Agriculture Reference
In-Depth Information
transformed plants exhibited reduced stem growth compared with untrans-
formed controls and two transformed clones showed reduced (
c
.
%) dry
weight, internode length and shoot and root dry weight.
Dwarfing gene transfer
The GA
oxidase gene controls shoot elongation in apple stems. It has been
cloned and inserted back into the apple cv. 'Greensleeves', producing trees
identical with the parent in every way except that they are dwarfed ( James,
).
Gene transfer to prolong storage life
Ethylene plays a key role in fruit ripening (see Chapter
). Its precursor,
methionine, is converted via
S
-adenosyl-L-methionine (Ado-met) to ACC by
ACC synthase, and ACC is converted to ethylene by ACC oxidase. Ripening-
associated ethylene production in fruits is regulated by both ACC synthase
and ACC oxidase activities (Oetiker and Yang,
) and can be inhibited,
in tomato, to varying degrees by creation of transgenic plants with down-
regulation of either the oxidase or the synthase genes (Picton
et al.
,
).
) found that slow-ripening (e.g. 'Fuji') and
rapid-ripening (e.g. 'Golden Delicious') cultivars had corresponding differ-
ences in ethylene production, and these have different allelic forms of the
ACC oxidase gene. James (
In apple Castiglione
et al.
(
) found that adding an extra copy of the apple
ACC synthase or oxidase genes to the cultivar 'Greensleeves' (a rapid-ripening
progeny of 'Golden Delicious') resulted in the fruits, in many cases, producing
much less ethylene than the controls.
Gene transfer for resistance to fungi
Plants which are infected by pathogens synthesize defence-related proteins
such as PR proteins, and anti-microbial peptides including defensins and lipid
transfer proteins. An anti-fungal defensin, Rs-AFP
, has been isolated from
seeds of
Raphanus sativus
and an anti-microbial peptide, Ace-AMPI, from seeds
of
Allium cepa
. The cDNAs encoding each of these have been cloned in a
binary plant transformation vector and transferred to 'Jonagold' apple us-
ing
Agrobacterium
-mediated transformation. Protein extracts from transformed
shoots showed an
express-
ingshoots),orafour-foldincreaseinanti-fungalactivity(Ace-AMPIexpressing
plants) relative to control plants (De Bondt
et al.
,
-
-fold increase in anti-fungal activity (Rs-AFP
).
Trichoderma harzianum
produces chitinolytic enzymes, endochitinase and chi-
tobiosidase, which are active against a number of fungi: chitin being a major
component of the cell walls of ascomycete and basidiomycete phytopathogens,
