Phytohormonal and physiological responses of <i>Solanum
      lycopersicum</i> to strong soils
Creators: name: Donaldson, Sarah
Publisher: name: Lancaster University
Year: 2019
Subjects: soil compaction
soil strength
XYLEM SAP COMPOSITION
gibberellins
jasmonic acid
Plant water relations
Leaf water potential
shoot water potential
root water potential
plant growth
phytohormones

description: Soil compaction occurs when external pressures (from heavy machinery or
      grazing animals) exerted on the soil surface increase soil bulk density,
      reducing porosity and aggregation. Nutrient, air and water holding
      capacities of the soil are reduced, and plant roots encounter increased
      mechanical resistance as they grow. Soil compaction also stunts shoot
      growth, with hydraulic and chemical signalling systems between below- and
      above-ground parts allowing the plant to adapt to this multi-stress
      environment. However, relatively few studies have characterised
      root-to-shoot signalling systems of plants with mechanically-impeded
      roots.
      
      Tomato plants (Solanum lycopersicum cv. Ailsa Craig) were grown under low
      and high soil bulk densities, and allowed to dry the soil to investigate
      plant physiological responses. Compact soil stunted plant growth,
      decreased stomatal conductance of well-watered plants and decreased plant
      water status at higher soil water contents. Multi-hormone analyses of root
      xylem sap and foliar tissues revealed that high bulk density soils
      attenuated the soil drying-induced increase in xylem [ABA]. Moreover, high
      bulk density soil increased xylem jasmonic acid concentrations and
      decreased foliar bioactive gibberellins, which were correlated with
      reduced shoot growth.
      
      Root drenches of bioactive gibberellic acid (GA3) were then applied to
      determine its ability to improve tomato shoot growth in compact soil. GA3
      was transported from root to shoot tissues and significantly increased
      leaf expansion, but at the expense of plant water status. Further
      multi-hormone analyses indicated that GA3 application increased foliar
      cytokinin (trans-Zeatin) levels and decreased xylem jasmonic acid
      concentrations.
      
      Finally, to isolate soil strength from possible confounding effects of
      nutrient and water availability, tomato plants were grown in a sand
      culture system. A light foam block or 17 kg weight was placed upon the
      surface of the sand to increase substrate strength, while tanks were
      supplied with ample nutrients and water by capillary action. While GA3
      again rescued shoot growth, shoot and leaf water potentials were reduced.
      Furthermore, xylem jasmonic acid concentration consistently decreased in
      both sand- and soil-grown plants as soil strength increased, which was not
      attributed to any decrease in leaf water status.
      
      Taken together, this thesis is the first to employ multi-hormone analyses
      on tissues and sap from plants growing in compact or strong soils. Novel
      roles for gibberellins and jasmonic acid in regulating plant growth when
      roots are mechanically impeded were discovered. GA3 appears to promote
      shoot growth against water potential gradients. Further study of the
      physiological significance of xylem-transported jasmonic acid and its
      cross-talk with gibberellins seem necessary to help determine how plants
      respond to soil mechanical stresses.