Explain why, for sugars to enter or leave a cell, molecules such as SWEETs are required.
Suggest how a SWEET is anchored within the membrane bilayer.
The bacterium, Xanthomonas oryzae (Xoo), is the cause of bacterial leaf blight in rice plants. It infects the intercellular spaces of the leaves of the host plant by switching on SWEET genes in the mesophyll cells, and this stimulates the secretion of glucose into the intercellular spaces. Several different recessive alleles have been found in rice plants from different countries, and these confer resistance to bacterial leaf blight. All of these alleles contain a mutation in the promoter of the SWEET gene. The effect of Xoo on wild type and resistant rice plants is compared in Fig. 3.2. Using the information in Fig. 3.2, explain this resistance of rice plants to Xoo.
Explain why it would be difficult to transfer this resistance into susceptible rice plants by genetic engineering.
Explain why the presence of large numbers of Xoo in the intercellular air spaces of rice plants reduces the plants' ability to grow with their roots submerged in water.