Glandular Trichomes and Insect Resistance in
Crops
Several crop species have glandular trichomes that either singly,
or in combination with non-glandular trichomes, provide
resistance to insect pests (Figure 1). Chemicals produced by glandular trichomes vary in the mechanisms by which they
confer resistance, which include insecticidal and/or repellent
effects, as well as behaviour-modifying effects such as feeding or
oviposition inhibition.
When brinjal or potato are cut and exposed to the air, the colour
of the cut surface changes. Phenols in these cut pieces are
oxidized by atmospheric oxygen and become black. Glandular
trichomes on potato and tomato leaves release phenols and
phenol oxidizing enzymes which react to form a sticky substance
which hardens to entrap small-bodied insects. Aphids, for
example, get coated with sticky phenols when they land on these
plant surfaces. In the struggle to escape, they disrupt a second
type of trichome which releases polyphenol oxidases (PPO).
The PPOs oxidize the phenols into quinone, entrapping the
aphids like hardening of cement, resulting in its death.