Fundamentals of Plant Physiology

Introduction

Plant physiology is a discipline of botany concerned with physiological processes and activities of plants. It’s a descriptive study of variation and structure at the molecular and cellular level that leads to investigation of ecological, physiological, and biochemistry-related elements of plants.

Plant physiology is the study of all of a plant’s internal functions, including the chemical and physical mechanisms that are connected with life in plants. This encompasses research at many scales of size and time. Photosynthesis, molecular interactions and internal diffusion of water, minerals, and nutrients are at the molecular level. Plant development, seasonality, dormancy, and reproductive control are all activities that take place on a large scale. Phytochemistry and phytopathology are two major subfields of plant physiology.

Plant physiology is the initial line of defence and the primary means of interaction with the environment and climate.

Table of Contents

• What Is Plant Physiology?
• Water and Nutrients in Plants
  • Water Transport
  • Nutrient Production and Transportation
• Production of Primary and Secondary Metabolites
• Physiology of Plant Growth and Development
• Frequently Asked Questions (FAQs)

What Is Plant Physiology?

Plant physiology is the study of plant function and behaviour, and it includes all of the dynamic processes of growth, reproduction, metabolism, defence, and communication that keep plants alive.

Because the majority of these activities occur at the level of cells, tissues, and organs, there is a close connection between plant physiology and plant anatomy, owing to the close association between structure and function in plants. Furthermore, because much of the metabolic activity within a live cell occurs at the molecular level, a thorough grasp of a plant’s physiology requires a strong foundation in chemistry and physics.

Plants rely on soils for mineral nutrients and water, which are replenished via biogeochemical cycles. Water and minerals must be carried through the xylem once they have been absorbed, and this movement is propelled by the loss of water vapour from leaves (transpiration) and the cohesive and adhesive characteristics of water.

Sugar-rich assimilate must also be transported (or translocated) through the phloem. Plant hormones are crucial for delivering messages throughout the plant body. The concentration of carbon dioxide in the leaves, the positioning of stems, roots, and leaves, and the transport and retention of water are all examples of how plants regulate their internal conditions throughout this section.

Water and Nutrients in Plants

Water is essential for the survival of plants. In most organisms, it is the most abundant component. Water makes up more than 70% of the weight of non-woody plant parts in most cases. The water content of plants fluctuates on a regular basis. The continual flow of water through plants is critical for their growth and survival.

Water Transport

Water is required for plant development to occur. Plants have a complicated xylem system that transports water from the soil to the leaves, where it is converted to energy. Through a process known as transpiration, the xylem transports water absorbed in the roots to the top of the plant. As the water in the leaves evaporates, more water flows upward to fill the void. Consider it a plant’s blood vessel system: the leaves serve as the plant’s heart – a driving force that moves water throughout the plant – and the xylem serves as the blood vessels. Properties of water such as adhesion and cohesion, in which water adheres to itself and the xylem walls, aid in the water’s upward movement.

Nutrient Production and Transportation

Plants, like humans, require nutrients to grow and develop, yet unlike humans, they make their own nutrients. Chlorophyll is a substance found in all plant cells that allows them to capture solar energy and produce glucose (or sugar). Photosynthesis is the process through which plants produce glucose. Glucose is the sugar found in meals such as candy and bread.

Because the entire plant, not just the green leaves, requires this sugar, plants have created a system called phloem to transport sugar and other nutrients throughout the plant. Phloem is similar to xylem in that it is a network of tubes within the plant that transport nutrients, but there is one major difference: xylem only travels in one direction, like blood, whereas phloem distributes nutrients throughout the entire plant, much like our digestive system.

Production of Primary and Secondary Metabolites

Metabolites are the intermediate products of metabolism, which are catalysed by a variety of enzymes found naturally within cells. Antibiotics and pigments are examples. Small molecules are commonly referred to as metabolites. Fuel, structure, signalling, catalytic activity, defence, and interactions with other species are all functions of metabolites.

Plants, humans, and bacteria all create metabolites. There are two types of plant metabolites:

• Primary Metabolites
• Secondary Metabolites

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Metabolites And Biomacromolecules

Primary Metabolites

These are the chemical substances that are created during the processes of growth and development. They also play a significant role in respiration and photosynthesis, two of the most basic metabolic activities. During the growth phase, the primary metabolites are produced. They are known as central metabolites and are responsible for maintaining the body’s physiological functioning. They are intermediate products of anabolic metabolism that the cells use to produce major macromolecules.

Amino acids, vitamins, and organic acids are some of the most common industrial metabolites. Alcohol is the most commonly produced primary metabolite on a wide scale.

Secondary Metabolites

It can be difficult to distinguish between primary and secondary metabolites. Primary and secondary metabolites share many of the same intermediates and are produced from the same core metabolic pathways at the biosynthetic level. Secondary metabolites are found in small amounts in most cases, but not always, and their production can be widespread or limited to specific families, genera, or even species.

The adaptive importance of most secondary metabolites was unrecognised for many years. These substances were formerly assumed to be metabolic wastes, or non-functional end products of metabolism. Many secondary metabolites have vital ecological functions in plants, as we now know:

• Plants are protected from herbivores and microbiological diseases by secondary metabolites.
• Pollinators and seed-dispersing animals are attracted to them by their odour, colour, and taste.
• They play a role in plant-microbe symbioses as well as plant-plant competition.

The ecological roles of secondary metabolites have a significant impact on plants’ ability to compete and survive.

Terpenes, phenolics, and nitrogen-containing compounds are three chemically separate groups of secondary metabolites found in plants.

Physiology of Plant Growth and Development

Biogenesis and Expansion of the Cell Wall

Although the chemical composition and microscopic structure of the cell walls of prokaryotes, algae, fungi, and plants differ, they all fulfil two basic functions: maintaining cell volume and defining cell shape. Plant cell walls are complex and varied in structure and composition due to their many functions.

The plant cell wall is significant in human economics in addition to these biological activities. Plant cell walls are used commercially as a natural product in the production of paper, textiles, fibres (cotton, flax, hemp, and others), charcoal, lumber, and other wood products. Extracted polysaccharides, which have been manipulated to generate polymers, films, coatings, adhesives, gels, and thickeners in a wide range of goods, are another prominent usage of plant cell walls.

An Overview of Plant Growth and Development

A precise and well-ordered sequence of events leads to the maturation of a plant from a single fertilised egg. The zygote, or fertilised egg cell, splits, develops, and differentiates into more sophisticated tissues and organs. Finally, these actions result in the intricate organisation of a mature plant, which blossoms, yields fruit, senesces, and dies. Development is the total of these events, as well as their underlying genetic instructions and biochemistry, as well as the many other elements that lead to an orderly progression through the life cycle.

Growth, differentiation, and development are three phrases commonly used to describe the various changes that a plant goes through over its life cycle.

Plant Growth

Growth is a quantitative concept that primarily refers to changes in size and mass. Growth is essentially an unstoppable rise in volume for cells. Growth in tissues and organs is usually accompanied by an increase in both cell number and cell size. A number of quantitative measurements can be used to assess growth.

Phases of plant growth includes:

Formative Phase

Plants develop by cell division. Existing cells divide to produce new ones. Mitosis is the name given to the process of cell division in plants. It is accomplished in two steps:

• Karyokinesis is the division of the nucleus.
• Cytokinesis is the division of cytoplasm.

Cell division begins in the meristematic area of higher plants.

Cell Enlargement and Differentiation

The development of protoplasm, water absorption, forming vacuoles, and the addition of cell walls to thicken and permanently increase the size of cells, tissues, and organs happen at this stage.

Cell Maturation

At this stage, the enlarged cells take on a definite shape and form. This helps in the differentiation of cells and tissues.

Plant growth is influenced by a number of factors, including:

1. Temperature: As the temperature rises, growth accelerates.
2. Light: The intensity, duration, and quality of light all have an impact on various physiological processes in plants.
3. Water: Water is a necessary component of plant growth. They thrive when given enough water to flourish. They even react when there is a lack of water.
4. Plant Nutrients: Plants require a sufficient amount of nutrients to grow properly. Plant growth is influenced by the quality and quantity of nutrients.
5. Regulators of Plant Growth: Auxin, cytokinin, gibberellins, and other plant growth regulators are supplied to plants to control their growth.

Differentiation

The process through which cells specialise into morphologically and physiologically different cells is known as differentiation. Dedifferentiation is the process by which mature cells divide and differentiate afterwards. This is most common in tissues that have been injured. The wound is repaired because the parenchyma cells are dedifferentiated.

Development

The term “development” refers to all of the changes that occur during a plant’s life cycle. Plants respond to their surroundings by taking various pathways and forming various structures. In comparison to adult plants, the leaves of a young plant have different structures.

The sum of growth and differentiation is development. It is controlled by both extrinsic and intrinsic variables.

The events of growth, differentiation, and development are all interconnected. If the cells do not grow and differentiate, the plant will not develop.

Plant Stress Physiology

Energy is required for the organism’s structural organisation to be maintained throughout its lifetime. Maintaining such a complicated arrangement over time requires a steady flow of energy.

The outcome is a constant flow of energy across all living creatures, providing the dynamic driving force for critical maintenance activities like cellular biosynthesis and transport, allowing them to preserve their unique structure and function, as well as their ability to replicate and expand. Homeostasis is a meta-stable condition resulting from the maintenance of a steady-state.

Any change in the environment has the potential to disturb homeostasis. Biological stress is defined as the modulation of homeostasis by the environment. As a result, plant stress denotes an adverse effect on a plant’s physiology caused by a sudden transition from an optimal environmental condition in which homeostasis is maintained to a suboptimal condition destroying this initial homeostatic condition.

Thus, plant stress is a relative phrase since measuring a physiological phenomenon in a plant species under a suboptimal, stress environment versus measuring a similar physiological occurrence in the same plant species under optimal conditions is always used to assess the impact of stress.

The following types of stress are experienced by plants:

• Salt stress – The presence of excessive levels of sodium and calcium salts in the plant body causes salt stress. It causes a change in the structure of the cell, as well as dehydration and disruption of metabolic activities. As a consequence, cell and plant growth are reduced.
• Water stress – It refers to both an excess and a scarcity of water. If there is a lack of water, plants become yellow and wilt. Excess water in the soil inhibits the growth of shoots and roots, resulting in the blackening of root tips and the yellowing of leaves.

Related Links:

• Passive Transport
• Phases of Growth in Plants
• NEET Flashcards: Plant Growth and Development
• NEET Flashcards: Transport in Plants
• NEET Flashcards: Photosynthesis in Higher Plants
• NEET Flashcards: Respiration in Plants