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1.
Lipoxygenases (LOX) belong to a large family of plant enzymes that catalyze the hydroperoxidation of polyunsaturated fatty acids. Most of them are expressed during senescence and contribute to membrane deterioration and biosynthesis of jasmonic acid, a known senescence enhancer. In this work, we cloned a fragment of a gene encoding a LOX from broccoli (BoLOX1). The analysis of the sequence revealed that BoLOX1 is closely related to other LOX from higher plants. Furthermore, we analyzed the expression of BoLOX1 and detected a larger increase during postharvest senescence. A slight increase of total lipoxygenase activity was also found during senescence. In other sets of experiments, broccoli heads were treated with plant hormones, such as cytokinin and ethylene, as a way to assess the effect of such compounds on the expression of BoLOX1. Cytokinin treatment delayed the increase of BoLOX1 expression and lipoxygenase activity whereas ethylene accelerated both processes. Also, several postharvest treatments were applied in order to delay senescence in broccoli florets and to evaluate their effects on BoLOX1 expression. Samples treated with modified atmosphere, hot air, UV-C or white light showed a delay in chlorophyll degradation and degreening. In most cases, the treatments also delayed the increase of BoLOX1 expression, reaffirming the relationship between the expression of this gene and senescence. However, treatments like modified atmospheres and visible light markedly increased lipoxygenase activity, which suggests a lack of correlation between BoLOX1 expression and lipoxygenase activity.  相似文献   

2.
Postharvest yellowing of broccoli (Brassica oleracea L. Italica Group) is an important indicator of quality deterioration and occurs with chlorophyll (Chl) degradation. Postharvest ethanol vapor treatment could delay the yellowing of broccoli florets, through the suppression of Chl degradation. As the first step in identifying the mechanism of this delay, the effects of postharvest ethanol vapor treatment on activities and gene expression of the Chl catabolic enzymes in broccoli were determined. Broccoli branchlets were placed in a perforated polyethylene bag with or without (control) an ethanol pad and stored at 20 °C in darkness. The Chl contents of the control broccoli florets decreased remarkably after three days in storage, whereas the contents of the ethanol-treated broccoli showed no significant changes except at day one. Changes in chlorophyllase activity in the ethanol-treated broccoli were similar to those of the control until three days in storage, but then the activity tended to decease. Mg-dechelatase and Chl-degrading peroxidase activities, which increased greatly with senescence in the controls, remained unchanged in the ethanol-treated broccoli. BoCLH1 expression showed changes almost similar to those of chlorophyllase activity. BoPAO expression in the control broccoli increased greatly at day one in storage and was maintained at a high level until three days. In contrast, this expression in ethanol-treated broccoli was suppressed until two days. BoRCCR expression in the control broccoli increased until two days in storage, while the expression in the ethanol-treated broccoli showed no change during storage. These results show that postharvest ethanol vapor treatment suppressed the activities and gene expression of Chl catabolic enzymes, resulting in delayed yellowing of broccoli florets.  相似文献   

3.
Degreening caused by chlorophyll degradation is the most important feature that determines postharvest loss of quality in broccoli. Chlorophyll molecules are assembled to several thylakoid proteins, from which chlorophylls must be released in order to be catabolized. Stay-Green (SGR), a chloroplast-located protein, specifically interacts with light harvesting complex subunits helping toward their destabilization and to the release of chlorophylls. In this work, a fragment of a gene encoding a SGR from broccoli (BoSGR) was cloned. The expression of BoSGR was analyzed and detected an important increment during postharvest senescence, simultaneously with chlorophyll degradation. In order to analyze the effect of different growth regulators, different groups of broccoli heads were treated with cytokinins, ethylene and 1-MCP. Cytokinins and 1-MCP delayed the increment of BoSGR expression whereas ethylene accelerated the process. In addition, several postharvest treatments that delay degreening in broccoli florets were applied to evaluate their effects on BoSGR expression. Samples treated with modified atmosphere, hot air, UV-C or white lights showed a delay in chlorophyll degradation and degreening. In most cases, the treatments also delayed the increment of BoSGR expression during senescence, reaffirming the relationship between the expression of this gene and chlorophyll degradation.  相似文献   

4.
Potato leaves infected with Phytophthora infestans produced a serine protease inhibitor (PLPKI) with specificity for microbial proteases. Sequencing of the first twenty residues at the NH2‐terminus of the mature PLPKI polypeptide demonstrated that PLPKI is a novel member of the potato protease inhibitor I family. PLPKI inhibited the activity of extracellular proteases produced by two pathogens of potato, P. infestans and Rhizoctonia solani, but was inactive against proteases secreted into the culture media by the binucleate Rhizoctonia N2, a non‐pathogenic fungus for potato. Western blot analysis showed a positive correlation between the levels of PLPKI and the degree of horizontal resistance, showing its highest accumulation in clone OKA 5632.11, which has been described as highly resistant. This correlation, together with the ability of PLPKI to completely abolish the secreted serine protease activity of P. infestans, suggests that PLPKI may have an active role in protecting potato plants from this pathogenic oomycete and that it could be used as a suitable biochemical marker to help breeders in the selection of cultivars with high degree of horizontal resistance.  相似文献   

5.
Pheophytinase (PPH) activity and gene expression of chlorophyll (Chl)-degrading enzymes relating to UV-B treatment in postharvest broccoli (Brassica oleracea L. Italica Group) florets were determined. PPH is involved in the dephytylation of Mg-free Chl a, pheophytin (Phy) a. However, in vitro chlorophyllase (Chlase, EC.3.1.1.14) also uses Phy a as a substrate to produce pheophorbide (Pheide) a by dephytylation. For an accurate determination of PPH activity, the PPH protein fraction was separated from Chlase protein by ammonium sulfate precipitation. The protein precipitated by 45-60% saturated ammonium sulfate included a little bit of Chlase activity and was suitable for PPH determination. PPH activity in broccoli florets treated with a UV-B dose of 19 kJ m−2 was repressed for the first 2 d of storage at 15 °C, whereas it increased gradually with senescence of control broccoli florets. The expression level of BoCLH1 was reduced in broccoli florets on day 4 of storage, while BoCLH2 and BoCLH3 were up-regulated with UV-B treatment. A high BoPAO expression level was found in senescent broccoli florets, and the up-regulation of this gene was delayed by UV-B treatment. The highest expression level of BoPPH was found in the control, and its expression was clearly repressed by UV-B treatment on day 2 of storage. We suggest that the up-regulation of Chl-degrading enzyme genes could be delayed by UV-B treatment, resulting in the suppression of floret yellowing in stored broccoli.  相似文献   

6.
Broccoli (Brassica oleracea L.) tissue held in a controlled atmosphere (CA; 10% carbon dioxide and 5% oxygen) senesces more slowly than tissue held in air. CA-treated broccoli tissues lose less water and soluble sugars, have lower protease activity, and have no significant loss of color (hue angle, chlorophyll content) for 96 h after harvest (20 °C, dark) compared to tissue held in air that starts to senesce and yellow after 48 h. The current study examined differential gene expression in broccoli tissues in response to postharvest CA treatment. This genetic analysis was undertaken to identify CA-responsive genes that may act as signaling elements and repress postharvest senescence processes. CA-responsive genes with up- and down-regulated expression (compared to air controls) were isolated after a 6 h CA treatment by differential display-polymerase chain reaction. The candidate CA-responsive genes included a number of novel genes without previously assigned functions, and genes of known function previously found to be regulated by stress (e.g. dehydration, salt stress, low temperature, and sugar starvation).  相似文献   

7.
Central broccoli heads (cv. de Cicco) were harvested and treated with UV-C light (4, 7, 10, or 14 kJ m−2). All treatments delayed yellowing and chlorophyll degradation at 20 °C but the irradiation dose of 10 kJ m−2 allowed retaining the highest chlorophyll content yet had lower amounts of pheophytins than every treatment other than 7 kJ m−2. This dose was selected to analyze the effect of UV-C on postharvest broccoli senescence at 20 °C. The UV-C treatment delayed yellowing, chlorophyll a and b degradation, and also the increase in pheophytins during storage. The activity of chlorophyll peroxidase and chlorophyllase was lower in UV-C treated broccoli. Instead, Mg-dechelatase activity increased immediately after the treatment, but after 4 and 6 d this activity was lower in UV-C treated florets than in controls. Treated broccoli also displayed lower respiration rate, total phenols and flavonoids, along with higher antioxidant capacity. The results suggest that UV-C treatments could be a useful non-chemical method to delay chlorophyll degradation, reduce tissue damage and disruption, and maintain antioxidant capacity in broccoli.  相似文献   

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11.
Membrane lipid degradation catalyzed by phospholipase D (PLD) results in postharvest browning and senescence of litchi fruit. The effects of n-butanol, a specific PLD inhibitor, on enzymatic browning and oxidative stress during storage of litchi fruit at room temperature were evaluated. n-Butanol-treated fruit had a lower browning index and disease index than untreated fruit. n-Butanol treatment also decreased PLD activity. As a result, the decompartmentalization of litchi polyphenoloxidase and substrates was reduced. The conversion of substrates (−)-epicatechin and procyanidin A2 into quinones was slowed down and enzymatic browning of litchi pericarp tissues was lower after 6 d storage. Additionally, n-butanol-treated fruit possessed significantly lower malondialdehyde contents than untreated fruit after 4 d storage. Analysis of antioxidative enzyme activities showed that n-butanol treatment inhibited oxidative stress mainly by maintaining high catalase activity in litchi pericarp tissues. Consequently, senescence of litchi fruit during storage was moderated.  相似文献   

12.
Persimmon (Diospyros kaki Thunb.) fruit undergoes intensive cell wall modification during postharvest fruit softening. Xyloglucan metabolism is important in cell wall disassembly. We cloned cDNAs for two xyloglucan endotransglycosylase/hydrolase genes (DkXTH1 and DkXTH2) from ‘Saijo’ persimmon fruit treated with dry ice to remove astringency. In order to determine the ethylene dependence of XTH gene expression, fruit were exposed to 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, prior to removal of astringency. Ethylene production increased in mature control and 1-MCP-pretreated fruit after dry-ice treatment, and flesh firmness decreased to the same extent during dry-ice treatment in the control and 1-MCP-pretreated fruit. After dry-ice treatment, control fruit softened completely, but fruit firmness was maintained in 1-MCP-pretreated fruit. Accumulation of DkXTH1 mRNA was induced simultaneously with commencement of ethylene production in mature control fruit. Pretreatment with 1-MCP delayed accumulation of DkXTH1 mRNA. DkXTH2 expression also coincided with fruit softening but was intensified by 1-MCP treatment during the deastringency treatment. These results indicate that fruit softening was related to both DkXTH1 and DkXTH2 expression in ‘Saijo’ persimmons.  相似文献   

13.
Flower senescence of the potted gentian (Gentiana scabra) ‘Shinbisei’ was investigated in relation to ethylene sensitivity and production. ‘Shinbisei’ flowers were used for all experiments except for those with inflorescences. Exposure to ethylene at 0.5 μL L−1 or higher concentrations for 24 h markedly accelerated flower senescence, indicating that G. scabra flowers are highly sensitive to ethylene. Treatment with 0.2 or 0.5 mM silver thiosulfate complex (STS) and 2 μL L−1 1-methylcyclopropene (1-MCP), ethylene action inhibitors, and 50 mM α-aminoisobutyric acid, an inhibitor of 1-aminocyclopropane-1-carboxylate (ACC) oxidase, did not delay flower senescence. However, treatment with 1 mM l-α-(2-aminoethoxyvinyl) glycine, an inhibitor of ACC synthase, slightly delayed flower senescence. Pollination significantly accelerated petal senescence of G. scabra flowers. Ethylene production of petals, gynoecium, and stamens in unpollinated flowers slightly increased during senescence. Pollination significantly increased ethylene production of petals, gynoecium and stamens 1 day after pollination. To clarify whether 1-MCP delays senescence of cut gentian inflorescences, cut G. scabra ‘Yuki-hotaru’, G. scabra × Gentiana triflora ‘Aoi-kaze’, and G. triflora ‘Koharu’ inflorescences with various stages of flowers, including buds with colored petals, were treated with 2 μL L−1 1-MCP for 24 h. 1-MCP treatment delayed flower wilting of cut inflorescences of ‘Aoi-kaze’ and ‘Yuki-hotaru’ more than that of ‘Koharu’, suggesting that there is species variation in the effect of 1-MCP in delaying flower senescence of cut gentian inflorescences.  相似文献   

14.
1-MCP处理对采后青花菜内源激素变化的影响   总被引：1，自引：0，他引：1  
王丽宁 《中国农学通报》2008,24(10):291-295
以青花菜品种"曼陀绿"(Brassica olracea L. var. italica)为试材,研究了1-MCP处理对青花菜采后叶绿素含量、乙烯释放速率和内源玉米素(ZR)、赤霉素(GA)、生长素(IAA)、脱落酸(ABA)含量的影响。结果表明：1-MCP延缓了叶绿素降解,降低了组织对乙烯的敏感性,延缓了GA的分解,推迟了ABA的积累。经1-MCP处理的青花菜ABA/GA和ABA/IAA比值上升缓慢。  相似文献   

15.
Fresh broccoli heads contain relatively high levels of beneficial phytochemicals, particularly glucosinolates and flavonoids, but it is not clear whether or not the levels are affected by postharvest handling conditions. Accordingly, broccoli heads (Brassica oleracea var. italica) were stored at temperatures of 1 or 4 °C, 99% relative humidity (RH), for 2, 7, 14 or 28 days to simulate domestic and export transport conditions. After removal from cool storage, heads were then placed at 8, 15 or 20 °C, with 99, 90 or 70% RH, respectively, for 3 days to simulate marketing conditions. At the end of both phases, heads were rated for visual quality, turgor, presence of rots and yellowing, and the contents of glucoraphanin, quercetin and kaempferol were measured. Visual quality declined significantly with increasing temperature and length of storage, caused primarily by increasing yellowing and loss of turgor. Glucoraphanin, quercetin and kaempferol contents were not significantly affected by storage and marketing temperature and time. These results suggest that current transport and marketing practices are not likely to have a deleterious effect on the levels of aliphatic glucosinolates and flavonols in broccoli.  相似文献   

16.
Fresh basil (Ocimum basilicum L.) is a highly perishable leafy green vegetable with a storage life of 4–5 d at room temperature. Exposure of basil leaves to temperatures below 12 °C during storage results in chilling injury; therefore, refrigeration cannot be used to extend postharvest life of basil. Typically, leafy vegetables are stored in darkness or extremely low irradiance. Darkness is known to induce senescence, and the initial phase of senescence is reversible by exposure to light. In this work, we studied the effects of low-intensity white light pulses at room temperature on postharvest senescence of basil leaves. Daily exposure for 2 h to 30–37 μmol m−2 s−1 of light was effective to delay postharvest senescence of basil leaves. Chlorophyll and protein levels decreased, ammonium accumulated and leaves developed visual symptoms of deterioration (darkening) during storage in darkness. Light pulses reduced the intensity of these senescence symptoms. The photosynthesis light compensation point of basil leaves was 50 μmol m−2 s−1 i.e., higher than the intensity used in this study, and the effect of treatment with red light was the same as with white light, while far red light was ineffective. Light pulses exerted a local effect on chlorophyll loss, but the effect on protein degradation was systemic (i.e., spreading beyond the illuminated parts of the leaf blade). The results of this study indicate that daily treatment for 2 h with low intensity light (30–37 μmol m−2 s−1 every day) during storage at 20 °C is an effective treatment to delay postharvest senescence of basil leaves. The delay of postharvest senescence by low intensity light pulses seems to be mediated by phytochromes, and it is systemic for protein, and partially systemic for chlorophyll degradation.  相似文献   

17.
The effects of postharvest application of fruit hardening chemical agents on fig (Ficus carica L. cv. Poona) fruit were compared with untreated figs during storage. The impact of calcium chloride (4%) was notable in terms of retention of fruit color, texture and increased accumulation of ascorbic acid, compared to untreated control figs. Pretreatment with calcium chloride (4%) was found to be most effective in checking the growth of both mesophilic aerobic bacteria and yeast and molds at low temperature (1 ± 0.5 °C; 95–98% RH) storage and it further delayed ripening and senescence of figs and was beneficial in prolonging the postharvest life twofold. Treated figs without microbial spoilage could be used for short term storage, transportation, distribution and marketing for long distance domestic markets in India.  相似文献   

18.
Wheat grain yield and protein content are significantly influenced by the onset of senescence and the duration of the grain filling phase. The onset of senescence also affects Nitrogen use efficiency (NUE) through interacting pathways involving N accumulation and translocation of N into the grains. The objective of this study was to relate variation in NUE and its components with two groups of the NAM-A1 gene alleles; (i) early onset of senescence in cultivars carrying the NAM-A1a allele, (ii) delayed onset of senescence in cultivars carrying the Non-NAM-A1a allele (b, c, d) in wheat cultivars grown under Western Australia conditions. A field trial was carried out over two seasons examining 19 cultivars under different N rates and time of N application. The Normalized Difference Vegetation Index was utilized to determine the onset of senescence after anthesis. The early onset of senescence results in high grain yield, harvest index, and NUE due to improvements in the N utilization ability. Accelerating the onset of senescence results in a short grain filling period leading to grain maturity before the onset of unfavourable summer conditions. The function of alleles of NAM-A1 gene in controlling senescence hence the NUE is highly regulated by environmental conditions. This study concluded that the function of NAM-A1a allele induces the onset of senescence with a positive effect on the NUE and its components under Western Australian conditions.  相似文献   

19.
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20.
From harvest to consumption, tomato (Solanum lycopersicum L.) fruit are exposed to several exogenous factors that enhance product deterioration. Phospholipase D is a key enzyme involved in membrane deterioration that occurs during fruit ripening and senescence. Hexanal, an inhibitor of phospholipase D has been successfully used for pre- and postharvest treatment of fruit, vegetables and flowers. In this study, effectiveness of pre- and postharvest application of an aqueous hexanal formulation and an enhanced freshness formulation (EFF) containing hexanal and other ingredients were evaluated by monitoring changes in quality parameters during postharvest storage of greenhouse tomatoes. Tomatoes subjected to preharvest spray with EFF containing 1 mM hexanal twice a week had better colour, and firmness than untreated fruit and hexanal formulation treated fruit. EFF treated tomatoes also showed low hue angle values indicative of enhanced red colour. Preharvest spray with 1 mM hexanal twice a week resulted in higher levels of ascorbic acid and soluble solids in fruit than those subjected to EFF treatment, and the control. Postharvest dip application of harvested tomatoes in 2 mM hexanal as EFF resulted in enhanced brightness and hue angle values, reduced red colour, increased fruit firmness and ascorbic acid content after 21 days of storage, indicative of better quality. The results suggest that hexanal has the potential to enhance shelf-life and quality of greenhouse tomatoes.  相似文献   

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