Digital Theses Archive


Tesi etd-06032017-115506

Type of thesis
Salt and drought stress in olive tree (Olea europaeaL.): an integrated approach.
Scientific disciplinary sector
relatore Prof. SEBASTIANI, LUCA
  • Desaturases
  • Fatty acid
  • Frantoio
  • Fruit Mesocarp
  • Inorganic cations
  • Leccino
  • Non-structural carbon
  • Olive
  • Phenols
  • Salinity
  • Water regime
Exam session start date
Olive tree is a widespread cultivated tree among Mediterranean area. Despite this, Mediterranean climate is not the best for its cultivation, basically for drought and salinity environmental problem.<br>The study of physiological, biochemical and molecular response to salinity in olive fruit it has been studied in salt-sensitive Leccino cultivar, able to translocate Na+ to aerial part. In our experimental conditions, results shown a stress response concentrated in early veraison stage (&lt;50% of purple skin). In fact, irrigating with saline water from pit-hardening to harvest, Na+ concentration reach the highest values in fruit flesh of Maturation group 1 (MG1, &lt;50% of purple skin). Particularly, up to 600 mg Kg -1 when subjected to 60 mM NaCl irrigation water and about 2214 mg kg-1 when is irrigated with 80 mM NaCl water. With the advance of ripening, Na+ concentration in flesh is reduced, suggesting a re-translocation in vegetative portion to permit a suitable accumulation of oil droplets in cells. Also antioxidant response is MG-related, showing an increase of DPPH%, PAL activity, Total Phenols and Anthocyanins content (respectively, +15%, +16%, +58% and around doubled). Anatomical traits under salt stress reveal a thickening in all fruit tissue layers (Cuticle, epidermis, Hypodermis and Outer Mesocarp), that could be useful for biotic agent protection.<br>Fatty acid profile of Triacyl-glicerol (TAGs) under salt stress record major changes in MG1, showing an increment of oleic acid (+5%), a decrement of linoleic acid (-2.36%) and a consequent increment of oleic/linoleic ratio and a related transcriptional down-regulation of FAD6 genes. Low Electron Transport Rate (ETR) between photosystems recorded in the leaves closest to the infructescence could allow to a more oxidized state of those complexes, causing a reduction in the activity levels of the FAD6 enzyme. Also the up-regulation of FAD2-2 seems to have a role in salt stress response, mainly for maintaining plasmatic membrane stability. Anyway, total fatty acid richness fraction is not affected by salt stress.<br>Simultaneous salt and drought stress response it has been studied in cultivars Leccino and Frantoio, differentially-sensitive to both stress.Water status of simultaneous stressed plants were monitored with non-destructive innovative methodologies (Zim-probes), revealing the typical inversion phenomena of Pp curve shape due to an unfavorable air/water ratio typical of plant’s osmotic injuries. <br>Physiological and biochemical data shown that simultaneous drought and salt stress didn’t impair growth, total plant fresh and dry weight and Na+ concentration in Leccino leaves (6359 mg kg-1), although water loss in lysimeters recorded by wheighing (assumed as effective evapo-transpiration) at the end of experiment is influenced (-62% in Leccino vs -53.5% in Frantoio, respect to control). Anyway, Na+ content on a whole-plant basis is reduced by water scarcity (-47.6% in Leccino vs -31.6% in Frantoio), explaining the lack of effect on growth and biomass allocation. Major effects of simultaneous drought and salt stress is focused in leaves: non-structural carbon partitioning toward mannitol (39 mg g-1 in Leccino vs 22 mg g-1 in Frantoio on a dry weight basis) and cations stechiometrical ratios (K/Na ratio 22 times higher in Frantoio and Ca/Na ratio 11 times higher in Frantoio). PCA analysis help to conclude that in simultaneous drought and salt stress conditions only at leaves level is evident a cultivar related response, mainly for higher K/Na and Ca/Na ratios level in leaves. <br>