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					      Lecture 30


    Plant Defense

        and

Secondary Metabolites


                           BIOL
                           350
                          Spring
                        1   08
                   Plant Defense Responses

   Passive (constitutive) defense     Active (inducible) defense




                                                                        BIOL
Cutin, waxes, suberin help reduce transpiration and pathogen   invasion 350
                                                                       Spring
                                                                     2   08
Structural Defence (passive)




                                  BIOL
                                  350
                                 Spring
                               3   08
Surface wax deposits form the top layer of the cuticle
               Brassica oleracea (cabbage…)




                                                      BIOL
                                                      350
                                                     Spring
                                                   4   08
          Cutin, Waxes, and Suberin
Cutin



                   Wax




Suberin


                                         BIOL
                                         350
                                        Spring
                                      5   08
           Preformed Biochemical Defense
- Plants produce large and diverse array of organic compounds –
  secondary metabolites – that do not have function in growth
  and development
- Primary metabolites: amino acids, sugars, nucleotides, lipids →
  found throughout the plant kingdom
- Secondary metabolites: found in only one plant species or
  related group of species; Example: glucosinolates are only
  present in Brassicaceae (cabbage, mustard, Arabidopsis)
- Secondary metabolites display antimicrobial activity → play
  important role in plant defense
      - protection against herbivory and pathogens
      - attractants (smell, color, taste) for pollinators, and seed-
        dispersing animals
      - agents for plant-plant competition, plant-microbe                 BIOL
                                                                          350
        symbioses                                                        Spring
                                                                       6   08
Three Groups of Secondary Metabolites




  Alkaloids        Flavonoids      Limonoids
   Nicotine       Anthocyanins     Saponins
  Morphine        Salicylic acid     Pinene
   Cocaine           Lignin
   Caffeine
Glucosinolates
                                            BIOL
                                            350
                                           Spring
                                         7   08
Secondary Metabolite Biosynthesis




                                       BIOL
                                       350
                                      Spring
                                    8   08
            The Terpenoids



                                      Limonene
                                        Menthol




           Clary Sage




                                              BIOL
Phytol                       Gibberellin      350
                                             Spring
Retinol (vitamin A)                        9   08
Monoterpenes serving as defenses against insects




                                                BIOL
                                                350
                                               Spring
                                            10   08
Essential Oils are Stored in Surface Glands




Glandular hair of young
leaf of spring sunflower
                                                  BIOL
                                                  350
                                                 Spring
                                              11   08
Two Triterpenes serving as insect feeding deterrents
                          Neem Tree (Azadirachta indica), Africa, Asia




                                Fern (Polypodium vulgare)




                                                                  BIOL
                                                                  350
                                                                 Spring
                                                              12   08
 Terpenes released form insect-attacked plants
            attract natural enemies




 Volatile terpenes released form the leaves of a maize
plant after attack of a lepidopteran larva (and aphids)
                                                              BIOL
attract parasitic wasps that are natural enemies of the       350
                                                             Spring
                  lepidopteran larvae.                  13     08
                     Parasitic Wasps




- Females lay eggs singly in aphid nymphs
- Wasp larvae consume aphids from inside
- As larvae mature and aphids are killed, aphids turn into
  mummies
- After larvae pupate, adult wasp emerge through exit hole cut BIOL
                                                                350
  in mummy                                                     Spring
                                                              14   08
Volatiles guide host
location and host
selection by parasitic
plants (Cuscuta, dodder)




                       BIOL
                       350
                      Spring
                   15   08
                           Runyon et al. 2006
Parasitic Cuscuta Plants   Science 313 p. 1964




                                          BIOL
                                          350
                                         Spring
                                      16   08
       Cuscuta uses volatile cues for host location

Cuscuta pentagona responds
to terpenoids from tomato,
wheat and Impatiens

C. pentagona could
distinguish between tomato
and wheat volatiles

Grows preferably toward
tomato


http://www.sciencemag.org.www.libproxy.wvu.edu/content/vol313/issue5795/images/data/1964/DC1/1131371_S1.mov

                                                                                                       BIOL
                                                                                                       350
 Runyon et al. 2006 Science 313 p. 1964                                                               Spring
                                                                                                   17   08
  Nitrogen-containing secondary metabolites –
                 Glucosinolates

- glucosinolates = mustard oils

- found in Brassicaceae, the Cabbage family

- are broken down by the enzyme myrosinase to release
  defensive substances




                                                      BIOL
                                                      350
                                                     Spring
                                                  18   08
                         BIOL
                         350

The Cabbage Family   19
                        Spring
                          08
                Some important insect pests
Green peach aphid (Myzus       Cabbage looper (Trichoplusia ni)
persicae) feeding on cabbage   feeding on various crucifers




                                                               BIOL
                                                               350
                                                              Spring
                                                           20   08
     Myrosinase-Glucosinolate System


Myrosinase                  Glucosinolates




Various toxic and distasteful breakdown products

                                                       BIOL
                                                       350
                                                      Spring
                                                   21   08
  Insect defense - The myrosinase-glucosinolate system
           Myrosinase               Glucosinolates in vacuoles
        (-thioglucoside            and sulfur-containing cells
        glucohydrolase)                     (“S-cells”)
        in myrosin cells
                               Herbivory      R     S─Glc
R = side chain
                                                  N─OSO3¯
derived from Met, Trp,
Phe
                         Myrosinase
                                              H20
                           R    S
                                             + Glucose
                               N─OSO3¯

              R-N=C=S      R-C≡N            R-S-C≡N              BIOL
            Isothiocyanate Nitrile         Thiocyanate           350
                                                                Spring
                                                             22   08

				
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