Lecture 15: Compatible solutes Flashcards
a compatible solute is an
organic solute compatible with metabolic activity at high concentration
- typically sugars and amino acids such as sucrose, proline, glycine betaine
where do we find them?
- dry cells
- low temperatures
- salt stress
compatible solutes accumulate to
- balance the high salt
- replace the salts which would be damaging to the cell
In drying cells compatible solutes: - Ziziphus mauritiana
- Ziziphus mauritiana (pop. fruit tree) of india and other areas in Asia
- solute accumulation in conferring drought resistance
- Concluded that solute accumulation was a significant contributor to maintaining cell volume during drought thereby allowing the plant to grow for several days more during a drought event.
- sugars and amino acids accumulate as plant begins to dehydrate
in the cell: in response to salt stress compatible solute accumulation
- high Na+ and high osmolarity are sensed by sensors at plasma membrane
- induce increase in cytosolic [Ca2+]
- Na+ pumped out, H+ pumped in
‘compatible’ meaning
it doesn’t do any damage to the cell
compatible solutes can act as an osmoticants BUT
they can be energetically costly
- sodium 3.5 moles of ATP
- Mannitol 34
- sucrose 52
- –> Can be costly, but sodium toxic to cell, CS are not
- CS often dont accumulate to a high enough conc sufficient to be very significant osmoticants
what is CS role if they are not acting as osmoticants?
they acc act as targeted protectors of proteins
xerophytes
adapted to survive with little water
resurrection plants
- display modified poikilohydry
–> The rate of drying is retarded by a variety of
mechanisms; stomatal closure, thick cuticles etc. - Become air dried in 12-24 hours (faster they will die)
- in order to survive water loss must:
— limit any damage to a repairable level
–- Maintain physiological integrity in the dried state
–- Mobilise repair mechanisms on rehydration
drought tolerance
tolerance of moderate dehydration
- to a moisture content below which there is no bulk cytoplasmic water present
desiccation tolerance
- tolerance of further dehydration
- the hydration shell of molecules is gradually lost
drought tolerant plants & desiccation: protein structure stabilisation during water loss
1) in fully hydrated cells, molecules are widely dispersed and the normally folded form of a protein is stable, destabilisers are present tho (- destabiliser example = NA )
- WATER LOSS
- drought tolerant cells = compatible solutes are preferentially excluded from the protein, maintaining surface hydration and thereby protein integrity.
- desiccation tolerant cells = further water loss sugar
molecules (not other compatible solutes) replace water via
hydrogen bonding, thus stabilising the protein in a dried (glassy) cytoplasm.
cs = effects function of the protein but its not damaged
the water replacement hypothesis= =
- during severe dehydration water dissipates from the water shell of macromolecules.
- the hydrophobic effect responsible for
structure and function is lost. - Sugars can replace the dissipating water
upon dehydration the chlorophylls ____ and associated membranes are ____
disintegrate, disrupted
