Algae Growth Mechanisms: BDC221/BDC231 Unit 3.2

• Unit 3.2 focuses on the growth of lower plant diversity and algae, typically taught in BDC221/BDC231 courses.
• The unit emphasizes understanding the various growth mechanisms, distinguishing types of growth, and factors controlling growth.

Objectives

• Understand the variety of growth mechanisms algae exhibit.
• Distinguish among different types of growth.
• Solve problems determining the type of growth via written info, drawings, or graphs for algae, and justify the decision.
• Understand internal and external factors that control growth.
• Define growth rate in various algae.
• Solve problems interpreting growth rate data in graphs or tables.
• Understand saturation and limitation of growth.

Background Concepts

• Essential to know distinguishing features of prokaryotes and eukaryotes at the cellular level.
• Classify the algae.
• Grasp the concept of rate that is also defined as change per unit of time.
• Understand basic photosynthesis, and factors affecting rates of photosynthesis.
• Know the concept of plant nutrients.

Reading Guidelines

• Skimming involves briefly reviewing text for headings and highlighted areas, like quickly scanning a newspaper.
• Reading consists of going through all text to understand an overview, do not get bogged down in details.
• Studying requires reading the text and taking notes, highlighting important points.
• Thorough study includes reading, taking notes, highlighting, rearranging points non-linearly (mind mapping), answering questions, identifying difficulties, and consulting additional references.
• Revising involves reviewing material studied previously.
• This document requires a thorough study.
• Readings and links on growth & organization are read and studied.

Growth in Lower Plants

• Multicellular lower plants have different growth patterns, from diffuse growth to localized meristems.
• Complexity of thallus increases, leading to more cell specialization and localized cell division in meristems.

Types of Growth

• Diffuse growth involves any cell being capable of cell division.
• Blue-green alga Oscillatoria, green alga Ulothrix, and brown alga Ectocarpus exhibit diffuse growth.
• Localized growth restricts cell division to meristematic regions (apical, intercalary, or basal).
• Apical growth: Meristem is at the apex (tip) of the thallus's upright part, primary meristem often consists of a single cell or multiple apical cells.
• In single apical cell cases, one cell cuts off and divides to form thallus cells.
• Apical growth is typical in Dictyotales, Sphacelariales, and most red algae.
• Intercalary growth: meristematic region not apical or basal but within the thallus.
• Trichothallic growth occurs when cell division happens at the base of a filament or colorless hair and is seen in Phaeophyceae like Tilopteridales and Desmarestiales.
• Regional growth, a type of intercalary growth, is common in parenchymatous lower plants, with the meristematic zone inside the thallus, not at the base of a filament or hair.
• Laminariales sporophytes exhibit regional growth, meristem is in the transition zone between blade and stipe. New blade cells cut off above, stipe cells below this meristem. Multi-bladed forms have each bladelet with its own meristem at the attachment point.
• Laminariales features a secondary superficial meristematic region called the meristoderm for increasing thallus girth (thickness).

Control of Growth

• Endogenous (internal) and exogenous (external) factors influence growth, typically working together.
• Hormones usually control endogenous growth
• Environmental factors control exogenous growth.
• Rhodomorphin is a hormone in red alga Griffithsia for wound repair; hormonal control in algae lacks clear evidence though.
• Growth in annual/ephemeral algae slows/stops at reproductive maturity.
• Young Saccorhiza dermatodea sporophytes grow until autumn in eastern Canada, reproductive maturity gets induced by short daylength conditions, which stops length growth.
• Sterile paraphyses and zoosporangia get produced at this time.
• Cessation of linear growth is potentially due to shortage of energy reserves that divert energy to sori production, decreasing nutrient availability, or hormonal control.
• Exogenous control: environmental factors affect growth in all algae; seasonal algae show seasonal growth changes, often because of the environment.

Influences on Algal Growth

• Algal growth influenced by changes in environmental variables like light, nutrients, temperature, herbivory, and the release of growth substances.
• Light quantity (irradiance), exposure duration (daylength) and light quality (spectral composition) are all light environment aspects which affect algal growth.
• Different algae have varying Pmax, different compensation points, and different photoinhibition levels, varying concentration and composition of photosynthetic pigments, and thallus optical properties.
• Daylength controls algal growth/development, especially reproduction onset (photoperiod effects).
• Growth can be affected by light exposure duration which is independent of photoperiodic effects.
• Spectral composition changes with water depth/quality, varying photosynthesis and growth based on pigment concentration, and, to a lesser extent, pigment composition within an alga.
• High pigment concentrations enable many algae to compensate for less light in deep/shady areas, and therefore harvest the available light.
• Temperature affects growth via the Q10 effect on enzyme-catalyzed reaction rates, different algae adapt better to various temperatures due to enzyme optimum temperatures.
• Nutrients besides CO2 and water, algae require nutrients from their surroundings.
• Algae may release growth inhibitors that affect other potential competitor growth.
• Herbivores can increase understorey species growth by removing larger canopy algae that create shade.
• Some algae such as coralline red alga Clathromorphum circumscriptum need grazing to survive.

Saturation and Limiting Factors

• Saturation effects: there's a level where one particular increase will not increase growth.
• Limiting factors: If increasing a factor will not favor any affect on growth
• Growth is also impacted by the main inorganic nutrients, including nitrogen, phosphorus, calcium, magnesium, sulphur, iron, manganese, copper, zinc, molybdenum, sodium, chlorine, boron, cobalt, bromine, and iodine.