Changes in the growth, leaf water relations and cell ultrastructure in Argyranthemum coronopifolium plants under saline conditions

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Summary Pregerminated seeds of Argyranthemum coronopifolium grown in a hydroponic culture under growth chamber conditions were exposed to 70 mmol/L NaCl nutrient solution 45 days after sowing. The saline treatment was imposed for 15 days. Saline stress reduced the relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR). Leaf water potential (Ψ 1 ) and leaf osmotic potential (Ψ s ) decreased significantly in the treated plants while the leaf turgor potential (Ψ p ) increased due to osmotic adjustment (decrease of the leaf osmotic potential at full turgor, (Ψ os ). This osmotic adjustment was not sufficient to avoid decreases in stomatic conductance (g 1 ) and net photosynthesis (P n ). The data obtained by X-ray microanalysis on individual cells from the epidermis, mesophyll and palisade showed that saline stress led to a similar pattern of Na + and Cl − accumulation and loss of K + in all leaf tissues. Salinity increased the number of lipid bodies in the cytoplasm and induced variations in the chloroplasts, whose size increased significantly as did their content of starch grains. These alterations were common in mesophyll and palisade cells although more noticeable in the latter. Transfer cells were observed in the leaf. However, they did not confer salt-tolerance and some were seriously damaged by the salt. The results showed that Argyranthemum coronopifolium , although a wild native from littoral areas, is not a salt tolerant species.