidly while the root remains depressed. No changes in hydroxyproline content were detected in soluble or insoluble fractions of root tissue. Relief of stress caused considerable transport of proline from the roots, suggesting that redistribution of nitrogen compounds plays an important role in seedling growth. A significant amount of proline is liberated from the roots into the external solution. This loss of solutes is related to the cessation of root growth when the seedlings are returned to conditions where water is available.