Question

1. How can the operation of the plasma membrane H+-ATPase affect (a) the diffusion of K+ through membrane channels, and (b) the accumulation of sugars from the apoplast into the cell?

2. There is current concern that the level of CO2 is increasing in the biosphere due to the burning of fossil fuels. If the level of atmospheric CO2 were to double, how would photosynthetic rates of C3 plants be affected?

3. Nuclear encoded chloroplast proteins are synthesized in the cytosol, and then selectively translocated into the various chloroplast membrane compartments (eg outer membrane, inner membrane space, inner membrane, stroma or thylakoid membranes). You suspect that a protein you are studying in the lab as a graduate student is one that transported to the chloroplast. Explain the set of experiments you might do to test your hypothesis. Remember your controls!

Answer 1

Answer:

1):

a):

Role of plasma membrane H+ ATPase on the diffusion of K+ through membrane channels :

• The experiment was conducted using Beta vulgaris L.( Red beet) showed -
• In case of partially purified preparation of red beet plasma mebrane - For Plasma membrane vesicles , ATP dependent K+ efflux was partially inhibited by 100 [mu] vandate.
• In case of partially purified preparation of red beet plasma membrane and reconstitued in proteoliposomes - For plasma membrane vesicles, ATP dependent K+ efflux was fully inhibited by 100 [mu] vandate.
• When it is reconstituted with planar bilayer membrane, there was very little effect on K+ being imposed on the bilayer membrane.
• The above experiments shows that plasma membrane H+ -ATPase does not mediate direct K+ transport chemically linked to ATP hydrolysis.
• But ATP provides a driving force for cellular K+ update through other secondary mechanisms like K+ channels or H+/K+ symporters.

b):

Role of plasma membrane H+ ATPase on the accumulation of sugars from the apoplast into the cell :

• Plant plasma membrane H+ ATPase acts as a primary transporter via proton pumping which regulates various physiological responses.
• Phoshorylation of penultimate threonine and subsequent binding of proteins in C terminus of the enzyme activates H+ATPase.
• Light reversibly phosphorylated H+ ATPase and this process was inhibited by pharmacological and genetic suppression of photosynthesis. T
• experiment was conducted on Arabidopsis leaves .
• Immunohistochemical and biochemical analysis showed light induced phosphorylation of H+ATPase occured in the mesophyll cells along with accumulation of sugars from the apoplast into the cell.
• This sugars again promoted phosphorylation .

This is how the photosynthesis activated H+ATPase influenced the sugar production in mesophyll cells from the apoplast into the cell.

2):

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