1. IMPAIRMENT OF CHLOROPLAST MOVEMENT
REDUCES GROWTHAND DELAYS REPRODUCTION OF
ARABIDOPSIS THALIANA IN NATURALAND
CONTROLLED CONDITIONS
Journal review by: Mily Gandhi
2. Why I chose this
paper?
◦ I chose this paper because as a plant
science major I want a way to use
biochemistry to help understand plants.
In this paper they discuss chloroplast
movement and NPQ (non-photochemical
quenching) on growth.
◦ This figure shows what Arabidopsis
thaliana looks like. It is a common plant
seen as weed, native to Eurasia and
Africa.
3. Background
knowledge
◦ Chloroplasts move towards more light to
absorb more light waves and be more efficient
in photosynthesis.
◦ NPQ stands for non-photochemical quenching
which occurs when from high light intensity is
dissipated into heat.
◦ Plants only use about 5% of the sunlight they
receive for metabolic processes. Some of it
goes to heat loss and fluoresces.
◦ In this paper they investigated growth and
reproduction of several Arabidopsis
thaliana mutants to assess the relative
importance of photoprotection via chloroplast
movement and NPQ.
4. Hypothesis
◦ Investigating growth and reproduction of several Arabidopsis thaliana mutants
to assess the relative importance of photoprotection via chloroplast movement
and NPQ.
◦ Chloroplast movement and NPQ are used to optimize photosynthesis and they
affect the growth of the plant. They assume that mutant plants have less
biomass than regular plants. In this paper they are using phot2, phot1phot2,
and chup1 mutants to measure the chloroplast avoidance response.
◦ Using more ecologically relevant conditions plus controlled conditions will
give them more relevant results.
5. The plant varieties
◦ The phot1 mutants cannot accumulate their chloroplasts.
◦ Phot2 plants accumulate their chloroplasts at the top of the palisade cells and do not show an
avoidance response.
◦ Phot1phot2 mutants accumulate their chloroplasts regardless of the specific light intensity.
◦ The wild type variety has evidence that temperatures modulate the chloroplast movement. For
example, chilling temperatures induce a stronger avoidance response at non-saturating strong light
intensities than moderate temperatures.
◦ chup1 mutant have chloroplasts that are permanently clustered at the bottom of the palisade cells,
and leaves are prone to photoinhibition.
◦ Mutants with impaired ability for NPQ such as the npq1 mutant are more prone to photoinhibition,
especially at lower temperatures.
6. Methods and design
◦ The mutants were sown in potting media in
individual square pots and for the first 3 weeks
grown in a 12-h photoperiod of 160 µmol
photons m‐2 s‐1 and 22°C day/20°C night. The
plants were either kept in a growth chamber or
transferred outdoors.
◦ Outdoors they received 14-5 h of light with light
intensities reaching 1200 µmol photons m‐2 s‐1
and temperatures ranging from 15°C at night to
35°C during the day.
7. Methods and design 2
◦ In the growth chamber, plants were grown with 16 h of light and 15°C
day/13°C night. The light period consisted of cycles of 50 min of 400 µmol
photons m‐2 s‐1, followed by 10 min of 160 µmol photons m‐2 s‐1, mimicking
a variably cloudy day.
◦ Plants were fertilized weekly with an all‐purpose fertilizer and watered as
needed. Grew plants for 8 weeks then harvested when in growth state.
Harvested the youngest fully expanded leaf of each plant at the end of the
photoperiod the day before final growth. Dark adapted for 15 min before data
was collected using the PAM 200 fluorometer.
8. Results
◦ Mutants were most affected in natural conations with
varieties phot1phot2 and chup1 most severely impacted.
Once the mutants bolted, they collected leaves and there was
less biomass and fewer secondary influences. In controlled
conditions, the mutants were unaffected except phot1phot2
which had less secondary inflorescence.
◦ In both conditions, phototropin and chup1 mutants were
more adversely impacted than the npq1 mutant. In natural
conditions, when comparing mutant plants to wild type at
week 4, phot1, phot1phot2, and chup1 plants had reduced
rosette diameters and fewer leaves, while in the controlled
conditions, npq1 showed an increase and phot1phot2 a
reduction in both variables. In natural conditions, leaf
numbers at week 4 were also reduced in npq1 and phot2
plants.
9. Discussion
◦ They provide evidence that chloroplast movement that is
more significant than NPQ in the reproductive stage.
When they impaired chloroplast movement in
phot1phot2 and chup1 plants were strong in natural
growth conditions. Their research also shows that there is
a relationship with chloroplast movement and vegetative
and reproductive performance. This also suggests an
importance to other phototropic-mediated responses.
10. Conclusion
◦ Chloroplast accumulation and avoidance, but not
NPQ, are crucial for achieving the highest growth
potential and reproductive success, particularly
when plants were grown in natural conditions for a
determined period.
11. Critique
◦ The research done was important and relevant but lacked
in a proper conclusion and concise language. There were
many grammatical errors and lack of explanation in the
paper.
◦ They could have worked on making the research paper
easier to read and more organized. I hope for future
research they work on plants that are used in agriculture
rather than a weed.
◦ The paper was useful for me because I understood how
plant can have too much sunlight and how much damage
it can cause.
