A study of salt tolerance in Arabidopsis thaliana and Hordeum vulgare.
PhD thesis, University of Glasgow.
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The original objective of this work was to compare the cellular processes in salt tolerant
and salt sensitive plants cells to gain insight into the mechanisms that confer
halotolerance. Halotolerant and salt sensitive cell lines were derived from the model
glycophyte Arabidopsis thaliana; in addition cell suspension cultures from the dicot
halophytes Beta vulgaris and Atriplex halimus were also generated. Unfortunately,
severe disruptions were encountered following a serious fire; persistent power failures,
and failures of new equipment hampered progress with this work. For this reason, only
comparisons between the Arabidopsis cell lines were completed. The halotolerant
(HHS) cell lines survival strategy is to prevent Na accumulation when grown in < 100
mM NaCl. Wild type (WT) cells grow faster than HHS cells in the absence of NaCl, but
rapidly take up Na in 50 mM NaCl where their growth is severely affected, and fail to
grow completely above 100 mM NaCl. No evidence was found to suggest this growth
impairment arose from osmotic stress or nutrient ion deficiencies. Protein profiling of
HHS cells identified a number of proteins whose abundance is regulated by salt stress.
These included proteins involved in ion transport, central metabolism, and general stress
responses. The implications of these findings are discussed.
In a separate project, a whole plant approach was taken to establish the physiological
mechanisms that account for the reported difference in halotolerance between two
commercially grown barley lines originating from China. Measurements on growth and
development, plant water status, tissue ion profiling, photosynthesis rates, and
transpiration rates suggested the tolerant line (Zhou 1) enters the reproductive phase of
its life cycle approximately one week earlier than the sensitive line (Zhou 85), and this
critical period allows floral development resulting in improved yields. This early
flowering is not associated with the well characterized PpD-H1 locus controlling early
flowering in cereals.
The main conclusion from this study is that for glycophytes that do not complete a full
life cycle above 100 mM NaCl (which includes all of the world’s major crops), it is the
ionic component of salinity stress that impairs growth and yield. Further research on
salinity stress in crops should focus on understanding the processes that control ionic
balance rather than osmoregulation.
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