Grant Cramer

My major interest is in the regulation of plant growth and cell expansion. In particular, my laboratory is focused on to environmental problems, soil salinity and elevated carbon dioxide, and how these conditions affect growth.

There is a very strong linkage between cell elongation, plant productivity and crop yields. The production of all plant parts is dependent upon the supply of external resources, such as water, mineral nutrients or carbon. Cell elongation is important for the capture of these resources, particularly when they are limiting growth. An increase in cell size will increase cell surface area, enabling roots to explore more of the soil for water and minerals, and leaves to capture more photosynthetic radiation. The size of a stressed plant is dependent upon cell production and cell expansion, both of which may be affected by stress. The intensive use of resources by man has had it side-effects. Two notable effects are the increase in atmospheric CO2 leading to the “greenhouse effect” and the increase of salinized soils of irrigated lands leading to reductions in crop productivity on those soils. In general, plants have not yet adapted to fully utilize the resources in these new environments. Through the use of new techniques in biotechnology, we can make better plants, which are more suitably adapted to these environmental conditions.

Recently, my lab has been investigating the effects of elevated atmospheric CO2 on cell wall composition and biosynthesis. We believe we can alter cell wall biosynthesis and growth in transgenic plants to enable them to better utilize the more abundant carbon source.

By inserting extra copies of the gene for UDP-Glc dehydrogenase, we have increased the activity of this key enzyme involved in the biosynthesis of plant cell walls and we have evidence that we are able to increase plant growth as a result. Such plants are likely to be more productive thereby increasing crop yields. We would expect that these plants would perform even better in an elevated CO2 environment. This hypothesis is addressed in our current investigations.

For the last two decades, my research has focused on salinity stress. The inhibition of plant growth by salinity involves two components. Initially, the plant experiences a water stress, but with time salts accumulate in the plant creating an additional ionic stress. In my laboratory, we are currently focusing on how salinity inhibits plant growth by these two components. The water stress component has been investigated by studying the immediate effects of salinity on the growth parameters regulating leaf elongation. We found that salinity increases the apparent yield threshold of the cell walls in the growing region of the leaf, which results in lower growth rates. We have interesting correlations of the plant response to the plant growth regulator, abscisic acid with salinity stress, particularly the effects on growth, cell wall yield threshold and cytosolic calcium. We are now actively investigating the effects of salinity on secretion of proteins, poly- and oligosaccharides to the cell wall.

We are investigating the ionic stress component by developing methods for quantifying cytosolic calcium and sodium activities. We are interested in the mechanisms by which the salts are absorbed into or excluded from the plant. We are investigating the regulation of sodium and calcium activities using state of the art fluorescent techniques combined with confocal microscopy in living tissues. Finally, the identification and characterization of the mechanisms regulating plant growth under saline conditions is leading to the molecular characterization and manipulation of proteins associated with salt-tolerance in plants and the stimulation of growth by elevated carbon dioxide. Currently we are investigating the effects of these environmental conditions on the expression and regulation of key proteins involved in cell wall synthesis and secretion.