Effects of high temperature coupled with high light on the balance between photooxidation and photoprotection in the sun-exposed peel of apple

The sun-exposed peel of 'Gala' apple with or without sunburn was compared in terms of photooxidation and photoprotection, and a controlled experiment was conducted to probe the initial responses of PSII to high light and high temperature. The content of carotenoids, lutein and xanthophylls on a chlorophyll basis was higher in the sunburned peel although they were lower expressed on a peel area basis. Significant loss of beta-carotene and neoxanthin was observed relative to chlorophylls in the sunburned peel. O(2) evolution rates and the activity of key enzymes in the Calvin cycle were lower in the sunburned peel, but the activity of these enzymes decreased to a lesser extent than the O(2) evolution rates. The activity of antioxidant enzymes in the ascorbate-glutathione cycle and the level of total ascorbate, total glutathione, and reduced glutathione were higher in the sunburned peel. However, the sunburned peel had higher H(2)O(2) and malondialdehyde contents. Fruit peels treated with high temperature (45 degrees C) alone showed a clear "K" step in their chlorophyll fluorescence transients whereas high temperature coupled with high light (1,600 mumol m(-2) s(-1)) led to the disappearance of the "K" step and a further decrease in F (V)/F (M) (similar to what was observed in the sunburned peel). We conclude that high temperature coupled with high light damages the PSII complexes at both the donor and acceptor sides. Although both the xanthophyll cycle and the antioxidant system are up-regulated in response to the photooxidative stress, this up-regulation does not provide enough protection against the photooxidation.     

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     

苹果日烧病程中果皮抗氧化系统与细胞超微结构的变化

以富士品种为试材研究了苹果果实日烧病程中果皮组织细胞膜脂过氧化、抗氧化酶类、酚类物质的变化规律,并用电镜观察细胞超微结构的变化.结果表明膜脂过氧化导致日烧发生并进一步使日烧程度加重.相应地,抗氧化酶类在果皮变白期活性激增,但是,细胞结构仍较完整,只是叶绿体膨胀、类囊体结构部分解体,线粒体周缘模糊,细胞质中含大量的空泡;以后果皮变褐,绿原酸、槲皮素、芦丁、杨梅酮积累,同时靠近上表皮几层细胞解体,由密集的电子致密物充塞,细胞壁加厚.     

高温强光胁迫对苹果果皮PPO活性的影响

苹果果实日烧是一种普遍发生的生理病害,最常见的特征之一就是在果实表面出现褐变。通常认为PPO与植物的酶促褐变密切相关。研究了自然和控制条件下,高温强光胁迫对果实PPO活性的影响,以便揭示高温强光胁迫下苹果果实褐变与PPO活性之间的联系。结果表明：高温和强光胁迫与果皮PPO活性变化密切相关。就树冠不同方位而言,西南方位是高温和强光胁迫最严重的区域,其外围裸露果实的PPO活性也最强。在一定范围内,随着处理温度和光照强度的升高,果皮PPO活性也逐渐增强。短时间剧烈升温能够引起PPO活性骤然上升。在同样程度的高温胁迫下,提高环境湿度有利于抑制果皮PPO活性,从而减轻褐变症状的发生。室内外试验一致证实：果实日烧褐变现象与高温强光胁迫下果皮组织PPO活性大幅度提高有直接关系。     

Polyphenol gene expression and changes in anthocyanins and polyphenols in the skin of ‘Braeburn’ apples after the autumn application of prohexadione-calcium

Prohexadione-calcium (Pro-Ca) transient inhibits 2-Oxoglutarate-dependent dioxygenases and causes significant changes in the flavonoid spectrum of apple. In the present study the influence of two autumn preharvest applications of Pro-Ca on the polyphenol metabolism in apple peel during the advanced maturation was investigated. Pro-Ca was sprayed in two doses, approximately five and 3 weeks before the technological maturity. Changes in the concentrations of hydroxycinnamic acids, dihydrochalcones, flavonols, flavanols and anthocyanins as well as their related gene expression and enzyme activities in the apple peel were monitored six times during the advanced maturation until the technological maturity of the fruits. To evaluate its influence on red coloration differences in the chromatic values a*, h° and L* between the treated and untreated apples were monitored. The parameters showed a temporary effect of Pro-Ca on the intensity of red coloration, which was not detected anymore at the technological maturity of apples. The application of Pro-Ca decreased the flavanone 3-hydroxylase activity and slightly inhibited activities of all the enzymes analyzed. Concomitantly, the concentrations of anthocyanins in the peel of the treated apples decreased, whereas the concentrations of hydroxycinnamic acids, dihydrochalcones and flavan 3-ols increased. Flavonol concentrations, however, remained unchanged. The expression of ANS, ANR, FGT and MYB10 was downregulated after the Pro-Ca treatment. The results indicate that the autumn application of Pro-Ca modulates the biosynthetic pathway resulting in distinct changes in the flavonoid composition in the apple peel of ‘Braeburn’ apples. However, the changes are temporary and are generally suspended during apple storage.     

Enzyme activity of the phenylpropanoid pathway as a response to apple scab infection

The study was performed on apple trees, ‘Golden Delicious' cv., which is a scab-susceptible cultivar. The phenolic content of apple fruit was determined in different parts of the peel. The phenolic compounds were analysed in the scab spot, in the tissue around the spot and in the healthy tissue. We determined the concentration of various phenolic compounds and related enzyme activities. Infection with the Venturia inaequalis fungus enhanced the metabolism of phenolic compounds at the scab spot, around the spot and in healthy peel. Compared with the healthy tissue and the tissue around the spot, the scab spot showed higher enzyme activity for all tested enzymes, except for dihydrochalcone 2′-O-glucosyltransferase, which had lower activity in the scab spot. In comparison to the healthy peel, the scab spot showed up to 3.4 times more hydroxycinnamic acids, up to 1.1 times more dihydrochalcones and up to 1.4 times more flavan-3-ols. In contrast, the healthy peel showed up to 1.6 times more flavonols than the scab spot.     

Improving photosynthetic performance and some fruit quality traits in mango trees by shading

Excess solar radiation under hot climate can lead to decline in photosynthetic activity with detrimental effects on growth and yield. The aim of this study was to evaluate the use of a transparent plastic roof as shading for diurnal changes in photosynthetic gas exchange, chlorophyll fluorescence, fruit set and quality of mango (Mangifera indica L.) cv. ‘Nam Dok Mai’ growth in the field conditions. Fully expanded leaves were examined either shaded by the plastic roof or sunlit under natural conditions. Leaf temperature and leaf-to-air vapour pressure deficit of the shaded leaves measured on the clear day were lowered compared to those of the sunlit leaves. It resulted in increased stomatal conductance and photosynthetic rates of the shaded leaves compared to those of the sunlit leaves, especially from the morning to midday. Furthermore, the reversible decrease of the maximal quantum yield of PSII was more pronounced in the sunlit leaves than that in the shaded ones. Shading increased the total fruit number; the shaded fruits developed better external color than that of the sun-exposed fruits. Our results indicated that shading could maintain the high photosynthetic activity by reducing stomatal limitations for carbon supply and was effective in alleviating the photoinhibitory damage to PSII during bright and clear days with excessive radiation. Finally, shading could increase the number of fruits and improve mango peel color.     

苹果日烧病程中果皮抗氧化系统在细胞超微结构的变化

以富士品种为试材研究了苹果果实日烧病程中果皮组织细胞膜脂过氧化、抗氧化酶类、酚类物质的变化规律,并用电镜观察细胞超微结构的变化。结果表明膜脂过氧化导致日烧发生并进一步使日烧程度加重。相应地,抗氧化酶类在果皮变白期活性激增,但是,细胞结构仍较完整,只是叶绿体膨胀、类囊体结构部分解体,线粒体周缘模糊,细胞质中含大量的空泡;以后果皮变褐,绿原酸、槲皮素、芦丁、杨梅酮积累,同时靠近上表皮几层细胞解体,由密集的电子致密物充塞,细胞壁加厚。     

The shaded side of apple fruit becomes more sensitive to photoinhibition with fruit development

Developmental changes of photochemical and non-photochemical processes and the antioxidant system in the shaded peel vs the sun-exposed peel of 'Gala' apple and their responses to sudden exposure of high light were determined to understand the susceptibility of the shaded peel to high light damage with fruit development. As fruit developed, actual PSII efficiency of the shaded peel decreased, whereas non-photochemical quenching (mainly the slow component) increased at any given PFD. Photochemical quenching coefficient of the shaded peel decreased at any given PFD with fruit development. As fruit developed, the activity of superoxide dismutase, ascorbate peroxidase and dehydroascorbate reductase and the level of reduced ascorbate and total ascorbate decreased; the activity of monodehydroascorbate reductase and glutathione reductase remained low, whereas catalase activity and the level of reduced glutathione and total glutathione increased in the shaded peel. Exposure to high light (1500 micromol m(-2) s(-1)) for 2 h significantly decreased the maximum quantum efficiency of PSII (F(V)/F(M)) in the shaded peel at each developmental stage, with the decrease being larger with fruit development. The F(V)/F(M) of the sun-exposed peel was also decreased by the high light treatment, but the decrease was much smaller than that in the shaded peel at each developmental stage. We conclude that the shaded peel of apple fruit becomes more sensitive to photoinhibition with fruit development, and this increased sensitivity is apparently related to the decease in the overall capacity for photosynthesis and photoprotection of the shaded peel with fruit development.     

Significance of skin flavonoids for UV-B-protection in apple fruits

An attempt has been made to assess the UV-B-protective capacity of phenolic compounds accumulated in superficial structures of plants using apple fruit as a model. Two apple (Malus domestica Borkh.) cultivars (Braeburn and Granny Smith) differing in response to high fluxes of solar radiation were selected and exposed to increasing doses of UV-B radiation. The extent of UV-B-induced damage to photosystem II of apple skin correlated with its quercetin glycoside (but not anthocyanin) content. Granny Smith apples did not demonstrate a pronounced response to high sunlight in terms of the accumulation of phenolic substances in the skin and exhibited similar patterns of Fo, Fm, and Fv/Fm changes in the course of UV-B irradiation both on sun-exposed and shaded surfaces of a fruit. Unlike Granny Smith, Braeburn fruits were characterized by a significant accumulation of quercetin glycosides in sun-exposed skin, however, shaded skin contained these compounds in similar amounts to those in Granny Smith. Accordingly, photosystem II in sun-exposed skin of Braeburn apples was resistant to high doses of UV-B radiation (up to 97 kJ m-2), whereas the susceptibility of the photosynthetic apparatus in shaded skin of Braeburn to UV-B-induced damage was much higher and similar to that of both sun-exposed and shaded skin of Granny Smith fruits. Anthocyanins, at least in the amounts found in Braeburn, did not show an additional effect in UV-B protection.     

Polyphenol metabolism of developing apple skin of a scab resistant and a susceptible apple cultivar

During fruit development, the concentration of main polyphenols (flavonols, flavanols, dihydrochalcones, hydroxycinnamic acids, anthocyanins) and the activities of related enzymes (phenylalanine ammonia lyase, chalcone synthase/chalcone isomerase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, flavonol synthase, peroxidase) were monitored in apple (Malus domestica Borkh.). The seasonal survey was performed at five different sampling dates and included the healthy peel of the resistant cultivar ‘Florina’ and healthy peel, scab symptomatic spot and the tissue around the infected spot of the susceptible cultivar ‘Golden Delicious’. From all enzymes tested, chalcone synthase/chalcone isomerase had the highest activity in both cultivars, while phenylalanine ammonia lyase had the lowest. The healthy peels of the susceptible and the resistant cultivar did not show differences in the accumulation of the main polyphenol groups present in the apple skin. However, in the resistant cultivar ‘Florina’, an increase of polyphenol enzyme activities could be observed in late stages of fruit development, which seems to be related to the anthocyanin accumulation in ripe fruits. Significant differences in the polyphenol metabolism were observed in the three different tissues of the susceptible cultivar ‘Golden Delicious’. Increased concentrations of hydroxycinnamic acids, dihydrochalcones and flavan-3-ols were found in the scab symptomatic spots and surrounding tissues. Phenylalanine ammonia-lyase, dihydroflavonol 4-reductase, flavanone 3-hydroxylase and peroxidase showed higher activities in the scab symptomatic spot compared to other analysed tissues, whereas the activities of other enzymes remained unchanged. Highest induction of polyphenol accumulation after scab infection was observed in early developmental stages, whereas enzyme activities were increased in later stages.     

Variation and genetic parameters of fruit colour and polyphenol composition in an apple seedling population segregating for red leaf

Red flesh colour is a relatively new target for apple breeding programmes and understanding genetic relationships between this trait and other fruit characters, including polyphenol compounds, is important for both breeders and marketers of new red flesh cultivars. In this study, fruit peel and flesh colours and concentrations of up to 20 individual fruit polyphenols within each tissue were examined in fruit harvested from a 14-family apple seedling population segregating for red and green leaf. Red leaf seedlings always produced red flesh fruit that varied from pale red to complete dark red cortical tissue (type 1 red flesh). Some (20 %) of green leaf seedlings also produced fruit with red flesh, albeit at low intensity (type 2 red flesh). Cyanidin 3-O-galactoside was the dominant anthocyanin in both fruit tissues, with concentrations being 1,900 times higher in the flesh and 2.5 times higher in the peel of fruit from red than from green leaf seedlings. Red leaf seedlings also had 59 % more flesh epicatechin and 17 % less total peel flavonols, but other polyphenols were not associated with leaf colour. Heritability estimates for red flesh colour, flesh cyanidin 3-O-galactoside, flesh and peel catechins were high in red leaf and low in green leaf seedlings. Conversely, estimates for red peel coverage and two peel anthocyanins were higher in green compared to those from red leaf seedlings. Other than these, heritability estimates were high only for dihydrochalcones and hydroxycinnamic acids from each tissue for both leaf colours but low for all other flesh and peel flavan-3-ols, procyanidins and most peel flavonols irrespective of leaf colour. Genetic correlations between polyphenol compounds varied considerably, but were broadly similar for red and green leaf seedlings. Genetic correlations were mostly moderate to high between compounds of the same metabolic group, but low between compounds from different groups. These results are discussed in relation to the genetic control of flesh colour and polyphenol accumulation in apple, as well as to implications for breeding red flesh apples with altered polyphenol composition.     

Distribution and metabolism of ascorbic acid in apple fruits (Malus domestica Borkh cv. Gala)

The objective of this study was to determine ascorbic acid (AsA) distribution, biosynthesis and recycling in different tissues of young and mature fruit of cv. Gala apple (Malus domestica Borkh). Our results showed that the peel of ‘Gala’ apple had the highest AsA levels among all the tissue types, which resulted from a combination of, lower ascorbate peroxidase (APX, EC 1.11.1.11) activity consuming AsA, and higher dehydroascorbate reductase (DHAR, EC 1.8.5.1) and monodehydroascorbate reductase (MDHAR, EC 1.6.5.4) activities used to recycle AsA. Exogenous feeding of AsA synthesis precursors demonstrated that the peel was capable of de nono AsA biosynthesis via l-galactose and d-galacturonic acid pathways whereas the flesh and seed were only able to synthesize AsA via l-galactose pathway. The young fruit had higher AsA concentration and stronger capability of AsA biosynthesis and recycling. The sun-exposed peel had higher AsA concentration and stronger capability of recycling AsA than the shaded peel, while there was no difference in the flesh between the sun-exposed side and the shaded side. Abundant AsA was found in fruit vascular tissue, which suggests that AsA can be transported to vascular tissues of fruit or vascular tissues could synthesize AsA itself in ‘Gala’ apple.     

Fruit Juice Supplementation Alters Human Skin Antioxidant Levels <Emphasis Type="Italic">In Vivo</Emphasis>: Case Study of Korean Adults by Resonance Raman Spectroscopy

Carotenoids, found in many fruits and vegetables, are antioxidants that protect human skin from UV radiation. In humans, fruit and vegetable intake increases carotenoid contents in skin, which are conventionally assessed by invasive blood tests. In this study, 47 healthy Korean subjects (volunteers) consumed fruit juice containing tomato, apple, strawberry, or grape three times per week for 6 weeks. Skin antioxidant levels were measured by non-invasive resonance Raman spectroscopy. The correlation between skin carotenoid (SC) score with demographic data (age, height, weight) and juice supplementation and changes in SC scores among groups were analyzed. Variations in skin antioxidant levels increased with juice supplementation (p < 0.05). Fruit juice intake was significantly correlated with SC score, indicating increased skin antioxidant levels. Grape and tomato increased skin antioxidant levels and showed higher antioxidant activity than other fruits. Fruit juices containing high levels of carotenoids and antioxidants may provide modest benefits to human health.     

Comparison of thermotolerance of sun-exposed peel and shaded peel of ‘Fuji’ apple

The thermotolerance of the sun-exposed peel and the shaded peel of ‘Fuji’ apple (Malus domestica Borkh.) fruit was evaluated by measuring pigments, chlorophyll a fluorescence transients and O₂ evolution or uptake after exposure to 25, 35, 40, 42, 44, 46 or 48 °C for 30 min in the dark. A major effect of heat stress at 46–48 °C on the chlorophyll a fluorescence transients was the appearance of a very clear K step at 200–300 μs for both peel types. The K step was slightly more pronounced in the sun-exposed peel than in the shaded peel, suggesting that the resistance of oxygen-evolving complex to heat stress is slightly lower in the sun-exposed peel than in the shaded peel. Minimal fluorescence (F_O), relative to the value at 25 °C, increased to a greater extent in the shaded peel than in the sun-exposed peel after exposure to 46–48 °C, but the temperature dependencies of F_O changes were similar for both peel types. Maximum quantum yield of PSII (F_V/F_M) decreased to a similar extent in the sun-exposed peel and the shaded peel as temperature rose from 25 to 44 °C, but the sun-exposed peel reached slightly lower values at 46–48 °C. Correspondingly, gross O₂ evolution rate, relative to that at 25 °C, was also slightly lower in the sun-exposed peel than in the shaded peel at 46–48 °C. In response to heat stress, the ratio of Q_A-reducing reaction centers (RCs) to total RCs and the ratio of Q_B-reducing RCs to Q_A-reducing RCs decreased, but both of them decreased to lower values in the sun-exposed peel than in the shaded peel at 46–48 °C, indicating that the capacity of electron transfer between P₆₈₀⁺ and Q_B via Q_A was damaged to a greater extent in the sun-exposed peel than in the shaded peel. At each given temperature, dark respiration was similar between the two peel types. Overall, it appears that the exposure to higher surface temperature under high light does not make the sun-exposed peel more tolerant of heat stress than the shaded peel of apple fruit.     

Primary and secondary metabolism in the sun‐exposed peel and the shaded peel of apple fruit

The metabolism of carbohydrates, organic acids, amino acids and phenolics was compared between the sun‐exposed peel and the shaded peel of apple fruit. Contents of sorbitol and glucose were higher in the sun‐exposed peel, whereas those of sucrose and fructose were almost the same in the two peel types. This was related to lower sorbitol dehydrogenase activity and higher activities of sorbitol oxidase, neutral invertase and acid invertase in the sun‐exposed peel. The lower starch content in the sun‐exposed peel was related to lower sucrose synthase activity early in fruit development. Dark respiratory metabolism in the sun‐exposed peel was enhanced by the high peel temperature due to high light exposure. Activities of most enzymes in respiratory metabolism were higher in the sun‐exposed peel, but the concentrations of most organic acids were relatively stable, except pyruvate and oxaloacetate. Due to the different availability of carbon skeletons from dark respiration in the two peel types, amino acids with higher C/N ratios are accumulated in the sun‐exposed peel whereas those with lower C/N ratios are accumulated in the shaded peel. Contents of anthocyanins and flavonols and activities of phenylalanine ammonia‐lyase, UDP‐galactose:flavonoid 3‐O‐glucosyltransferase and several other enzymes were higher in the sun‐exposed peel than in the shaded peel, indicating the entire phenylpropanoid pathway is upregulated in the sun‐exposed peel. Comprehensive analyses of the metabolites and activities of enzymes involved in primary metabolism and secondary metabolism have allowed us to gain a full picture of the metabolic network in the two peel types under natural light exposure.     

A study of the effects of ‘Candidatus Phytoplasma mali’ on the psyllid Cacopsylla melanoneura (Hemiptera: Psyllidae)

Cacopsylla melanoneura is a univoltine psyllid vector of ‘Candidatus Phytoplasma mali’, the etiological agent of apple proliferation (AP), a severe disease in European apple orchards. The influence of ‘Ca. P. mali’ on the fitness of C. melanoneura was studied. In the spring of 2007, male-female pairs of field-collected adults were exposed to ‘Ca. P. mali’-infected or healthy ‘Golden Delicious’ apple shoots. Exposure to these diseased shoots did not affect the life span of the adult psyllids. However, significantly fewer eggs were laid on the diseased shoots. Furthermore, fewer of the eggs that were laid on the infected plants hatched. Data suggest a detrimental effect of AP phytoplasma on the fitness of C. melanoneura.     

Oviposition behavior of Anastrepha fraterculus in apple and diel pattern of activities in an apple orchard in Brazil

The oviposition behavior and diel pattern of activities of Anastrepha fraterculus (Wied.) (Diptera: Tephritidae) were observed in an apple orchard and fruit characteristics involved in oviposition preferences were investigated in field cage tests. Fruit size influenced fruit acceptability as an oviposition site by females which did not discriminate among the cultivars Gala, Fuji, and Golden Delicious when same-size fruits were presented simultaneously. Oviposition behavior in apples was basically the same as that described for primary hosts. Hourly census of fly activity indicated that adults did not overnight in the orchard and that they entered the orchard around 1100 h when temperature reached about 21 °C . Bird droppings were an important food item for adults. Behavioral differences between males and females might account for a significant biased sex ratio both in the orchard and at the edge of the native surrounding vegetation. Implications for fruit fly management in Brazilian apple orchards are discussed.