Gabriel O. Sozzi

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.

Gibberellic Acid, Synthetic Auxins, and Ethylene Differentially Modulate α-l-Arabinofuranosidase Activities in Antisense 1-Aminocyclopropane-1-Carboxylic Acid Synthase Tomato Pericarp Discs

α-l-Arabinofuranosidases (α-Afs) are plant enzymes capable of releasing terminal arabinofuranosyl residues from cell wall matrix polymers, as well as from different glycoconjugates. Three different α-Af isoforms were distinguished by size exclusion chromatography of protein extracts from control tomatoes (Lycopersicon esculentum) and an ethylene synthesis-suppressed (ESS) line expressing an antisense 1-aminocyclopropane-1-carboxylic synthase transgene. α-Af I and II are active throughout fruit ontogeny. α-Af I is the first Zn-dependent cell wall enzyme isolated from tomato pericarp tissues, thus suggesting the involvement of zinc in fruit cell wall metabolism. This isoform is inhibited by 1,10-phenanthroline, but remains stable in the presence of NaCl and sucrose. α-Af II activity accounts for over 80% of the total α-Af activity in 10-d-old fruit, but activity drops during ripening. In contrast, α-Af III is ethylene dependent and specifically active during ripening. α-Af I released monosaccharide arabinose from KOH-soluble polysaccharides from tomato cell walls, whereas α-Af II and III acted on Na2CO3-soluble pectins. Different α-Af isoform responses to gibberellic acid, synthetic auxins, and ethylene were followed by using a novel ESS mature-green tomato pericarp disc system. α-Af I and II activity increased when gibberellic acid or 2,4-dichlorophenoxyacetic acid was applied, whereas ethylene treatment enhanced only α-Af III activity. Results suggest that tomato α-Afs are encoded by a gene family under differential hormonal controls, and probably have different in vivo functions. The ESS pericarp explant system allows comprehensive studies involving effects of physiological levels of different growth regulators on gene expression and enzyme activity with negligible wound-induced ethylene production.

Improvement of postharvest storage quality of ‘Red Clapp’s’ pears by treatment with 1-methylcyclopropene at low temperature

Summary ‘Red Clapp’s’ is a red pear (Pyrus communis L.) cultivar having a short storage life. ‘Red Clapp’s’ pears were treated with 0 (control), 0.1 or 0.2 µl l–1 1-methylcyclopropene (1-MCP) at 0–1°C for 24 h and stored at –0.5°C for 15, 30, 45 or 60 d. After cold storage, fruit were allowed to ripen at 20°C for 1, 7 or 14 d. No differences were detected between control and 1-MCP-treated fruit 1 d after cold storage. 1-MCP appeared to have a very limited effect on slowing ripening and preventing physiological disorders when applied at 0.1 µl l–1. In contrast, pears treated with 0.2 µl l–1 1-MCP softened at a noticeably lower rate than control fruit after 7 d at 20°C. Fruit firmness was considered appropriate for pear consumption (18–26 N) after 14 d at 20°C, irrespective of the time stored at –0.5°C. Physiological disorders (watery and core breakdown) were prevented during ripening at 20°C when 0.2 µl l–1 1-MCP was applied. No differences were detected in soluble solids content and titratable acidity between treated and untreated fruit after 45 and 60 d of storage at –0.5°C plus 1 or 7 d ripening at 20°C. Results suggest that 0.2 µl l–1 1-MCP, combined with cooling techniques, delay ‘Red Clapp’s’ pear ripening and maintain quality during storage, and thus is a promising alternative for overcoming problems associated with the marketing of ‘Red Clapp’s’ pear.

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.

Nutritional Quality of fruits and vegetables

The nutritional value of fruits and vegetables depends on their composition, which shows a wide range of variation depending on the species, cultivar, and maturity stage. This chapter describes the general characteristics of the components of fruits and vegetables, related to their benefits as food sources. There are two types of acids, namely aliphatic (straight chain) and aromatic acids. The most abundant acids in fruits and vegetables are citric and malic (both aliphatic) acids. However, large amounts of tartaric acid occur in grapes. Malic acid is the major component in oranges and apples. The acid content of fruits and vegetables generally decreases during maturation. Aromatic organic acids occur in several fruits and vegetables, but in very low concentrations. Benzoic acid occurs in cranberries, quinic acid in bananas, and chlorogenic acid in potatoes. In general, vegetables are a richer source of minerals than fruits, but both vegetables and fruits are considered nutrient-dense foods in that they provide substantial amounts of micronutrients, such as minerals and vitamins, but relatively few calories. Minerals have both direct and indirect effects on human health. The direct effects of minerals focus on the consequences of their consumption on human nutrition, while the indirect effects refer to their incidence in fruit and vegetable quality and subsequent consumer acceptance. From a direct nutrition standpoint, potassium has the biggest presence in both fruits and vegetables, but nitrogen and calcium show major impacts on horticultural crop quality.

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

Improvement of caper (Capparis spinosa L.) seed germination by breaking seed coat-induced dormancy

Different dormancy-breaking pretreatments were assessed in order to improve germination of caper (Capparis spinosa L.) seeds. High germination percentages were obtained using concentrated sulfuric acid, followed by either a 90-min soaking procedure in a 100 ppm gibberellin (GA4 + 7) solution, or adding 0.2% potassium nitrate to the test substrate. Results obtained by means of a surgical treatment clearly suggest that the dormancy of the caper seed is imposed by its covering structures.

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.

Physiological changes in boysenberry fruit during growth and ripening

Summary Boysenberries (Rubus hybrid) were harvested at five developmental stages (green, “turning”, pink, red and purple) to study changes associated with flavour, colour and firmness, with a particular focus on the different enzymes involved in chlorophyll degradation or cell wall degradation. The level of reducing and non-reducing sugars increased 109- and 52-fold, respectively, between the “turning” and the purple stage. Titratable acidity increased by 84% between the green and the pink stage, but dropped by 41% between the red stage and full ripening. Total phenols displayed their highest values in green and “turning” fruit. Chlorophyll a and b degradation occurred mainly during the early stages of development, and was paralleled by a 2.3-fold increase in chlorophyllase activity and a 5-fold increase in Mg-dechelatase activity between the green and the red stages. Chlorophyll peroxidase activity was high at the green stage, but did not change significantly after the “turning” stage. This is the first report on the activity of chlorophyll-degrading enzymes in Rubus spp. fruits. Anthocyanins increased 11-fold between the “turning” and the pink stages, and an additional eight-fold between the pink and the purple stages. Fruit firmness decreased noticeably during ripening, with a concomitant 10.75-fold increase in polygalacturonase activity, beginning at the “turning” stage. Endo- -1,4-glucanase and -galactosidase activities rose 9.2- and 6.7-fold, respectively, after the pink stage and paralleled the major softening process taking place between the pink and purple stages, when fruit firmness decreased from 3.83 N to 0.29 N. Pectin methylesterase activity was high in pink and red fruit, but decreased by 21% as the fruit turned from red to purple. This is the first report on cell wall enzyme activities whose combined action might be required for the breakdown of natural cell wall substrates during ripening in boysenberry, as happens in other soft fruits.