THE INORGANIC NO3--NH4+ RATIO INFLUENCES PLANT-REGENERATION AND AUXIN SENSITIVITY IN PRIMARY CALLUS DERIVED FROM IMMATURE EMBRYOS OF INDICA RICE (ORYZA-SATIVA L)

We have investigated whether the inorganic NO3-: NH4+ ratio can influence indica rice plant regeneration from primary callus and the response of these calli to an exogenous auxin source, 2,4-D. Various NO3-: NH4+ ratios were tested that correspond to the NO3-: NH4+ ratios commonly used for rice cell culture. Plant regeneration, after callus induction on 2 mg/L 2,4-D, was supported by a wide range of NO3-:NH4+ ratios (from 85:15 [21.25mM NO3-:3.75 mM NH4+] to 50:50 [12.5mM NO3-: 12.5mM NH4+]). However, lowering the NO3- :NH4+ ratio from 80:20 (the original basal medium composition) to 75: 25 resulted in a three-fold increase in plant height and root growth. As the NO3- NH4+ was lowered even further, the shoots became shorter and thicker while the roots became more truncated and formed fewer secondary roots. The NO3-: NH4+ ratio also affected the response of these calli to different concentrations of 2,4-D. At a NO3- : NH4+ ratio of 80: 20 there was a strong doseresponse curve to 2,4-D while at a NO3-: NH4+ ratio of 50: 50 this dose-response curve was much flatter. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.