Abstlaet. Callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) was grown on callus-proliferating (CP) and shoot-forming (SF) media with elevated sodium sulfate (Na: SO,) concentrations either in the light or dark for more than one year. An increase in Na2SO 4 concentration resulted in a decrease in callus growth index, an increase in percent dry weight of callus tissues grown on both media, and a decrease in both number of caUi forming shoots and number of shoots per callus in SF medium. The CP callus grown in the light spontaneously began to form shoots after the 5th monthly transfer, and spontaneous root formation occured after the 16th transfer in the presence of 0.75 and 1.0% Na~SO4. Both water (q,) and osmotic (q's) potentials of the callus increased with increasing Na2SO4 concentration; and callus exhibited greater q, and • I, s in the light than dark for both CP and SF media.
Callus cultures of Nicotiana tabacum L cv. Wisconsin 38 were initiated and grown on shoot-forming (SF) and callus proliferation (CP) medium with or without Na2SO 4. Two cultures were maintained on SF medium with 0, 0.75, 1 or 1.5% Na2SO 4 for 2.5 and 3.5 years. In the older culture only callus grown on salt formed shoots throughout the maintenance period, while in the younger culture the control responded best and Na 2 SO 4 was inhibitory. Callus from the older culture which had been grown on salt continued to form shoots in the absence of salt. Na 2 SO 4 caused adventitious shoot formation in three cultures on CP medium. These shoots were present for 7 subcultures after removal of Na2 SO4; but established, control callus, did not form shoots when transferred to Na 2 SOn. Callus initiated and maintained on NaC1 or mannitol showed a slight increase in shoot initiation. On NaC1, Na 2 SO4 or mannitol, the tissue osmotic potential became more negative and proline concentration increased.
Callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) was grown in the light on shoot-forming medium in the presence of Na2SO4 for over a year. An increase in Na2SO4 concentration resulted in decreasing callus growth, decreasing percentage of calli producing shoots and number of shoots per callus, and increasing callus percent dry weight. Regeneration of shoots from callus grown in the absence of Na2SO4 began to decline after 14 months in culture, and shoot regeneration capacity was completely lost after 18 months. In contrast, 18-month old callus continuously grown in the presence of Na2SO4 retained the ability to form shoots. The highest percent of callus pieces that formed shoots and the maximum number of shoots per callus occurred at 70 mM (1%) Na2SO4. All plants arising from the 18-month old callus were polyploid. Both 9- and 18-month old callus exhibited more negative water and osmotic potentials in the presence of increasing Na2SO4 concentration.
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