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Levels and histochemical localization of peroxidase and polyphenol oxidase, and levels of anthocyanins and (+)-catechin, were studied in fruit of two strawberry (Fragaria ×ananassa Duch.) cultivars (`Oso Grande' and `Chandler'), which show different degrees of susceptibility to enzymatic browning after processing. Although the levels of anthocyanins at the processing-ripe stage may be important in determining pigment stability, and therefore market suitability, the color stability of `Chandler' is apparently determined by the lower endogenous levels of peroxidase and polyphenol oxidase in the processing-ripe stage, which are also accompanied by a lower (+)-catechin content. Polyphenol oxidase was localized almost exclusively in the cortex and to a lesser extent in the pith, showing a complementary pattern to that shown by peroxidase, which was localized in the vascular bundles. Since peroxidase and polyphenol oxidase showed a complementary localization pattern in the fruit, these results strongly suggest a synergic role for these two oxidative enzymes in pigment decay and the associated browning reaction, which occurs in processed strawberry fruit and their derived foods.
Resistance (R) to preloaded gas diffusion was used to follow the evolution of R during cherimoya fruit maturation and senescence. Cherimoya ethane diffusion was linear and gave an R value of 2048 ± 167 s·cm-1 for preclimacteric fruit. R increased linearly during maturation, and significant differences were noted between fruit in which diffusion through the stem scar was or was not blocked with petroleum ielly.
We have compared the ethylene and polyamine metabolism of senescing flowers from two cultivars of carnation (Dianthus caryophyllus L.), one showing climacteric (`Arthur') and the other non climacteric behavior (`Killer'). `Arthur' carnations showed the first symptoms of senescence at day 7, coinciding with maximum ethylene and CO2 production, a peak in the ethylene-forming enzyme (EFE) activity, and a 7-fold increase in free ACC content in respect to the initial value. In `Killer' carnations, however, onset of senescence was 15 days after harvest, and no ethylene or CO2 peak was detected. The lack of ethylene production was due to a constantly low level of free ACC and a low EFE activity. Free polyamine distribution was similar in the two cultivars at the preclimacteric stage, with the spermidine content being about three times that of putrescine. But as senescence progressed, this situation was reversed in `Arthur' carnation, with a predominance of putrescine during the senescence, while it was maintained in `Killer', with no significant changes during senescence. No free spermine was found at any stage of senescence in either cultivar. Thus, a correlation exists between ACC level, distribution of polyamides, and longevity of cut carnation flowers. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).
Two experiments were conducted to assess the ability of a water-absorbing synthetic polymer to reduce water stress injury of seedlings of Pinus pinea L. under greenhouse and field conditions. In both experiments, two rates of hydrated hydrogel, corresponding to 200 and 400 cm3 of stored water, and a control treatment without hydrophilic polymer were tested. Survival periods for the pine seedlings were 1.4 and 2.0 times longer for the 200- and 400-cm3 treatments, respectively, than for a control treatment in a greenhouse assay. In the field assay, only differences in seedling survival between both hydrogel treatments and control were measured. Leaf water potential values of control plants were significantly lower than hydrated polymer treatments in both experiments. From these results, we conclude that the use of hydrophilic polymers may be an important method of increasing the success of reforestation in semiarid regions.