Differences in the physiological responses of two clones of Eucalyptus microtheca selected for their salt tolerance

Two Eucalyptus microtheca clones (clones 42 and 43) suspected to be salt tolerant were rooted and grown in a greenhouse. Five-month old cuttings were watered for 2 months with and without 200 mM NaCl. During the salt stress period, mineral (Na, Ca, K and Cl) and organic (soluble amino acids and proline) compounds were determined in roots, stems and leaves. Changes in protein profiles induced by salt stress were investigated after 2 weeks of salt treatment. Clone 42 demonstrated a delayed growth during salt stress while clone 43 showed a complete inhibition of shoot length. Salinity had a significant effect on mineral compounds: whatever the duration of the salt treatment, the uptake of sodium in roots was 2.5 times higher in the more tolerant clone 42 than in clone 43. Regarding potassium and calcium contents in roots, clone 42 demonstrated an increase in its amount whereas clone 43 showed a decrease. The increase in soluble amino acids induced by the stress in the different organs of the two clones was not significantly different whereas a higher content of proline was determined in clone 42 relative to clone 43. Salinity had significant effects on the content of one predominant polypeptide with an apparent molecular weight of 18 kDa which was specifically induced under salt stress in roots of clone 43. In clone 42, this polypeptide was present in low amounts in control conditions and salt treatment increased its synthesis.