plant surface microbiology.pdf

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Bernard R. Glick and Donna M. Penrose
bacteria may vary from one species of plant to another, as well as according to
the age of the plant.
2 Ethylene
In higher plants ethylene is produced from L-methionine via the intermediates,
S-adenosyl-L-methionine (SAM) and 1-aminocyclopropane-1-carboxylic
acid (ACC; Yang and Hoffman 1984). The enzymes involved in this
metabolic sequence are SAM synthetase, which catalyzes the conversion of
methionine to SAM (Giovanelli et al. 1980); ACC synthase, which is responsible
for the hydrolysis of SAM to ACC and 5¢–methylthioadenosine (Kende
1989) and ACC oxidase which further metabolizes ACC to ethylene, carbon
dioxide, and cyanide (John 1991).
Ethylene, which is produced in almost all plants, mediates a range of plant
responses and developmental steps. Ethylene is involved in seed germination,
tissue differentiation, formation of root and shoot primordia, root elongation,
lateral bud development, flowering initiation, anthocyanin synthesis, flower
opening and senescence, fruit ripening and degreening, production of volatile
organic compounds responsible for aroma formation in fruits, storage product
hydrolysis, leaf and fruit abscission, and the response of plants to biotic
and abiotic stress (Matoo and Suttle 1991; Abeles et al. 1992; Frankenberger
and Arshad 1995). In some instances, ethylene is stimulatory while in others it
is inhibitory.
The term “stress ethylene” was coined by Abeles (1973) to describe the
acceleration of ethylene biosynthesis associated with biological and environmental
stresses, and pathogen attack (Morgan and Drew 1997). The increased
level of ethylene formed in response to trauma inflicted by chemicals, temperature
extremes, water stress, ultraviolet light, insect damage, disease, and
mechanical wounding (Bestwick and Ferro 1998) can be both the cause of
some of the symptoms of stress (e.g., onset of epinastic curvature and formation
of arenchyma), and the inducer of responses which will enhance survival
of the plant under adverse conditions (e.g., production of antibiotic enzymes
and phytoalexins).
Chemicals have been used to control ethylene levels in plants. The application
of compounds such as rhizobitoxin, an amino acid secreted by several
strains of bacteria, and its synthetic analog, aminoethoxyvinylglycine (AVG),
can inhibit ethylene biosynthesis; silver thiosulfate can inhibit ethylene action,
and 2-chloroethylphosphoric acid (ethephon), regarded by some researchers
as “liquid ethylene”, can release ethylene (Abeles et al. 1992). Sisler and Serek
(1997) discovered that cyclopropenes can block ethylene perception and are
potentially useful for extending the life span of cut flowers and the display life
of potted plants. In addition, tropolone compounds were isolated from wood
by Mizutani et al. (1998). These compounds, which can inhibit the growth of