Biol 458 Reading #1 (Discussion on Sept 21st)

Wong et al, Seasonal patterns of reserve and soluble carbohydrates in mature sugar maple

Can J Bot 81: 780 (2003).

This is an interesting study of the dynamics of starch and sugars in sugar maple, which as perennials have interesting interchange and dynamics of starch and sugars. This should be straightforward paper and you don't need to be too worried about analytical methods section if you don't understand these. (You might recognize some of the enzyme names used in their sugar assaays, however.....).

Please note that there is an error, and that there is a reversal in the legends to Fig. 1 and Fig. 2. Fig 1. is about twigs and branches, whereas Fig. 2 has data on leaves. On Monday we will look at various sugars including stachyose and raffinose that you might not have heard of, but otherwise this should be familiar territory.

Here are some questions to guide the reading. Please answer these on one page or less, and be ready to hand them in next Thurs. They will also be the basis of discussion in class, so please be prepared to speak up!

Note that the content of the papers may be examined in tests, for those questions and discussion points that we cover.

1. In what tissues of the tree can you find starch?

2. What is the major period of starch accumulation in twigs? (Does the age of the tree impact the amount and pattern of twig starch accumulation?).

3. Why do you think starch is degraded in mid-winter in twigs (Dec-Jan-Feb)? What is it used for, according to this paper?

4. Is there also a peak of starch accumulation in leaves, and when?

5. Is wood in the tree trunk important for starch storage? Can 25-year old wood still be active in starch metabolism? Which cells in the wood are likely the ones to accumulate starch?

6. What is the most abundant sugar that is measured by the authors?

7. Xylose does not have a known role in this context, though it is part of the cell wall. Does the pattern of accumulation shown here give any clues as to it's function? (Does it behave like a storage molecule, for example?)