Lecture 8- Coping with aridity and drought II

Question 1

Why is CAM photosynthesis so good?

Answer 1

• cam plants have stomata, and open them to let gas in and water out (CO2 goes in and H2O escapes)
• open stomata during the night when it is cool and less water evaporates
• you have to present CO2 at the same time as light but CAM gets around it

Question 2

What happens in a CAM plant at night?

Answer 2

stomata open and CAM plants have a biochemical mechanism a CO2 pump that fixes CO2 and that pumping mechanism stores CO2 in the large vacuoles the CAM plants have

• CO2 is stored as organic acid (malic acid), organic acids have the COOH signature COO is the CO2 and can be released
• during the photosynthesis doesn’t happen (no light) but CO2 storage is occuring
• the pump is mostly PEP carboxylas, fixes CO2 and creates the organic acid
• CO2 pumped into storage at night
• pump is called PEP carboxylase
• storage= vacuole (malic acid)

Question 3

What happens in a CAM plant during the day?

Answer 3

-stomata close in the early morning
-water trapped in the plant
-CO2 concentrated in the plant, used by photosynthesis
-photosynthesis stimulated, photorespiration is inhibited
-during the day the CO2 is released
but stomata closed during the day (so water cannot escaped as it heats up)
-CO2 is released from the organic acid by a decarboxylating enzyme

Question 4

What is photorespiration?

Answer 4

oxidative photosynthetic carbon cycle, or C2 photosynthesis) is a process in plant metabolism which attempts to ameliorate the consequences of a wasteful oxygenation reaction by the enzyme RuBisCO. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin-Benson cycle, however approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), producing a product that cannot be used within the Calvin-Benson cycle. This process reduces efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in C3 plants.

Question 5

What are the advantages of having CAM photosynthesis?

Answer 5

• water cannot evaporate, and CO2 levels go up rapidly, the more you make of it the better photosynthesis runs
• secondary advantage= inhibits photorespiration= undesirable pathway

Question 6

What is CAM aidling?

Answer 6

• extereme water stress adaptation
• for example if you break off bit of prickly pear or if plant under mega stress
• the stomata then stay always closed!
• no gas exchange happening
• the CO2 that is made during respiration at night, is picked up by the CAM system and stored as maleate and that is then released during the day and used in photosynthesis
• goes around in a cycle
• no net gain of CO2 or loss

Question 7

What is CAM cycling?

Answer 7

• not pure CAM, it is a variation on CAM
• the C02 released by respiration at night normally drifts but here it is picked up and stored
• and here stomata are closed at night, so regular plants not CAM plants
• CO2 collected from respiration at night when stomata closed
• CO2 released during the day from storage so stomata do not have to open as much

Question 8

How efficient is CAM photosynthesis when compared to C3 and C4?

Answer 8

CAM is good in water efficiency

• how many liters of water it takes to make 1kg of biomass
• hugely efficient relative to the other plant types
• CAM 50-100g
• C4- 250-300g
• C3- 400-500g

Question 9

What are the two techniques by which CAM plants can be identified?

Answer 9

1: Taste test
2: Stable carbon isotope composition

Question 10

What is the taste test?

Answer 10

• -as the malic acid is accumulated in the plant overnight=so it is sour, more bitter
• during day= sweeter

Question 11

What is the stable carbon isotope composition test?

Answer 11

-discrimination between C13 and C12
-carbon existes as two stable isotopes = 13 and 12C, most is 12 but some is 13 (1.1%)
-
-plants that fix CO2 prefer 12 CO2 to 13CO2
-the CO2 pump in CAM plants isn’t as discriminative to 13C than the other plants, so CAM plants have more 13C

Question 12

How was the isotope composition test used in drug screening in Tour de France?

Answer 12

• carbon signature of testosterone - the 13C to 12C ratio
• Landa’s testosterone C ratio was wrong
• the artificial testosterone was made from soybean, yams,= more C3 plants, special signature

Question 13

What is typical of succulents?

Answer 13

• low surface to area ratio
• many are CAM plants
• not all are CAM plants but most are

Question 14

Does Australia have CAM plants?

Answer 14

• almost none

- many succulents but don’t have CAM

Question 15

What is the first Australian succulent CAM plant?

Answer 15

• Calandrinia polyandra (genus: Montiaceae= REMEMBER)
• desert dwelling
• not obligate CAM plant= facultative CAM plant
• can switch CAM on if water stressed

Question 16

What is the stomatal behaviour in Calandrinia?

Answer 16

• this is in the Australian CAM plant
• CO2 fixation normal when enough water
• if water stressed then get CAM pattern, during day stomata closed, no net CO2 fixation, then at night get CO2 fixation
• switch it on via regulatory enzymes

Question 17

Where does Calindrinia occur?

Answer 17

• all over Australia
• pink flowers
• was discovered in 1699 by a UK captain

Question 18

What are some other CAM plants in Australia (non-succulent)?

Answer 18

• 53 epiphytic orchids show significant CAM
• there are other CAM plants in australia but the one above is the only arid, succulent CAM plant that we know of
• the orchids are in tropics or subtropics
• not in arod areasl can be said to be succulent
• over a half show the CAM isotope signature
• epiphytes in wet areas, grow on other plants so hard to get water

Question 19

What is another non-succulent CAM plant in Australia?

Answer 19

• caustic vine

- Sarcostemma australe (Asclepiadacae)

Question 20

What is the strange example of a CAM plant (aquatic)?

Answer 20

• aquatic CAM plants
• primitive plants, grow underwater, Isoetes(genes)
• exception to the CAM norm
• some primitive underwater plants show CAM (e.g. Isoetes= quillworts)
• during the day photosynthetic algae rapidly deplete CO2 in water
• CAM gets around this by fixing CO2 at night

Question 21

How is prickly pear used for food?

Answer 21

• In Central America, pads grown for food since before Spanish arrived
• Eaten raw in salads, boiled and fried like eggplant, pickled with spices, or cooked with shellfish, pork, chilies, tomatoes, eggs, coriander, garlic, and onion
-prickly pears- have been used in Americas for a long time
-cactus candy= made of prickly pear, very good

Question 22

What are the attributes of prickly pears?

Answer 22

• Drought resistant (CAM, succulence, cuticle)
• Sexual and asexual reproduction (underground bulbs - some species)
• Pads and fruit can root (floods)
• Yummy fruit
• Bounty placed on heads and eggs of emus
-reproduction= can break off a part and it will grow from it= can have asexual reproduction
-sprout from underground
-can be carried in water and then grow wherever they land
-yummy fruits= emus, bounty on emus because they were dispersing the seeds, almost wiped out

Question 23

Are there more species of prickly pear in Australia?

Answer 23

• yes

- 14 naturalized species in Victoria alone

Question 24

How did people find the insects capable of dealing with Opuntia stricta (prickly pear)?

Answer 24

• Study began in 1912 • 150 insects studied world wide • 52 brought to Australia • Tested for host specificity • 18 insects and 1 mite released • 9 insects and the mite survived

Question 25

What is a biological agent?

Answer 25

introduced= insect that keeps it in control

• biological control
• bringing of a biological agent

Question 26

What were the two most promising insects for dealing with the prickly pear?

Answer 26

• Cactoblastis cactorum (stem boring moth – most effective against common and spiny pest pear)= the one who did it
• Dactylopius spp. (cochineal mealybug – 5 species)
• (Females spend life attached to plants; covered in waxy secretion; yield redish colour when crushed)

Question 27

Who and how did they find the catcoblastis cactorum?

Answer 27

• Commonwealth Prickly Pear Board entomologist Alan Dodd was collecting predators in southern USA in 1924
• Took initiative to visit Argentina where he collected female moths of C. cactorum
• Collection arrived in Australia in 1925 and the rest is history (2nd time lucky - 1914)

Question 28

How was the Cactoblastis cactorum distributed across Australia?

Answer 28

• > 1 billion eggs provided free to landowners
• 80,000 eggs produced >22 million in the next generation
• 2 generations per year
• Trillions of larvae consumed >1.5 billion tonnes in less than a decade

Question 29

How can Cactoblastis cactorum find the prickly pear?

Answer 29

• Some insects can measure CO2 (moths, butterflies, flies, bees, mosquitoes, ticks)
-how did it work? how does the moth connect to the prickly pear= moth can sense CO2, (like mosquito = can sense CO2 being breathed out)
- 1 parts in million
-• Most nutritious plant parts are most metabolically
active • Take up and give off the most CO2
-• CAM plants “breath” in CO2 when all of the other plants are “breathing” out.
• Patches of prickly pear cannot hide from Cactoblastis
• There is an additional volatile signal from Opuntia (Pophof et al. 2005 J Chem Ecol 30, 51-68).
-so was seeking domains of low CO2 as there are no CAM plants in Australia so all the others releasing CO2 at night