Plant Growth and Development

• Plants: Form & Function covers plant development, morphogenesis, differentiation, and tissue types.

Animal vs. Plant Development

• In animal development, the zygote divides into eight cells, forming a blastula, then a gastrula.
• This process leads to an adult animal (e.g., a sea star) through cell movement and differentiation.
• Plant development starts with a zygote dividing into two cells, eventually forming an embryo within a seed.
• This develops into a plant with observable cell differentiation in seed leaves, shoot apical meristem, and root apical meristem.

Morphogenesis & Pattern Formation

• Pattern formation involves the development of specific structures in specific locations.
• Positional information determines pattern formation through signals like genes and hormones, indicating each cell's location.
• Polarity is a type of positional information characterized by structural differences at opposite ends of an organism.
• Morphological and physiological differences, such as roots and shoots, exemplify axial polarity.

Embryo Development

• The first mitotic division of the zygote is transverse, resulting in a basal cell and a terminal cell.
• The zygote develops into a terminal cell and basal cell.
• These then form a proembryo and suspensor.
• Subsequently developing into cotyledons, shoot apex, and root apex, enclosed by the seed coat and endosperm.

Stages of Plant Embryo Development

• Initial stages include the globular stage, heart stage, torpedo stage, and cotyledonary stage.
• The development of the young plant includes stages with foliage leaves, cotyledons, hypocotyl, and radicle, as seen in common garden beans and maize.

Control of Plant Morphogenesis & Differentiation

• Intrinsic controls, expressed at intracellular and extracellular levels, regulate plant development.
• Intracellular controls are genetic and require a programmed sequence of gene expression.
• Extracellular controls are hormonal, involving chemical messengers that enable cell communication.
• Extrinsic controls involve environmental cues like light, temperature, and gravity.

Genomic Equivalence

• Developing organism cells synthesize different proteins and diverge in structure and function while sharing a common genome.
• Mature cells from a leaf or root (explant) can dedifferentiate in tissue culture and give rise to diverse plant cell types, exhibiting totipotency.

Cell Type Differences

• Differences in cell types are due to differential gene expression i.e. the controlled expression of different genes by cells with the identical genome.
• This involves regulating transcription and translation, resulting in specific protein production.

Flow of Genetic Information

• DNA contains the information cells need to synthesize proteins and replicate; it is the storage repository for cellular function.
• Genes are DNA sequences which tells cells to produce specific proteins, which determine traits.

Gene Expression Control in Eukaryotes

• Gene expression in eukaryotes can be controlled at multiple steps:

• Transcriptional control: Regulating the transcription of DNA into RNA.

• Processing control: Modifying the primary RNA transcript.

• Transport control: Selecting which mRNA molecules are exported to the cytoplasm.

• Translational control: Determining which mRNAs are translated by ribosomes.

• mRNA degradation control: Selectively destabilizing certain mRNA molecules in the cytoplasm.

• Protein activity control: Selectively activating, deactivating, or compartmentalizing specific protein molecules after their production.

Cellular Control of Proteins

• Cells controls proteins by controlling when and how often a given gene is transcribed. It also controls how the primary RNA transcript is processed. Furthermore, it regulates selection of which completed mRNAs in the cell nucleus are exported to the cytoplasm and which mRNAs in the cytoplasm are translated by ribosomes.

Differential Gene Expression

• Different cell types vary in structure and function.
• These differences result from changes in gene expression rather than gene loss.
• Genes are expressed when the protein product appears in the cell.
• The cell types in multicellular organisms become distinct because they synthesize and accumulate varying sets of RNA and protein molecules.

Common Types of Plant Cells

• Plants as multicellular organisms are defined by cellular differentiation, where cells specialize in structure and function.

Three Fundamental Cell Types

• Parenchyma cells have thin primary walls, are typically alive at maturity, with many functions.
• Collenchyma cells have unevenly thickened primary walls, are typically alive at maturity, and provide plastic support.
• Sclerenchyma cells have primary and secondary walls, are often dead at maturity, provide elastic support, and are involved in water transport.

Plant Tissues

• Simple tissues consist of one basic cell type.
• Parenchyma tissues include chlorenchyma, aerenchyma, epidermis, and meristematic tissues.
• Collenchyma tissues include angular, lamellar, and lacunar types.
• Sclerenchyma tissues include conducting vessels and tracheids, and non-conducting fibers and sclereids.
• Complex tissues have more than one basic cell type.
• Xylem conducts water and minerals and includes parenchyma, tracheary elements (vessels & tracheids), fibers, and sclereids.
• Phloem conducts food and includes parenchyma, sieve elements, companion cells, and fibers.

Parenchyma Cells

• Mature parenchyma cells have thin, flexible primary walls and lack secondary walls.
• These cells are the least specialized, perform the most metabolic functions, and retain the ability to divide and differentiate.

Aerenchyma Cells

• Aerenchyma tissues ensure wetland and waterlogged plants keep the levels of O₂ to support respiration.
• Aerenchyma cells have structural parenchyma to transport oxygen continuously from leaves to roots.
• Pneumatophores have continuous intercellular spaces with submerged roots, exchanging O2 in O2-deficient roots.

Chlorenchyma Cells

• Photosynthetic parenchyma can be classified as chlorenchyma cells with a cutile, sclerenchyma fibers, and stoma.
• Chlorenchyma cells are located within the palisade and spongy mesophyll.

Collenchyma Cells

• Collenchyma cells are often grouped in strands and help support young parts of the plant shoot.
• They have thicker and uneven cell walls and lack secondary walls.
• These cells flexibly support growth without restraining it.

Sclerenchyma Cells

• Sclerenchyma cells are rigid because of thick secondary walls, strengthened with lignin.
• They are characteristically dead at functional maturity.

Tracheids and Vessels

• Tracheids and vessels are water-conducting cells within the xylem.
• Secondary wall patterns vary between annular, spiral, reticulate, scalariform, and pitted forms.

Xylem Conducting Cells

• Water-conducting cells called tracheids and vessel elements.
• Both are dead at maturity.
• Tracheids are found in the xylem of all vascular plants.
• These include angiosperms & gymnosperms.
• Tracheids are more common in gymnosperms.
• Angiosperms have both tracheids and vessels.
  • Fibers - Supporting cells.
  • Xylem Parenchyma - Storage.

Pholem Conducting Cells

• Sieve-tube elements are alive at functional maturity, although they lack organelles.
• Each sieve-tube element as a companion cell, which provide a nucleus and ribosomes.
• Sieve plates are porous end walls facilitating fluid flow between cells.

Plant Tissue Systems

• Each plant organ contains dermal, vascular, and ground tissues, which each form a tissue system.
• Vascular tissue of a stem or root is collectively called the stele; in angiosperms, this is a solid central vascular cylinder.
• Vascular tissue in stems and leaves divides into vascular bundles, strands of xylem and phloem.
• The vascular tissue system supports a long-distance transport of materials.
• Ground tissue includes cells specialized for storage, photosynthesis, and support.

Meristems & Indeterminate Growth

• Meristems support indeterminate for perpetually embryonic, dividing tissues and allow for indeterminate.
• A plant can grow throughout its life; this is indeterminate growth.
• Some plant organs cease to grow at a certain size; this is called determinate growth.

Types of Growth

• Apical meristems are at the tips of roots and shoots and at the axillary buds of shoots.
• Apical meristems elongate shoots and roots, and in a process called primary growth.
• Lateral meristems add thickness or girth to woody plants, a process is called secondary growth.
• The vascular cambium adds layers of vascular tissue, i.e. secondary xylem (or wood) and secondary phloem
• The cork cambium replaces the epidermis with periderm, which is thicker and tougher.
• Primary and secondary growth occur simultaneously but in different locations in woody plants.
• Secondary growth occurs in stems and roots of woody plants, but rarely in leaves.
• Secondary growth is characteristic of gymnosperms and many dicots, and not monocots.

Explore plant growth mechanisms, including indeterminate growth via meristems and differences between primary and secondary growth. Learn about vascular cambium function, axial polarity, and positional information's role in plant development. Discusses morphogenesis and the impact of mutations on hormone distribution.