- You have isolated a gene whose expression is confined solely to the developing leaf
primordia, and have obtained a loss-of-function mutant for this gene. Speculate as to
what phenotype might result in this mutant, and explain the basis for your
speculation. - What is the difference between a daylength-neutral and a long-day plant?
- Describe the ABC model of flower development and speculate as to what phenotype
would result if a C function gene were overexpressed in all whorls. - In snapdragon,Floriculamutants contain shoots with the characteristics of an
inflorescence meristem in place of a floal meristem. Hypothesize what the wild-
type function of theFloriculagene is, and speculate as to why investigators are
interested in overexpressing this gene in Aspen trees. - Describe the major effects of plant hormones on growth and development. Also,
describe how each hormone is percieved by the plant cell and how the signal is
transduced throughout the cell.
4.1 Plant Anatomy and Morphology
Before considering the developmental and physiological processes that can impact plant
biotechnology, one should have some basic knowledge of plant anatomy and morphology.
This section is designed to provide a closer look at internal structures and cells within
the plant.
Most plants are composed of theshoots, or aboveground tissues, androots, the below-
ground tissues (Fig. 4.1). The shoot apex consists of the topmost tissues of a seedling or
plant and contains theshoot apical meristem(SAM) and the developing leaves or leaf pri-
mordia. The SAM is a dome-shaped region of dividing cells at the tip of the stem (Fig. 4.1).
Figure 4.1.Plant anatomy and morphology. The seedling shoot and root systems are indicated, as are
the shoot and root apical meristems, tissues that direct the major growth and differentiation of plants.
Active cell division within the meristem is shown in the last panel; note the presence of two
nuclei in some cells. Modified with permission from Dr. Dale Bentham’s Website (http://
biology.nebrwesleyan.edu/benham/plants/index.html).
84 PLANT DEVELOPMENT AND PHYSIOLOGY