The major goal of my dissertation research was to use genetic approaches to identify and characterize the components (genes) that are important for salt tolerance in Arabidopsis. Identification and characterization of such genes might provide insights into why these genes are important, and how these genes function in salt response and salt tolerance in higher plants. During my dissertation research, the sos3-1 mutant was isolated and characterized. The mutant plants are hypersensitive to Na⁺ and unable to grow with low K⁺. Increased Ca²⁺ levels can partially suppress the growth defect of the mutant plants under salt stress and fully restore their growth under low K⁺. These results suggest that SOS3 may be a Ca²⁺-mediated regulator that controls K⁺ and Na+ homeostasis in Arabidopsis. The SOS3 gene was cloned by map-based cloning techniques. SOS3 encodes a protein sharing significant sequence similarity with the B subunit of calcineurin from yeast and neuronal calcium sensor from animals. SOS3 contains three putative EF-hand calcium binding domains and a putative myristoylation motif at its NH₂-terminus. SOS3 binds calcium and is myristoylated in vitro. A mutation in SOS3 that destroys the conserved myristoylation motif abolishes SOS3 myristoylation, but not its calcium binding in vitro. Furthermore, the defect in Ca²⁺ binding of the sos3 does not affect its myristoylation. These results indicate the independence of calcium binding and myristoylation of SOS3. Mutant sos3-1 has a nine-base-pair deletion in the second conserved EF-hand Ca²⁺ binding domain, which leads to misfunction. of sos3 in vivo. To determine if myristoylation is also important for SOS3, the wild-type SOS3 cDNA and the SOS3 cDNA with a disrupted conserved myristoylation sequence were tested for their capability to complement the sos3-1. It was found that an intact conserved myristoylation sequence is essential for SOS3 function. These results indicate that both calcium binding and myristoylation are essential for the function of SOS3.

Amount and activity of the primary carboxylating enzyme of photosynthesis, photosynthetic gas exchange, and leaf anatomical parameters were measured in two strawberry species, RCP37 (Fragaria chiloensis) and 'Midway' (Fragaria x ananassa). Photosynthetic capacity was greater in RCP37, as indicated by a greater CO₂ assimilation rate at ambient CO₂ concentration (350 μmol mol⁻¹), Rubisco amount, carboxylation efficiency, residual conductance, ratio of mesophyll surface area to leaf area, and leaf N content, compared to 'Midway'. The ratio of mesophyll surface area to leaf area, mesophyll layer thickness and palisade layer thickness were significantly different between RCP37 and 'Midway'. The large surface area of palisade cells in RCP37 accounted for the difference in the ratio of mesophyll surface area to leaf area. Results show that RCP37 has higher photosynthetic capacity than 'Midway'. RCP37 might provide promising resources of germplasm for improving photosynthetic rate or yields of cultivated strawberry varieties.

Pinus brutia var. eldarica is often considered to possess photosynthetic characteristics that make it highly tolerant to drought conditions. However, very little is known about it's photosynthetic response to water stress under either laboratory or field imposed drought conditions. The purpose of this study was to utilize laboratory gas-exchange measurements to determine the effects of water stress and recovery from stress on photosynthetic capacity of potted Pinus brutia via. eldarica plants. Analysis of the rate assimilation (A) versus intercellular CO₂ (Cᵢ) data indicates that recovery of carboxylation efficiency (g'm) (i.e. Rubisco activity and amount) does occur after daily re-watering of moderately stressed (ψ₂ ≃ -2.0 MPa) Pinus brutia. However, these same data indicate that irreversible damage to cell membranes results in an inability to re-generate RubP. Although inferences on the effect of stress on A in field grown Pinus brutia is tenuous, these laboratory results indicate that Pinus brutia may not be as drought tolerant as commonly believed.

Digitaria californica is a warm-season grass native to western hemisphere deserts. This study was conducted to measure: (1) seed dormancy, and the effects of (2) wetting and drying on germination, and (3) glumes on water uptake and loss. Dormancy was measured with weekly germination trials for 12 weeks. Complete and naked caryopses were exposed to a 24-h dry period after 12, 24, 36, and 48-h imbibition, and rewetting for 2 weeks. Water uptake and loss patterns were also measured. Germination percentage increased from about 40% initially to 94% after 9 weeks. Germination speed decreased from 5 days to about 2 days over the same period. Drying reduced percent germination of the 36- and 48-h imbibition treatments for complete caryopses, and that of the 24-, 36-, and 48-h imbibition treatments for naked caryopses. Complete caryopses also seemed to imbibe faster. Moisture loss for complete and naked caryopses appeared similar. Short imbibition periods do not induce germination in this species.

A greenhouse pot experiment was conducted to study the amount of selenium accumulation and the effect of selenite on growth of carrots, squash, and sudan grass. Selenium was added to sandy soil as sodium selenite at five rates (0.02, 0.08, 0.32, 1.28, and 5 mgn) in a randomized complete block design including a control, in three replicates. Addition of 5 mg/l selenium reduced the total biomass (in carrots and squash) as much as 97% and as much as 85% in sudan grass. Crops in the control treatment and those exposed to 0.02 mg/l did not accumulate selenium to levels considered toxic to animals and humans. All other treatments resulted in levels of accumulation that could pose hazards when consumed by animals and humans. Based on the interpolated irrigation concentration that caused 50% yield reduction (observed data), sudan grass was the most tolerant crop (4.0 mg/l)while squash plants were the least tolerant (0.9 mg/l) and carrots were intermediate (2.2 mg/l).

The aim of this work was a reinvestigation of the role of Cl('-) ions in the reactions on the oxidizing side of photosystem II in chloroplasts. It was found that thylakoid membranes retained photosynthetically active Cl('-) during their isolation in Cl('-)-free media. This Cl('-) was readily released only when the thylakoids were incubated in uncoupler-containing media at alkaline pH in the dark. Once the residual Cl('-) was released by such treatment, photosynthetic electron transport became dependent on added Cl('-) under all conditions. / The effect of Cl('-) deficiency on the stability of the higher oxidation states of the Mn-containing water photooxidase was investigated. While at least two oxidizing equivalents were accumulated on this enzyme in the absence of Cl('-), they were not as stable in the dark as when Cl('-) was present. The postulate that Cl('-) serves only as a counter ion to positively charged oxidation states of the water splitting enzyme could not be supported. / In addition to facilitating the release of Cl('-) from thylakoids, uncouplers were found to also accelerate the release of bound Mn from PS II in dark-adapted chloroplasts. This suggested that a metastable proton gradient could persist in thylakoids form some time in the dark. It is postulated that both the photosystem II Cl('-) site and the water splitting enzyme reside in a special proton sequestering domain located within the thylakoid membrane which is isolated from the bulk solutions by barriers that are nearly impermeable to protons. The experimental evidence suggests that this domain may be identical to that postulated by Dilley's research group (Baker, G. M., Bhatnager, D. and Dilley, R. A., 1980, Biochemistry 20: 2307-2315). / Source: Dissertation Abstracts International, Volume: 42-09, Section: B, page: 3520. / Thesis (Ph.D.)--The Florida State University, 1981.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3353. Adviser: Stephen P. Long. Includes bibliographical references (leaves 109-116) Available on microfilm from Pro Quest Information and Learning.

In spite of the fact that it is one of the most widely researched subjects in plant biology, the physiology of salt tolerance is still not well understood. This research was undertaken to investigate salt tolerance in the extreme halophyte, Salicornia bigelovii Torr. Halophytes, plants that are naturally salt tolerant, are well suited to research on salt tolerance because millions of years of evolution have fine tuned their adaptation to high salinity to the extent that their growth is inhibited when they are grown in reduced salinity. S. bigelovii was grown in different concentrations of NaCl and growth responses were compared. My emphasis was on salinity effects on cell wall extensibility, wall yielding threshold (minimum turgor required for growth), and water relations. When S. bigelovii was grown in low salinity, relative growth rate was slower, fresh and dry weight, relative water content and succulence were reduced, and both epidermal and cortex parenchyma cells were smaller. The plants also accumulated less Na⁺ and more K⁺, Ca²⁺ and Mg²⁺. These results prompted two specific questions. Was the excess Ca²⁺ accumulated by the plants grown in low salinity bound to cell walls and did it cause reduced cell wall extensibility and increased yield threshold? Was growth inhibition a consequence of low turgor due disturbances in water relations? Even though there was three times more Ca²⁺ in the walls of the plants grown in I salinity, cell wall extensibility was not significantly different between salinity treatments. However, the wall yielding threshold of the plants grown in low salinity was significantly lower. Turgor was also significantly lower in these plants. But, since the minimum turgor required for growth was even lower, reduced turgor was not responsible for growth inhibition. Based upon the results of this research, I have concluded that growth inhibition in S. bigelovii in reduced salinity was not due to disturbances in water relations nor was it the result of detrimental changes in cell wall properties. It is becoming increasingly clear that specific ion effects play an important role in limiting the growth of S. bigelovii in low salinity. This research has led to the identification of several new directions for future investigation into the salt tolerance mechanisms of this unique plant.

Sugars are thought to affect many plant developmental processes; however, little is known about the mechanisms involved. Ultimately, gaining an understanding of these mechanisms may help improve crop yield. As a first step, this work characterized the Arabidopsis sugar-insensitive2 ( sis2) mutant. Previous work shows that sis2, unlike wild type, develops a substantial shoot system on high concentrations of glucose, sucrose, and sorbitol; in addition, the sis2 mutant germinates on paclobutrazol, a gibberellin biosynthesis inhibitor. This thesis demonstrates that sis2 exhibits resistance to the effects of gibberellin and brassinosteroid biosynthesis inhibitors during germination, but not during later developmental stages. In addition, sis2 is resistant to the combined inhibitory effects of glucose and paclobutrazol on germination. These results suggest a novel connection between phytohormone and sugar response pathways.

Plants respond to a variety of stimuli from their environment, including mechanical stimulation and changes in temperature or light. In Arabidopsis thaliana, morphological changes occur following touch stimulation, and this phenomenon is preceded by upregulation of expression of the TCH genes. The TCH3 transcription unit is 1522 base pairs (bp) and contains three 367-bp repeats which are highly identical. TCH3 encodes a 324 amino acid calcium-binding protein which is 58-60% identical to the Arabidopsis calmodulins and contains six potential Ca$\sp{2{+}},$ binding sites. To isolate the cis-regulatory elements responsible for upregulation of expression of TCH3 following touch, darkness, heat shock, and cold shock, transgenic plants harboring fusion genes containing 5$\sp\prime$ fragments of the TCH3 locus fused to the reporter gene uidA were created. A 43 bp sequence adjacent and 5$\sp\prime$ to the transcription unit of TCH3 is sufficient for induction of reporter gene expression following touch, darkness, and heat shock, and a 127 bp sequence which includes these 43 bp is sufficient for induction of expression in response to cold shock. Furthermore, it was determined that the 57-base 5$\sp\prime$ untranslated region of the TCH3 mRNA is important for post-transcriptionally regulated instability of the transcript. Sequences upstream of TCH3 direct reporter gene expression to the growing regions of roots, root/shoot junctions, apical meristems, leaf vasculature, and trichomes. Expression patterns of the fusion genes suggest TCH3 is required in regions of the plant which are subjected to stress, either applied externally or generated during development. It has been suggested that responses of plants to mechanical stimulation involves the plant hormone ethylene. To test this, Arabidopsis mutants defective in ethylene responses were examined for the ability to respond to touch. As in wild-type plants, the ethylene response mutants show reduced flowering stem elongation following touch stimulation and are capable of upregulation of TCH gene expression. This suggests that the loci defective in these ethylene response mutants are not required for developmental or molecular responses to touch stimulation in Arabidopsis.