4: responses to environment

• Physical injury to plants breaks cells and release the content of cells. In response, plants produce enzymes to heal the injury such as oxidative reactions that cause browning and other chemical reactions to start the process of cell division.
• Environmental or biological stresses can make plants express genes to produce chemical signals that lead to chemical products to deal with the stress
• Plants grow and become green in response to light
• Phototropism is the bending of a plant towards light
• Sunflowers track the sun by experiencing stem growth on the west side at night to face the east when the sun rises. In the daytime, stem growth is on the east side to track the sun which ends in them facing the sunset in the west.
• Gravitropism is the plants response to gravity.

  • positive gravitropism: roots grow down
  • negative gravitropism: stems grow against gravity
• Thigmotropism is the plants response to touch

  • ex: wrapping its stem or leave across a wooden pole for structural support.
• Photoperiod is a plants response to different lengths of time being exposed to light

  • ex: short day plants flowering only when period of darkness exceeds a critical night length
  • ex: long day plants flower when a period of darkness is less than a critical night length
• Light has no effect on the growth of day neutral plants
• Phytochrome proteins within a plant are used to detect light, specifically being activated by red light to induce seed germination, flowering, etc.
• Some plants only come out of their seeds when the temperatures raise.
• The spring growth response is the tendency of some plants to start growing when the day lengths become longer and the temperatures raise.
• Ethylene is a hormone used to induced fruit ripening, resulting in cell wall structure changing, pigment accumulation, and the conversion of starches to sugars.
• Auxin is a hormone used to increase cell elongation in phototropism, thigmotropism and gravitropism in plants.
• Phyochrome is a protein involved with plants that respond in changes of daylength (short day or long day plants)