Root and foliar applications of 24-epibrassinolide (EBL), an immobile phytohormone with antistress activity, were evaluated for their effects on reducing fusarium wilt and their influence on antioxidant and phenolic metabolism in roots of cucumber plants (Cucumis sativus L. cv. Jinyan No. 4). EBL pretreatment significantly reduced disease severity together with improved plant growth and reduced losses in biomass regardless of application methods. EBL treatments significantly reduced pathogen-induced accumulation of reactive oxygen species (ROS), flavonoids, and phenolic compounds, activities of defense-related and ROS-scavenging enzymes. The enzymes included superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, catalase as well as phenylalanine ammonia-lyase and polyphenoloxidase. There was no apparent difference between two application methods used. EBL applications triggered a slight increase in H2O2 concentration followed by increases in the transcript levels of WRKY transcription factor and defense-related genes. This study demonstrated that EBL enhanced resistance to fusarium wilt by a novel mechanism that was not related to its active transport or increase in antioxidant system.
Ju Ding, Kai Shi, Yan-Hong Zhou, and Jing-Quan Yu
Mohamed S. Elmongy, Xiuyun Wang, Hong Zhou, and Yiping Xia
Auxins and humic acid (HA) were investigated for their roles in adventitious root induction in azalea microshoots in our previous study. To reveal the regulatory mechanisms of auxins and HA in this process, measurements of the levels of reactive oxygen species (ROS), carbohydrates, and phenolic compounds and gene expression during in vitro root development were performed. During the adventitious root induction process, ROS levels in shoots treated with auxins and HA increased compared to untreated shoots, especially during the earliest period after transfer to the media. Media supplemented with NAA experienced increases in H2O2 contents by 480%and 250%, respectively, after 7 and 14 days of culture. The phenolic compound levels were also enhanced in the shoots treated with auxins and HA, reflecting the different rooting-promoting abilities of both auxins and HA. The highest levels of total phenolic [68.6 mg·g−1 fresh weight (FW)], polyphenolic acids (121.72 μg caffic acid/g FW), and total flavonols (162.42 μg quercetin/g FW) were recorded after 21 days for NAA media, but the maximum levels of anthocyanins (49.76 μg cyanindin/g FW) were recorded after 21 days for IBA medium. Soluble carbohydrate, starch, and soluble protein levels were increased in the shoots treated with all treatments; however, the influence of NAA treatments was stronger than that of other treatments for most investigated parameters. The NAA significantly enhanced soluble carbohydrates by 30%, 37%, and 25%, respectively, at 14, 21, and 28 days compared with untreated microshoots. Expression of the POD1 gene increased in the shoots submitted to HA treatment media. Expression levels of auxin response factors (ARFs) increased with IBA- and NAA-treated explants, suggesting that ARFs may have diverse regulatory roles in adventitious root induction in evergreen azalea. Moreover, the profiles of the IAA1, IAA9, IAA14, and IAA27 transcripts were analyzed to reveal their roles in the adventitious rooting of evergreen azalea microshoots. These results indicate that auxins and HA promote adventitious root induction in Rhododendron plants through their impact on ROS, carbohydrate contents, phenolic compound levels, and expression levels of different genes related to root development in evergreen azalea plants.
Hong-Wei Zhou, Lilian Sonego, Ruth Ben-Arie, and Susan Lurie
Harvested nectarine fruit [Prunus persica (L.) Batsch `Flavortop'] were held for 5 days at 20 °C, or stored at 0 °C either immediately (control), or after 2 days at 20 °C (delayed-cooling). Observations were conducted after removal from storage for 1, 3, or 5 weeks and a shelf life of 5 additional days at 20 °C. After 5 weeks storage, 87% of control fruit developed woolliness (mealiness in texture accompanied by dry tasting fruit as a result of reduced juice content), while only 7% of delayed-cooling fruit showed signs of woolliness. Firmness of fruit in the delayed-cooling treatment was less at the beginning of ripening than control fruit, but after shelf life in both treatments, fruit reached the same final softness. Expressible juice was lower in woolly fruit (46%) than in healthy fruit (65%). Along with woolliness, viscosity of the resuspended alcohol insoluble residue (cell wall material) of expressed juice increased, implying accumulation of large molecular-weight polymers. The high performance liquid chromatography profile confirmed there were more large pectin polymers (2000 to 76 Ku) in the cell wall components of juice from woolly fruit and a lower arabinose content in these polymers reflected greater side chain removal from pectins in the juice of woolly fruit. Accumulation of larger sized pectin polymers along with high viscosity correlated with lower polygalacturonase activity in woolly fruit. Degradation of soluble pectin released into the juice of woolly fruit may have been impeded by repressed polygalacturonase activity.
Wei Zhou, Hong Wang, De-Zhu Li, Jun-Bo Yang, and Wei Zhou
Luculia pinceana Hook. (Rubiaceae) is a typical distylous species with dimorphic and long-styled monomorphic populations. Within this study, we developed 13 microsatellite markers from L. pinceana using a modified biotin–streptavidin capture method. Polymorphism of each locus was assessed in 30 individuals from four dimorphic populations and one monomorphic population. The average allele number of these microsatellites was 4.153 per locus ranging from three to seven. The observed and expected heterozygosities were from 0.040 to 0.840 and from 0.571 to 0.769, respectively. Additionally, all 13 identified microsatellite markers were successfully amplified in its related species, L. yunnanensis, 10 of which showed polymorphism. These microsatellite markers could provide a useful tool for further study of the breeding system and the population genetic structure in this species and within other Luculia species.
Bing Liu, Hong Zhou, Sha Cao, Yi-ping Xia, and Rajeev Arora
Seasonal deacclimation was investigated during Jan. to Mar. 2014 in leaves of 10 azalea cultivars (Rhododendron section Tsutsusi) under natural conditions in eastern China. Based on the midwinter leaf freezing tolerance (LFT), these cultivars were grouped as “more-hardy” vs. “less-hardy.” Eight of the 10 cultivars first showed deacclimation when daily mean temperature over 2-week period preceding the LFT measurement was ≈9.5 °C. Deacclimation for other two cultivars was somewhat delayed and might have involved deacclimation–reacclimation cycling before eventual deacclimation. Our data indicate that the “more-hardy” group deacclimated slower than the “less-hardy” ones over the first half of the deacclimation period. This trend reversed during the second half of the deacclimation period. Accordingly, “more-hardy” and “less-hardy” cultivars depicted a “curvilinear” and “reverse curvilinear/linear” deacclimation kinetics. “More-hardy” cultivars generally had higher total soluble sugars (TSS) than “less-hardy” ones at acclimated state. TSS declined during deacclimation in all cultivars, and the loss was positively correlated with the loss in LFT. Leaf starch content generally followed opposite trend to that of TSS, i.e., it was at lowest during acclimated state and increased during deacclimation.
Hui-juan Zhou, Zheng-wen Ye, Ming-shen Su, Ji-hong Du, and Xiong-wei Li
Heat treatment induces resistance to low temperature in horticultural crops. Changes in soluble protein and heat-stable protein (HSP) contents, the total soluble solids (TSS), titratable acidity (TA), reducing sugar, weight loss and firmness of honey peach (cv. Hujingmilu) during heat treatment and refrigerated storage were investigated. Low-temperature storage alone led to decreasing of TA and reducing sugar and caused severe fresh mealiness. The hot-air treatment before low temperature combined with the use of a plastic bag (thickness of 0.03 mm) could counteract this effect. Heat treatment before refrigerated storage increased both soluble protein and HSP contents, and the ratio of heat-stable to soluble protein. The most favorable effect was obtained with 46 °C for 30 minutes. In addition, heat treatment before storage retarded the increase in fruit firmness, maintained the highest contents of the TSS and reducing sugar and inhibited the decline of TA during refrigerated storage. Treatment for 30 minutes at 46 °C before low-temperature storage in combination with a 0.03-mm plastic bag might be a useful technique to alleviate chilling injury (CI) and maintain honey peach fruit quality during cold storage.
Hong-Wei Zhou, Lilian Sonego, Andrai Khalchitski, Ruth Ben-Arie, Amnon Lers, and Susan Lurie
Most `Flavortop' nectarines [Prunus persica (L.) Batsch (Nectarine Group)] that were placed directly into 0 °C storage developed chilling injury after removal, while preconditioning fruit for 2 days at 20 °C (delayed storage) reduced chilling injury substantially. Chilling injury was expressed as the development of a dry, woolly flesh texture during ripening. Delayed-storage fruit were as firm as control fruit when placed in storage, but softened more during storage. Analysis of cell wall components showed that in woolly fruit a higher percentage of pectin was retained in the sodium carbonate fraction, although during ripening polymers in this fraction decreased in molecular mass (Mr). In the guanidine thiocyanate hemicellulose fraction of woolly fruit, the associated pectin and hemicellulose remained as large polymers, while in delayed-storage fruit they decreased in Mr during ripening. Endo-polygalacturonase (PG), pectin esterase (PE), and endo-glucanase (EGase) activities of delayed-storage fruit were the same as control fruit at the beginning of storage, although exo-PG was higher. However, differences were observed at the end of storage. Endo-PG activity was lower in control than delayed-storage fruit at the end of storage while PE activity was higher, and exo-PG and EGase activities were similar. These differences in activity were not reflected in the mRNA abundance of the respective enzymes. Endo-PG and PE message was similar in all fruit at the end of storage and increased during ripening, while EGase message was low at all times except in control fruit after storage and development of woolliness. Prevention of chilling injury by delayed storage appears to be due to the ability of the fruit to continue a progressive, slow cell wall degradation in storage which allows normal ripening to proceed when the fruit are rewarmed. Regulation of the softening process did not appear to be by enzyme synthesis, since mRNA levels of the enzymes did not correspond with enzyme activity.
Stephen M. Southwick, Kitren G. Weis, James T. Yeager, and Hong Zhou
Whole-tree sprays of Release LC [predominantly gibberellic acid] (GA,) were applied in a commercial peach [Prunus perisca (L.) Batsch.] orchard in the California Central Valley on three dates from mid-June (about 90 days after full bloom = 28 days before harvest) to late July (14 days postharvest) 1993 at 50, 75, 100, and 120 mg·liter-1. Gibberellin (GA) reduced the number of flowers differentiated in 1993, thereby reducing fruit density in 1994, when sprays were applied by early July 1993. Sprays in late July did not reduce flowering and fruiting density in the following year. In 1994, there were fewer fruit located on the proximal third of the shoot after GA sprays of 75,100, and 120 mg-liter' applied on 15 June compared to hand-thinned controls, and reduction was linear with increase in GA rate. Fruit numbers in the middle and distal sections of shoots were reduced by all 15 June and some 9 July GA sprays, with fewer fruit as concentration increased. However, the distribution of fruit within shoot sections, after GA treatments during floral differentiation, expressed as a percentage of the total number of fruit along fruiting shoots, showed even fruiting compared with hand thinning. Due to reduced flowering in response to GA treatments in June and early July 1993, the hand-thinning requirement was significantly reduced, with no thinning required in 1994 from 15 June 1993 GA sprays. All sprays applied in early July resulted in 40% to 60% fewer fruit removed during thinning than the nontreated controls. Sprays in late July were ineffective. Sprays of GA applied in mid-June at 50,75, 100, and 120 mg·liter and sprays of 120 mg·liter-1 GA applied in early July (4 days preharvest) increased the firmness of `Loadel' cling peach (about 26% improvement in June sprays) in 1993. The salable yield of fruit (after removal of the undersized fruit) was the same on hand thinned and on non-hand thinned trees treated with GA on 15 June at 50 mg·liter-1. The salable yield of fruit was increased by GA sprays of 50 and 75 mg·liter applied on 9 July 1993 compared to controls. There were no differences in fruit size (by weight or diameter) among the aforementioned treatments and hand thinning. GA sprays of 75,100, and 120 mg-liter' applied on 15 June 1993 tended to reduce salable yield, but fruit size increased with decreased yield. Based on the results obtained in 1993 and 1994, we believe that Release LC has good potential for chemically thinning peaches in California.
Chao Zhou, Haide Zhang, Yixing Li, Fenfang Li, Jiao Chen, Debao Yuan, and Keqian Hong
The mechanism regulating procyanidin (PA) accumulation in banana (Musa acuminata) fruit is not understood. During this study, the effects of PA treatment on the activities of banana PA biosynthetic enzymes and transcriptomic profiles were investigated. The results showed that PA treatment delayed the decreases in leucoanthocyanidin reductase and anthocyanidin reductase activities, which affected the accumulation of PA. Furthermore, the peel samples of the control fruit and the PA-treated fruit on day 1 were selected for transcriptomic analysis. The results revealed that PA treatment induced 1086 differentially expressed genes. Twenty-one key genes, including those encoding biosynthetic enzymes and regulatory factors involved in PA biosynthesis, were validated using a quantitative real-time polymerase chain reaction. The results showed that these genes were upregulated by PA treatment during banana storage. Taken together, our study improves current understanding of the mechanism underlying PA-regulated banana senescence and provide new clues for investigating specific gene functions.
Hui-juan Zhou, Xia-nan Zhang, Ming-shen Su, Ji-hong Du, Xiong-wei Li, and Zheng-wen Ye
To investigate the influence of ultraviolet-C (UVC) radiation pretreatment on the sugar metabolism of yellow peaches (cv. Beinong2 × 60–24–7) during storage, the concentrations of soluble sugar (sucrose, fructose, glucose, and sorbitol), and related gene expression were determined. During UVC pretreatment, peaches were subjected to a dose of 4 kJ·m−2 when they were placed at 15 cm under a UVC lamp tube for 10 minutes at 25 °C. Then, they remained at 15 ± 2 °C for 10 days. Peaches stored at 15 ± 2 °C immediately after picking were used as the control group (CG). UVC pretreatment reduced the ethylene production rate and resulted in a significant increase in the accumulation of sucrose during days 2 to 8 of the storage period, followed by a lower concentration of fructose and glucose and the upregulation of PpaSS1. The expression levels of PpaSPS2, PpaSS1, and PpaST3 were significantly correlated with fructose concentration, and those of PpaSPS2 and PpaST2 were significantly correlated with glucose concentration. The enzyme activity of sucrose phosphate synthase (SPS) was positively correlated with PpaSPS2, PpaSS2, and PpaST2. The enzyme activities of sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) were positively correlated with PpaSS1, PpaST1, and Ppani, respectively. Expressions of PpSPS1 and PpSPS2 in UVC-pretreated peaches were upregulated on storage days 8 and 2, and there was a UVC-induced peak in SPS activity on storage days 4 and 8, which resulted in the rapid accumulation of sucrose. UVC pretreatment could upregulate the gene expression of PpaSS1 on day 2, which could improve and maintain the quality of peaches for consumption.