Growth and Physiological Characterisation of Micropropagated Citrus macrophylla Explants as Affected by NaCl Stress

摘要

Salinity is one of the major abiotic stresses affecting arable crops worldwide and constitutes the most stringent factor in limiting plant distribution and productivity. In the present study, the possible use of in vitro culture to evaluate the growth and physiological responses to salt-induced stress in cultivated explants of Citrus macrophylla has been analysed. To this purpose, micropropagated adult explants were grown in DKW medium supplemented with six different concentrations of NaCl (0, 30, 60, 90, 120 and 150mmol/L). After eight weeks in the culture media, the growth parameters (shoot numbers, length, productivity and fresh and dry weight) significantly decreased by the NaCl, which was accompanied by the visible symptoms of salt injury in the shoots; necrotic and fallen leaves were observed from 60mmol/L NaCl and apical necrosis from 120mmo]/L NaCl. Malondialdehyde (MDA) increased with increasing salinity, indicating a rising degree of membrane damage. The concentration of total chlorophyll significantly decreased in the presence of NaCl; explants exhibited a highly chlorotic appearance from 60mm NaCl. The Na and Cl concentrations in the explants significantly increased with the salinity level, but chloride increased more than sodium (with 150mmol/L NaCl the concentrations of Cl and Na were 30 and 8 times higher, respectively, than with Ommol/L NaCl). For osmotic adjustment, high concentrations of compatible solutes (proline and quaternary ammonium compounds QAC-) accumulated in salt-stressed plants. Proline and QAC were correlated highly with sodium and chloride concentrations in the explants, indicating a possible role of these compounds in osmotic adjustment. The plant concentrations of NO3- , K+ , Mg2 + , Ca2 + and Fe were also affected by the NaCl concentration of the medium. We suggest that the important deleterious effects on the in vitro explants of Citrus macrophylla, grown at increasing NaCl concentrations, are due mainly to toxic effects of saline ions, mainly Cl -, at the cellular level.