DEVELOPMENT & MORPHOGENESIS

• TROPIC RESPONSE/TROPISM - A growth response oriented with regard to the stimulus.
• POSITIVE TROPISM - is growth toward the stimulus;
• • NEGATIVE TROPISM - is growth away from the stimulus.
• • PLAGIOTROPISM - is growth at an angle.
• THIGMOTROPISM – when touch is the stimulus, this is the response.
• POSITIVE THIGMOTROPISM occurs when a tendril touches an object and, by growing toward it, wraps around it.
• NEGATIVE THIGMOTROPISM when a plant grows away from a contact stimulus.
• CHEMOTROPISM - is defined as the growth of organisms navigated by chemical stimulus from outside of the organism.
• ·       POSITIVE CHEMOTROPISM – directed toward the [chemical] stimulus.

  -example: growing along the style to the ovary by following a gradient of chemical released from the ovule, probably from the synergids.
• ·       NEGATIVE CHEMOTROPISM – growth response away from the [chemical] stimulus.
• • DIFFERENTIAL GROWTH a feature of cells, the organs which they construct and the whole plant itself.
• *Changing direction involves differential growth: One side of the tendril must grow more than the other.

         *This can occur by: (1) growth on the contact side slowing, (2) growth on the opposite side accelerating, or (3) both.
• • NASTIC RESPONSES A nongrowth response that is stereotyped and not oriented with regard to the stimulus.
• DIURNAL SPECIES – active in day.
• NOCTURNAL SPECIES – active in night.
• PHOTONASTIC in response to light (and not just in the direction of the light source).
• • SLEEP MOVEMENTS blade elevated in the day, lowered at night in response to onset of darkness.
• MORPHOGENIC RESPONSE sometimes called a morphogenetic response.

  -causes a change in the “quality” of the plant; that is, a fundamental change occurs in the metabolism of a tissue or even the entire plant.
• • TAXIC is a response in which a cell swims toward (positive taxis) or away from (negative taxis) a stimulus.
• Hormones -are naturally occurring, organic substances that, at low concentration, exert a profound influence on physiological processes.
• HORMONES - are organic chemicals produced in one part of a plant and then transported to other parts, where they initiate a response.
• Hormones -A chemical that is produced by one part of a plant, often in response to a stimulus, and then is transported to other parts and induces responses in appropriate sites.
• PLANT HORMONES:

  • Auxins
  • Gibberellins
  • Cytokinins
  • Abscisic acid
  • Ethylene
• AUXINS – synthesized in the stem and root apices.

  -       capacity to stimulate cell elongation.

  -       root initiation.

  -       Vascular differentiation.

  -       Tropic responses.

  -       development of axillary buds, flowers, and fruits.

  -       first plant hormone discovered.
• Auxins was later identified as being:

  Indoleacetic acid (IAA)
• o   Indoleacetic acid (IAA): which could be synthesized artificially and applied to plants under various conditions to find other responses that IAA might either mediate or inhibit.
• Indoleacetic acid (IAA) - Most common naturally occurring plant hormone of the auxin class.
• *NATURAL & SYNTHETIC AUXINS:

  Natural:

  ·       Indole-3-acetic acid (IAA)

  ·       Indole-butyric-acid (IBA)

  Synthetic:

  ·       Naphthalene-acetic-acid

  ·       2,4-Dichlorophenoxyacetic acid (2,4-D)
• GIBBERELLINS – A class of hormones involved in stem elongation, seed germination, and other processes.
• Gibberellins -are known, and rather than being named, they are just numbered: GA1 , GA2 , . . . GA125.
• Gibberellins - Produced by both fungi and higher plants.
• Exogenous application of gibberellins causes hyper elongation of intact stems.
• Gibberellins - Involved in seed germination, mobilization of endosperm reserves during early embryo growth, as well as flower and fruit development.
• CYTOKININS – were named for the fact that their addition to a tissue culture medium containing auxin and sugar stimulates cell division—cytokinesis.
• CYTOKININS -       Class of hormones involved in cell division, apical dominance, and embryo development among other things.
• Kinetin was the first cytokinin to be isolated.
• Zeatin was the most widespread naturally occurring cytokinin in higher plants.
• CYTOKININS -       Stimulates cell division.
• CYTOKININS -       Influence shoot and root differentiation in tissue culture, the growth of lateral buds and leaf expansion, chloroplast development, and leaf senescence.
• ABSCISIC ACID - A hormone involved in resistance to stress conditions, stomatal closure, and other processes.