SHORT-TERM STUDIES OF (NO3-)-N-15 AND (NH4-N-15 UPTAKE BY MICROPROPAGATED STRAWBERRY SHOOTS CULTURED WITH OR WITHOUT CO2 ENRICHMENT())

The uptake of (NO3-)-N-15 and (NH4+)-N-15 has been examined in 5-,10- and 28-day-old micropropagated strawberry (Fragaria x ananassa Duch. c v. Kent) shoots rooted in one-half strength Murashige and Skoog (MS) l iquid medium on cellulose plugs (Sorbarods). The results indicated tha t the plantlets absorbed both NO3- and NH4+ during the culture with a greater uptake of NH4+ at 5 days of culture. Furthermore, a pronounced reduction in NO3- and NH4+ uptake at 10 and 28 days of culture Ras ob served within 6 h of the short-term uptake study. This reduction could be explained by the low CO2 concentration in test tubes during the ph otoperiod, since no reduction in nitrogen uptake occurred in the CO2 e nriched condition. The results are interpreted as an indication of the important role for photosynthetic CO2 fixation in the process of nitr ogen uptake by the plantlets during the rooting stage.