Final answer:
GFP fusion constructs are not suitable for protein localization in Landoltia due to the acidic pH of plant cell walls affecting GFP fluorescence, whereas tagRFP is a more viable option for its stability at low pH levels.
Step-by-step explanation:
The use of a GFP fusion construct is not effective in determining protein localization in Landoltia due to the plant cell wall's acidic nature, which affects the fluorescent properties of GFP. The fluorescence intensity of GFP and its variants, such as mEGFP and YFP, diminishes in environments with a pH below 6, which is commonly found in plant cell walls. In the given study, tagRFP was selected as the fluorescent reporter because of its low pKa value, which stands at 3.1, indicating its stability and fluorescence retention even in low pH conditions. This is demonstrated in the N. benthamiana leaf epidermal cells, where the usage of tagRFP allowed for clear visualization of the protein of interest within the cell periphery, and specifically, the cell wall, despite changes in environmental conditions such as plasmolysis induced by glycerol or CaCl2.