recap

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38.3 recap

Plants that live in continually dry or water-saturated environments have structural adaptations to cope with those conditions. Mechanisms that protect plants from drought stress are initiated by a signaling pathway involving abscisic acid. Heat shock proteins help plants acclimate to high and low temperatures. Halophytes have several adaptations to saline habitats, most of which involve mechanisms that lower their water potential. Some plants can tolerate heavy-metal-rich soils that are toxic to most other plants.

learning outcomes

You should be able to:

  • Analyze and compare different methods by which plants respond to saturated environments.

  • Discuss factors that trigger inducible responses to drought in plants, and describe the possible responses.

  • Describe, analyze, and evaluate methods by which plants are able to remove excess salt.

  • Relate phytoremediation to hyperaccumulating plants, and explain how phytoremediation is applied to restore contaminated environments.

Question 1

In the coming decades, climate change may have significant effects on the growth and productivity of plants, in particular the crops on which we depend for our food. What are the physiological effects, and possible genetic responses, of the following, in terms of plant breeding?

  1. In Pakistan, reduced rainfall causes a reduction in wheat yields.

  2. In the Mekong Delta of Vietnam, rising sea level inundates rice fields, causing a drastic reduction in yields.

  1. The effects of reduced rainfall could include dehydration and osmotic stress. Genetic responses might include alterations in leaf anatomy, with a thicker cuticle to reduce evaporation; a more extensive root system to obtain water; and accumulation of solutes in the roots, which would reduce root water potential and result in more water uptake in dry soils.
  2. Flooding reduces the amount of O2 available to the plants and results in reduced respiration. Genetic responses might include increased production of pneumatophores or aerenchyma to supply air to submerged plant tissues.

Question 2

Irrigation leads to increasing salinization of soil. An agricultural researcher wants to develop grain crops able to withstand higher salt concentrations. What type or types of genes might she add to the genomes of the crop plants, and how would these genes function to help the plant withstand salt?

She could add genes encoding proteins that produce salt glands or genes that encode membrane proteins that store excess salt in the vacuole. Sequestering salt in the vacuole keeps it away from the rest of the cell, where it can harm chemicals and reactions. (See Chapter 18 for salt-tolerant plants.)

Question 3

One disadvantage of using hyperaccumulators to clean up toxic waste sites is that some hyperaccumulators grow slowly and produce little biomass.

  1. Why would this be a disadvantage?

  2. Suggest ways in which this disadvantage might be overcome.

  1. The lack of a plant cover would allow the accumulation of toxic ions in the soil.
  2. The genes involved might encode proteins that keep the toxic ions away from the plant cells (e.g., store the ions in glands) or away from the plant cells’ cytoplasm (e.g., store the ions in vacuoles).