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Week 7 Handout A03: Amanda Rajapaksa

arajapak@ucsd.edu

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 todeal with ______________.

ABA inhibits seed growth by working __________________ GA. ABA blocks GA-

induced 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 intemperature is gradual? What are some of the physiological effects (caused by ABA) which help aplant survive cold weather?

Q: ABA also helps plants survive under drought conditions. Where is the ABA made in thissituation, 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 farmerswho 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?

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Roots:

Roots are the plants 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 ______________ intactand 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 thatturgor pressure.

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

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Phloem:

Phloem moves photosynthates (_________) from leaves to the roots. This is not a rigid one-directional 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 andthe 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 intosource cells; sucrose____________ occurs at the sink cells.