English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Received for publication 29 Nov. 2001. Accepted for publication 30 Nov. 2001. This research was supported by the Florida Agricultural Experiment Station, and approved for publication as Journal Series No. R-08293. I gratefully acknowledge support by the Florida Dept. of Citrus and the Univ. of Florida for this work. Professor. A fundamental element of plant development is abscission of mature or ripe fruit, senescent tissues, or damaged organs. Abscission is a complex, organized, and regulated process that occurs in predetermined and defined areas in plants called abscission zones. During abscission, cytoplasmically dense cells, located in abscission zones of plants, undergo division and elongation, followed by increased gene expression and activity of enzymes involved in cell wall modification, such as cellulase, polygalacturonase, and pectinesterase (Roberts et al., 2000). These events have been documented in citrus fruit and leaves (Burns and Lewandowski, 2000; Burns et al., 1998; Goren, 1993; Kazokas and Burns, 1998). The cell wall hydrolases are believed to degrade the middle lamella of adjoining cells in the abscission zone, greatly weakening the bond between organ and parent plant. Cells that line the developing fracture plane eventually differentiate into peridermal scar tissue (Bleecker and Patterson, 1997) and, as such, form a barrier to desiccation and pathogen attack. The plant hormones ethylene and auxin affect abscission. Ethylene promotes abscission, whereas auxin is thought to delay the process (Brown, 1997). Abscission in citrus fruit and leaves can be impeded by the use of ethylene action inhibitors, such as silver thiosulfate (STS) or 1-methylcyclopropene (1-MCP; Pozo and Burns, unpublished data). Ethylene action inhibitors block the binding of ethylene to ethylene receptor(s) located within in the plant and thereby prevent downstream events that lead to abscission or other ethylene-related responses. Ethylene perception is thought to be controlled by a family of five genes in Arabidopsis. Two of these genes, ETR1 and ERS1, encode proteins similar to “two-component receptor systems” and contain an ethylene-binding site within their membrane-spanning domains (Bleecker and Kende, 2000; Hall et al., 2000). Although similar in many respects, notable differences in predicted structure, affinities for downstream interaction with CTR1, and ethylene inducibility of ETR1 and ERS1 transcripts suggest that differential responses to ethylene could be related to the presence or expression of ETR1 and/or ERS1 genes in tissues. During the course of development, plants often shed leaves, fruit, and flowers independently. This suggests that mechanisms exist to preferentially abscise mature fruit without affecting leaves, flowers, or developing fruit. Two major objectives of our abscission research program at the Citrus Research and Education Center in Lake Alfred are to: 1) define changes that occur during the abscission process in citrus fruit and leaves and 2) translate this information into viable abscission agents for the Florida citrus industry. Currently, there are no registered abscission materials that can be used for citrus in the United States. A number of abscission materials have been tested in several citrus fruit–producing countries over several decades. From these materials, Ethrel (2-chloroethyl phosphonic acid) and 5-chloro-3methyl-4-nitro-1H-pyrazole (CMN-P, formerly known as “Release”) emerged as effective fruit looseners for citrus. After application to plant surfaces, Ethrel is transported into the more alkaline intracellular compartments and, as a result, releases ethylene (Cookle and Randall, 1968). Ethrel has been useful as an abscission aid for harvesting plums, cherries (Bukovac et al., 1969; Flore and Bukovac, 1982), and olives (Martin et al., 1981). However, at the higher concentrations often necessary to elicit a desirable effect on mature fruit abscission in citrus and cherry, Ethrel can cause excessive leaf abscission and gummosis (Bukovac et al., 1969; Pozo and Burns, unpublished data). In contrast, CMN-P at low concentrations is a very effective abscission material for citrus because it rapidly elicits mature fruit abscission without causing defoliation, immature fruit drop, or floral abscission (Hartmond et al., 2000b). We used Ethrel and CMN-P to cause abscission in ‘Valencia’ and searched for unique gene expression induced by these compounds. In this communication, results are presented on induction and characterization of abscission-related genes 48 h after application of abscission materials. Data are presented that demonstrate the use of such information to select abscission materials for citrus.

Using Molecular Biology Tools to Identify Abscission Materials for Citrus