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Daniel L. Ward, Eric P. Beers, Ross E. Byers, and Richard P. Marini

Preharvest abscission of apple [Malus ×domestica (L.) Borkh.] fruits causes significant crop loss in many years. In this study, fruit cutting was used to induce abscission in August and September. Abscission zones of `Redchief Delicious' Mercier strain fruits were sampled 0, 2, 4, and 6 days after cutting. Thin-layer-plate assays were developed and used to identify hydrolytic enzymes active in the abscission zone (AZ) after induction. Increased activity of cellulase, but not polygalacturonase, was detected in the AZ following cutting. Cellulase activity was consistently high in AZs 4 days after cutting. Both AVG (652 mg·L–1) and NAA (10 mg·L–1) applied 2 or 4 days after cutting delayed drop, but NAA delayed drop 1.6 days longer than did AVG. Fruits treated with AVG dropped over a longer period than did control or NAA-treated fruits. Chemical names used: aminoethoxyvinylglycine (AVG); naphthaleneacetic acid (NAA).

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Yoshiko Yambe and Kiyotoshi Takeno

The germination percentage of Rosa multiflora Thunb. achenes was greatly increased when they were treated with 1% Driselase, a macerating enzyme, for 36 hours. The seeds germinated more rapidly when the achenes were treated with the enzyme for a longer period. Treatment with Cellulase Onozuka improved seed germination at a lower concentration than did Driselase. Pure preparations of pectinase and cellulase had effects similar to treatment with the enzymes noted. Treatment with pectinase was more efficient than treatment with cellulase. These enzymes likely loosened the bond between cells along the suture of the pericarp and forced the pericarp to split.

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William C. Kazokas and Jacqueline K. Burns

Mature and immature `Valencia' orange [Citrus sinensis (L.) Osbeck] and immature `Valencia' orange and `Tahiti' lime (Citrus latifolia Tan.) fruit with attached pedicels were treated with 8 μL·L-1 ethylene for periods up to 24 hours. Endo-β-1,4-glucanase (cellulase) activity and gene expression were determined in fruit abscission zones during and after ethylene exposure. Cellulase activities were not detected in mature `Valencia' orange and immature `Tahiti' lime fruit abscission zones immediately following harvest and after 6 hours of ethylene treatment. After 12 hours of ethylene treatment, cellulase activity increased and was highest after 24 hours. Cellulase gene expression preceded the rise in cellulase activity and was detectable after 6 hours of ethylene treatment, but then declined after 12 hours. Following transfer to air storage, abscission zone cellulase activity in mature `Valencia' fruit remained high, whereas activity in immature `Tahiti' fruit declined. After 168 hours air storage, activity in abscission zones of mature `Valencia' fruit decreased slightly, but activity in abscission zones of immature `Tahiti' lime fruit increased to the highest level. Expression of abscission zone cellulase gene Cel-a1 in abscission zones of mature `Valencia' fruit markedly increased after transfer to air and was highest after 48 hours air storage. Cel-a1 expression returned to low levels after 168 hours of air storage, but expression of cellulase gene Cel-b1 remained at low levels throughout the air storage period. Expression of Cel-a1 and Cel-b1 declined in fruit abscission zones of immature `Valencia' and `Tahiti' lime fruit upon transfer to air. After 168 hours of air storage, expression of Cel-a1 again rose to high levels but Cel-b1 remained low. The results suggest that differences in cellulase activity and gene expression measured in mature and immature fruit abscission zones during ethylene treatment and subsequent air storage may, in part, explain the differential response of mature and immature fruit to abscission agents.

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Daniel Ward and Richard P. Marini

In three experiments, apple trees (Malus ×domestica Borkh.) were sprayed, when fruits were 20 to 30 mm in diameter, with a combination of ethephon (800 mg·L-1) and carbaryl (600 mg·L-1) to induce abscission of all fruits on the tree. Two days after treatment (DAT), most treated fruits stopped or slowed increasing in diameter, fruit water potential was less negative, and starch accumulation was less than for nontreated fruits. Cellulase activity appeared in the abscission zone by 4 DAT. Fruit growth cessation following treatment was probably due to inadequate assimilate supplied to the fruit, but assimilate flow slowed before cellulase activity was apparent in the abscission zone. Chemical names used: 2-chloroethyl phosphonic acid (ethephon); 1-naphthyl (N-) methylcarbamate (carbaryl).

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F.M. Woods, J.S. Kotrola, D.G. Himelrick, T.M. Brasher, and F.M. Basiouny

Fruit of two rabbiteye blueberries (Vaccinium ashei Read cvs. Premier and Tifblue) were analyzed at five stages of growth and development for cell wall softening enzymes in relation to pectin solubilization. The enzymes examined were β-galactosidase, cellulase, pectinesterase, and polygalacturonase. The decrease in fruit firmness was associated with increased activities of cellulase, polygalacturonase, and pectinesterase, which preceded the former enzymes. The activity of β-galactosidase remained relatively unchanged throughout. The pattern of enzyme activities from both cultivars were similar. Results from this study indicate that these enzymes may play a crucial role in overall fruit shelf life and hence postharvest marketing duration.

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Jim Downer, Ben Faber, and John Menge

Mulches can exert positive (disease controlling) or negative (disease enhancing) potential when applied to young avocado (Persea americana) trees. Regulation of root disease in avocado is a complicated process that is affected by host resistance, inoculum density, temperature, soil salinity and soil water potential. There are short-term immediate effects from mulching and subtle long-term effects that regulate disease caused by the root rot pathogen Phytophthora cinnamomi. Short-term effects include increased soil moisture and soil temperature moderation. Long-term effects include increases of: soil mineral nutrients, soil aggregation and drainage; microbial activity; and cellulase enzyme activities. Biological control of Phytophthora in mulched soil is partially regulated by cellulase enzyme activities. This soil enzyme concept of biological control is discussed in regard to the classical Ashburner method of biological control.

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Lanqing Wang, Yinfeng Li, Dehai Liu, Chaohui Zhang, Yuancheng Qi, Yuqian Gao, Jinwen Shen, and Liyou Qiu

weight of inoculated substrates. Respiration intensity of immobilized spawn and solid spawn was determined using the small-skep method based on carbon dioxide (CO 2 ) absorption ( Chinese Society of Plant Physiology, 1985 ). Cellulase activity, including

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Wei Deng, Yunling Xie, and Yilan Qiu

released their contents, including two sperm cells. Ovule dissection. Pepper contains a polycarpous ovary with more than 100 anatropous ovules. These ovules were incubated in an enzyme solution containing 0% to 1.5% (w/v) cellulase RS (Yakult Pharmaceutical

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Kang-Di Hu, Xiao-Yue Zhang, Sha-Sha Wang, Jun Tang, Feng Yang, Zhong-Qin Huang, Jing-Yu Deng, Si-Yuan Liu, Shang-Jun Zhao, Lan-Ying Hu, Gai-Fang Yao, and Hua Zhang

consumer acceptability ( Giovannoni, 2007 ; Grierson et al., 1986 ; Musse et al., 2009 ). Fruit softening is a complex process that results from loosening of the cell wall. Many enzymes such as pectinmethylesterase, polygalacturonase, cellulase, and

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Shulin Li and Preston K. Andrews

The activities of the fruit ripening enzymes cellulase, polygalacturonase (PG) and pectin methylesterase (PME) were detected during the development of sweet cherry (Prunus avium L.) fruit. Cellulase and PG activities of pericarp tissue increased 4-10 times between hypanthium abscission and harvest. PME activity remained high throughout this period of fruit development. There was a positive correlation between the anthocyanin content of the pericarp and both cellulase and PG activities. Concomitant with the increases in the activities of these ripening enzymes was a decrease in fruit firmness. The increases in cellulase and PG activities were checked following two-weeks storage at 10 C after harvest. The purification and characterization of the putative cellulase and PG enzymes will be discussed, together with attempts to chemically inhibit their activities and modify fruit softening.