Amanda's Handout Week 7

Week 7 Handout

A03: Amanda Rajapaksa [email protected] OH: M 3-4@CLICS /by appt.

Plant Hormones: Part II ABA: Abscisic acid is a phytohormone which is needed for seed ___________, and also helps plants to deal with ______________. ABA inhibits seed growth by working __________________ GA. ABA blocks GAinduced hydrolase secretion by the _____________, and also blocks GA stimulation of ___________ growth. Abscisic acid also helps plants to adapt to changes in their environment. Q: Explain the phrase “cold hardening”. Why are some plants able to survive if the drop in temperature is gradual? What are some of the physiological effects (caused by ABA) which help a plant survive cold weather?

Q: ABA also helps plants survive under drought conditions. Where is the ABA made in this situation, and how does it help the plant reduce water loss?

ETHYLENE: Ethylene, a gaseous hormone, was first discovered __________________________________ who noticed that trees around gas street lamps senesced much earlier than other trees. Citrus farmers who had previously relied on kerosene burners to stagger their fruit ripening, noticed that they were not able to do so when they used electric heaters. From these observations, it was discovered that a combustion product was required to cause senescence (and ripening). Q: What are some of the important effects that ethylene has on plants? (2)

Nutrients: Q: What are the macronutrients? The micronutrients? What does “soil solution” refer to?

Roots: Roots are the plant’s means of taking up water and nutrients Q: Draw the cross-section of a root. Label the important parts (i.e.: epidermis, root hair, root meristem, cortex, root tip, casparian strip stele, and endodermis)

Q: The vascular system of the plant (phloem and xylem) is surrounded by a water-tight barrier. What is the name of this barrier, and how do nutrients bypass this barrier to gain access to the xylem?

Q: What is the apoplasm? The symplasm?

Transpiration: There is a movement of water and ions from the _________ to the __________ which is driven by _________________. Water evaporation out of the leaves causes a _________ (higher/lower) water potential in the leaf, which causes water to water to be pulled up the shoot. Cohesion between the water molecules (as a result of hydrogen bonding) keeps the ______________ intact and allows water to be pulled from the roots to the shoot. Stomates regulate water loss and gas exchange. Stomates are formed by two _________ cells that create an open pore when they swell up with turgor pressure, and a closed pore when they lose that turgor pressure.

Q: What are the signals which cause the stomates to open? To close?

Phloem: Phloem moves photosynthates (_________) from leaves to the roots. This is not a rigid onedirectional system; the photosynthates flow from the source to the sink. In the summer, lots of photosynthesis occurs so photosynthates flow from the mature leaves in the shoot to the roots and trunk. However, in the spring when the first buds emerge, the sink is now the buds in the shoot and the source is the sucrose stored in the root/trunk. Q: What are some examples of sources? Of sinks?

Osmotic-pressure flow theory: Movement through the phloem is driven by ________________. Sucrose is actively pumped into the phloem at the source cells, and then transferred to the sink cells via plasmodesmata. “Sucrose loading” is the term for sucrose actively being pumped into source cells; “sucrose____________” occurs at the sink cells.