In vitro response of date palm (Phoenix dactylifera L.) to K/Na ratio under saline conditions.

Background: Salinity is a serious factor limiting the productivity of agricultural plants. One of the potential problems for plants growing under saline conditions is the inability to up take enough K(+). The addition of K(+) may considerably improve the salt tolerance of plants grown under salinity. It is assumed that increasing the K(+) supply at the root zone can ameliorate the reduction in growth imposed by high salinity. The present study aims to determine whether an increase in the K/Na ratio in the external media would enhance the growth of date palm seedlings under in vitro saline conditions.

Methods: Date palm plants were grown at four concentrations of Na + K/Cl (mol/m(3)) with three different K/Na ratios. The 12 salt treatments were added to modified MS medium. The modified MS medium was further supplemented with sucrose at 30 g/l.

Results: Growth decreased substantially with increasing salinity. Growth expressed as shoot and root weight, enhanced significantly with certain K/Na ratios, and higher weight was maintained in the presence of equal K and Na. It is the leaf length, leaf thickness and root thickness that had significant contribution on total dry weight. Na(+) contents in leaf and root increased significantly increased with increasing salinity but substantial decreases in Na(+) contents were observed in the leaf and root with certain K/Na ratios. This could be attributed to the presence of a high K(+) concentration in the media. The internal Na(+) concentration was higher in the roots in all treatments, which might indicate a mechanism excluding Na(+) from the leaves and its retention in the roots. K/Na ratios up to one significantly increased the leaf and root K(+) concentration, and it was most pronounced in leaves. The K(+) contents in leaf and root was not proportional to the K(+) increase in the media, showing a high affinity for K(+) uptake at lower external K(+) concentrations, but this mechanism continues to operate even with high external Na(+) concentrations.

Conclusion: Increasing K/Na ratios in the growing media of date plam significantly reduced the absorption of Na(+) less than 200 mM and also balance ions compartmentalization.