The Influence of Phytochrome A-202 on the Rate of Senescence in Arabidopsis thaliana
Adam R. Gailey, 2010 (Advisor: Dr. Ann Kleinschmidt)
The rate of senescence in plants is generally measured by the loss of chlorophyll. Oxygen free radicals also have an essential role in senescence. Different antioxidants and senescence-associated genes are enlisted by plants to combat these reactive oxygen species. Plants also contain photoreceptor proteins such as phytochromes that absorb different wavelengths of light. Phytochrome A (phyA) captures far-red light, which is an environmental factor that also induces senescence. The rates of senescence of a wild-type plant and a mutant lacking phyA-202 of Arabidopsis thaliana were compared. Short-term analysis following visible inflorescence demonstrated that chlorophyll levels showed a different trend than RT-qPCR analysis of catalase 2, ascorbate peroxidase 1 and the transcription factor WRKY53 in the progression of senescence, indicating that the loss of chlorophyll may not be the most accurate marker for the start of senescence. Catalase 2 showed similar trends in both protein activity and mRNA transcription levels following bolting; however there is a difference in gene regulation between ascorbate peroxidase 1 and WRKY53 in the phyA and wild-type Arabidopsis plants. WRKY53 is a highly regulated transcription factor at the beginning of senescence and phyA may act as a repressor for this gene.
This research was supported in part by the Class of 1939 Student Research Fund.
The Effects of CuSO4 and Na2Cr2O7 on Ascorbate Peroxidase, Class III Peroxidase, and Lipid Peroxidation in the Leaves and Roots of Pistia stratiotes
Matthew J. Govora, 2010 (Advisor: Dr. Ann Kleinschmidt)
The aquatic plant, Pistia stratiotes, was analyzed for measures of oxidative stress in response to CuSO4 and Na2Cr2O7. P. stratiotes was placed in a fertilizer solution containing concentrations of 40 μM or 500 μM CuSO4 or Na2Cr2O7 for 24 or 72 hours. Because the higher concentration was too damaging to the plants, and the greatest effect was seen when the plants were exposed to the heavy metals for 24 hours, it was decided to expose P. stratiotes to 40 μM CuSO4 or Na2Cr2O7 for 24 hours. After harvesting, P. stratiotes leaf and root tissue was analyzed for changes in the levels of ascorbate peroxidase (APX) and class III peroxidase (POX) activities and lipid peroxidation. The amount of APX activity in the root tissue of plants exposed to 40 μM CuSO4 for 24 hours decreased 50% compared to that observed in the control. However, the amount of APX activity in the root tissue of plants exposed to 40 μM Na2Cr2O7 for 24 hours did not increase, while the amount of APX activity in the root tissue of plants exposed to 40 μM Na2Cr2O7 for 72 hours increased 20% compared to that observed in the control. The amount of POX activity in the leaf tissue of plants exposed to 40 μM CuSO4 for 24 hours was two times greater than that observed in the control, while the amount of POX activity in the leaf tissue of plants exposed to 40 μM Na2Cr2O7 for 24 hours was seven times greater than that observed in the control. The amount of lipid peroxidation in the leaf tissue of plants exposed to 40 μM CuSO4 for 24 hours decreased 25% compared to that observed in the control, but the amount of lipid peroxidation in the leaf tissue of plants exposed to 40 μM Na2Cr2O7 for 24 hours increased 25% compared to that observed in the control. Overall, the level of APX activity in the leaf tissue of P. stratiotes was higher than that observed in the root tissue. But, the level of POX activity of lipid peroxidation in the root tissue of P. stratiotes was higher than that observed in leaf tissue.
Comparative Signaling and Gene Expression in Response to Synthetic Auxins in Nicotiana plumbaginifolia
Alyssa Gumkowski, 2010 (Advisor: Dr. Catharina Coenen)
The class of phytohormones based around the action and structure of indole-3-acetic acid interact with plant matter not only to cause growth but to kill selected weed targets. According to conformation-change hypothesis, auxins change alignment in order to better connect the TIR1 protein to AUX/IAA protein in order to activate auxin-responsive genes. This study predicted that sterically hindered synthetic auxins would induce less or slower gene activity than less hindered auxins. GH3::LUC, a reporter gene system in which a single photon is released per reaction, conveniently allows for the measure of current promoter activity and promoter activity over time. Assays revealed that molecules with one-atom tethers, such as IAA, induced the highest promoter activity, followed by zero-atom tethers and two-atom tethers. It is still unknown whether or not the synthetic auxins are binding to the auxin recognition protein, TIR1. It is also unknown whether or not a conformation change does occur during binding and subsequent action.
An investigation of the signaling pathway to activate heat shock factor A2 in Arabidopsis thaliana
Casey L. Harvey, 2010 (Advisor: Dr. Ann Kleinschmidt)
Plants have an elaborate system, called the heat shock response, to cope with the stress they encounter every day due to a range of temperatures. Many studies have suggested a link between heat stress and oxidative stress. Heat stress and oxidative stress produce many heat shock proteins (Hsps) and heat shock factors (Hsfs) that aid in maintaining homeostasis. Heat shock factor A2 (HsfA2) has been found to be important in the heat shock response by regulating ascorbate peroxidase (APX) at the transcriptional level, and leading to thermotolerance. HsfA2 has also been suggested to be regulated by hydrogen peroxide levels within the plant. To investigate these pathways, this project investigates the hydrogen peroxide-HsfA2 signaling pathway, along with the potential activation of HsfA2 gene by heat, oxidative stress, or both. Arabidopsis thaliana wildtype and HsfA2 t-DNA insertion plants were submitted to heat and oxidative stress conditions. To determine if hydrogen peroxide was a signaling molecule for HsfA2, APX mRNA levels were examined. APX mRNA levels had a greater increase in expression in knockout plants exposed to heat and oxidative stress treatments compared to wildtype plants; this suggests that hydrogen peroxide was not a strong regulator of HsfA2. HsfA2 mRNA was greatly expressed in wildtype plants after heat stress, but not after oxidative stress suggesting that HsfA2 is regulated by heat stress and not oxidative stress. However, strong conclusions cannot be made until replication of results occurs.
This research was supported in part by the Class of 1939 Student Research Fund.
The Effect of Class III Peroxidase Knockouts on Senescence in Arabidopsis thaliana
Sara M. Hendrickson, 2010 (Advisor: Dr. Ann Kleinschmidt)
In this study, chlorophyll levels, POX activities, and CAT activities were measured on days 0, 2, and 4 after the onset of the bolt in Arabidopsis thaliana ecotype Columbia wild-type, T-33, T-40, T-66, and ein3-1 plants. These measures were used to determine the similarities and differences between the wild-type and mutant plants while entering senescence. The POX assay did not yield any consistent results. The total chlorophyll and CAT activities results indicated that the ein3-1 mutant likely is delayed in senescence compared to the wild-type. It is possible that T-40 is also delayed in senescence but nothing could be inferred about the rate of senescence for T-33 or T-66. Further studies include repetition of the chlorophyll, POX, and CAT assays to yield more consistent patterns, testing more class III peroxidase knockouts, and using additional measures of senescence such as APX and SOD activities.
This research was supported in part by the Class of 1939 Student Research Fund.
Effects of E1 Ubiquitination Inhibitor on Auxin-Induced Promoter Activity
Sylvia V. Kauffman, 2010 (Advisor: Dr. Catharina Coenen)
Auxins constitute a class of plant growth hormones critical to a wide range of developmental processes. Indole-3-acetic acid (IAA) is the most abundant form of auxin in plants, but the mechanism by which IAA induces gene transcription has not been fully elucidated. A model was recently developed to explain the pathway of auxin-induced gene transcription in which IAA enables the ubiquitination-dependent degradation of Aux/IAA proteins to initiate gene transcription. To further test this hypothesis, a ubiquitination inhibitor, UBEI-41, was utilized. UBEI-41 disrupts the first stage of ubiquitination, protecting Aux/IAA from degradation and thus inhibiting auxin-induced gene transcription. Nicotiana plumbaginifolia seeds, transformed with an auxin-responsive GH3::luciferase promoter::reporter construct, were used to obtain time-dependent, quantitative measurements of auxin-induced promoter activity. In the presence of 0.1 μM IAA and 50 μM UBEI-41, approximately half of GH3 promoter activity was inhibited after a 100 minute delay, while no inhibition was observed with concentrations lower than 10 μM UBEI-41. The current model was modified by hypothesizing that an equilibrium exists between four states of Aux/IAA binding.
This research was supported in part by the Class of 1939 Student Research Fund.
A Structural and Thermodynamic Characterization of Single Adenosine Group I and Group II Bulge Loops Closed by Watson-Crick Base Pairs in RNA Hairpins
Geoffrey F.S. Lim, 2010 (Advisor: Dr. Marty Serra)
In this investigation, six RNA hairpins containing single adenosine group I or group II bulge loops on the 3′-side of a tetraloop were structurally analyzed using the method of in-line probing. These hairpins, along with their analogous parent hairpins without the bulge, were also optically melted and their thermodynamic parameters were analyzed. The thermodynamic data for the bulge-containing hairpins in this study was combined with that of a parallel study of single nucleotide bulge loops located on the 5′-side of the tetraloop (Merz unpublished). This investigation intended to address the ambiguity associated with group II single nucleotide bulges, as well as determine and predict the effect of single nucleotide group I and group II bulge loops on hairpin stability. The unpaired nucleotide of group II bulges was unable to be definitively determined from in-line probing analysis. For both types of bulges, a positional effect was observed in which bulges closer to the tetraloop are more destabilizing than those closer to the end of the stem. Current methods for modeling the stability of group I and group II bulges in RNA duplexes were adapted to include the first mismatch of the tetraloop and were generally effective at predicting the free energy contribution of the bulge within ±0.5 kcal/mol (Blose et al. 2007; Serra unpublished; Longfellow et al. 1990; Znosko et al. 2002). Based on the models for the bulge, another model was developed to predict the thermodynamic parameters of hairpin formation. This was found to be a relatively poor model for predicting the stability of bulge-containing hairpins. Future studies are needed in order to increase the number of bulge-containing hairpins analyzed and expand upon the present understanding of bulge motifs.
Investigation of peroxidase expression in Alliaria petiolata
Giiulia Molinaro, 2010 (Advisor: Dr. Ann Kleinschmidt)
Peroxidase expression was analyzed in the stem, leaf, and flower bud tissues of Alliaria petiolata by comparing it to the expression patterns of Arabidopsis thaliana and Brassica rapa. RNA was isolated from each of the three plants stem, leaf, and flower bud tissues. Gene specific primers were designed for A. thaliana, B. rapa, and A. petiolata from sequences obtained from previous research. These primers, along with primers designed for the control actin, were used in Real Time PCR to determine peroxidase specific mRNA levels for each plant and tissue type. A. petiolata showed the highest levels of mRNA for both peroxidases in all tissue types. There were very low levels of peroxidase 52 mRNA observed in A. thaliana, which was consistent with past research. The varying levels of mRNA for both peroxidases indicate the changes in peroxidase expression due to duplication of a set of genes. This could lead to the acquisition of a new function for one set while the other genes maintain the original function (neofunctionalization) or function is divided between both sets of genes (subfunctionalization).
This research was supported in part by the Class of 1939 Student Research Fund.
Synthetic approaches to sodium sulfonate analogs of plant growth regulatory compounds
Jaimie M. Mong, 2010 (Advisor: Dr. Shaun Murphree)
Both naturally-occurring and synthetic compounds have been determined auxins, a class of regulatory growth hormones that elicit responses such as cell elongation and differentiation. Pertinent to the advancement of knowledge about this class’s mechanism of action is the use of analogous compounds in biochemical assays. The synthesis of three synthetic analogs of known auxins is studied (scheme 1). Each target was designed to challenge a suggested finding about an auxin’s entrance into the cell or binding to the receptor site of the. The synthetic route described is straightforward, invoking a three-step sequence of reduction, halogenation, and sulfonylation. Synthesis of 1-methylnaphthyl- sodium sulfonate 11 is described (0.130g, 0.50mmol, 54%), as well as the synthesis of intermediates of both Indole-3-propyl sodium sulfonate 4 and Indole-3-butyl sodium sulfonate 8.
Salicylic acid inhibition of indole-3-acetic acid-induced GH3 promoter activation
Julia H. Muntean, 2010 (Advisor: Dr. Catharina Coenen)
Auxin (IAA) and salicylic (SA) are two important plant hormones, the former regulating plant growth and the latter regulating plant defense. Their pathways are known to be mutually antagonistic. The mechanism by which SA inhibits the auxin-inducible GH3 promoter was explored using the GH3::Luc reporter complex, allowing for quantitative and in vivo data to be obtained. It was originally hypothesized that SA competitively inhibited IAA at the TIR1 auxin-binding site given preliminary data and the similarity in structure between the two molecules. As a negative control, 4-hydroxybenzoic acid (HBA) was used. A decrease in transcription with increasing SA or decreasing IAA concentrations was expected. The data obtained did not support this prediction. When 0.1 mM IAA was combined with concentrations of SA from 0.1 mM to 100 mM, a continuous decrease in promoter activation was not seen. When SA concentrations of 100 mM and 1 mM were combined with IAA concentrations from 0.1 mM to 30 mM, increasing IAA concentrations resulted in increased, rather than decreased, inhibition. Inhibition by SA was seen rapidly, within one hour, in many treatments. Rather than having a neutral effect on GH3 induction, HBA greatly increased promoter activation. The observed effects of SA on IAA induction of the GH3 promoter are consistent with a model in which high SA concentrations increase the expression of AUX/IAA repressor proteins and decrease the expression of TIR1 binding sites in a rapid manner. HBA possibly acts as an SA competitor in these tasks, thereby preventing the effects of the SA and increasing promoter activation.
The effects of magnesium on the duplexation kinetics of 3’GTGTCGTG5’/5’CACAGCAC3′
Michael Peroski, 2010 (Advisor: Dr. Alice Deckert)
Duplexation kinetics and the effects of magnesium on duplexation are important in the development of DNA-based biosensors, polymerase chain reaction techniques, and genetic technologies. However, the kinetics of DNA duplexation has not been substantially investigated nor has the effect of magnesium on duplexation kinetics been established. To better understand the mechanism of duplexation and the effects of magnesium on duplexation, the duplexation of 3’GTGTCGTG5’/ 5’CACAGCAC3′ was studied using stopped flow spectroscopy. Magnesium concentration did not affect the activation barrier to duplexation; changes in the activation barrier were attributable to the pre-exponential factor. This finding supported a two-step mechanism of duplexation and an early transition state. Entropy and enthalpy appeared to follow no trend with magnesium concentration. The change in enthalpy for duplexation was very low. The change in entropy for duplexation was low and negative. This change in entropy is due to the single strands aligning before hydrogen bonds form and base stacking occurs, and is not due to the salt concentration or the organization of water molecules about the reactants or the transition state. These findings support the two-step Wetmur-Davidson mechanism for DNA duplexation.
Effect of an arginine-cysteine substitution on the structure and activity of the Pisum sativum ascorbate peroxidase
Benjamin G. Quinn-Elmore, 2010 (Advisor: Dr. Ann Kleinschmidt)
Ascorbate peroxidase is an essential protein found in plants used to reduce harmful levels of hydrogen peroxide to water. Sequence homologies of different APX proteins from many species indicate a high level of conservation and mechanism of H2O2 scavenging is generally the same throughout different types of ascorbate peroxidase. The rate at which APX proteins function does vary when ascorbate peroxidase from plants in the legume family are compared to other species of APX. Along with this difference in kinetics, is the presence of an arginine-cysteine motif just below the ascorbate peroxidase heme in most other species whereas APX from plants in the legume family only have two alanines at this location. This motif is hypothesized to raise the heme orientation leading to a smaller hydrogen binding site. A smaller H2O2 pocket is theorized to slow the rate of Compound I formation thus slowing the overall kinetics of ascorbate peroxidase. Electronic spectra of the mutant APX proteins indicate that the iron of the heme has some six coordinated characteristics when compared to UV/Vis spectra of PsAPX in which the iron showed a five coordinated arrangement. Ascorbate steady-state kinetics showed overall a difference in the enzymatic kinetics between the wild type APX and the RC-PsAPX mutant but this difference is theorized to be from the rate of Compound I formation and the rates of specifically oxidation of ascorbate is still the same. Steady-state kinetics of the rate of o-dianisidine oxidation was inconclusive but if the arginine-cysteine motif does change the orientation of the heme, than it would be predicted that this substrate would show a significantly larger difference in the rates of oxidation between PsAPX and the RC-PsAPX mutant. This is hypothesized because of the suggested characteristic of aromatic substrates to donate electrons to the oxidized APX protein in the hydrogen peroxide pocket. With the hypothesized smaller H2O2 binding site, there would be a slowing of the reduction of oxidized heme peroxidase by this aromatic substrate in addition to the decrease in the rate of Compound I formation.
The Effects of Soy-Phytoestrogens in Female Sprague-Dawley Rats on their Pregnancy and Offspring
Christina L. Rotoloni, 2010 (Advisor: Dr. Susan Rankin)
As soy is becoming a more popular protein source in diets, there is increasing concern about its ability to act as an endocrine disruptor. This study tested the effects of different concentrations of soy intake on the pregnancy of Sprague-Dawley rats. Each rat was randomly assigned one of the following diets: no soy (control), 400 mg soy/Kg BW/day, 800 mg soy/Kg BW/day, or 50 ng estradiol/g BW/day (positive control). Specific attention was directed towards the weight gain of the mothers, ovaries and uterus size, the litter size, the sex ratio of the litter, the weight gain of the pups, and the pups’ blood estrogen level. Although the results were not significant, the sizes of the ovaries and uterus showed a trend of increasing, and the litter size decreased with increasing soy intake. Only the increase in weight gain of the pups with increasing soy intake was significant. These results suggest that soy intake at commercial diet levels are harmful during pregnancy.
This research was supported in part by the Class of 1939 Student Research Fund.
An investigation of the vitamin-c biosynthetic pathway: The effects of jasmonic acid on vtc1 mutants in Arabidopsis thaliana
Sarah E. Sckena, 2010 (Advisor: Dr. Ann Kleinschmidt)
Vitamin-c, or ascorbate (AsA), is the most abundant antioxidant in plants. AsA plays an essential role in oxidative stress response, acting as a substrate for ascorbate peroxidase (APX) in reducing H2O2 to H2O. The AsA biosynthetic pathway has been identified only recently, so there are few studies examining the regulation of proteins within this pathway.
This study examined the regulation of the AsA biosynthetic pathway in Arabidopsis thaliana by comparing levels of mRNAs of enzymes involved in both the major and hypothesized minor pathways of AsA. Vtc1 mutants, which contain a mutation of the first enzyme in the major AsA biosynthetic pathway, were examined to determine how this mutation influences the level of expression of genes downstream in the major AsA biosynthetic pathway and genes in alternative pathways. Treatment with jasmonic acid (JA), a plant hormone known to induce mRNA levels of genes within the major AsA biosynthetic pathway, was investigated to determine how this hormone influences mRNA levels in wild-type and mutant plants. APX mRNA levels were also examined to determine if there is a correlation between APX mRNA levels and the mRNA levels of genes within the various AsA biosynthetic pathways. By using RT-qPCR analysis, GDP-mannose pyrophosphorylase and myo-inositol oxygenase were identified as jasmonate responsive genes. The alternative AsA biosynthetic pathway stemming from myo-inositol was found to be utilized in vtc1 mutants. The level of APX mRNA was the same regardless of plant strain or treatment.
This research was supported in part by the Class of 1939 Student Research Fund.
The effects of NaCl concentrations and temperature variances on DNA duplex formations and their kinetic properties
Audra L. Sinclair, 2010 (Advisor: Dr. Alice Deckert)
Stopped-flow spectroscopy was used to obtain rate constants for the duplexation of a DNA strand in different NaCl buffer concentrations at six different temperatures, ranging from 273 K to 303 K. The DNA oligomer used (5′-CACAGCAC-3’/5′-GTGCTGTG-3′) was high in GC content to increase stability, and this specific strand was chosen because hairpins are not formed in single strand form. DNA concentrations ranged from 2 μM to 7 μM. Data were obtained under second-order conditions and the stopped-flow kinetic profiles were fit well by the second order integrated rate equation suggesting a simple second order reaction mechanism. A no trend relationship was obtained between NaCl concentration and activation energies indicating DNA in its transition state has a higher charge density and behaves more like single stranded DNA than double stranded DNA. This study’s data gives evidence that supports the Wetmur-Davidson model of DNA duplexation.
Class III peroxidase activity in petiole and leaf tissue of Arabidopsis thaliana following flowering
Hannah J. Smith, 2010 (Advisor: Dr. Ann Kleinschmidt)
Class III peroxidase (POX) activity in senescent Arabidopsis thaliana petiole and leaf blade tissue were compared using spectrophotometric analysis, to identify overall POX activity patterns, and agarose gel electrophoresis, to identify the diversity of active peroxidases present in each tissue. Ascorbate peroxidase (APX) activity was measured in both tissue types using only spectrophotometric analysis. As the last stage in a plant’s life, senescence causes the degradation of cellular components as a result of oxidative stress within the plant. This investigation looked at whether petiole and leaf blade tissue combat the increase in reactive oxygen species (ROS) in a similar manner, as measured by POX activity. Results suggested that the petiole and the leaf blade have differing amounts of peroxidase activity during a 36 hour time frame following bolting. Petiole tissue was found to have a greater overall POX activity level with the highest amount of activity occurring at 24 hours after bolting. Petiole tissue also displayed a greater diversity of active peroxidase isoenzymes in comparison to leaf blade tissue.
EPR Characterization of Manganese (II) Containing Superoxide Dismutase II Mimics
Noah R. Snyder, 2010 (Advisor: Dr. Doros Petasis)
Small molecule chelator complexes coordinated with high spin Mn(II) can help elucidate information about the active site of Mn(II) SOD II and potentially mimic the metalloproteins function. Chelator complexes containing non-octahedral coordination of the Mn(II) ion ([Mn(II)(H2 1,2-pdta)(H2O)]·3H2O 4, [Mn(II)(ClO4)(Bipy)2(H2O)]ClO4 6) or large spin relaxation times (H2[Mn(II)(edtp)] 3) did not show resolved hyperfine structure at liquid nitrogen temperatures. However, the hyperfine structure of Mn(II)EDTA 1 was able to elucidate the hyperfine structure of the SOD II EPR spectra. Further more the chelator Mn(II) phthalocyanine demonstrated the potential for superoxide dismutation by a redox mechanism similar to the one utilized by the SOD II protein.
Effects of exposure to metribuzin on the steelhead trout (Oncorhynchus mykiss)
Troy J. Speicher, 2010 (Advisor: Dr. Susan Rankin)
The effects of in vivo exposure of organochlorine, triazine pesticides on non-target water-dwelling species is very important for maintaining the well-being of aquatic life as well as public health. The aim of this study was to test the effects of metribuzin on the steelhead trout (Oncorhynchus mykiss), a common game fish in the United Sates. Steelhead trout exposed to 0, 1.8μg/L, 18 μg/L, and 166.7 μg/L of metribuzin in a 30 L aquaria were tested for changes in levels of glutathione S-transferase enzymes in liver and cortisol level in gills. Metribuzin (2mg metribuzin/100μL ethanol) was added directly to the tanks holding the fish and results were monitored for the four groups on days 0, 5, and 10 of exposure. On day 5, fish exposed to 166.7μg/L metribuzin showed higher levels of GST expression than those exposed to 1.8μg/L and18μg/L. On day 10, there was no difference in GST expression among the groups. Cortisol levels were not different across any group on days 0, 5, or 10.
Cloning and analysis of the coding and non-coding regions of several class III peroxidases in members of the Brassicaceae family
Rachel E. Stamateris, 2010 (Advisor: Dr. Ann Kleinschmidt)
Class III heme-containing peroxidases belong to a superfamily of genes responsible for scavenging reactive oxygen species (ROS) and reducing H2O2 to H2O. They are present in all land plants from the time of germination until senescence and are primarily found in the apoplast. There are 73 known class III peroxidases in Arabidopsis thaliana, but not much is known about their specific roles. Therefore, studying sequence conservation at the nucleic acid level can be an important tool for learning more about their potential structures and functions. The goal of this study was to clone several peroxidases out of various members of the Brassicaceae family and analyze levels of sequence conservation in both the coding and non-coding regions. The 3′ UTR was chosen for study because of recent hypotheses that suggest it may play a role in stabilization of mRNAs, regulation of mRNA metabolism, cellular localization, control of transcription and nonsense-mediated mRNA decay (NMD). Overall, the coding regions showed a higher level of sequence conservation than their 3′ UTR counterparts, suggesting that the structure and function of the peroxidase is highly conserved. The 3′ UTRs showed a moderate level of sequence conservation, suggesting that there is overlap in the regulation of these mRNA molecules. Continued study of sequence conservation of these peroxidases will eventually help us to better understand the precise roles of these genes in all land plants.
This research was supported in part by the Class of 1939 Student Research Fund.