Responses of Phospholipase D and Antioxidant System to Mechanical Wounding in Postharvest Banana Fruits

Banana fruits are susceptible to mechanical damage. The present study was to investigate the responses of phospholipase D (PLD) and antioxidant system to mechanical wounding in postharvest banana fruits. During 16 d storage at 25°C and 90% relative humidity, PLD activity in wounded fruits was significantly higher than that in control (without artificial wounding fruits). The higher value of PLD mRNA was found in wounded fruits than in control. PLD mRNA expression reached the highest peak on day 4 in both groups, but it was 2.67 times in wounded fruits compared to control at that time, indicating that PLD gene expression was activated in response to wounding stress. In response to wounding stress, the higher lipoxygenase (LOX) activity was observed and malondialdehyde (MDA) production was accelerated. The activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in wounded fruits were significantly higher than those in control. The concentrations of reactive oxygen species (ROS) such as superoxide anion (O2•-) and hydrogen peroxide (H2O2) in fruits increased under mechanical wounding. The above results provided a basis for further investigating the mechanism of postharvest banana fruits adapting to environmental stress.

Can artificial wounding of beech stems induce necroses?

The paper presents data on the induction of necroses after small injuries to beech stems caused by electrodes during measuring cambium electric resistance. Altogether 121 beech stems of tree class 1–3 (according to Kraft) were evaluated. Among 2,904 mechanical injuries in 121 stems evaluated (24 per stem), 155 injuries induced necroses, hence each 19^th injury induced necrosis. Most stems (33.06%) showed one necrosis, few stems (4.96%) showed even four necroses. 28.93% of stems did not show any necrosis. In order to prevent the infection of wounds and subsequent induction of necroses the authors recommend to treat any wounds with a suitable fungicide after using an equipment causing even negligible wounds of stems.

(474) A Selected Yeast for Control of Aspergillus flavus in Pistachio Orchards

Aspergillus flavus produces aflatoxin, a cancer-causing contaminant of pistachio in many production areas. A superior yeast strain of Pichia anomala has been demonstrated to inhibit the growth of A. flavus in the laboratory. It was selected for further study and potential release based on tests of durability and ability to inhibit A. flavus growth. This strain has been tested in the field for the past two years to evaluate its ability to survive in a field environment and to inhibit A. flavus production. The yeast was evaluated in the field to determine if: 1) the biocontrol yeast can survive in pistachio orchards; 2) the yeast has no phytotoxic effects on the pistachio trees or nuts; and 3) the yeast can be demonstrated to control A. flavus in the field. Studies during 2003 were conducted using a replicated experiment with three yeast concentrations and a water control. Treatments applied later in the season were found to be most effective. Highest yeast concentrations were observed just prior to harvest. Three spray concentrations and a water control were applied to evaluate possible phytotoxic effects on pistachio during 2004. No differences in leaf or nut appearance, in nut percent splits, or dry weight were observed for any of the treatments when compared to the water control. Artificial wounding experiments were also conducted during 2003 and 2004 to simulate the occurrence of early split nuts, the primary repository for A. flavus contamination. A 5× reduction in A. flavus colonization was observed on treated wounded nuts vs. untreated wounded nuts. A 5× reduction in A. flavus sporulation was also observed on treated wounded nuts vs. untreated wounded nuts.

Effects of light intensity and artificial wounding on monoterpene production in Myrica cerifera from two different ecological habitats

The contributions of multiple factors to plant defense and herbivory in different habitats has received limited study. This study examines the contributions of genotypic differentiation and modification by physical factors to chemical defense and herbivory of Myrica cerifera L. in contrasting habitats. The constitutive leaf monoterpene content of M. cerifera was higher in a sunny habitat than in an adjacent shady habitat at a southeastern USA coastal site. Leaf area loss was higher in the shady habitat than in the sunny habitat. A significant negative correlation of monoterpene content and leaf area loss suggests that monoterpenes may play toxic or deterrent roles in these plants. When plants from the two habitats were grown under uniform greenhouse conditions, the contents and compositions of leaf monoterpenes were not significantly different, implying that two ecotypes were not involved. The plants treated in high light intensity had significantly higher monoterpene content, higher growth rate, and denser glandular trichomes than the plants treated in low light intensity. Artificial wounding induced a significant increase of monoterpene production. However, the wounding responses of the plants from the two habitats were not different, nor did irradiance modify the response.Key words: ecotype, herbivory, light intensity, monoterpenes, wounding induction, Myrica cerifera.

Changes in cortical and wood terpenes in Sitka spruce in response to wounding

Terpene levels were measured in bark and wood samples of Sitka spruce (Picea sitchensis (Bong.) Carrière) trees. The trees that had been selected as early or late flushing were subjected to artificial wounding to simulate attack by the white pine weevil, Pissodes strobi (Peck). Samples were taken at four times during the growing season: before wounding, shortly after wounding, and two times later in the season. Terpenes were extracted with hexane and quantified by capillary gas chromatography. There were no significant differences in total bark terpenes between early- and late-flushing trees or between control and wounded trees over all sampling times. There were no significant differences in total wood terpenes between early- and late-flushing trees or among sampling times, but a statistically significant difference was found between control and wounded trees. Eleven individual terpenes accounted for the majority of the terpenes in the extracts. Four bark terpenes showed significant differences with sampling time, two with flushing class, and none with treatment. Five wood terpenes showed significant differences with sampling time, two with flushing class, and nine with treatment. We concluded that flushing had only a minor effect on bark and wood terpene profiles and that wounding significantly increased terpene concentration in wood shortly after injury.

Seasonal Variation in Traumatic Resin Canal Formation in Chamaecyparis Obtusa Phloem

Trunks of Chamaecyparis obtusa were injured to examine seasonal differences in traumatic resin canal formation in secondary phloem. Even after wounding during winter, differentiation of axial parenchyma into epithelium was initiated, and vertical resin canals formed. After winter wounding, resin canal development was slower and the tangential extent of resin canals was narrower than after spring wounding, and it took one to two months until resin secretion began. After spring wounding, the sites of resin canal formation were the 1- and 2-year-old annual rings of phloem. In August, the location of resin canal formation shifted into the current and 1-year-old annual ring. Resin canals never formed in secondary phloem areas that were 3 or more years old. In C. obtusa trunks that are affected by the resinous stem canker, numerous tangentiallines of resin canals are found throughout the phloem, not just recent and 1- to 2-year-old phloem. The present research indicates that these many lines of resin canals were not formed at one time, and that the stimuli that induce traumatic resin canals must occur repeatedly over many years. The data on artificial wounding effects are useful for understanding resinous stem canker.