As sessile organisms, plants are subject to numerous environmental insults. Of these, salinity is one of the most widespread and important in terms of limiting plant distribution and productivity. Molecular studies have established that plants challenged by high salinity respond by increasing expression of specific genes. A functional role for the products of such genes in stress tolerance has not been established, however, and little is known about the biochemical mechanisms that allow plants to tolerate osmotic stress. Mesembryanthemum crystallinum is a facultative halophyte capable of adjusting to and surviving in highly saline conditions. I have generated and screened a subtracted cDNA library to identify mRNAs that accumulate during this plant's adaptation to salt stress. Three mRNAs were identified that increased in abundance in leaf tissue of salt stressed plants. Patterns of induction for these mRNAs differed. The most dramatically-induced mRNA, Imt1, was characterized in depth. Imt1 expression was induced in leaves and, transiently, in roots. Nuclear run-on assays indicated that the gene is transcriptionally regulated. In several respects, the expression of Imt1 differed from that of other salinity-responsive genes involved in photosynthetic metabolism in M. crystallinum: The mRNA was induced by salinity and low temperature, but not by drought, and its induction by stress was not influenced by plant age. Imt1 encoded a predicted polypeptide of Mr 40,250 which exhibited sequence similarity to several hydroxymethyl transferases. The IMT1 protein was expressed in E. coli and identified by functional assay as a myo-inositol methyl transferase that catalyzes the first step in the biosynthesis of the cyclic sugar alcohol pinitol. The presence of high levels of sugar alcohols has been correlated with osmotolerance in a wide range of organisms, and the stress-initiated transcriptional induction of IMT1 expression in a facultative halophyte provides the strongest support to date for the importance of sugar alcohols in establishing tolerance to osmotic stress in higher plants. The ability of this methyl transferase to generate a putative osmoprotectant from a ubiquitous plant substrate makes it an attractive candidate enzyme for the creation of stress-resistant transgenic plants.

No description available.

The overall aim of the research presented in this thesis was to evaluate the importance of arbuscular-mycorrhizal ( AM ) colonization of plants in management of saline lands. Some aspects of application of AM fungi in revegetation of saline lands are also reported. Effects of AM pre-inoculation on mycorrhiza-responsive and non-responsive plant growth and establishment were evaluated under glasshouse conditions. The advantages of mycorrhizal fungal inoculation in increasing plant salinity tolerance and establishment in saline conditions were related to the responses of host species to AM fungi. Pre-inoculation with Glomus intraradices increased plant growth, nutrient uptake and establishment of mycorrhiza responsive Trifolium subterraneum in saline conditions, but non-mycorrhiza responsive Festuca arundinacea did not get growth benefits from AM in saline conditions. The main mechanism underlying increased plant growth and establishment in saline conditions in mycorrhiza responsive plants was increased plant nutrient uptake, particularly phosphorus ( P ) , at an early growth stage. The improvement could be explained by higher soil volume exploration by hyphae and / or roots, faster nutrient uptake and microbial changes in the soil rhizosphere. AM inoculation and P application effects on salinity tolerance were compared in Trifolium subterraneum. Application of P increased plant growth and salinity tolerance in saline conditions, but AM inoculation increased nutrient uptake and plant salinity tolerance more efficiently than P application. Effects of salinity on AM colonization of chenopods were investigated under glasshouse conditions. Salinity had no effects on AM colonization of Atriplex nummularia, but AM inoculation increased plant growth and nutrient uptake. The growth improvement was attributed to benefits from low AM colonization, and changes in bacterial community composition in the rhizosphere. Roles of AM fungi in influencing P leaching from soil were investigated in experiments with repacked cores under both non-saline and saline conditions. Increased plant size via AM inoculation significantly decreased P leaching in the soil profile under both non-saline and saline conditions in low P soils. Increased root volume and extension external hyphal network were the main effects of AM fungi in increasing plant size under saline and non-saline conditions, which led to scavenging more P and depleting more soil available P, thereby decreasing P losses via leaching. Application of P increased plant size and decreased P leaching, but on the other hand increased soil available P and decreased AM colonization. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2004.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Thesis (M.S. - Soil and Water Science)--University of Arizona, 1986. / Bibliography: leaves 82-88.