Physiological and Proteomic Analyses of Drought Stress Response in Holm Oak Provenances

Responses
to drought stress by water withholding have been studied
in 1 year old Holm oak (Quercus ilex subsp. ballota [Desf.] Samp.) seedlings from seven provenances
from Andalusia (southern Spain). Several physiological parameters,
including predawn xylem water potentials and relative water content
in soil, roots, and leaves as well as maximum quantum efficiency and
yield of PSII were evaluated for 28 days in both irrigated and nonirrigated
seedlings. The leaf proteome map of the two provenances that show
the extreme responses (Seville, GSE, is the most susceptible, while
Almerı́a, SSA, is the least susceptible) was obtained.
Statistically significant variable spots among provenances and treatments
were subjected to MALDI-TOF/TOF-MS/MS analysis for protein identification.
In response to drought stress, ∼12.4% of the reproducible spots
varied significantly depending on the treatment and the population.
These variable proteins were mainly chloroplastic and belonged to
the metabolism and defense/stress functional categories. The 2-DE
protein profile of nonirrigated seedlings was similar in both provenances.
Physiological and proteomics data were generally in good agreement.
The general trend was a decrease in protein abundance upon water withholding
in both provenances, mainly in those involved in ATP synthesis and
photosynthesis. This decrease, moreover, was most marked in the most
susceptible population compared with the less susceptible one.