Research Interests


Chilling Tolerance in Maize Seedlings

Maize is a crop of tropical origin and is easily damaged by low temperature conditions during germination and early seedling growth. Even nonfreezing, low temperatures can dramatically affect stand establishment. However, if seedlings are hardened by exposure to a milder low temperature, seedlings can become acclimated and are able to tolerate subsequent exposure to more severe conditions. We are interested in examining the molecular changes that occur during this acclimation process. By observing how maize seedlings defend themselves against chilling stress, we will attain a better understanding about the mechanisms of chilling damage and identify strategies to enhance chilling tolerance through genetic manipulation.


The cartoon above illustrates how maize seedlings that are accustomed to a balmy growth environment have a traumatic future if they are exposed to a severe low temperature. The photo to the left shows that in dark-grown seedlings, the mesocotyl region is the most susceptible to chilling stress, with cellular disruption, discoloration, and collapse of the tissue. However, seedlings that are allowed to acclimate are much more robust. We've demonstrated that this is associated with induction of antioxidant enzymes and a higher level of lignification. Recently, we've shown that glutamine synthetase, a key enzyme in the assimilation of nitrogen, is significantly impaired by chilling stress but maintains its activity in acclimated seedlings.
In light-grown seedlings, mesocotyls are less susceptible to chilling stress. When light is first detected as seedlings break the soil surface, mesocotyl elongation ceases. Chilling damage in light-grown seedlings is more prominant on the leaves. Damage is manifested as occasional whitish patches (presumably a result of photooxidation) as well as necrosis along the leaf margins and tips. The photo on the right also shows a characteristic chlorotic patch on one leaf. This region corresponds to the cells of the intercalary meristem that were immature when the chilling stress was applied. It appears that growing tissues, either from the elongating mesocotyl or from the intercalary meristem, are especially susceptible to chilling. Acclimated seedlings show little damage, even in growing tissues.


Cold & Chlamy

Collaboration with Drs. Karen Fawley and Marvin Fawley, University of Arkansas - Monticello,
Dr. Ron Hutchison, Richard Stockton College of New Jersey, and Dr. Robert Wise, University of Wisconsin - Oshkosh

"What the heck are these little green balls?"

This is the scientific commentary that accompanies examining a lake water sample under a microscope. Green algae are ubiquitous photosynthetic organisms that are present in all bodies of water, often in extremely dense populations when temperatures and nutrient levels are optimal. Understandably, algal populations decline dramatically during the wintertime. However, there are some species of algae, one of which has been identified as Chlamydomonas altera, that have been found to thrive in mid-winter beneath the ice of Lake Itasca in Minnesota and Arrowwood Lake (below) in North Dakota.

We're interested in Chlamydomonas altera from a number of perspectives. They are phylogenetically related to a number of other Chlamydomonads isolated from harsh environments. From an evolutionary perspective, this suggests that a common environmental stress directed the divergance of this lineage. Ecologically, their place within the algal community is virtually unknown and we are interested in the ability of C. altera to compete with other species as the seasons change. Physiologically, its facinating that C. altera is capable of carrying out normal metabolic processes at such an extreme temperature and beyond that, they exhibit a high level of biochemical plasticity by being able to quickly adapt to warm growing conditions. From an economic perspective, we're interested in identifying novel cold tolerance mechanisms in C. altera that can be applied to agricultural crops. While cold tolerance in terrestrial plants is usually limited to merely avoidance of permanent damage, C. altera has the ability to maintain metabolic coordination under a wide range of temperatures. If any of these cold-adaptive characteristics can be transferred to maize, for example, its agromomic performance would be greatly enhanced.

Clhamydomonas altera


Minimization of Respiratory Sucrose Loss in Sugarbeets

Collaboration with Dr. Karen Klotz, Northern Crops Science Laboratory, USDA-ARS
and Dr. Fernando Finger, Universidade Federal de Vicosa, Brazil

Loss of sucrose to cellular respiration during post-harvest storage of sugarbeet roots is a significant problem for the sugarbeet industry. Following harvest, sugarbeets are stored in piles for up to 200 days, during which time respiratory processes oxidize sugars and reduce the quantity of extractible sucrose. It has been estimated that up to 250 g of sucrose is lost per ton of sugarbeets each day and 50-70% of this loss is due to respiration.

In any plant, mitochondrial respiration is required to provide energy for metabolic processes and to provide carbon skeletons for other necessary metabolites. Sucrose is ultimately the carbon source for these processes. While a basic level of cellular respiration is necessary in living sugarbeet roots, specific metabolic requirements are largely unknown. We have found that total respiration is much higher in dermal tissue than in cortical tissue and that wounding causes a significant increase in respiration. Current handling practices that commonly result in considerable external damage to the sugarbeet roots, may contribute to an increased loss of sucrose during post-harvest storage (the photo on the left exhibits severe mechanical damage to a sugarbeet root). We are continuing to characterize factors that promote respiratory sucrose loss with an ultimate goal to develop strategies that minimize the demand for sucrose in stored sugarbeet roots.



The Tumor-like Growth Response of Sunflower
Infested with Sunflower Midge

Collaboration with Dr. Gary Brewer, University of Nebraska

This project is no longer active, although I remain interested and may renew it in the future.

The sunflower midge is a serious pest of cultivated sunflower, causing a severe head distortion and loss of harvestable seed. This abnormal growth, a form of "plant cancer", is a result of larval feeding among the bracts and florets of a developing sunflower bud. It is currently unknown how midge larvae cause this abnormal growth and we are interested in exploring the molecular events that occur during the distortion process. In other examples of insect- or pathogen-induced galls, altered levels of plant hormones such as auxins or cytokinins have often been implicated as responsible. Consequently, we are examining whether levels of these hormones change as a result of midge larval feeding. We are also searching for sunflower genes that are responsive to midge infestation. Identification of midge-responsive genes will hopefully give us clues about the mechanism of damage and allow us to develop strategies to improve the level of midge tolerance in sunflower.
Sunflower midge adults are small dipteran insects about 1 to 2 mm in length. Females (left) lay eggs between bracts and among the developing florets. Heavily infested heads may have several thousand larvae that survive and progress through 3 larval instars within the sunflower head. Feeding by midge larvae causes a dramatic distortion of the sunflower head (below) in which the margins grow inward, enveloping the florets. Sunflower heads with damage this severe contribute nothing to seed yield.