Rubidium chloride tolerant callus cultures of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) accumulate more potassium and cross tolerate to other salts

Callus cultures from salt tolerant (CSR-10) and susceptible (Swarnadhan) varieties of Oryza sativa L. were established in Murashige and Skoog’s (MS) medium containing lethal concentrations (50 mM) of rubidium chloride (RbCl) as a selective agent. While 95–100% cells were viable in callus cultures grown without RbCl, viability was 75% in 50 mM RbCl selected cultures. Growth of RbCl selected calli in presence of salt was comparable to that of callus grown without it. Cells tolerant to RbCl showed more vacuoles and accumulated more K⁺ in comparison with their corresponding controls. Suspension cultures were established and uptake of ⁸⁶Rb⁺ was measured at 10 and 20 min intervals, which revealed a linear relationship between the absorption of K⁺ and time. Callus cultures (560-day-old) tolerant to 50 mM RbCl regenerated shoots with 35–40% frequencies in both the varieties, but the same age-old callus grown in the medium devoid of RbCl did not show any organogenesis. Callus cultures that are tolerant to 50 mM RbCl when exposed to 25 mM LiCl, 50 mM NaCl, 50 mM KCl and 25 mM CsCl also exhibited cross tolerance in both the varieties. This is the first time that a callus line of rice resistant to RbCl was raised and shown to accumulate a major cation K⁺ and also an increased influx of it.