Variation of cell wall degrading enzyme activities and tissue firmness from the petal senescence to overripe stages of fruit development was studied in greenhouse-grown cucumbers (Cucumis sativus L. cv. Heinz 3534). Cucumbers exhibited a typical sigmoidal growth curve with a short lag phase (0–8 days after pollination) and extended log phase (8–28 days) followed by a stationary phase. Mesocarp firmness decreased between 10 and 20 days after pollination, then increased until 32 days after pollination. This decrease of mesocarp firmness was accompanied by increased activity of cellulase (3.5-fold), polygalacturonase (20-fold), pectin methylesterase (4-fold), and xylanase (9-fold). By contrast, carpel tissue firmness declined from 8–20 days after pollination, and remained low until 32 days after pollination. Only polygalacturonase and xylanase activities exhibited significant increases (5- and 6-fold, respectively) during softening of this tissue. Further, these peaks of enzyme activity in the carpel occurred 10 days before the corresponding peaks in the mesocarp. These data suggest that mesocarp and carpel tissues of cucumber soften by similar, but not identical mechanisms.
1991. Partial purification and properties of an endo-xylanase from cucumber seeds. -Physio!. Plant. 81: 327-334.An endo-xylanase. 1.4-^-D-xylan xylanohydrolase (EC 3.2.1.8) from immature cucumber (Cucumis sativus L. cv. Heinz 3534) seeds was partially purified using ammonium sulfate fractionation and chromatography on SP-Sephadex and Sephadex G-100 in order to determine its role in xylan metabolism during development. Attempts to further purify the enzyme using chromatography on DEAE-Sephadex, Bio-Gel HTP hydroxylapatite, Sephadex G-200 and con A-Sepharose 4B and native polyacrylamide ge! electrophoresis resulted in a significant decrease or complete loss of enzyme activity. Endo-xylanase had a native molecular weight of 96 kDa as determined by gel filtration, exhibited optimal activity ai pH 5.0 and 48°C, and was most stable from pH 4.0 to 5.0. Using beechwood 4-o-methyl-t)-glucurono-D-xylan dyed with Remazol Brilliant Blue R as substrate, the K^ was estimated to be 0.70 mg ml '. HgCI, at i mM inhibited endo-xylanase completely. Other metal ions inhibited the enzyme in the order Cu^* > Fe'* > Zn'+ > Ca-+ > Mn'*. The eihanol-soluble products of endo-xylanase action on beechwood xylan were isolated and characterized by consecutive chromatography on Bio-Gel PIO and P-2. The major reaction products were xylo-oligosaccharides [degree of polymerization (dp) > 10] but traces of xylobiose and free xylose were also isolated. The formation of xylo-oligosaccharides indicated that the reaction was catalyzed primarily by an endo-xylanase. The partially pure enzyme had no activity towards other cell wall polysaccharides such as cellulose, carboxymethyl cellulose, sodium carboxyi cellulose, potato starch, orange pectin, polygalacturonic acid, arabinogalactan and /J-giucan. However, it was able to hydrolyze larchwood and oat spelts xylan and a polysaccharide component from purified cucumber cell walls. The ability to utilize a substrate from cucumber cell walls supports the hypothesis that endo-xylanase is involved in the development of cucumber seeds.
Treatment of tomato transplants (Lycopersicon esculentum Mill.) with (2-chloroethyl)phosphonic acid (ethephon) at 100 to 500 ppm when flower buds were visible but not open resulted in flower abscission of the first fruiting cluster, adventitious root formation on the plant stem, increased dry-matter content and more rapid plant recovery following transplanting than untreated and/or clipped plants. Fruit maturity was earlier and more uniform on treated than untreated plants. Treatment of transplants with ethephon at 0.28 kg per ha, combined with a fruit-ripening ethephon treatment at 0.9 kg per ha, increased ripe-fruit yield from a once-over harvest compared with untreated or either treatment alone. Flower abscission on transplants was erratic from treatment with 2,500 or 5,000 ppm of butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide), dry matter was increased, no adventitious roots developed, and transplant recovery was similar to that observed with untreated and/or clipped plants. Daminozide treatment had no influence on fruit maturity and yield.
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