AMMONIUM AND NITRATE UPTAKE AND NITRATE REDUCTASE-ACTIVITY OF PHOTOAUTOTROPHIC CALLUS-CULTURES OF THE FERN PLATYCERIUM-CORONARIUM (KOENIG) DESV

The uptake of nitrate and ammonium by callus of Platycerium coronarium from the culture medium was examined. Nitrate reductase activity of p hotoautotrophic callus cultures under CO2 enrichment was significantly lower compared to the cultures without CO2 enrichment, but higher tha n that of heterotrophic callus cultured on medium with 2% (wt/vol) suc rose. When sucrose concentration of the heterotrophic culture was lowe red to 0.2%, nitrate reductase activity increased. The level of nitrat e reductase activity increased by about 25% in the heterotrophic callu s with an increase in 2,4-D from 2 mu M to 10 mu M, despite a decline in fresh weight gain. However, photoautotrophic cultures with 1% CO2 e nrichment showed 20% decline in nitrate reductase activity and 45% dec line in fresh weight gain with a similar increase in 2,4-D level. The rate of uptake of nitrate from the culture medium was unrelated to the level of nitrate reductase activity in the callus. For photoautotroph ic callus under CO2 enrichment, the presence of 1% (vol/vol) CO2 gener ally resulted in the highest rate of nitrate uptake. The rate of uptak e of ammonium was higher for callus cultured on 2 mu M 2,4-D compared to that on 10 mu M 2,4-D.