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Plant transport (ch. 31, Understanding Biology, Mason, edition 1) (Ploem…

- - - - Guard cell - specialized cells that work in pairs to exchange gases and water vapor. Open stomata through turid state bowing and bulding; have theicker cell walls on inside than elsewhere, and only epidermal cells with cholorplasts; turgor pressure in guard cells results from active uptake of potassium, chloride, and malate; and in evenings pump sucrose out of cells closing them.
  - - - Water potential - a way to represent free energy (in megapascals) and is used to predict movement (higher to lower concentration gradients). Physical forces and turor pressure (pressure against cell walls) or concentration of solutes determines this potential; turgor pressure increases with this potential and the total of this is the sum of turgor pressure and solute potential.
        
        Solute potential - conecntration of solute in each solution. The smallest amount of solute potential stopping osmosis; increase leads to a decrease in solute potential (negative).
        
        Halophytes - palnts that tolerate high amounts of salt. Some produce high concentrations of organic molecules within their roots; and decreases water potential increasing uptake.
        
        Tensile strength - cohesion of water molecules creates a diameter based inverse relationship of strength. Tracheids and vessels are tiny and have a strong cohesive force; and long columns are stabilized further by adhesion.
        
        Cavitation - air bubbles breaking the tensile strength of a water column. Can block tracheids or vessels; and adaptations include small pore sizes and alternate pathways for a water column.
        
        Rate of transpiration - over 90 % of water absorbed by the roots are lost to the atmosphere. Photosynthesis requires CO_2 from the atmosphere; stomata regulate the intake of CO_2 and the loss of water; increases in temperature and wind velocity increase water loss; pathways regulate stomatal opening/closing; abscisic acid regulates signal pathways in droughts by opening K^+, Cl^-, and Malate channels; stomata close for high CO_2 concentrations, open for blue light enhanced uptake of K^+, and close for high temperatures (30-34 degrees celcius), low water, and alternative photopathways (CAM).
        
        Adaptations to flooding - systems adapted to depleted oxygen levels. Abnormal growth by large lenticels and adventitious roots; formation of aerenchyma (loose parenchymal tissue with large air spaces); and transport of oxygen to submerged plant parts by aerenchyma.
        
        Pneumatophores - long and spongy air-filled roots that emerge above water and supply oxygen to submerged roots; while controlling the balance of salts. Succulent leaves contain water to maintain salt; and may secrete salt or block salt uptake. Ex. mangroove roots.
        
        Water stress response - adaptations to prevent water loss. Dormancy, loss of leaves (deciduous), covering leaves with wooly trichomes, reducing stomata amount, and having stomata in pits on leave surfaces.
- - - - Function of auxin - Aux/IAA proteins bind and repress proteins that activate the expressions of ARF genes. Auxin response factors (ARFs) can enhance or suppress transcription; two families of proteins (ARF and IAA) mediate auxin changes in gene expression; TIR1 is the auxin receptor; unique to animal hormones, the hormone auxin is unpridictability; and, unqiue to plant hormones, the hormone auxin is sent to the bottom of the plant.
      - Effect of auxin - one of the direct responses is an increase in plasticidy of cell walls. Only found in young lacking extensive secondary form; and hypothesized that cells actively transport hydrogen ions from the cytoplasm into the cell wall space, which drops pH and activates enzymes that breaks down bonds between cell wall fibers.
      - Synthetic auxin - abscission prevention (apples and berries) and flowering/fruiting of pineapples done by Napthalene acetic acid (NAA) and Indolebutyric acid (IBA). 2, 4 - dichorophenoxyacetic acid (2, 4 - D) is a herbicide used to kill broad leaf weeds.
    - - Effects of cytokinins - work with other hormones to regulate growth (especially laterial buds in branches). Inhibit the formation of later roots (auxin does the reverse).
  - - - Phytochrome - light-activated/inactivated directional growth/germination.
        
        Pr - phytochrome that absorbes 660 nm, is inactive, and converts to Pfr when red is available.
        
        Pfr - phytochrome that absorbs 730 nm, is active, and converts back to Pr when far-red light is available.
        
        Phytochrome function - involved in signaling pathways that lead to gene expression. Consists of chromophores (light-receptive) and apoprotein (facilitates expression of light-response genes); Pr in cytoplasm enters nucleus when converted to Pfr; Ptr binds to other proteins to form a transcription complex that leads to the expression of light-regulatory genes; and over 2,500 genes involved in phytochrome signaling.
        
        Phytochrome signaling - the initiation and result of protein-kinase (pathway) signaling cascades. Pr is converted and its protein kindase domain causes autophosphorylation or phosphorylation of another protein; Pr conversion initiates a signaling cascade of transcription (active) factors and leads to expression of light-regulating genes; Pfr is regulated by degradation; and, to keep the right amount, Ubiquitin tags Pfr for transport to the proteasome.
        
        Growth response of phytochrome - seed germination, shoot elongation and detection of plant spacing. Germination is inhibited by far-red and stimulated by red; only germinates while under direct sunlight; Shoot etiolation (long/weak stems, smaller leaves, and a pale yellow leaf color) caused by lack of red light; brassinosteroids play a role in responses to light through phytochrome; and plants measure the amount of far-red light reflected by neighboring plants.
        
        Circadian clocks - 24 hour rhythms of eukaryotes that continue in absence of external light, can be reset or trained through phytochrom actions, and can compensate for temperature differences.
      - Blue-light response - phototropin 1 has 2 light sensing regions that conform in response to blue-light and stimulates kinase regions to autophosphorylate. Triggers signal transduction.
  - - - Areas of gravity perception - shoots and roots.
        
        shoots gravity perception - sense along the lengths of stems in endodermal cells that are around vascular tissues. Signal toward outer epidermal cells; stem accumulates auxin on lower side of stem that creates asymmmetric cell elongation and a upward curve; and two arabidopsis mutants scarecrow (SCR) and Short Root (SHR) lack gravitational responses due to the lack of a functional epidermis (amyoplast) and therefore cannot sense gravity.
        
        Root gravity perception - the cap signals trigger differential cell elongations and divisions in the elongation zone. Cells will undergo asymmetrical growth reguardless of auxin.
- - - - Macronutrients - nutrients used in large amounts. C, O, H, N, K, Ca, Mg, P, and S.
      - Micronutrients - nutrients used in small amounts. Cl, Fe, Mn, Zn, B, Cu, and Mo.