Outline the sequence by which $T.\,aestivum$ evolved from wild grasses.
Wheat seeds start to germinate when they are kept warm and able to absorb water. Fig. 4.1 shows a germinating wheat seedling.
An investigation was carried out into the role of a gene, TaSUT1, which codes for a sucrose transporter protein, in the germination of wheat seeds. Wheat seeds were germinated and allowed to grow for 3, 7 or 10 days. Samples of tissue from the roots, seeds and shoots of the seedlings were tested for the presence of mRNA transcribed from TaSUT1. The extracted mRNA was mixed with a probe, and then loaded onto an agarose gel across which a voltage was applied. The results are shown in Fig. 4.2.
Suggest why the researchers chose to look for mRNA transcribed from the TaSUT1 gene instead of the gene itself.
Explain what the results in Fig. 4.2 show about the order of TaSUT1 activity, from day 3 to day 10, in the root, seed and shoot of a seedling.
TaSUT1 codes for the sucrose transporter protein, SUT. This protein transports only sucrose. To investigate where this protein was present in a germinating wheat seedling, a fluorescent antibody for SUT was added to sections of tissues from the seedling.
Suggest how this allowed the researchers to work out the regions where SUT was found.
Immediately after germination began, SUT was detected in the membranes of cells in the aleurone layer. It was also found that the most common sugar in the endosperm in the first hours after germination was sucrose. Explain how these results support the hypothesis that the first source of sugar for the embryo during germination is sucrose from the aleurone layer and not sugars produced by the hydrolysis of starch.
SUT appeared in developing phloem tissue within three days of germination beginning. Outline how sucrose moves in phloem.