An improved procedure for plant regeneration from indica and japonica rice protoplasts.

Plant regeneration from protoplasts of two commercially cultivated Indian indica rice varieties, Pusa Basmati 1 and Java, has been accomplished by plating embryogenic cell suspension-derived protoplasts on the surface of filter membranes overlying agarose-embedded feeder cells of Lolium multltiflorum and Oryza ridleyi, combined with the use of a maltose-containing shoot regeneration medium. Embryogenic cell suspension cultures of Pusa Basmati 1 and Jaya were initiated from mature seed scutellum-derived calli in liquid R2 medium modified by the addition of 560 mg l(-1) of proline and 1.0 % (w/v) maltose. In both varieties, protoplast plating efficiencies up to 0.4 % were obtained, depending on the nature of the feeder cells. L. multiflorum feeder cells induced a 6-fold higher plating efficiency than feeder cells of O. ridleyi. In combination, O. ridleyi and L. multiflorum feedercells further enhanced protoplast plating efficiency. Protoplast-derived cell colonies were not obtained from protoplasts of either indica varieties in the absence of feeder cells. MS-based medium containing kinetin (2.0 mg l(-1)) and α-naphthaleneacetic acid (0.5 mg 1(-1)), together with sucrose and maltose both at 1.5 % (w/v), induced green shoot regeneration in 44 % of protoplast-derived tissues, depending on the feeder cells used for protoplast culture. In both varieties, tissues obtained using O. ridleyi feeder cells were more morphogenic than tissues obtained using L. multiflorum feeder cells, either alone or in combination with cells of O. ridleyi. In the japonica rice variety Taipei 309, this new procedure resulted in a 30-fold increase in plant regeneration from protoplasts compared to previous published procedures.