CAM

Question 1

what is CAM

Answer 1

Crassulacean acid metabolism; carbon fixation reaction over 24h over a light/dark cycle. CCM

Question 2

What happens during CAM? Phase I

Answer 2

4 phases
Phase I: stomata open, dark CO2 uptake. PEP +HCO3–> OAA, catalysed by PEPC.
OAA->Malate. –>vacuole -> malic acid

NIGHT

Question 3

What happens during CAM? Phase II

Answer 3

transitional period PEPC switch to Rubisco. Peak of net CO2 uptake

Question 4

What happens during CAM? Phase III

Answer 4

Stomata close. Malate efflux from vac –> chloroplast.
Decarboxylation to CO2 and Pyruvate.
CO2 fixed by Rubisco in calvin cycle.
water saved

DAY

Question 5

What happens during CAM? Phase IV

Answer 5

Transitional phase from Rubisco to PEPC

Question 6

What is PEPC?

Answer 6

Phosphoenolpyruvate-carboxylase

Question 7

What is OAA?

Answer 7

Oxaloacetate

Question 8

What is PEP?

Answer 8

Phosphenolpyruvate

Question 9

OAA –> Malate requires what?

Answer 9

NADH -> NAD+ via NADP-ME NAD-malicdehydrogenase enzyme

Question 10

an ecologically diverse

CO2 concentrating mechanism found in —— of plants

Answer 10

6%

Question 11

CAM has evolved how?

Answer 11

Multiple independent origins of CAM over past 100-150 million years (35 lineages)

• evolution of CAM can occur with relative ease
• product of strong selection pressure in certain environments
• Water or CO2 limiting environments

Question 12

CAM plants have good plasticity ? explain

Answer 12

CAM plants have good plasticity for adjusting C in response to diff environmental conditions – some can take up CO2 for 24h

Question 13

Regulation of PEPC is by what?

Answer 13

Malate inhibits

Sensitivity changes

Question 14

Whats the Ki equation for PEPC/Malate.

Explain high and low Ki

Answer 14

Ki = [malate] that inhibits PEPC activity by 50%

PEPC activated at night - too much malate is inhibitory

• HIGH Ki, need a lot of malate to inhibit PEPC (insensitive) (night)
• LOW Ki, little malate need to inhibit (sensitive) (day)

Question 15

What are the four shades of cam?

Answer 15

Consituatve, facultative, idling, cycling

Question 16

Explain faculative

Answer 16

C3–.CAM in response to environmental stress (low water/high salinity)
Mesembryantheum crystallinum
Kalanchoe
Clusia (tree)

Question 17

Examples fo constituative cam

Answer 17

Agave

Pineapple

Question 18

Discuss engineering succulenece? why?

Answer 18

Succulence of CAM plants

1. Required to accommodate overnight accumulation of malate
2. Fill/refill water stores –control consumption of internal reserves
3. Reduced surface area: volume

Thick succulent leaves - succulent; larger vacuoles v. important for storing mallic acid + water balance

Question 19

Examples of succulence engineering

Answer 19

A study done on Arabidopsis thaliana and
Nicotiana sylvestris showed that an overexpression of the transcription factor VvCEB1, found in the CAM plant Vitis vinifera, led to an increase in plant cell and vacuole size.
overexpression was induced by multi gene genetic circuits using TNT and Gibson isothermal assembly
2015

Question 20

Study were partial CAM was engineered

Answer 20

Arabidopsis thaliana incorporated dark inducible promoters (Din10
and Din6) to overexpress PEPC during dark periods. Moreover, an engineered S. tuberosum PEPC with a reduced Km for PEP and increased substrate affinity compared to the wild-type

The resulting C3 plant exhibited:
increased stomatal conductance
higher transpiration and dark respiration rates.
Improved CO2 assimilation
increased number of stomatal openings in dark adapted leaves.

2012

Question 21

Omics and CAM study

Answer 21

The proteome of Agave americana leaves over a 24-h light-dark cycle was monitored. Protein abundances were measured and clustered based on abundance patterns. Agave (CAM) and Arabidopsis (C3) clusters were compared to identify CAM related genes.3

Results identified the upregulation of proteins which drive respiratory electron transport and ATP synthesis at night allowing CAM to operate properly. Scientists were unaware of this upregulation prior to this complex cluster analysis.3