Introductory Biology III BIOL 100C: Introductory Biology III Primary Growth in Roots and Stems Dr. P. Narguizian Fall 2012 Principles of Biology

Vascular and Ground Tissue The majority of tissue in a plant stem is called ground tissue and basically fills the space around the vascular tissue. The three types of ground tissue: parenchyma, collenchyma and sclerenchyma. -enchyma = root word means 'cellular tissue.' Parenchyma is the most common form of tissue in plants and provides a variety of functions, including the storage of food and water. Collenchyma tissue helps support young stems and roots. Lastly, sclerenchyma tissue provides rigid support and protection for the plant stem. The Greek term sclera means 'hard.' This can help you remember that sclerenchyma is hard tissue that provides rigid support.

Shoot System Review The shoot system is the above-ground structure of plants including the leaves, buds, stems, flowers and fruits of plants. We'll focus on the growth of the stem for now, but later on we'll look at other plant structures.

Figure 5 Shoot system (Nodes & Buds). Plant Anatomy Figure 5 Shoot system (Nodes & Buds). The main function of the leaves and stems-which together constitute a plant's shoot system-is harvesting sunlight. The stem of a vascular plant supports the plant, stores nutrients, generates new tissue, and makes and supports leaves. The stem of a vascular plant makes leaves at special sites called nodes. Between two nodes is a segment called an internode. Together, they make up the majority of the stem. In eudicots, the very tip of a stem, where most growth occurs, is called the apical bud (terminal bud). Branches develop from lateral buds called axillary buds, which grow at the upper angle between leaves and the stem. In most plants, the apical bud is dominant over the axillary buds. This phenomenon is called apical dominance. Principles of Biology

The Role of the Meristem in Plant Growth and Development Most animals show determinate growth and stop growing once they reach a certain age. Most plants, however, have indeterminate growth and keep growing their entire lives. Plants maintain undifferentiated stem cells in special areas called meristems for life. Apical meristems, located at the tips of roots and shoots, produce cells that cause the plant to become longer. Stem cells in lateral meristems produce cells that thicken a plant. Principles of Biology

The Meristem and Primary Growth The main location of all growth in the stem is found at the meristems, which are the tissues of the stem capable of cell division. There are two types of meristem in the plant stem: apical meristem, which is found at the tip of the stem, and lateral meristem, which is found surrounding the stem. The growth at the apical meristem that we will now look at is considered primary growth. This type of growth increases the length of the stem, making the plant taller. It happens in both monocot and dicot plants.

Plant Growth and Development Figure 1 Meristems. Plants maintain several regions with undifferentiated cells that can divide and produce cells to build stems and leaves. Root apical meristems extend the roots to allow greater soil, water, and nutrient access. Shoot apical meristems produce the primary plant tissues and body. Axillary meristems can produce branches; they are often activated when an apical meristem has been removed or damaged. Principles of Biology

Primary Growth in Plants Plant Growth and Development Primary Growth in Plants Primary growth: growth coming from the activity of the apical meristem. Primary growth is lengthening growth. The apical meristem also makes roots by producing a series of elongated cells behind a group of tough cells called the root cap. Allows stems and leaves to access more sunlight and permits roots to spread through the soil to access water and minerals. Principles of Biology

Primary growth takes place in the root. Plant Growth and Development Primary growth takes place in the root. A growing root has three distinct regions: The zone of cell division occurs at the apical meristem where new root cells grow in multiple directions. In the zone of elongation, located just behind the root tip, root cells elongate and force the root tip into new areas of soil. In the zone of differentiation, cells differentiate to produce the three fundamental tissue systems found in roots and shoots: dermal tissue, ground tissue, and vascular tissue. Principles of Biology

Plant Growth and Development Figure 2 Plant root micrograph. The different areas of root cell growth are visible in this micrograph of a plant root (Arabidopsis thaliana). The root is stained blue to indicate collagen-rich areas of the root, and highlight cells. (Arrowheads indicate nuclei. C, cortex; En, endodermis; Ep, epidermis; RC, root cap. Scale bar = 100 um). Principles of Biology

Primary growth takes place in the root. Plant Growth and Development Primary growth takes place in the root. Roots that branch from other roots are called lateral roots. Form from a tissue layer called the pericycle, a thin layer of meristematic cells within the roots located between the vascular cylinder and the cortex. As they continue to grow, they reach the epidermis, rupture it, and enter the soil. Principles of Biology

Plant Growth and Development Figure 4 Lateral roots grow outwards from the central tissues of a primary root. Lateral roots begin growing from the internal pericycle of a primary root. The pericycle bulges into the lateral root tissue as it grows. The primordial lateral root continually expands toward the epidermis of the primary root. Eventually, the lateral root breaks through the epidermis of the primary root and enters the soil. Principles of Biology

Plant Growth and Development Primary growth occurs in the shoots, which includes the growth of stems and leaves. The apical meristem produces dermal, ground, and vascular meristems that make the cells for all the tissues of the stem, similar to the root. Principles of Biology

Plant Growth and Development Figure 6 Stem tissues. Like all plant parts, stems have three types of tissues. Compare the different arrangements of tissues in dicots and monocots. Principles of Biology