Abstract

The difference in biochemical and physiological parameters of selected tolerant, medium tolerant and sensitive genotypes of cucumber (Cucumis sativus L.) derived from in vitro screening was investigated in order to put forward the relative tolerance or sensitivity of the genotypes and to identify parameters that can be used as index for in vitro evaluation of salt tolerance in cucumber. On the basis of our comparative analysis, the salt tolerant genotype (Hazerd) successfully tolerated highest salinity level (120 mM) by accumulating significantly higher levels of free proline and exhibited higher antioxidant enzyme (superoxide dismutase (SOD) and peroxidase (POD)) activities than the moderately tolerant (Poinsett 97 and Pingwang) and sensitive genotypes (HH1-8-57 and L6). The tolerant genotype (Hazerd) showed less vulnerability against high salinity by showing low lipid peroxidation and electrolyte leakage with slight reduction in photosynthetic pigment. Furthermore it seems that higher salinity tolerance in the tolerant genotype also correlated to limited translocation of Na⁺ ions to leaves resulting in the maintenance of high K⁺/Na⁺ ratio. Soluble sugars and protein showed decreased with increasing salinity in all the genotypes tested irrespective of their tolerance level. Taken together, our data partly explain the mechanism use to avoid salt stress by cucumber plants, when excessive in the culture medium.

Key words: Cucumis sativus L., salinity, sodium chloride.

Abbreviation

SOD, Superoxide dismutase; POD, peroxidase; CAT, catalase; MS, Murashige and Skoog; BAP, benzyl amino purine; TI, tolerance index, DW, dry weight; FW, fresh weight; MDA, malondialdehyde; Chl, chlorophyll; EDTA, ethylenediaminetetraacetic acid; PVP, polyvinylpyrrolidone.