31.1:
Plant Tissues
Plants are composed of leaves, stems, and roots. The primary function of a leaf is photosynthesis, while the stem lends support and the root anchors the plant allowing the absorption of water and minerals.
Each plant organ comprises meristematic or actively dividing tissues that specialize to become non-dividing permanent tissues. Meristems differentiate into three main types.
Dermal tissue covers the plant in a waxy cuticle that prevents water loss through evaporation. Specialized pores in the cuticle, called the stomata, allow the exchange of gasses.
Vascular tissue such as the xylem transports water and dissolved nutrients from the root throughout the plant. In contrast, phloem distributes organic compounds from sites of photosynthesis to other plant parts.
Ground tissue performs different metabolic functions depending on the cell type and location. For example, parenchyma, collenchyma, and sclerenchyma provide a supporting matrix to the vascular tissue, help store water, and dissolved sugars, and provide structural support to the stem.
31.1:
Plant Tissues
Plants are multicellular eukaryotes with tissue systems made of various cell types that carry out specific functions. Different tissues work together to perform a unique function and form an organ. Organs working together form organ systems. Vascular plants have two distinct organ systems: a shoot system and a root system. The shoot system consists of two portions: the vegetative (non-reproductive) parts of the plant, such as the leaves and the stems, and the reproductive parts of the plant, which include flowers and fruits. The shoot system generally grows above ground, absorbing the light needed for photosynthesis. The root system, which supports the plants and absorbs water and minerals, is usually underground.
Plant tissue systems comprise meristematic and permanent (or non-meristematic) tissue. Cells of the meristematic tissue are found in meristems, which are plant regions of continuous cell division and growth. Meristematic tissue cells are either undifferentiated or incompletely differentiated and continue to divide and contribute to the plant's growth. In contrast, permanent tissue consists of plant cells that are no longer actively dividing.
Meristematic tissues consist of three types, based on their location in the plant. Apical meristems contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length. Lateral meristems facilitate growth in thickness or girth in a maturing plant. Intercalary meristems occur only in monocots, at the bases of leaf blades, and at nodes (the areas where leaves attach to a stem). This tissue enables the monocot leaf blade to increase in length from the leaf base; for example, it allows lawn grass leaves to elongate even after repeated mowing.
Secondary tissues are either simple (composed of similar cell types) or complex (consisting of different cell types). Dermal tissue, for example, is a superficial tissue that covers the outer surface of the plant and controls gas exchange. Vascular tissue is an example of a complex tissue made of two specialized conducting tissues: xylem and phloem. Xylem tissue transports water and nutrients from the roots to different plant parts. It includes three cell types: vessel elements, tracheids (both of which conduct water), and xylem parenchyma. Phloem tissue transports organic compounds from photosynthesis to other plant parts and consists of four different cell types: sieve cells (which conduct photosynthates), companion cells, phloem parenchyma, and phloem fibers. Unlike xylem conducting cells, phloem conducting cells are alive at maturity. The xylem and phloem always lie adjacent to each other. In stems, the xylem and the phloem form a vascular bundle. In roots, this is termed the vascular stele or vascular cylinder.
Adapted from Openstax biology 2e, section 25.1
Suggested Reading
- Reinhardt, Didier, and Cris Kuhlemeier. "Plant architecture." EMBO reports 3, no. 9 (2002): 846-851.
- Spatz, H., L. Kohler, and K. J. Niklas. "Mechanical behaviour of plant tissues: composite materials or structures?." Journal of Experimental Biology 202, no. 23 (1999): 3269-3272.
- Bell, Adrian D., and Alan Bryan. Plant form: an illustrated guide to flowering plant morphology. Timber Press, 2008.