Fruit abscission and ethylene production of four blackberry cultivars (Rubus spp.)

In all cultivars the force required to harvest fruit declined during ripening. The fruit retention strength (FRS) of ripe fruit varied between cultivars with ‘Ashton Cross’ and ‘Chehalem’ being easier to remove than ‘Bedford Giant’ or ‘Oregon Thornless’. The cultivars ‘Ashton Cross’ and ‘Oregon Thornless’ showed no increase in ethylene production during fruit ripening whereas ‘Bedford Giant’ and ‘Chehalem’ had increased rates of ethylene production (EPR) in the ripe fruit. Exogenous ethylene accelerated abscission, ethylene production and pigment changes in ‘Ashton Cross’ fruit at all stages of development. 1-amino-cyclopropane-1-carboxylic acid (ACC) supplied to fruit at all stages of development was converted to ethylene at levels in excess of those found naturally. The differences between cultivars are discussed with reference to the role of ethylene in both machine harvesting and post-harvest storage of blackberry fruit.     

Superoxide dismutase and catalase activities in apple fruit during ripening and post‐harvest and with special reference to ethylene

Oxidative stress is involved in many biological systems, among which are fruit ripening and senescence. Free radicals play an important role in senescence and ageing processes. Plants have evolved antioxidative strategies in which superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) are the most efficient antioxidant enzymes, influencing patterns of fruit ripening. Variations in total SOD and CAT activities were determined at regular intervals during ripening and senescence in on‐tree and cold‐stored apple fruits of the cultivars Fuji and Golden Delicious. In all fruits, internal ethylene concentration was also measured. The results suggest that the onset of ripening, signalled by ethylene burst, is closely related to SOD and CAT activities. In on‐tree fruits the climacteric peak in ethylene was associated with the peaks of SOD and CAT activity in both cultivars. Quite different results were obtained in cold‐stored fruits: Ethylene concentration increased in both cultivars during the storage. CAT activity doubled in both cultivars. SOD activity decreased in Golden Delicious and peaked in Fuji.     

Recent Advances in the Regulation of Citric Acid Metabolism in Citrus Fruit

The regulation of citric acid metabolism during fruit ripening has a major impact on the production of high-quality fruit. The impact of citric acid on organoleptic fruit quality attributes, fruit storage performance and the synthesis of several secondary metabolites has led to an exponential increase in research efforts during the last two decades. Recent research has focused on the relationship among citric acid biosynthesis, transportation, storage, and utilization. Among citrate metabolic processes, activities of a proton pump, especially the plasma membrane H⁺-ATPase on tonoplast and citrate catabolism in cytosol play important roles in the regulation of citrate accumulation in cell vacuoles. Moreover, we highlight recent advances and provide an overview of citrate metabolism, postharvest physiology of citrate metabolism, and the influence of agro-climatic factors on citrus fruits. It is the first review that provides a comprehensive model for citrate metabolism in citrus fruit juice sacs. We anticipate that this model for the regulation of citrate metabolism will facilitate the study of fruit acidity in citrus and other nonclimacteric fruits.     

Formation of Pungent Principles in Fruits of Sweet Pepper,Capsicum annuum L. var. grossum during Post-harvest Ripening under Continuous Light

Pungent principles (Capsaicinoid(s)) were found to be produced in fruits of sweet pepper, Capsicum annuum L. var. grossum, during post-harvest ripening under continuous light. The initial formation was observed after 4 days’ ripening. After 7 days’ ripening, the capsaicinoids content in placenta increased to 12.9 μg per fruit, which was 2.5-fold of that in pericarp. No pungent principles were detected in fruits during ripening in the dark and in seeds under continuous light. In placenta, the formation of dihydrocapsaicin and nordihydrocapsaicin which are the vanillylamides of saturated branched fatty acids was higher than that of capsaicin which is the vanillylamide of an unsaturated one. Remarkable formation and accumulation of carotenoid were also observed during post-harvest ripening under continuous light.     

Peach (Prunus persica) fruit response to anoxia: reversible ripening delay and biochemical changes

The use of modified atmospheres has been successfully applied in different fruits to delay the ripening process and to prevent physiological disorders. In addition, during normal ripening, hypoxic areas are generated inside the fruit; moreover, anaerobic conditions may also arise during fruit post-harvest storage and handling. In consequence, the fruit is an interesting model to analyze the metabolic modifications due to changes in oxygen levels. In this work, a 72 h anoxic treatment by using an N(2) storage atmosphere was applied to peaches (Prunus persica L. Batsch) after harvest. Ripening was effectively delayed in treated fruits, preventing fruit softening, color changes and ethylene production. Metabolic changes induced by anoxia included induction of fermentative pathways, glycolysis and enzymes involved in both sucrose synthesis and degradation. Sucrose, fructose and glucose contents remained unchanged in treated fruit, probably due to sucrose cycling. Sorbitol was not consumed and citrate was increased, correlating with citric acid cycle impairment due to O(2) deprivation. Malate content was not affected, indicating compensation in the reactions producing and consuming malate. Changes in malic enzymes and pyruvate orthophosphate dikinase may provide pyruvate for fermentation or even act to regenerate NADP. After fruit transfer to aerobic conditions, no signs of post-anoxia injury were observed and metabolic changes were reversed, with the exception of acetaldehyde levels. The results obtained indicate that peach fruit is an organ with a high capacity for anoxic tolerance, which is in accord with the presence of hypoxic areas inside fruits and the fact that hypoxic pre-treatment improves tolerance to subsequent anoxia.     

Cloning of FaPAL6 gene from strawberry fruit and characterization of its expression and enzymatic activity in two cultivars with different anthocyanin accumulation

The accumulation of anthocyanin pigments is one of the most important traits that turn strawberry fruit attractive to consumers. During ripening, strawberry fruit color development is associated to anthocyanin synthesis through the phenylpropanoid pathway. Phenylalanine ammonia-lyase (PAL) is a key enzyme in this pathway, having a determining role in strawberry fruit quality. In this work, we studied the level of anthocyanins during fruit ripening of two cultivars that differ in color development (Camarosa and Toyonoka). Toyonoka showed a lower anthocyanin accumulation that was limited to external fruit tissue, while Camarosa accumulated higher amount of anthocyanins in both internal and external sections. In addition, we cloned a full-length gene (FaPAL6) and analyzed its expression in different strawberry plant tissues. The expression of this gene is fruit specific, and increases during fruit ripening in both cultivars along with anthocyanin accumulation. The mRNA level of FaPAL6 was higher in Camarosa. PAL enzyme activity increased at similar rates in both cultivars at early ripening stages, but at the end of ripening PAL activity diminished in Toyonoka while it rose markedly in Camarosa. PAL activity was higher in internal fruit tissue, showing no correlation with anthocyanin level of the same section in both cultivars. The higher FaPAL6 expression and activity detected in Camarosa could be associated to the enhanced anthocyanin accumulation found in this cultivar.     

Changes in the Alkaloid Content of Developing Fruits of Tomato (Lycopersicon esculentum Mill.): I. ANALYSES OF CULTIVARS AND MUTANTS WITH DIFFERENT RIPENING CHARACTERISTICS

Normal ripening red-, orange- and yellow-fruited cultivars oftomato showed similar patterns of fruit growth and tomatineaccumulation to those of non-ripening mutants. In all fruits,the tomatine concentration declined continuously from an earlystage although the absolute amount per fruit showed a biphasicpattern of accumulation and decline. The turning point' occurredat an earlier developmental stage in normal fruits than in mutants.Normal fruits also had a lower initial and higher final tomatinecontent than mutants on a per fruit basis although, on a unitweight basis, their initial concentration was higher and finalconcentration lower. Small, prematurely-ripened red fruits hadalkaloid levels intermediate between large, unripe, green fruitsand large, ripe, red fruits. It is concluded that growth andripening processes may both contribute to the decline in fruittomatine. Key words: Tomato, Fruit ripening, Tomatine     

Tomato fruit continues growing while ripening,affecting cuticle properties and cracking

Fruit cuticle composition and their mechanical performance have a special role during ripening because internal pressure is no longer sustained by the degraded cell walls of the pericarp but is directly transmitted to epidermis and cuticle which could eventually crack. We have studied fruit growth, cuticle modifications and its biomechanics, and fruit cracking in tomato; tomato has been considered a model system for studying fleshy fruit growth and ripening. Tomato fruit cracking is a major disorder that causes severe economic losses and, in cherry tomato, crack appearance is limited to the ripening process. As environmental conditions play a crucial role in fruit growing, ripening and cracking, we grow two cherry tomato cultivars in four conditions of radiation and relative humidity (RH). High RH and low radiation decreased the amount of cuticle and cuticle components accumulated. No effect of RH in cuticle biomechanics was detected. However, cracked fruits had a significantly less deformable (lower maximum strain) cuticle than non‐cracked fruits. A significant and continuous fruit growth from mature green to overripe has been detected with special displacement sensors. This growth rate varied among genotypes, with cracking‐sensitive genotypes showing higher growth rates than cracking‐resistant ones. Environmental conditions modified this growth rate during ripening, with higher growing rates under high RH and radiation. These conditions corresponded to those that favored fruit cracking. Fruit growth rate during ripening, probably sustained by an internal turgor pressure, is a key parameter in fruit cracking, because fruits that ripened detached from the vine did not crack.     

Phosphofructokinase and ripening in lycopersicon esculentum fruits

The relative activity and the kinetic properties of phosphofructokinase (PFK) during the various stages of tomato ripening were investigated. There were no significant changes in the extractable activity of the enzyme during ripening but there was an apparent change in the molecular form of the enzyme as the fruits entered the climacteric and senescence stages. While the enzyme extracted from preclimacteric fruit existed solely in an oligomeric form, that extracted from fruits in the later stages of ripening was present as a mixture of the monomeric and oligomeric forms. Changes in the regulatory properties of the enzyme extracted at the various stages of ripening were explicable in terms of the dissociation of the oligomeric form of the enzyme to smaller units. PFK from the preclimacteric fruit is more resistant to inhibition by citrate and salts than the enzyme from the post climacteric fruit. On the other hand, the preclimacteric enzyme is stimulated by Pi and ADP while the post climacteric enzyme is not. The significance of these effects in relation to the physiology of tomato ripening and senescence is discussed.     

The comparison of protease activity and total protein in three cultivars of kiwifruit of Northern Iran during fruit development

This study, for the first time, investigated the total protein changes and protease activity pattern of three cultivars of kiwifruit including Abbott, Allison and Hayward, cultivated in the north of Iran, during 6 months of fruit development from July to December 2008. During the last month of sampling, fruits were stored in ambient temperature. According to the result of fruit extracts, pattern of changes in total protein concentration showed three significant steps: low concentration of protein during the early stages of fruit development until middle of July for Allison and Hayward and early August for Abbott, increasing protein concentration until middle of October for Allison and Hayward and late October for Abbott, and steady state level of protein concentration until harvesting time. During storage time of fruits, all three cultivars showed increasing level of total protein concentration. Among the cultivars, Hayward and Allison showed the lowest and highest total protein concentration, respectively. Protease activity showed increasing pattern in all of the investigated cultivars significantly until harvesting time. During postharvest time, Hayward did not show any significant change in protease activity but, the other two cultivars had increasing pattern from 10 to 20th of storage and then decreased significantly. Among the cultivars, Abbott showed the lowest and Allison the highest level of total protease activity at harvesting and postharvesting time. SDS-PAGE, ion-exchange chromatography and zymogram native-PAGE of fruits extraction showed that dominant protein and protease activity in these cultivars during fruit development and ripening process is related to actinidin.     

Changes in the antioxidative systems in mitochondria during ripening of pepper fruits

The presence of enzymes of the ascorbate–glutathione cycle was studied in mitochondria purified from green and red pepper (Capsicum annuum L.) fruits. All four enzymes, ascorbate peroxidase (APX; EC 1.11.1.11), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione reductase (GR; EC 1.6.4.2) were present in the isolated mitochondria of both fruit ripening stages. The activity of the reductive ascorbate–glutathione cycle enzymes (MDHAR, GR and DHAR) was higher in mitochondria isolated from green than from red fruits, while APX and the antioxidative enzyme superoxide dismutase (SOD; EC 1.15.1.1) were higher in the red fruits. The levels of ascorbate and L-galactono-γ-lactone dehydrogenase (GLDH; EC 1.3.2.3) activity were found to be similar in the mitochondria of both fruits. The higher APX and Mn-SOD specific activities in mitochondria from red fruits might play a role in avoiding the accumulation of any activated oxygen species generated in these mitochondria, and suggests an active role for these enzymes during ripening.     

Differences in sucrose metabolism relative to accumulation of bird-deterrent sucrose levels in fruits of wild and domestic Vaccinium species

We examined variability in sucrose levels and metabolism in ripe fruits of wild and domestic Vaccinium species and in developing fruits of cultivated blueberry (V. ashei and V. corymbosum). The objective was to determine if sufficient variability for fruit sucrose accumulation was present in existing populations to warrant attempts to breed for high-sucrose fruit, which potentially would be less subject to bird predation. Threefold differences in fruit sucrose concentration were found among Vaccinium species, ranging from 19 to 24 mg (g fresh weight)^?1 in V. stamineum and V. arboreum to approximately 7 mg (g fresh weight)^?1 in cultivated blueberry (V. ashei and V. corymbosum) and V. darrowi. Hexose levels were similar among species, ranging from 90 to 110 mg (g fresh weight)^–1, and glucose and fructose were present in equal amounts. Soluble acid invertase (EC 3.2.1.26) activity was negatively correlated with fruit sucrose concentration. There was no apparent correlation between fruit sugar concentration and either sucrose synthase (EC 2.4.1.13) or sucrose phosphate synthase (EC 2.4.1.14) activities, both of which were low for all species studied. Developmental increases in fruit sugar levels of cultivated blueberry followed a pattern similar to that observed in fruit fresh weight accumulation. Hexose concentrations ranged from 6 to 30 mg (g fresh weight)^?1 during the first 60 days after anthesis. Between 60 days and fruit ripening (80 days), hexose levels rose from 30 to 80 mg (g fresh weight)^?1. Sucrose was not detected in fruits until ripening, when low levels were found. Insoluble acid invertase activity was relatively high early in fruit development, decreasing as soluble acid invertase activity increased. Between 60 days and fruit ripening, soluble acid invertase activity increased from 3 to 55 μmol (g fresh weight)^–1 h^–1. Both sucrose synthase and sucrose phosphate synthase activities were low throughout development. The extent of sucrose accumulation in fruits and the degree of variability for this trait among Vaccinium species support the feasibility of developing high sucrose fruits, which would be a potentially valuable addition to current strategies of minimizing crop losses to birds.     

Patterns of pigment changes in apple fruits during adaptation to high sunlight and sunscald development

Reflectance spectra of four apple (Malus domestica Borkh.) cultivars were studied and chlorophyll, carotenoid, anthocyanin and flavonoid content in sunlit and shaded peel was determined. In all cases sunlit peel accumulated high amounts of phenolics (flavonoid glycosides). Adaptation to strong sunlight of an apple cultivar with limited potential for anthocyanin biosynthesis (Antonovka) was accompanied by a decrease in chlorophyll and a significant increase in total carotenoid content. The increase in carotenoids also took place in sunlit sides of the Zhigulevskoye fruits, accumulating high amounts of anthocyanins, but chlorophyll content in sunlit peel was higher than that in shaded peel. Significant increases in carotenoids and anthocyanins were detected during fruit ripening when chlorophyll content fell below 1.5–1.8 nmol cm^–2. Chlorophyll in sunlit fruit surfaces of both cultivars was considerably more resistant to photobleaching than in shaded (especially of Zhigulevskoye) sides. Induced by sun irradiation, the photoadaptive responses were cultivar-dependent and expressed at different stages of fruit ripening even after storage in darkness. The development of sunscald symptoms in susceptible apple cultivars (Granny Smith and Renet Simirenko) led to a dramatic loss of chlorophylls and carotenoids, which was similar to that observed during artificial photobleaching. The results suggest that apple fruits exhibit a genetically determined strategy of adaptation of their photoprotective pigments to cope with mediated by reactive oxygen species photodynamic activity of chlorophyll under strong solar irradiation. This includes induction of synthesis and accumulation of flavonoids, anthocyanins and carotenoids that could be expressed, if necessary, at different stages of fruit development     

Polyamine levels in pollinated and auxin-induced fruit of tomato (Lycopersicon esculentum) during development

The changes taking place during fruit development in the concentration of the 3 polyamine fractions, i.e. free, perchloric acid-soluble conjugates and perchloric acid-insoluble bound polyamines, were analyzed in tomato fruits ( Lycopersicon esculentum Mill, cv. F121) induced to set by either pollination or auxin application. Before the onset of cell division, total polyamines were 50% higher in auxin-treated fruits than in pollinated ones, most of the polyamines being found as perchloric acid-soluble conjugates in both fruit set treatments. At the onset the level of polyamines in both fruit types was 100 times higher than during cell expansion or ripening. The highest polyamine found during cell division was perchloric acid-soluble conjugated spermidine in both fruit set treatments. After cell division, polyamine concentration was similar in both fruit set treatments. The concentration of polyamines in the jelly was similar in pollinated and auxin-induced fruits during cell expansion but not during ripening. At the onset of ripening there was an increase of one order of magnitude in the concentration of perchloric acid-insoluble bound putrescine in the jelly of pollinated fruits. Polyamines were more than 5-fold higher in unpollinated ovaries than in fruits induced to set by either pollination or auxins. It is suggested that pollinated and parthenocarpic fruits differ in their polyamine metabolism during the initial stages of development, but not after cell division. It is also suggested that polyamines undergo rapid turnover during cell division. Perchloric acid-insoluble bound putrescine might play a role in seed formation in tomatoes.     

Maturation and Ripening of Fruit ofAmelanchier alnifoliaNutt. are Accompanied by Increasing Oxidative Stress

The extent of oxidative stress during ripening of saskatoon(AmelanchieralnifoliaNutt.) fruit was examined. Lipid peroxidation duringfruit development from the mature green to the fully ripe (purple)stage was evidenced by the accumulation of ethane and 2-thiobarbituricacid reactive substances. Fruit polar lipid and free fatty acidconcentrations also declined during ripening. Moreover, thedouble bond index of fatty acids in the polar lipid fractionfell during ripening, reflecting a progressive increase in thesaturation of membrane lipids. This increase in saturation waspartly due to a 65% decline in the concentration of linolenicacid. Activities of superoxide dismutase (SOD) and catalase(CAT) fell about 4-fold and 18-fold, respectively, during development,indicating higher potential for the accumulation of cytotoxicH₂O₂. Peroxidase activity remained relatively low and constantfrom the mature green to the dark red stage of development,then increased towards the end of ripening as fruits turnedpurple. Lipoxygenase (LOX) activity increased 2.5-fold fromthe mature green to the fully ripe stage. Tissue prints showedLOX to be present throughout fruit development and Western analysisrevealed that the increase in activity during ripening was dueto increased synthesis of the enzyme. Collectively, these resultsprovide evidence that ripening of this climacteric fruit isaccompanied by a substantial increase in free-radical-mediatedperoxidation of membrane lipids, probably as a direct consequenceof a progressive decline in the enzymatic systems responsiblefor catabolism of active oxygen species. The role of glutathione-mediatedfree-radical scavenging was also examined as a potential systemfor coping with this increased oxidative stress. Concentrationsof reduced and oxidized glutathione (GSSG) increased 2-foldand GSSG increased as a percentage of total glutathione, reflectingthe increase in oxidative status of fruits during ripening.Tissue prints of glutathione reductase (GRase) and transferase(GTase) showed these enzymes to be distributed throughout thepericarp at all stages of fruit development. GRase and GTaseactivities rose sharply during the later stages of fruit ripening,correlating well with substantial increases in the levels ofboth enzymes. Hence, the glutathione-mediated free-radical scavengingsystem was up-regulated towards the end of ripening, perhapsin response to the increasing oxidative stress resulting fromthe accumulation of lipid hydroperoxides from increased LOXactivity, in conjunction with a decline in SOD/CAT activities.Copyright1998 Annals of Botany Company Amelanchier alnifoliaNutt.; saskatoon fruit; ripening; oxidative stress.     

草莓果实发育成熟过程中糖苷酶和纤维素酶活性及细胞壁组成变化

以丰香和红丰草莓为试材,对果实发育成熟过程中细胞壁水解酶活性和细胞壁成份变化进行了研究．结果表明：半乳糖苷酶和α-甘露糖苷酶活性随草莓果实成熟而提高,葡萄糖苷酶活性不随草莓果实成熟而提高．随着果实发育成熟,纤维素酶活性、果胶酶活性不断提高．果实中未检测到内切多聚半乳糖醛酸酶活性,外切多聚半乳糖醛酸酶活性变化不随果实成熟软化而提高．随果实发育成熟,细胞壁中可溶性果胶和半纤维素增加,而离子结合果胶和共价结合果胶及纤维素减少．