Plant Hormones & Growth

• hormones diffuse throughout the plant to promote growth and development
• plant hormone - a naturally-occuring compound which regulates change in physiology, growth or development of the plant
• 5 types of plant hormones

  • auxin
  • cytokinin
  • gibberellin
  • abscisic acid
  • ethylene
• tropism - plant's response to envrionment
• phototropism - response to light
• geotropism - response to gravity
• thigmotropism - response to touch
• auxin stimulates adventitious root formation
• adventitious - roots grow from stems/leaves rather than from the original root system of the plants
• how does auxin stimulates tropism?

  • auxin travels away from the sunlight and expands the cells
• internode - the part of the plant between two nodes/joints
• node - the part of the stem where stems leaves and buds emerge; point at which stems intersect and branch
• photoperiod - a plant's recognition of daylight length in a 24 hour period
• As daylight increases in the spring, the plant recognizes a longer photoperiod
• gibberellin triggers the plant to exit dormancy
• Japanese rice farmers discovered a fungus (Gibberella fujikuroi) that caused an increase in this hormone. they named this hormone, "gibberellin", after the fungus
• abscisic acid in a plant recognizes seasonal changes
• dormancy - a period of no growth
• as daylight decreases in the winter, the chloroplasts in the plant recognize a shorter photoperiod
• what causes my fruits and veggies to go bad?

  • ethylene
• ethylene - is the only plant hormone that exists in a gas form
• ethylene can be synthesized from anywhere in the plant. It can even diffuse outside the origin plant and affect another plant nearby
• abscisic acid - dormancy hormone
• ethylene - death hormone
• the 5 major groups of plant hormones are distinguished by their chemical structures and the response they evoke within the plant
• for any cell to respond to a hormone it must be competent to perceive the chemical
• competency to perceive a hormone depends on a cell's physiology when the hormone is present
• if the hormone is perceived, its unique chemical structure causes a chain reaction or signal transduction that involves changes in gene expression and cell morphology