Signalling 2 Flashcards
Sensing of mechanical stimuli
Mechanoperception is essential for responses to wind, gravity and touch.
Opening of mechanosensitive ion channels could be due to a pulling force of the membrane caused by membrane thinning under mechanical bending.
The roots of Arabidopsis plants mutated in a mechanosensitive ion channel gene are not able to push their way from soft agar into hard agar as well as wild type plants.
Getting rid of channel made the plants impaired to sensing They found this by groing plant in diff agar medium. Normal plants can adapt growth in the medium. Whereas mechnical plnats couldnt grow through boundry between the medium so hey couldnt adapt their groeth to the new density of the agar.
Transducing the signal of mechanical stimuli
Current research on mechanoperception signalling indicates a role for [Ca2+] peaks and downstream elements of calcium signalling pathways. Calcium is involved in the signal of mechanical stimuli as there is detected differences.
Photoreceptors associated with excess light responses
Distinct acclimations to excess light rely on the detection of different wavelengths (from different photoreceptors). The same response can depend on different photoreceptors in different species.
Phototropins detect blue light important for chloroplast movement.
Mechanism of phototropin light sensing
Under blue light flavin mononucleotides (FMN) bind covalently to the LOV domains (chromophores=protein domain absorbing certain wavelengths), changing the absorbance spectrum of the photoreceptor.
FMN-bound phototropins are activated: their kinase domain is able to carry out auto-phosphorylation, and afterwards phosphorylation of other proteins to transmit the signal of blue light detection.
Phototropin signalling and chloroplast movement
The signalling pathway between phototropins and actin relocation remains to be determined. CHUP1 interacts with filaments.
Cold signalling and CBF transcription factors
Plants that express more CBF transcription factors(CBF-OE) do not need acclimation to resist frost. Decrease in membrane fluidity, changes Ca channels which triggers different transcription factors and eventually affect the expression of genes for acclimation.
Cold signaling and CBF transcription factors
Plants that express more CBF (CBF-OE) show less membrane damage upon freezing than wild type plants.
phytochromes detect red lights. More red light in evening in autumn so provides seasonal information.
Plants that produce lots of CBF don’t need to be acclimated so more CBF is probably an outcome when being cold acclimated.
damage may be measured by electrolyte leakage
Heat shock factors control the expression of heat acclimation genes
Transgenic plants with decreased expression of heat shock factors are impaired for heat tolerance and development.
Heat shock proteins do the actual acclimation
Heat shock factors control expression of heat shock proteins and many different families.
Different heat shock factors of different families also affect each other.
Heat response signaling pathways
Cellular Ca2+ concentration rapidly increases during a heat shock.
Induction of HSPs requires ROS signal.
DPI is an inhibitor of NADP oxidases (like ROBDH)
high temp triggers changes in cytoskeleton
Heat is detected through associated cellular damages
HSF1 activation by heat:
Heat induces damages in proteins
Hsp90 associates with damaged proteins and dissociates from HSF1
HSF1 can trimerize and become active to induce the expression of HSPs
Other chaperones are probably involved as well as Hsp90.
Is ABA the only regulator of water stress responses?
ABA and proline accumulation of a mutant unable to synthesize ABA under water stress
There are also ABA-independent signalling pathways for water stress acclimation.
proline accumulates as ABA is made
Gene expression of DREB2A under stresses and ABA treatment
The pathway involving the DREB2 (cousin of CBS) transcription factors is used to induce the expression of stress response genes under drought, high salinity and heat, independently of ABA.
Salt stress signalling: SOS2, a multifunction kinase
The salt overly sensitive (SOS) pathway is used to maintain the Na+ concentration in the cytoplasm below toxic level.
SOS1 = Na+ antiporter
SOS2 = kinase
SOS3 and SCaBP8 = calcium sensor
salt stress leads to calcium signal then detects by calcium sensor
SOS1 requires energy to be activated by a proton gradient. This only works under salt stress
Abiotic stresses in real life
African rice
escape strategy was to grow variations that grow quickly
ONS (spike) for birds as an avoidance strategy
