Proline biosynthetic gene expression in tissue cultures of rice (Oryza sativa L.) in response to saline treatment

The regulation of proline biosynthesis has been examined in callus and cell cultures of the indica-type rice cultivar Khao Dawk Mali 105 (KDML105) in response to a saline treatment (250 mM NaCl) in terms of the expression of Δ1-pyrroline-5-carboxylate reductase (OsP5CR) and members of the gene family encoding the rate-determining enzyme, Δ1-pyrroline-5-carboxylate synthase (designated OsP5CS1 and OsP5CS2). Using friable callus, growth was retarded by treatment with 250 mM NaCl within 4 days, with a significant increase in the expression of OsP5CS2 by 24 h, and a less marked induction in OsP5CS1 and OsP5CR over the same time-course. Cell suspension cultures derived from the friable callus were also treated with 250 mM NaCl and an induction in OsP5CS2 was again observed, although this was not as marked as in the friable callus, and there was no significant change in OsP5CS1 and OsP5CR expression. This is the first report that details the expression of OsP5CS1 and OsP5CS2 in tissue culture and the results show that, in common with whole plants, OsP5CS2 displays a primacy of response to saline treatment. However, this response may require a community of communicating cells, as occurs in callus tissue, rather than cell suspension cultures. This difference has implications both in terms of the biology of signaling in response to increased salinity and in the use of tissue culture to screen for saline-tolerant germplasm.