Master of Science / Department of Biology / Jesse B. Nippert / In 1902, President Theodore Roosevelt signed and enacted the Reclamation Act, which would fundamentally alter the lowland hydrology of the arid southwest over the next century. Flow regulations, groundwater pumping, damming, and river channel changes have led to decreases in water table heights and periodic overbank flooding, and subsequently, increased soil salinity in the arid Southwest. During this period, native riparian tree species have declined significantly and an invasive tree species, Tamarix ramosissima, has increased in abundance and distribution. Increases in soil salinity negatively impact the physiology of native riparian tree species, but the impacts of soil salinity on Tamarix physiology are incompletely known. I studied the impact of increasing soil salinities on the physiology of Tamarix in both field and controlled environments. I first studied the impacts of increasing soil salinities on Tamarix physiology at two semi-arid sites in western Kansas. I concluded that physiological functioning in Tamarix was maintained across a soil salinity gradient from 0 to 14,000 ppm illustrating robust physiological responses. Using cuttings from Tamarix trees at both sites, I subjected plants to higher NaCl concentrations (15,000 and 40,000 ppm). Tamarix physiology was decreased at 15,000 ppm and 40,000 ppm. Tamarix physiological functioning was affected at the induction of treatments, but acclimated over 30-40 days. These results reveal a threshold salinity concentration at which Tamarix physiological functioning decreases, but also illustrate the advantageous halophytic nature of Tamarix in these saline environments. Many arid and semi-arid environments are predicted to become more saline, however, results from both studies suggest that increasing salinity will not be a major barrier for Tamarix persistence and range expansion in these environments.

Many plant species, in response to stresses, accumulate low molecular weight secondary metabolites called phytoalexins. Pea (Pisum sativum ) makes a pterocarpanoid phytoalexin called pisatin which is relatively unique among pterocarpans because its stereochemical configuration is different at two adjacent carbons from the corresponding carbons in pterocarpan phytoalexins synthesized by alfalfa, soybean, clover and other legumes. Previous research demonstrated that an (-) isoflavanone-synthesizing isoflavone reductase (EFR) is induced during (+) pisatin biosynthesis and the final step in the biosynthesis is the methylation of (+) cis-6a-hydroxymaackiain (HMK) by 6a-hydroxymaackiainmethyltransferase (HMM). And, contrary to a predominant model of (+) pisatin biosynthesis, the 6a-OH of pisatin was shown to involve oxygen from H₂O rather than O₂. This work describes the role of (-) isoflavanone (sophorol) in (+) pisatin biosynthesis. Radioactive tracer techniques were used both in vivo and in vitro to analyze metabolism of (-) sophorol and related isoflavonoids. I have found that, in vivo, the incorporation of (-) sophorol into (+) pisatin is more efficient than the incorporation of (+) sophorol and (+) maackiain, suggesting that the normal biosynthetic route to (+) pisatin utilizes (-) and not (+) sophorol and does not use maackiain. (+) Sophorol is not metabolized in vitro by pea protein extracts, although isoflavene, 7,2 '-Dihydroxy-4',5'-methylenedioxyisoflavanol (DMDI) and a novel diastereomer of HMK, trans-HMK, accumulate when (-) sophorol is used as substrate. A cDNA from pea, which encodes sophorol reductase (SOR), was cloned by homology to an alfalfa cDNA coding for isoflavanone reductase. The SOR cDNA was found to be transcribed in response to CuCl₂ treatment of pea seedlings, as was previously found for cDNAs of IFR and HMM, which are involved in pisatin biosynthesis. The SOR cDNA gene product specifically reduces (-) and not (+) sophorol in vitro. DMDI, the product formed by the activity from the recombinant protein, is incorporated in vivo into (+) pisatin. My current model of (+) HMK synthesis proposes that (-) sophorol and (3R) DMDI are normal in vivo pathway intermediates. However, trans-HMK is likely an artifact as it is a poor pisatin intermediate in vivo and is also a poor substrate in vitro for HMM.

The North American Monsoon provides half of the annual precipitation in Tucson, Arizona. The other half occurs dominantly during the winter and early spring. Late spring is the transitional period to the monsoon and is characterized by high temperatures and low humidity. The reliability of this hyperarid period, the consistency of the timing of monsoon onset, and the recognition that certain high-elevation trees produce annual false latewood bands in response to this transitional period, were critical to the design of this dissertation research. I hypothesized that subannual environmental signals might be fixed in stable oxygen isotopes in cellulose from such trees. Existence of a long-term dataset of deltaD and delta18O from Tucson precipitation provided impetus for the collection of a companion dataset at a high-elevation site in the Santa Catalina Mountains north of Tucson. Trees were sampled near the precipitation collection site. The relations between the stable isotope ratios in the precipitation and in the tree cellulose were identified through extraction of water from bimonthly samples of nearby soil, tree stems and needles. Spatial consistency of the cellulose stable isotope signals was measured using tree samples from seven additional sites across the U.S. desert Southwest. Correlations between Tucson summer precipitation delta18O and both local and extra-regional environmental parameters resulted in the identification of the dominant monsoonal moisture source for the Tucson area. Similar correlations with the cellulose delta18O timeseries from the post-false latewood cellulose, supported the previous interpretations, and suggest long-term reconstructions may be possible. Correlations between the earliest cellulose delta18O division and extra-regional environmental parameters suggest environmental measures may be reconstructable for the cool season. Comparison of the high and low elevation precipitation deltaD and delta18O datasets yielded many baseline measures of precipitation stable-isotope dynamics in the U.S. desert Southwest. Comparison of the high-elevation precipitation stable isotope record with soil and stem water deltaD and delta 18O from nearby confirmed that local trees were using dominantly deeper soil water. I noted correlations between measured needle-water stable isotope values and values calculated using a leaf-water model, but systematic departures suggest an additional unmodeled process may operate in this system.

In the southwestern United States, rising costs and limited availability of water have lead to irrigation scheduling based on plant stress indicators in an effort to conserve water. This research was conducted to better define the recovery rates of transpiration, stomatal resistance, and leaf water potential in field grown extra long staple cotton (Gossypium barbadense cv. Pima S-6) following varied durations of water stress. Three water stress treatments were maintained by scheduling irrigations at different Crop Water Stress Index (CWSI) values. Plants irrigated at 0.19 and 0.68 CWSI units needed 72 hours for plant water potential to recover, while plants irrigated at 0.41 CWSI units needed only 24 hours. Water stress had a smaller effect on the recoveries of stomatal resistance and transpiration. Stomatal resistance recovered within 24 hours for all plants regardless of water treatment. Transpiration recovered within 24 hours for plants irrigated at 0.19 CWSI units, and within 48 hours for plants irrigated at 0.41 and 0.68 CWSI units.

Germination responses of P.I. 237110 and 'Ganada' yellow bluestem (Bothriochloa ischaemum (L.) Keng.) were compared in four experiments. P.I. 237110 had the highest total germination for all seed conditioning treatments. At the lowest temperature (15.6°C) P.I. 237110 did not germinate and Ganada had a low total germination. P.I. 237110 and Ganada require high (>20°C) incubation temperatures for optimum germination. Seed conditioning treatments did not significantly increase total germination for P.I. 237110 or Ganada. The caryopsis treatment gave the highest percent germination for all germplasm except Ganada. P.I. 237110 had the fastest time to 50% germination for all seed conditioning treatments. Seed conditioning did not significantly affect time to 50% germination for P.I. 237110 or Ganada. Ganada had significantly higher respiration rates than P.I. 237110 at 0 and -0.4 MPa but not at -0.8 and -1.2 MPa. Respiration rates for both germplasm decreased as osmotic concentrations became more negative.

The effects of subjection of 15-day-old plants of tomato (Lycopersicon esculentum L. 'Contessa') to low night temperature (LNT) of 4°C for up to 21 nights and pre-chilling application of 10% sucrose solution on vegetative, reproductive and yield responses were examined under greenhouse conditions. Chilled seedlings exhibited severe inhibition of growth, with the degree of inhibition increasing with length of chilling. While sucrose treatment (ST) reduced such inhibition and promoted subsequent recovery, it transiently inhibited growth of the unchilled controls. In the long-term, inhibition of growth was observed only for the 0%-sucrose-treated plants cooled for 21 nights. Although LNT lowered the position of the first inflorescence in a direct relation to duration of exposure, this effect was reduced by ST. LNT had no lasting effects on the reproductive and productivity responses of the first two inflorescence (FTI), earliness of flowering, or potential yield and quality. ST promoted flowering of only the 21-day-cooled plants as well as numbers of flowers, fruit set and large fruit responses of FTI. The results indicate that, although early chilling stunts seedling growth, plants may recover at a later favorable temperature without loss to their reproductive capacity or yielding potential.

Water use by mature and sprout (coppice) forms of Emory oak (Quercus emoryi) was estimated by the sap-flow method. Five standards and five coppice trees were sampled in an area that had been harvested for fuelwood and five mature trees were sampled in an uncut area. Differences were recognized between coppice and standards in the cut area and between coppice trees and mature trees from the uncut area. Regression equations were derived relating estimated annual water use to tree diameter, height, and crown measurements for both cut- and uncut-area trees. Seasonal water use by each tree form showed relationship to precipitation, but little relationship to temperature and relative humidity. Woodland density and tree size measurements facilitate extrapolation of water use from the 15 sampled trees to a per area basis. Water use was approximately 1900 cubic meters per hectare per year, based upon drc measurements, for the uncut area and 3168 cubic meters for the cut area. Estimated water use on a per unit area was approximately 1.67 times greater for the cut area than the uncut area.

Master of Science / Department of Agronomy / Tesfaye Tesso / Cold temperature stress is an important abiotic constraint to grain sorghum production in temperate regions. In the United States, low temperature in late spring and early fall has limited sorghum production to a narrow growing period. Deployment of cold tolerance traits may widen this window and hence contribute to increased production. The objectives of this study were (1) to determine the effect of early and mid-season cold temperature stress on growth, phenology and yield components of sorghum, and identify key traits that are most sensitive to cold stress at seedling and flowering stages, and (2) to identify new sources of cold tolerance for use in breeding programs. Series of controlled environment (greenhouse/growth chamber) and field experiments were carried out. Three sorghum genotypes of variable response, Shan Qui Red (tolerant), SRN39 (susceptible) and Pioneer 84G62 (unknown) were subjected to cold (15/13ºC day/night) and normal (25/23ºC day/night) temperature at seedling (Experiment I) and flowering (Experiment II) stages. The genotypes were planted in a greenhouse using a 5L polytainer pots. Each pot consisted of a single plant and each plot was represented by three pots. A split-plot design with three replications was used in both experiments with temperature regimes as main plots and genotypes as sub-plots. Three days after emergence, experiment I plants were moved to the growth chamber and subjected to the designated temperature treatments. For experiment II, the treatments were assigned at heading stage immediately before anthesis had begun. The treatments lasted 10 d in both experiments. Data were collected on seedling characteristics and leaf chlorophyll content in experiment I, days to flowering, maturity, and yield components in both experiments, and anthesis duration in experiment II. For the field experiment, 150 sorghum germplasm collections of potential cold tolerance along with tolerant and susceptible checks were evaluated for emergence and seedling traits under early planting (April 13) at soil temperature of 20.1/13.4 ºC max/min. The normal temperature treatment was applied by planting at regular season (May 26) at soil temperature of 30.0/20.4ºC max/min. Twenty-four genotypes selected based on field emergence and seedling vigor were further screened under controlled environment. Early-season stress significantly reduced leaf chlorophyll content, all seedling traits (height, vigor and dry weight), and also delayed flowering and maturity. But it had no effect on final leaf number, plant height and yield components. Genotypic response to early stress was significant for all traits with the susceptible checks having the lowest score for all seedling traits. Mid-season cold stress prolonged anthesis duration, delayed maturity and highly reduced all yield components. Several genotypes among the 150 had higher seedling vigor and emergence than the tolerant check, Shan Qui Red. In conclusion, reduced seedling vigor as a result of early stress had no effect on final yield provided that stand establishment was not compromised while mid season stress is damaging to yield. The wide genetic variation for the traits indicates the potential for improvement of cold tolerance in sorghum.

Cultured tobacco mesophyll protoplasts were used as a model to studying the hormonal control of cell-cycle reactivation in plants. Tobacco mesophyll protoplasts were isolated from leaves in which cell division had ceased, and were then cultured. During the first three days in culture, the protoplasts dedifferentiate, resynthesize the cell wall, express wound-related transcripts, and reinitiate the cell cycle. Reinitiation depends on the hormones auxin and cytokinin. I examined the expression of one or two genes related to different aspects of protoplast development. The expression of following genes was examined: wound or stress response (extensin and PR-1a), cell-wall resynthesis (extensin), cytoskeletal reorganization (actin), and cell-cycle reactivation (cdc2, histones H3, and H4). I found that nuclear division began between 30 and 50 hrs of culture about 10-12 hours after the onset of DNA synthesis. By the third day, 70% of the protoplasts had divided. In freshly isolated protoplasts, histones H3 and H4, and cdc2 were not expressed. Expression of cdc2 was activated by 12 hrs of culture, histone expression was activated by 24 hrs concurrent with the initiation of DNA synthesis. Extensin showed a similar pattern of expression as the histones, but expression of PR-1 was activated more slowly. Actin was expressed in leaves and freshly isolated protoplasts, but its expression increased about 4-fold during protoplast culture. When either auxin or cytokinin was omitted from the media, the protoplasts did not divide and the histones and PR-1 were not expressed. Extensin and actin were expressed in the absence of hormones. Hormone delay studies suggested that auxin was required from the beginning of culture, whereas cytokinin was required before the cells enter S-phase. These results are consistent with auxin and cytokinin acting to induce a G$\sb0$ to G$\sb1$ / transition during protoplast development, possibly through initiation of transcription of cell-cycle required genes such as cdc2 and the histones. However, it appears that cdc2 and histone expression are not the primary target of the hormones because their expression is activated 12 hrs or more after the requirement for auxin has passed. Expression of genes associated with cell wall synthesis (extensin) and wounding (extensin and PR-1) do not appear to be required for reactivation of the cell cycle. / Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3665. / Major Professor: George W. Bates. / Thesis (Ph.D.)--The Florida State University, 1994.

The plants and sediments of two shallow, sub-tropical lakes in north Florida (Lake Jackson and Lake Hall located in Leon County) were sampled, identified, and analyzed for PAH content at 16 different stations quarterly. Stations were chosen so that areas affected by stormwater and relatively pristine areas were surveyed. Sediments from areas that received stormwater runoff were found to have elevated PAH concentrations, while stations distant were characterized by lower PAH concentrations. / The PAH content of rooted vegetation was found to have a significant relationship with the concentrations of PAHs in the sediments upon which they grew. There was no relationship between the PAH concentrations in non-rooted plants and the sediments where they were found. Plant growth and PAH assimilation experiments were performed on sixty-six plants that included indigenous rosette monocots and vittate dicots which were planted in sediments spiked with varying concentrations of PAHs. These sediments were completely segregated from the water column which was verified by analysis. / It was conclusively shown that the sediment PAHs exerted a deleterious effect on the growth of the subject aquatic macrophytes, and that the PAHs from the sediment entered the plants through their root systems. These experiments showed that the roots of aquatic plants will reach a PAH concentration almost nine times higher than the PAH concentrations of their shoots. There was a difference in the types of PAHs which were accumulated by the plants: the most readily accumulated PAHs were the most water soluble. The evidence indicates that partitioning occurs from the aqueous phase. / There were species-specific differences in the degree of accumulation of sediment PAHs. Saturation phenomena for PAH bioconcentration were observed. A model was developed that incorporated equilibrium constants, constants for adsorption and desorption, and saturation levels of PAHs for aquatic plants. The field data, the microcosm experiments and the model all lead to the conclusion that aquatic macrophytes accumulate sediment PAHs acropetally and transport them to their shoots. / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6491. / Major Professor: Robert J. Livingston. / Thesis (Ph.D.)--The Florida State University, 1995.