Photo Pathways
Order the four photosynthetic pathways in descending order of water use efficiency (WUE)
CAM, C4, C3-C4, C3
What was their light/dark exposure ratio for plant growth?
50/50 12hr light / 12hr dark
What was the general day-night trend/difference for both species for CO2 exchange?
Positive CO2 exchange during the day, negative CO2 exchange at night.
True or False: CAM cannot co-occur in leaves with C3-C4 intermidiate photosynthesis
False
Why is Rubisco such a crappy enzyme?
It fixes oxygen and CO2, wastes nitrogen and ATP, and produces toxic byproducts
What two variables were measured?
Net CO2 Exchange (μmol s−1) and Titratable Acidity (μmol H+)
Why did net CO2 exchange increase during the day with time generally?
The plant and its leaves grew with more photosynthetic activity
What future studies were suggested?
A larger comparison of nocturnal acidification including many species across Portulaca
True or False: Rubisco evolved in a time with lower oxygen concentrations than present
True
How much did temperatures decrease when the LED grow lights were turned off?
- 2°C
Which species had a higher increase in net CO2 exchange when exposed to 2% O2 air?
P. cryptopetala
Why did P. Cryptopetala increase its rate of photosynthesis when exposed to 2% O2 air
Because it is a C3-C4 intermediate (C3 plants can function well at low O2 levels)
True or False: CAM uses Phosphoenolpyruvate
carboxylase (PEP)
True
How old were the studied plants?
Which treatment stages of the species’ leaves exhibited increased nocturnal acidification?
Drought Stressed P. cryptopetala, Drought Stressed P. molokiniensis (and slightly in Rewatered P. molokiniensis, extra 100 if mentioned)
When did CAM in members of Portulaca evolve?
Pretty old CAM, thought to have evolved before C4 in ancestral C3-CAM plants
Briefly describe Krantz anatomy
Bundle sheath cells surround mesophyll cells in a wreath-like structure
What were the CO2 concentration in their cuvette?
400 parts per million (ppm)
How many times greater was nocturnal acidification in drought stressed P. cryptopetala than in unstressed P. cryptopetala?
25 X
What are the hypothesized out of study benefits of C4 and CAM photosynthetic traits in plant?
Increased productivity and better stress coping