BIOL 101 Lecture Week 2 (Plant Cell Structures) PDF

Vicia lens, Lens culinaris - commonly known as lentil, an edible legume - an annual plant known for its lens-shaped seeds - lens comes from lēns, the Latin name of lentil, because a double- convex lens is lentil- shaped Micrographia - by Robert Hooke - published in January 1665 that inspired a wi...

Vicia lens, Lens culinaris - commonly known as lentil, an edible legume - an annual plant known for its lens-shaped seeds - lens comes from lēns, the Latin name of lentil, because a double- convex lens is lentil- shaped Micrographia - by Robert Hooke - published in January 1665 that inspired a wide public interest in the new science of microscopy - this book originated the biological term cell. Quercus suber, cork under SEM Antonie Philips van Leeuwenhoek - using single-lensed microscopes of his own design and make, Van Leeuwenhoek was the first to observe and to experiment with microbes - improved lenses creating microscopes that established microbiology - worked on a variety of microscopic specimens from animal, plant and fungal tissues, bacteria and protozoa Cell Theory - Fundamental scientific theory of biology - Cells are the basic units of all living tissues - First proposed in 1838 by German scientists Theodor Schwann and Matthias Jakob Schleiden - in 1855, Rudolf Virchow proposed Omnis cellula e cellula ("all cells (come) from cells or generated by existing cells). THE PLANT CELL Compiled by Ma. Eleanor Calapatia – Salvador, MEM, MSc PLANT LIFE: Unifying Principles ◦ Earth’s primary producers, solar harvesters, light energy converters (be it a bryophyte, fern, gymnosperm or angiosperm) ◦ Other than certain reproductive cells, they are non-motile. They grow toward essential resources. ◦ Structurally reinforced to grow towards sunlight and against gravity. ◦ Lose water continuously and evolved mechanisms to avoid dessication. ◦ Have mechanisms to move water and minerals to sites of photosynthesis and growth, and also to move the products of photosynthesis to non-photosynthetic organs and tissues. Overview of Plant Structure Plant Cell New cells are produced by dividing tissues called meristems. Each plant cell is surrounded by a rigid cellulosic cell wall and each walled cell is cemented together by a middle lamella. Cell Wall Determines the mechanical strength of plant structures, allows vertical growth Glue cells together, preventing sliding past one another Acts as cellular “exoskeleton” controlling cell shape Allows high turgor pressures to develop and determines cell turgor pressure and cell volume Allows bulk flow of water in xylem requiring a mechanically tough wall that resists collapse as there is negative pressure in the xylem Major structural barrier to pathogen invasion Architecture of the Cell Wall Primary cell wall – thin composed of rigid cellulose microfibrils embedded in a matrix of polysaccharides called hemicelluloses (flexible) and gel-forming pectin with a small amount of structural protein Secondary cell wall – forms when primary wall expansion stops; thick as in tracheids, fibers and others that serve in mechanical support - composed of lignin that bonds tightly to cellulose; reduces digestibility of plant material by animals and attack by pathogens Components of Plant Cell Walls Biological Membranes According to Fluid-Mosaic Model, all biological membranes have the same basic molecular organization: - in the case of plasma membranes, a bilayer of phospholipids and various transport proteins - with chloroplasts, glycosylglycerides Membrane Fluidity Strongly influenced by temperature Generally, plants cannot generate body temperature. Membrane fluidity decreases as temperature decreases To avoid this, one of the fatty acids of phospholipids is saturated (no double bond), the other is unsaturated because of the cis double bonds that prevents tight packing of phospholipids Transport Proteins in Membrane Lipid Bilayer ◦ Integral Proteins – embedded in the lipid bilayer, serve as ion channels ◦ Peripheral Proteins – bound to the membrane surface by noncovalent bonds and could be disassociated, ex. Microtubules and microfilaments ◦ Anchored Proteins – bound to the membrane via lipid molecules like fatty acids  Nucleus ◦ Contains most genetic material of the cell (the remainder of the genetic information of the cell is contained in the chloroplast and mitochondrion) ◦ Surrounded by a nuclear envelope with nuclear pores ◦ Site of storage and replication of the chromosomes composed of DNA and proteins (histones) ◦ DNA-protein complex - Chromatin ◦ This chromatin when it forms a solid-like cylinder containing 8 histones forms a nucleosome. ◦ Consist also of a densely granular region which is the site of ribosome synthesis - nucleolus Endoplasmic Reticulum Network of internal membranes made of lipid bilayers and associated proteins, together form flattened or tubular sacs known as cisternae Continuous to the outer membrane of the nucleus Rough ER – site of synthesis of membrane proteins and also proteins secreted outside of the cell or into the vacuoles Smooth ER – site of lipid synthesis and membrane assembly Golgi Apparatus Proteins and polysaccharides for secretion are processed Consist of one or more stacks of three to ten flattened membrane sacs or cisternae, and an irregular network of tubules and vesicles called the trans Golgi Network (TGN) Each individual stack is called a Golgi body or dictyosome Secretory vesicles carry the polysaccharides and glycoproteins to the plasma membrane by fusion and emptying their contents to the cell wall; some participate in endocytosis, the process that brings soluble and membrane- bound proteins into the cell. Large Central Vacuole Surrounded by a vacuolar membrane or tonoplast Contains water and dissolved inorganic ions, organic acids, sugars, enzymes and a variety of secondary metabolites Like animal lysosomes, plant vacuoles contain hydrolytic enzymes Protein bodies - specialized protein-storing vacuoles abundant in seeds Lytic vacuoles – with hydrolytic enzymes that fuse with protein bodies to initiate breakdown of stored food in seeds Energy-Producing Organelles ◦ Mitochondria – cellular site of respiration ◦ From spherical to tubular, with smooth outer membrane and convoluted inner membrane called cristae, and the compartment enclosed by cristae is the mitochondrial matrix containing the enzymes needed for Krebs Cycle Energy-Producing Organelles ◦ Chloroplasts – belong to a group called plastids that contain chlorophyll ◦ Its membranes are known as thylakoids, and a stack of it is a granum ◦ Embedded in the thylakoid are proteins and other pigments ◦ The fluid compartment surrounding the thylakoid is the stroma which is analogous to the mitochondrial matrix ◦ Other plastids: ◦ chromoplasts (with carotenoids); ◦ leucoplasts (nonpigmented); ◦ amyloplasts (starch-storing plastid)  Semi-autonomous organelles in Plants ◦ Mitochondria and chloroplasts both contain DNA and machinery to synthesize protein ◦ Believed to have evolved from endosymbiotic bacteria: a. They divide by fission b. They have circular chromosomes instead of linear which are located in mitochondrial matrix or plastid stroma called nucleiods. * Although they have their own genomes and can divide independently, however, majority of the proteins of these organelles still depend on the nucleus hence the word “semi- autonomous” Interconvertible Plastids ◦ Found in meristem cells with few or no internal membranes, no chlorophyll, and incomplete enzymes to carry out photosynthesis ◦ Chloroplast development from proplastids are triggered by light ◦ Upon illumination, enzymes are formed inside the proplastid or imported from the cytosol producing light-absorbing pigments. Hence, chloroplasts develop only when a young shoot is exposed to light. ◦ Proplastids differentiate into etioplasts when seeds are germinated in the dark (if not in the soil) but after minutes of exposure to light, chlorophyll is produced which is derived from the protochlorophyll found in etioplasts; this can be reverted and the process is known as etiolation. Interconvertible Plastids ◦ Chloroplasts can be converted to chromoplasts ◦ Amyloplasts can be converted to chloroplasts Microbodies Single-membrane spherical organelles like: Peroxisomes - function in the removal of H2 from organic substrates: RH2 + O2 R + H2O2 Where R is the organic substrate. This produces a harmful peroxide which is broken in peroxisomes by catalase. Microbodies Glyoxysomes – present in all oil- storing seeds which contain enzymes that convert stored fatty acids into sugars (glyoxylate cycle) Oleosomes/Spherosomes/Lipid bodies – during seed development, triacylglycerol in the form of oil is stored in these bodies Lipids from oleosomes are broken down and converted to sucrose with the help of glyoxysomes Cytoskeleton ◦ The cytosol of a plant cell is organized by a 3- dimensional network of filamentous proteins which provides spatial organization of the organelles ◦ Serves as a scaffolding for the movement of organelles and other cytoskeletal components ◦ 3 cytoskeletal types found in plants: a. Microtubules – hollow cylinders with an outer dia.of 25 nm, composed of protein tubulin b. Microfilaments – solid with a dia.of 7 nm, composed of globular actin or G-actin c. Intermediate filaments – helically wound fibrous elements with 10 nm dia. composed of linear polypeptide monomers Microtubules ◦ An integral part of mitosis ◦ Form the Preprophase Band (PPB), a ring of microtubules encircling the nucleus before the start of prophase ◦ Form the prophase spindle (during prophase, analogous to centrosomes of animal cells) and mitotic spindle (during metaphase) ◦ Along with ER, forms phragmoplast (during late anaphase or early telophase)  Microfilaments ◦ Guides in cytoplasmic streaming (a coordinated movement of particles and organelles in the cytosol) involving actin and myosin proteins ◦ Guides vesicles of Golgi bodies with wall precursors which fuses to the plasma membrane which are deposited and assembled as cell wall material Plasmodesmata ◦ Tubular extensions of the plasma membrane ◦ Traverse cell walls connecting cytoplasms of adjacent cells ◦ Because of this interconnection, a continuum is form known as the symplast. *You can have your own home lab setup using the same dissecting materials that we will use in the CS laboratory for practice in observing plant cells. Find alternatives that we can find at home or in a nearby pharmacy/medical supply store. Be responsible in handling and storing sharp and glass materials!  From Beyond the Bean: Episode 1 (https://youtu.be/UWbGZMO4o_U) Specimen mounted on the slide is a whole leaf. No sectioning performed since plant material used is two-cells thick as described in the video.  From Beyond the Bean: Episode 1 (https://youtu.be/UWbGZMO4o_U)  From Beyond the Bean: Episode 2 (https://youtu.be/Jkk_FXTFsFc) Shown is a paradermal sectioning of Capsicum annuum fruit. Free hand sections such as this does not always provide a regular, even or thin sections. But this is adequate during preliminary observations in plant morpho-anatomy classes or in anatomical observations in various plant experiments. But if for publication purposes and under a research project, sophisticated cutting tools such as microtomes should be used with plant tissues. Hand and Rotary Microtomes  From Beyond the Bean: Episode 2 (https://youtu.be/Jkk_FXTFsFc) Plastids in Capsicum annuum fruit starts as a chloroplast then converts into a chromoplast.  From Beyond the Bean: Episode 3 (https://youtu.be/6H92NLVMhss) Epidermal peel of an inner epidermis from an onion fleshy scale leaf. This could be done with herbaceous or fleshy plant parts and must be gently done. If possible, do not do this with your hands as our fingers could easily destroy the thin tissues. Use forceps, fine soft paint brush and needle!  From Beyond the Bean: Episode 3 (https://youtu.be/6H92NLVMhss) Use of staining reagents are recommended but water as mountant is okay. Color stains though helps us to better appreciate the cellular structures in any sectioned biological materials. Different color stains have different chemical components which are created to provide a color stain with better affinity to the chemical structure of a given cellular part or tissues.  From Beyond the Bean: Episode 3 (https://youtu.be/6H92NLVMhss) Remember that the nucleus is not only always single or one in a cell. A plant cell could be multinucleated if it did not form a cell plate for the cell wall formation during anaphase and in turn failing to proceed to telophase. Also, the nucleus is not always in the middle with plant cells. Nucleus in the middle of plant cells are always found in young tissues or actively dividing cells. Why there are plant cells with their nucleus found at the periphery?  From Beyond the Bean: Episode 5 (https://youtu.be/GlCOQijkIKc) Cross or transverse sections (XS) are performed at a right angle to the long axis of the plant part. If you do not Make multiple sections! This is sooo true. know the long axis of a plant part, you’re doomed! (JK ☺) From Beyond the Bean: Episode 5 (https://youtu.be/GlCOQijkIKc)  From Beyond the Bean: Episode 5 (https://youtu.be/GlCOQijkIKc) How to distinguish which are epidermal cells, How to determine the 2 types of parenchyma, collenchyma and sclerenchyma cells, trichomes? and the tissues that these cells form?