Plant Responses to Internal and External Signals Chapter 39 Plant Responses to Internal and External Signals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Plant versus Animal Signal Responses In what ways do plant signaling and response pathways differ from animal pathways? Plant hormones do not circulate; animal hormones do. Plants do not respond to touch; animals do. Animal cells have many more protein kinases than plant cells. all of the above none of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Plant Hormones Spraying plants daily with compound X causes dwarfism, compared with untreated control plants. Is this evidence sufficient to conclude that compound X is a plant hormone? yes No, a receptor for compound X must be identified. No, compound X must work at nanomolar concentrations. No, a second messenger must be identified that transduces the compound X signal. No, plants must synthesize compound X at physiologically active concentrations. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Plant Hormone Genetics To study the signal transduction pathway for hormone Y, one should look for mutant plants that do which of the following? fail to respond when hormone Y is applied show a constitutive response even in the absence of hormone Y are rescued by application of hormone Y either a or b any of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Phytochrome Tomato plants grown in shade show increased susceptibility to herbivory by insects compared to plants grown in light. If this effect is mediated by phytochrome, then which of the following is/are true? It will be reversed by far-red light. It will be reversed by red light. Phytochrome-deficient mutants will be less sensitive to herbivores. Both a and c are true. Both b and c are true. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Stress Signaling An Arabidopsis mutant deficient in the G-protein-coupled receptor protein gene GCR1 exhibits hypersensitivity to abscisic acid in assays of gene expression and stomatal closure (S. Pandey & S. M. Assmann, Plant Cell 16 (2004):1616–1632). These results indicate that the role of GCR1 in abscisic acid signaling is which of the following? GCR1 is a receptor for abscisic acid. GCR1 is an inhibitor of abscisic acid signaling. GCR1 stimulates abscisic acid synthesis. Abscisic acid signaling inhibits GCR1. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

GCR1 GCR1 mutant plants are more drought resistant than wild-type plants. What other phenotypes may be expected of these mutants? cold resistance salt tolerance reduced seed germination all of the above none of the above Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

Gene-for-Gene Disease Resistance Why do bacteria have Avr alleles that are recognized by plant R genes? In other words, what prevents Avr alleles that do not interact with R genes from becoming fixed in the pathogenic bacterial populations? Avr genes cannot mutate without losing their function in pathogenicity. Plant R loci can mutate faster than bacterial Avr genes. Plants have numerous R genes, most of which have multiple variants, so any Avr allele will eventually encounter a host plant with an effective R gene. Bacteria limit their Avr alleles to those that won’t completely eliminate their host plants. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.