Plants exhibit diverse forms, from delicate herbs to towering trees. This variety is made possible by the versatility of plant tissues and cells.
A critical development in plant evolution was the formation of tissues that support and strengthen the plant body known as supporting tissues. These specialised structures allow plants to grow tall, spread their branches, and better withstand environmental stresses.
Supporting tissues represent a range of cell types and tissue systems tailored to meet the structural needs of different plant species.
Let’s explore plants’ primary supporting tissues and their vital roles.
Unlike animals, plants cannot move around their environments. Instead, plants must adapt their form and structure to optimise exposure to sunlight, resist mechanical damage, obtain nutrients and water, and accomplish reproduction.
Plant tissues facilitate shape, strength, and posture control in an otherwise soft, flexible organism. Supporting tissues provide mechanical strength, protect delicate cells and tissues, help transport water and nutrients, and enable plants to grow to greater heights to reach sunlight.
Here, we examine the significant types of plant-supporting tissues and the essential functions they serve.
The Evolution of Supporting Tissues
The need for supportive structures accompanied plants’ move onto land over 400 million years ago. Extensive supporting tissues are found only in vascular plants, enabling complex erect growth.
As plants evolved into larger forms, the proportion of dead, lignified cells increased to provide more complex tissues. The variety of specialised supporting cells gave rise to diverse plant sizes and shapes. From towering trees to tiny herbs, the strength of supporting tissues underlies the remarkable diversity of the plant kingdom.
The Crucial Roles of Supporting Tissues
Supporting tissues allow plants to colonize terrestrial environments by enabling erect growth. Plants face unique structural challenges as relatively soft, flexible organisms rooted in one place.
Gravity exerts a constant downward pull, requiring plants to have strong stems and trunks to avoid collapsing. Supporting tissues reinforce the plant body against bending stresses from wind and rain.
Plants spread their branches, leaves, and reproductive organs into the air and sunlight. Supporting tissues in stems and petioles allow plants to present leaves and flowers while resisting breaking.
Protective supporting tissues help shield inner delicate tissues from damage. Plant-supporting tissues also aid the vascular system in moving water and nutrients efficiently throughout the plant.
Major Types of Plant-Supporting Tissues
Plants have evolved and specialised supporting cell types are aggregated into three major supporting tissue systems: collenchyma, sclerenchyma, and vascular tissue. Each supporting tissue has unique properties to meet specific structural and transport needs.
Collenchyma
Collenchyma consists of living cells with unevenly thickened cell walls. It provides flexible support to actively growing parts of the plant that are still elongating, like young stems and petioles.
Collenchyma allows bending without breaking, then reforms cell walls after deformation to regain strength. Familiar with the epidermis, collenchyma gives mechanical resistance to growing shoots.
Sclerenchyma
Sclerenchyma consists of dead cells with extensively thickened walls containing lignin and cellulose. Two types of sclerenchyma cells exist fibres and sclereids. The cells are long, slender fibres bundled together forming strong cables running through stems and leaves.
Fibres woven into fabrics like flax and hemp demonstrate the strength of these cells. Isodiametric sclereids create complex layers covering seeds and drupes. Durable sclerenchyma lends mechanical rigidity to tissues that have finished elongating.
Vascular Tissues
Xylem and Phloem tissues form the vascular system for transporting water, minerals, nutrients and sugars throughout the plant.
The Xylem moves water and dissolved minerals from roots up stems and into leaves. Lignified xylem vessels and tracheids are hollow dead cells forming pipelines resistant to the pull of water columns. Phloem tissue transports sugars and other metabolites, relying on sturdy fibres for support.
Other Functions of Supporting Tissues
Supporting tissues provide additional benefits beyond mechanical strength. Collenchyma offers protection against herbivores with its resilient cell walls. Outer layers of cork sclerenchyma shield inner stem tissues from desiccation and pathogens.
Hard sclereid shells protect seeds and fruits from predation. Solid structural tissues also help pressurise and direct the flow of fluids through plant pipes and channels.
Conclusion
Supporting plant tissues are integral to the survival and success of plants on land. Mechanical strength, structural stability, and directional growth control allow plants to effectively colonise terrestrial environments.
The versatility of collenchyma, sclerenchyma and vascular tissues enables a vast range of plant morphology. Amazingly, these varied supporting tissues all arose from simple parenchyma ground cells.
The evolution of specialised supporting cell types facilitated the spread of plants across the planet. Next time you admire a stately tree or pick a strawberry, remember the crucial roles played by supporting tissues.
To learn more about common natural vegetative parts in plants, check out this post.