recap

35.5 recap

Carnivorous plants supplement their nutrition by extracting materials from animals. Rapid reflexes have evolved in some of these plants for trapping their prey. Parasitic plants, by contrast, get some or all of their sustenance from other plants. Holoparasites cannot function as autotrophs, having lost chloroplast genes coding for photosynthetic machinery. At least one parasitic plant responds to the same signaling molecule that the host plant uses to attract beneficial fungi.

learning outcomes

You should be able to:

  • Explain how carnivorous plants use nutrients from insects.

  • Create a hypothesis to explain the evolution of a parasitic plant species.

  • Analyze evidence that chemical signals involved in plant−bacteria and plant−fungi interactions represent an ancient process.

Question 1

Describe the process by which carnivorous plants get nutrients from their prey. What is the primary nutrient they acquire?

Carnivorous plants capture animals, digest their proteins, and absorb the amino acids. The primary nutrient they acquire is nitrogen.

Question 2

Some mutant Arabidopsis plants that are very bushy (their shoots are more highly branched than wild-type plants) cannot make strigolactones because of a mutation in a gene necessary for strigolactone biosynthesis. If an investigator applies strigolactones to the plants, they grow normally. What does this experiment suggest about the role of strigolactones in plant growth? How does this add to the story of strigolactones as signals for arbuscules and parasitic plants?

The experiment with mutant Arabidopsis suggests that Arabidopsis uses either its own or exogenous strigolactones for growth regulation and has the appropriate receptor and response mechanisms. This reinforces the idea that an ancient mechanism to attract beneficial microbes is also used for modern plant growth regulation. Or the reverse might be true: the original function of strigolactone might have been as a plant hormone, and its role in plant–microbe interactions might have evolved later.

Question 3

Holoparasitic plants have lost many of the morphological and genetic traits necessary for an autotrophic lifestyle. From an evolutionary standpoint, how do you think this happened? (Hint: Think about selection pressures.)

Holoparasitic plants can gain reduced carbon through association with hosts, so the genes encoding photosynthesis functions are not under selection pressure, because having them would not confer any survival and reproductive advantage for the parasites. So any mutation that renders such a photosynthesis gene nonfunctional will not be deleterious.