Embryogenesis Establishes the Essential Features of the Mature Plant

Plants differ from most animals in that embryogenesis does not directly generate the tissues and organs of the adult. For example, angiosperm embryogenesis forms a rudimentary plant body, typically consisting of an embryonic axis and two cotyledons (if it is a dicot). Nevertheless, embryogenesis establishes the two basic developmental patterns that persist and can easily be seen in the adult plant:

1. The apical-basal axial developmental pattern.

2. The radial pattern of tissues found in stems and roots.

Cauline (stem) leaf

Cauline (stem) leaf

Embryogenesis Angiosperms

Rosette leaf

FIGURE 16.1 Arabidopsis thaliana. (A) Drawing of a mature Arabidopsis plant showing the various organs. (B) Drawing of a flower showing the floral organs. (C) An immature vegetative plant consisting of basal rosette leaves and a root system (not shown). (D) A mature plant after most of the flowers have matured and the siliques have developed. (A and B after Clark 2001; C and D courtesy of Caren Chang.)

Rosette leaf

FIGURE 16.1 Arabidopsis thaliana. (A) Drawing of a mature Arabidopsis plant showing the various organs. (B) Drawing of a flower showing the floral organs. (C) An immature vegetative plant consisting of basal rosette leaves and a root system (not shown). (D) A mature plant after most of the flowers have matured and the siliques have developed. (A and B after Clark 2001; C and D courtesy of Caren Chang.)

Embryogenesis also establishes the primary meristems. Most of the structures that make up the adult plant are generated after embryogenesis through the activity of meris-stems. Although these primary meristems are established during embryogenesis, only upon germination will they become active and begin to generate the organs and tissues of the adult.

Axial patterning. Almost all plants exhibit an axial polarity in which the tissues and organs are arrayed in a precise order along a linear, or polarized, axis. The shoot apical meristem is at one end of the axis, the root apical meristem at the other. In the embryo and seedling, one or two cotyledons are attached just below the shoot apical meristem. Next in this linear array is the hypocotyl, followed by the root, the root apical meristem, and the root cap. This axial pattern is established during embryogenesis.

What may not be so obvious is the fact that any individual segment of either the root or the shoot also has apical and basal ends with different, distinct physiological and structural properties. For example, whereas adventitious roots develop from the basal ends of stem cuttings, buds develop from the apical ends, even if they are inverted (see Figure 19.12).

Radial patterning. Different tissues are organized in a precise pattern within plant organs. In stems and roots the tissues are arranged in a radial pattern extending from the outside of a stem or a root into its center. If we examine a root in cross section, for example, we see three concentric rings of tissues arrayed along a radial axis: An outermost

Casparian Strip Cross Section

Epidermis

Cortex

Endodermis

Pericycle

Casparian strip

Protoxylem

1 mm

Epidermis

Cortex

Endodermis

Pericycle

Casparian strip

Protoxylem

1 mm

FIGURE 16.2 The radial pattern of tissues found in plant organs can be observed in a crosssection of the root. This crosssection of an Arabidopsis root was taken approximately 1 mm back from the root tip, a region in which the different tissues have formed.

layer of epidermal cells (the epidermis) covers a cylinder of cortical tissue (the cortex), which in turn overlies the vascular cylinder (the endodermis, pericycle, phloem, and xylem) (Figure 16.2) (see Chapter 1).

The protoderm is the meristem that gives rise to the epidermis, the ground meristem produces the future cortex and endodermis, and the procambium is the meristem that gives rise to the primary vascular tissue and vascular cambium.

Was this article helpful?

+2 0

Responses

  • IGGI
    What are the ecencial fitures of a plant?
    7 years ago
  • adelinda
    What essential features of the mature plant are formed during embryogenesis?
    4 years ago

Post a comment