Photosynthetic Responses of Barley (Hordeum vulgare) to Salt Stress

Taylor, Anne Elizabeth (1987) Photosynthetic Responses of Barley (Hordeum vulgare) to Salt Stress. PhD thesis, University of Glasgow.

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Abstract

Agriculture in half of the world's irrigated land is affected by excess salts, mainly sodium salts. Salt-affected soils have a low fertility and tend to yield plants of poor quality. This project examined the effect on photosynthesis of stressing barley leaves with NaCl. Initially, a comparison was made of the growth (by measurement of the primary leaf) and Na+ content (by flame photometry) of control and salt-stressed leaves. Those leaves which were stressed by high external NaCl concentrations showed poor growth and contained high concentrations of Na+ ions. This suggested that barley survives at high salinities by tolerating, rather than simply avoiding, the salt in its external environment. The effect of NaCl on photosynthetic processes was examined by measuring two main parameters : oxygen evolution and chlorophyll fluorescence. These parameters indicated how effectively both the light and dark reactions of photosynthesis were functioning. In addition, the use of modulated and low temperature chlorophyll fluorescence enabled the distribution of light energy between photosystems I and II to be studied. Using these techniques, NaCl was found to reduce the rate of oxygen evolution and to inhibit the change in distribution of light energy from photosystem II to photosystem I under conditions of over-excitation of photosystem II. NaCl also affected the induction period of photosynthesis, causing a delay in the time taken to reach the S and M chlorophyll fluorescence levels and a decrease in the height of the M peak. When the water potentials of control and salt-stressed barley leaves were compared using a pressure chamber, NaCl-stressed plants were found to have a lower water potential. To determine whether the osmotic loss of water was responsible for the observed effects of NaCl on photosynthesis, or whether toxic effects of Na+ or Cl- ions were more important, barley leaves were stressed osmotically using solutions of the impermeable substance mannitol. The effects of mannitol stress were then compared to those of NaCl stress; toxic effects of salt ions were found to be the major factor affecting energy redistribution between the two photosystems, but both toxic and osmotic effects were involved in inhibiting growth and oxygen evolution. In conclusion, high external concentrations of NaCl inhibited photosynthesis in barley. This inhibition was, to a large extent, the result of NaCl affecting energy redistribution between the two photosystems. Although the effect of NaCl was mostly toxic, osmotic effects were also involved.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Agronomy, Agriculture
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-77606
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53
URI: http://theses.gla.ac.uk/id/eprint/77606

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