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The vegetative plant body consists of a root system and a shoot system. The plant body is modular, made up of repeated units called phytomers. Plants are characterized by apical meristems, totipotency, vacuoles, and cell walls. The tissues of the plant body develop along two axes: the apical–
learning outcomes
You should be able to:
Identify ways in which plants have overcome the problems of scarce resources and an inability to move.
Analyze major differences in plant and animal development.
Examine the process by which a zygote develops into an embryo with an apical−basal axis.
How do plants explore their environment for resources even though they cannot move?
Plant organs, such as leaves and roots, have structures that allow maximal acquisition of gases and nutrients. Also, plants can grow throughout their lifetimes, enabling them to respond to environmental cues. A plant can redirect its growth to exploit opportunities in its immediate environment.
Describe the primary ways that plant development differs from animal development.
Plants grow throughout their lifetimes; animal organs often stop growing at adulthood. Plant cells are totipotent; in animals, only the zygote and perhaps the earliest embryonic cells are totipotent. Plant cells divide unevenly in cytokinesis to orient organ development; in animal development, cell movements are prominent.
Explain how apical–
Apical–basal patterns develop in plants by unequal cell division leading to differentiation between daughter cells destined for the tip, or apex, of the plant and those destined for its base in the early embryo. Radial patterns develop by cell differentiation, whereby the embryo is first a sphere and then a cylinder.
A mutant strain of Arabidopsis lacks apical−basal polarity in the embryo. What would you expect the phenotype of the plant to be?
Without apical–basal polarity, there will be just a massive globular embryo, and root and shoot apices will fail to develop. So these organs will could arise at any place in the developing plant, or not arise at all.
In the next two sections we will look more closely at the unique characteristics of the plant body, by following its development from a zygote into an adult.