Seasonal changes in physio-biochemical responses of the xerophytic dwarf shrub Haloxylon salicornicum in the Kuwait desert

Description

Raw and processed data, including statistical analysis, of physio-biochemical parameters of Haloxylon salicornicum shoots in response to a combined high temperature and drought in the field.

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Ten experimental plants (>5 years old) were randomly selected and numbered to ensure a paired sampling of individuals. An equal volume of soil was sampled from the root zone area of each plant at 15 cm intervals in depth d1, d2, and d3 (15-30 cm, 30-45 cm, and 45-60 cm, respectively) using a hand auger with a 60 cm3 stainless steel cylinder. Green shoot samples (stem segments with scale leaves) were taken from the upper canopy of plants at two different times of the year. In summer, when plants were not exposed to high temperature or drought stress; and in spring, when the same plants were exposed to very high temperatures and minimal water availability in the upper soil layers. Shoot samples were freeze-dried (lyophilized) following the general procedure described by Antal et al. (2011). Drying was performed using the freeze-dryer Shell Freeze System (Labconco). Dried samples were then pulverized using a Planetary Mill PULVERISETTE 5 (Fritsch, Germany). For soil analysis, soil-water content (SWC) and moisture content (MC%) were measured directly using the gravimetric method (Evett, 2008). pH and total dissolved salt (TDS) values of the soil samples were measured as described by Chapman and Pratt (1962). For physio-biochemical analysis, relative water content of shoots was determined according to Turner (1981). The osmotic potential of shoots was measured according to Callister et al. (2006). Photosynthetic pigments were determined following the method of Wellburn (1994) . H2O2 content was determined according to Junglee et al. (2014). The rate of lipid peroxidation in terms of malondialdehyde (MDA) was determined as described by Hodges et al. (1999). Proline content was determined using the ninhydrin-based colorimetric method (Bates et al., 1973). Total soluble sugars content was estimated following the phenol-sulfuric acid method described by Chow and Landhäusser (2004). Simultaneous measurement of nutrient elements was performed in essence as described by Zarcinas et al. (1987). Total protein was quantified using the RC DC Protein Assay Kit with lyophilized bovine serum albumin as a protein standard. SOD activity was determined according to the modified NBT method (Beyer Jr and Fridovich, 1987). CAT activity was determined according to the method described by Aebi and Lester (1984). APX activity was determined according to the method described by Nakano and Asada (1981). GR activity was determined according to the method described by Smith et al. (1988). TFC was determined using the Folin-Ciocalteu colorimetric method (Singleton et al., 1999) using 80% methanol as a solvent. Instrumentation: for colorimetric assays, absorbance was recorded with a GeneQuant 1300 UV spectrophotometer. Osmolality was assessed with an Osmomat 3000 freezing point depression osmometer. Inorganic ions were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), controlled by Quantima auto-optimization software.

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