Bot 305; Summer 2000 Name: KEY

Test #1

Give succinct (40 words or less), precise answers in the space provided after each question.

Unless otherwise noted in the margin each section of each question is worth 3 points.

1. (a) Indicate two ways xylem and phloem cells are structurally similar.

Ans.: Both are arranged in long linear files; neither have nuclei; both have reinforced secondary walls.

(b) Indicate one principal way that xylem and phloem cells are structurally different.

Ans.: Xylem cells are completely dead and have no cytoplasm or plasma membrane; phloem cells are living and have both cytoplasm and plasma membrane.

(c) What powers the movement of water through the xylem?

Ans.: The evaporation of water from leaf cells powered by the heat of the sun.

2. (a) What structural feature of plant cells allows them to be “an interconnected commune of living protoplasts”, as they were called by Gunning? Ans.: _plasmodesmata

(b) What important short distance chemical communication occurs between the aleurone layer of a seed and the endosperm of that seed, and how does this communication affect seed germination?

Ans.: The aleurone layer secretes digestive enzymes into the endosperm and this helps promote germination.

(c) What chemical change occurs in many desert seeds during a rainstorm that helps promote their germination?

Ans.: The rain washes out a hormone that suppresses germination and helps maintain dormancy.

3. (a) If you spray a growth hormone on a plant and its growth changes, does this result necessarily mean that the hormone induced the growth change? Explain your answer.

Ans.: No, because the touch stimulus of the spray falling on the leaves could have induced the growth response.

(b) What control experiment would reveal whether the hormone sprayed on the plant was inducing the growth change?

Ans.: If spraying water on the plant induces the same growth response as spraying on the hormone, then the hormone is probably not inducing the growth response.

4. (a) Indicate one kind of general test you could do to learn whether a touch-induced increase in a certain chemical in a plant was important for transducing the effects of touch into a growth response.

Ans.: If that chemical is applied without touch, the plants should still show the touch response; or if the production of that chemical is blocked, there should be no touch response even if touch stimulus is given.

(b) The touch stimulus both stimulates growth and inhibits growth. Explain.

Ans.: Touch inhibits elongation growth and promotes radial growth

(c) Name a hormone that must be produced for thigmomorphogenesis to occur. Ans.: __ethylene_

5. (a) In Table 1, p. 4, what alternative hypothesis is disproved by the results obtained when the bean plants were rubbed 10 x with plastic gloves on?

Ans.: The alternative hypothesis disproved by the results in Table 1 is that the response observed is not due to touch, but rather is due to chemicals on the surface of the fingers.

(b) Tendrils maintained in darkness for three days do not coil when touched. Is this because they do not perceive the touch stimulus? Give evidence for your answer.

Ans.: No, because they will coil following illumination, indicating that the stimulus was perceived but energy was required before the response could occur.

6. (a) What is meant by the threshold level of a stimulus?

Ans.: This is the minimal level of stimulation needed to induce a response.

(b) What would be the disadvantage to the Venus fly trap if it had too low a threshold level of stimulus for closing the trap?

Ans.: The trap would be set off and close in response to such stimuli as rain, and thus be less available to trap insects (food).

(c) Contrast how long a Venus fly trap would stay closed if it closed on a small rock compared to if it closed on a fly. What mechanism is the basis of this difference?

Ans: It would be closed longer if it closed on a fly. Nutrients released from the digested fly keep the trap closed. No nutrients would be released from the rock, so the trap would open soon after it closed on it.

7. (a) What is a protease, and why does having more of a protease inhibitor help protect a plant against insect feeding?

Ans.: A protease is a protein that breaks apart other proteins. Insects cannot digest the plant parts it eats if its digestive proteases are inactivated by a protease inhibitor.

(b) Plants need proteases to control the turnover or "half-life" of their own proteins. Why does the protease inhibitor made in plants in response to injury not harm the plant?

Ans.: Because it stores the inhibitor inside its vacuole, away from its own proteases.

(c) Why do parts of the plant that are not injured begin to make protease inhibitor when another part of the plant is injured?

Ans.: Because a hormone signal moves from the site of injury to other parts of the plant where it induces the production of protease inhibitor.

8 (a) What do octadecanoid compounds like linolenic acid have to do with plant defense responses?

Ans.: They are intermediates in the biosynthetic pathway leading to the production of jasmonic acid, which can induce the protease inhibitor that blocks insect digestion.

(b) How could a sagebrush plant induce the production of more protease inhibitor in a nearby tomato plant enclosed in the same container?

Ans.: By releasing methyl jasmonate, a volatile compound that induces protease inhibitor.

(c) Plant A expresses an antisense RNA complementary to the sense mRNA of prosystemin. Is plant A less susceptible to insect feeding? Explain your answer.

Ans.: No, it is more susceptible, because it produces less prosystemin, a precursor of systemin, the hormone that induces protease inhibitor in uninjured parts of the plant.

9. (a) Where is volicitin made and what chemical esponse does it induce in plants?

Ans.: Volicitin is made by army worms and placed in the ir saliva. It induces the production of volatile substances in theplant that can serve as attractants to wasps that parasitize the army worms.

(b) How does the chemical response induced by volicitin help the plant?

Ans.: They attract parasitoid wasps to the army worms, and these wasps lay eggs in the worms. The larvae that hatch from the eggs feed on and kill the army worms, which ultimately reduces worm feeding on the plant.

10. (a) In Fig. 1 (p. 4), what is the question asked, what is the answer, and what is the significance of this answer in relation to understanding how plants defend themselves against pathogens?

Ans.: The question asked is does TMV (viral) infection induce the production of methyl salicylate [MeSA] in plants, and the answer is Yes. This is significant because it shows that viral infection can induce the production of a volatile compound[MeSA] that is known to be a compound that aids in plants' defense against pathogens..

(b) In Fig. 1(p. 4), what is meant by a mock inoculation and what alternative hypothesis is disproved by the results of the mock inoculation shown?

Ans.: A mock inoculation is one in which the plant is injected with water instead of with a pathogen. The alternative hypothesis disproved is that the response [MeSA production] was due to the injury of inoculation rather than to the virus.

(c) In Fig. 2 b, which gives the results of an experiment illustrated in Fig. 2a, the dark spots in the row marked PR-1 represent the amount of mRNA for PR-1. What do the R+ and R- columns mean and what conclusion can be drawn from the fact that in Fig. 2b there is more mRNA for PR-1 in the R- column than in the R+ column? Your answer should include an explanation of what PR-1 is.

Ans.: Pr-1 is a pathogen response protein or pathogen related protein that helps plants defend themselves against pathogens. R+ columns give the results when volatiles given off in the donor container are cleaned of MeSA before they move into the Receiver container. R- columns give the results when these volatiles are not cleaned of MeSA. The conclusion is that the MeSA gas given off by a plant inoculated in the donor container can turn on the genes that make the mRNA for a defense protein.

Bot 305; Test #1, continued Name:

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