CAM Flashcards
what is CAM
Crassulacean acid metabolism; carbon fixation reaction over 24h over a light/dark cycle. CCM
What happens during CAM? Phase I
4 phases
Phase I: stomata open, dark CO2 uptake. PEP +HCO3–> OAA, catalysed by PEPC.
OAA->Malate. –>vacuole -> malic acid
NIGHT
What happens during CAM? Phase II
transitional period PEPC switch to Rubisco. Peak of net CO2 uptake
What happens during CAM? Phase III
Stomata close. Malate efflux from vac –> chloroplast.
Decarboxylation to CO2 and Pyruvate.
CO2 fixed by Rubisco in calvin cycle.
water saved
DAY
What happens during CAM? Phase IV
Transitional phase from Rubisco to PEPC
What is PEPC?
Phosphoenolpyruvate-carboxylase
What is OAA?
Oxaloacetate
What is PEP?
Phosphenolpyruvate
OAA –> Malate requires what?
NADH -> NAD+ via NADP-ME NAD-malicdehydrogenase enzyme
an ecologically diverse
CO2 concentrating mechanism found in —— of plants
6%
CAM has evolved how?
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
CAM plants have good plasticity ? explain
CAM plants have good plasticity for adjusting C in response to diff environmental conditions – some can take up CO2 for 24h
Regulation of PEPC is by what?
Malate inhibits
Sensitivity changes
Whats the Ki equation for PEPC/Malate.
Explain high and low Ki
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)
What are the four shades of cam?
Consituatve, facultative, idling, cycling
Explain faculative
C3–.CAM in response to environmental stress (low water/high salinity)
Mesembryantheum crystallinum
Kalanchoe
Clusia (tree)
Examples fo constituative cam
Agave
Pineapple
Discuss engineering succulenece? why?
Succulence of CAM plants
- Required to accommodate overnight accumulation of malate
- Fill/refill water stores –control consumption of internal reserves
- Reduced surface area: volume
Thick succulent leaves - succulent; larger vacuoles v. important for storing mallic acid + water balance
Examples of succulence engineering
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
Study were partial CAM was engineered
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
Omics and CAM study
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
