Steroid Testing in Grapes
A recent report by Australian scientists indicates that brassinosteroids, a group of steroidal plant
hormones involved in normal grape plant growth, control ripening in grapes. The levels of the
brassinosteroid, castasterone (derived from horse chestnuts), increased 13 times in Cabernet grapes
once ripening began. The brassinosteroids control the expression of a large number of genes. At
veraison, they turn off genes controlling photosynthesis in the grapes and turn on genes associated
with flavor and sugar levels. Other hormones and ethylene may be involved in ripening fruit as well.
The researchers showed that brassinosteroids can be used to manipulate ripening as well. They
applied small amounts of synthetic brassinosteroids to the skin of some grapes prior to ripening and
treated others with brassinazole, a chemical that inhibits the synthesis of brassinosteroids. Brassinosteroid
application caused veraison to speed up, while brassinazole delayed it.
The practical application of this finding is that in cool climates, ripening may be hastened. At present
brassinosteroids are too expensive to spray grapes, but it would work and is safe. Plant breeders may
be able to use this information to select grapes with certain attributes that allow earlier ripening.
Table grape growers are using plant hormones already to influence maturation of grapes.