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Spatial and temporal alterations of gene expression in rice.Plett, Darren Craig January 2008 (has links)
Two problems hampering efforts to produce salt-tolerant plants through constitutive expression of transgenes include: 1. Spatial control. Particular cell-types must respond specifically to salt stress to minimise the amount of Na⁺ delivered to the shoot; and, 2. Temporal control. Transgenes are typically expressed in plants at similar levels through time, irrespective of the stress encountered by the plant, which may exacerbate pleiotropic effects and means that, particularly in low-stress conditions, costly and/or detrimental metabolic processes may be active, thus reducing yield. To address these issues, Gateway® destination vector constructs were developed combining the GAL4 UAS (upstream activating sequence) with the ethanol-inducible gene expression system to drive inducible cell-specific expression of Na⁺ transporter transgenes (or to silence salt transporter transgenes inducibly and cell-specifically). Rice (Oryza sativa L. cv. Nipponbare) GAL4-GFP enhancer trap lines (Johnson et al., 2005: Plant J. 41, 779-789) that express GAL4 and GFP specifically in either the root epidermis or xylem parenchyma (and therefore ‘trap’ cell-type specific enhancer elements) were transformed with this GAL4 UAS – ethanol switch construct, thereby allowing both spatial and temporal control of transgenes. In preliminary experiments, the expression system successfully limited the expression of RFP to specific cell-types after induction with ethanol. Other genes expressed using this system include PpENA1, a Na⁺-extruding ATPase from the moss, Physcomitrella patens, and AtHKT1;1, a Na ⁺ transporter from Arabidopsis thaliana. The two enhancer trap rice lines were also transformed with the GAL4 UAS driving stable expression of AtHKT1;1 and PpENA1 specifically in root epidermal or xylem parenchyma cells. Expression of AtHKT1;1 in root epidermal cells reduced Na⁺ accumulation in the shoots, while expression in the root xylem parenchyma appeared to have little effect on shoot Na⁺ accumulation. Using cryo-scanning electron microscopy (SEM) X-ray microanalysis, the outer cells of the roots of the line expressing AtHKT1;1 in the epidermal cells were found to accumulate higher levels of Na⁺ than the parental enhancer trap line. Additionally, this line had decreased unidirectional ²²Na⁺ influx. Similar results were observed for plants expressing AtHKT1;1 driven by the CaMV 35S / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1325289 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2008
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Physiology, comparative genomics and germplasm development for improvement of salt tolerance in hexaploid wheatMullan, Daniel John January 2006 (has links)
[Truncated abstract] Lophopyrum elongatum, a wild relative of wheat, can be used as a source of novel genes for improving the salt tolerance of bread wheat. Na+ `exclusion? is a major physiological mechanism for salt tolerance in the wheat L. elongatum amphiploid, and a large proportion (~50%) of the improved Na+ `exclusion? is contributed by a gene(s) on chromosome 3E. This study integrated physiological analysis with comparative genomics to identify gene orthologues that may regulate Na+ transport, and designed and implemented molecular markers for developing wheat L. elongatum recombinant lines with reduced portions of L. elongatum chromatin retaining the Na+ `exclusion? trait. Physiological analysis of leaf Na+ accumulation in wheat L. elongatum substitution lines confirmed that the 3E chromosome contributes a major effect on reduced leaf Na+ accumulation in wheat when grown at 200 mM NaCl. Candidate genes from the model plant, Arabidopsis thaliana, controlling Na+ transport into and from cells (SOS1, HKT1) or compartmentalisation within vacuoles (NHX1, NHX5, AVP1, AVP2) were targeted for comparative analysis in wheat. Wheat gene orthologues were identified by BLAST searching to identify either FL-cDNAs or ESTs, which were subsequently used to amplify genomic DNA, and orthologues confirmed by similar intron-exon structure between Arabidopsis and rice. Intron-exon comparisons showed the majority of exons were conserved between Arabidopsis, rice and wheat, but also indicated exon shuffling events since divergence from a common ancestor. Gene orthologues were assigned to homoeologous chromosomes and non-syntenic regions between wheat and L. elongatum, with the SOS1 orthologue located on group 3 chromosomes in wheat and L. elongatum. ... The recombinant line 524-568 contains a small introgression on the distal end of the long arm of wheat chromosome 3A and represents the most desirable line presently available for further germplasm development. The main outcomes of this thesis have been an increased understanding of the physiology and evolution of orthologues for Na+ transport in wheat and L. elongatum, improved methodologies for designing alien-specific PCR markers, and the development of overlapping recombinant lines that provide a source of novel genes for pyramiding into wheat and improving its tolerance to salt stress.
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Breeding investigations for salt tolerance in rice incorporating characterisation of salt affected soils and farmers perceptions and preferences for tolerant cultivars in north-eastern Tanzania.Kashenge-Killenga, Sophia. January 2010 (has links)
Rice (Oryza sativa L.) is the principal crop of North Eastern Tanzania but production is
threatened by salt affected soils, drought and the use of un-adapted cultivars, among other
constraints. Little research and hardly any breeding have been done on the aspects of salt
tolerance of the crop in sub Saharan Africa, leading to low yields and low production in
rice irrigation schemes under arid and semi arid conditions. A project was therefore
implemented in North Eastern Tanzania during 2007-2010 seasons to investigate the
possible breeding contributions to enhance productivity and production of the crop in salt
affected areas.
The objective of this study was to: a) determine farmers’ perceptions on both salt
problems and their effects on rice crop productivity as well as establishing farmers’
needs and preferences for rice varieties in the targeted irrigated environment; b)
determine the extent of salt problem in both soil and irrigation water in the available rice
irrigation schemes in the North-eastern Tanzania; c) identify the major physiological
mechanisms associated with salt tolerance in farmer-preferred native varieties and
landraces; and d) determine the mode of inheritance of salt tolerance in rice.
Participatory rural appraisal was conducted in Mkomazi and Mombo villages in Tanga
region with the aim of understanding characteristics of rice–based farm economy,
farmers’ perception of agriculture constraints and variety preferences in salt affected
areas of North-eastern Tanzania. This was followed by a preliminary study to understand
soil characteristics in relation to salt problems and its extent in selected nine rice
irrigation schemes. Studies was established under controlled conditions to assess the salt
tolerance of some rice farmers preferred rice cultivar and evaluate the putative traits in
the rice materials that contribute to the performance of a genotype under saline and
saline-sodic condition. Thereafter, genetic mechanism governing various morpho-physiological
parameters in selected Tanzania local farmers’ preferred varieties and salt
tolerant donors under saline and sodic soil conditions of North Eastern Tanzania were
determined.
A participatory rural appraisal (PRA) established that rice was a major staple food and
cash crop and rice farming was a major economic activity in the area. However, soil
degradation through increased salt affected soils was identified as the major factor
responsible for irrigated rice yield decline. Major varieties grown are salt sensitive, and
salt tolerant varieties were not available. The study also revealed that most farmers’
preferred traits of rice cultivars were high yield potential, aroma, early maturing, medium
plant stature, tolerance to salt and drought. Improvement of these characters in new salt
tolerant varieties would increase food production in fields with low or zero productivity
and the well-being of the poor farmers.
A soil characterisation study indicated the magnitude of the problem, whereby, seven out
of nine studied irrigation schemes were affected and sodic and saline-sodic conditions
were the dominant types of soils. Poor irrigation canals and management of irrigation
water were the driving factors that contributed to salts accumulation causing a decline in
productivity.
Experiments were established under controlled environments to evaluate the tolerance of
10 and 11 rice genotypes under saline and saline-sodic stresses, respectively. Significant
variation between genotype and significant interactions between genotype and salt
treatment (P<0.001) were observed for all characters studied. Genotype Pokkalli, IR
67076-2B-21-2 and IR 56 showed superior performance under saline, whereas CSR 27,
Nerica 2 and IR 56 had superior performance under saline-sodic. The study therefore
established that, all the local farmer preferred cultivars except IR 56 performed poorly
under both salt stress environments. High seedling vigour, less leaf injury, less Na+ and
high K+ accumulation in leaves, low Na+/K+ ratio of ion uptake, high spikelet fertility,
increased grains per panicle and 1000 grain weight were considered as the desirable
characteristics therefore can be used in developing lines for salt tolerance for production
under saline and saline - sodic conditions.
Gene action and combining ability studies for nine morpho-physiological traits were
studied under normal, saline and sodic soil environments. The rice populations were
generated through 7 x 7 full diallel crosses and advanced to F2. The parents comprised
two donors for saline tolerance, one donor for sodic tolerance and four salt sensitive
farmers preferred varieties. Both additive and non-additive gene effects were important in
the inheritance of the characters studied in all soil environments. However, additive
effects were more important for the number of tillers, shoot Na+, Na+/K+ ratio and plant
height. Both additive and non-additive gene effects were important for spikelet fertility,
days to 50% flowering, number of grains per panicle, 1000 grain weight, and grain yield;
however the magnitude of additive gene effect was higher than non additive effects.
Amongst the parental lines, the best general combiners for yield along with other traits
were TXD 306 and IR 67076-2B-21-2 under normal non-saline/sodic condition; IR 56,
Pokalli and TXD 306 under saline condition and CSR 27 and TXD 306 under sodic
conditions. The overall results from this study indicated the possibility of improving both
yield and salt tolerance from this set of germplasm; therefore contributing to increasing
rice yields in the marginal salt affected environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
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Variation in morphology, salinity and waterlogging tolerance and resource allocation in strawberry clover (Trifolium fragiferum L.) : implications for its use in mildly saline soils in southern Australian farming systemsMcDonald, Kathi January 2009 (has links)
[Truncated abstract] In southern Australian farming systems the replacement of deep-rooted perennial native vegetation with shallow-rooted annual crops and pastures has resulted in rising groundwater tables and an increased incidence of dryland salinity. It has been suggested that to address this issue by restoring hydrological balance, large areas of agricultural land need to be vegetated with perennial plants. One of the most agriculturally productive ways to do this is to introduce perennial pastures, both into upslope groundwater
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