| Postharvest process is an important step in fruit industry and also the research hotspot of Storage Physiology. Postharvest decay caused by microorganism and the change/loss of nutrition caused by continued metabolism are both involved in postharvest process. It is based on the two above key point that a series of postharvest technology have been developed Postharvest technologies include biophysics technology (low temperature, low pressure, dynamic controlled atmosphere, electric field, packaging and eatable film etc.) and biochemistry technology (synthetic fungicides, antagonistic yeasts and elicitor etc.). Nature elicitors have many advantages, such as remarkable effect in postharvest disease control, edible safety, low cost and nutrition protection. Burdock fructooligosaccharide (BFO) is an elicitor isolated from Arctium lappa root. Further studies have showed that BFO induced resistance in Nicoliana tabacum, Cucumis salivas and Lycopcrsicon esculenlum Other study have proved BFO act as an elicitor to induce systemic acquired resistance in plant. Also, Nature diseased and Botrylis cinerea infected tomato can be controlled by BFO. However there is no systemic research in the mechanism of BFO induced postharvest resistance.These studies include:1.The characteristic of BFO induced resistance in different fruits and its preliminary mechanism study. The BFO treatment concentration have been optimized among fruits, grape against Holiylis cinerca, apple agaist Penicillium expansum, banana agaist Calletotrrichum musae, kiwi fruit agaist Botrytis cinerea, citrus agaist Penicillium expansum, strawberry and Bartlett pear agaist nature disease. In banana and citrus, higher concentration (0.75%, w/v) is needed. In grape, apple and kiwifruit, medium concentration (0.5%, w/v) is needed. In strawberry and Bartlett pear, lower concentration (0.25%, w/v) is needed. Decay percentage has been analyzed, the results indicated that:The decay percentages of grape and apple have been notably decreased by BFO treatment. The decay percentages of banana, kiwifruit and citrus was also been decresed by BFO treatment. BFO treatment has little effect on strawberry and Bartlett pear. Disease index also been tested. We used the disease index to calculate the area under disease progress curve (AUDPC) and the control effect. These results indicated that BFO has high control effect (p<0.05) in grape (29.1%) and apple (26.2%) and has low control effect (p<0.05) in banana (14.9%), kiwifruit (10.6%), citrus (14.0%), strawberry (14.3%) and Bartlett pear (11.4%). Total phenol of7kinds of fruits post BFO treatment has been analyzed. The results indicated that total phenol of grape and apple has notably increased after BFO treatment. The total phenol of banana and strawberry was also increased after BFO treatment. BFO treatment has little effect on kiwifruit, citrus and Bartlett pear. Hydrogen peroxide (H2O2) content also been tested in a short time period after BFO treatment. A3h H2O2-peak has been observed in grape, banana and strawberry after BFO treatment. A6h H2O2-peak has been observed in apple and Bartlett pear. No H2O2-peak has been observed in kiwifruit and citrus after BFO treatment. There is a synergistic effect between H2O2signal molecular and SA signal molecular. The H2O2-peak indicated induction of SA-dependent pathway.2. The mechanism of BFO induced resistance in grape. Grape has been chosen as a model to investigate the underlying mechanism of BFO induced resistance. Gene expression, ezyme activity and important compound in grape skin associated with SA-dependent signaling pathway have been analyzed after BFO treatment. The results indicated that the H2O2content increased2.7folds (p<0.05) after BFO treatment. There is a synergistic effect between H2O2signal molecular and SA signal molecular. Nonexpressor of pathogenesis-related genes1(NPR1) can be activated by SA signal and then combined to the gene promoter. SA signal can also induce the NPR1expression. Our results indicated that, a3.1folds upregulation (p<0.05) of NPR1.1has been observed which associated with the basic resistance. A19.8folds upregulation (p<0.05) of NPR1.2have been observed after BFO treatment which associated with induced resisitance. PR1is the maker gene of SA induced resistance A3.1folds upregulation (p<0.05) of PRI have been tested The activity of chitinase and β-1,3-glucanase increased47%(p<0.05) and29.1%(p<0.05) after BFO treatment. These two enzyme are pathogenesis-related proteins can directly inhibit and kill fungi pathogen The most important phytoalexins is trans-resveratrol. Stilbene synthase (STS) is a key enzyme in the biosynthesis pathway Our results indicated that STS gene upregulated for2.8folds (p<0.05). Trans-resveratrol increased28folds (p <0.05). The SA-dependent signaling pathway further activated the biosynthesis of SA. Our results indicated that, BFO induced SA accumulation in grape skin but has little effect on SAG PAL gene upregulated for2.6folds (p<0.05), while PAL enzyme activity increased99%(p<0.05). The SA product can be further been synthetized into MeSA, which act as a long distance signal to activat SAR in other tissue.3. The effect of BFO on postharvest physiology in grape. There is a balance between reactive oxygen species (ROS) generation and elimination by active oxygen scavenging system to maintain a stable balance in plant cell. The active oxygen scavenging system includes SOD and CAT. Our results indicated that after BFO treatment delayed the decrease of SOD activity in grape and increased the activity of CAT and the CAT activity increased54%(p<0.05) than control. MDA has also been tested which was used as a marker of cell membrane integrity. Our results indicated that, after BFO treatment MDA decresed59%(p<0.05)compared with the control Kyoho grapes changes color rapidly after harvest, with close to90%of fruit showing color change6days post treatment. However, in the BFO-treated group,90%color change occurred10days post treatment, indicating a slower color change rate. In the control group, the POD enzyme activity increased gradually in postharvest grapes; however, BFO treatment repressed the POD enzyme activity, so that on the third and fourth day post treatment, the POD activity was lower than that of the control by28.3%(p<0.05) and25.7%(p<0.05), respectively (Fig.3B). BFO also slowed the dramatic increase in PPO enzyme activity compared to the control grape skins, showing42%(p<0.05) lower activity on the second day post harvest. The respiration rate in the control grapes elevated during storage. The respiration rate was restricted after BFO application. During storage, weight loss increased in both the control and BFO-treated grapes. A suppression of weight loss was observed in the BFO-treated grapes compared with the control. the TSS in grapes declined during the storage period in both the control and BFO-treated groups. There was a slight difference in TSS activity between BFO-treated grapes and the control. A notable TA decrease was observed in control groups, compared to the preserved high levels of TA in BFO treated groups. The difference reached20%(p<0.05). Vitamin C decresed after harvest. BFO treatment could inhibit the decrease of Vitamin C. The Vc content was9.4%(p<0.05) higher in BFO treated grape than control.In conclusion, BFO is an efficient elicitor can be widly used in postharvest fruits. It has great application potential. |
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