Abstract. After giveln an accumiiulation ratio greater thani one, but evidence for an active transport of this ionl is unclear because of siome apparent non-biological uptake (15). Since selenate and selenite are both assimilable ions (1,9,10,11,12,16,17), accunmulationi of selenium by these roots could be either ani accumulation of the ions against an electrochemical gradient or an accumulation of seleno-metabolites whose synthesis is energy dependent. The data presented here will show that selenate can accumulate largely unchanged in excised roots of 2 species of Astragaluts; much of the selenite however, is changed into other selenium comll)ounds or possibly adsorbed. Materials and MethodsPreparationi a(id Growth of Seedlings. Techni(quies described earlier for the preparation and growth of seedlings (15) were used in these 'experiments but moldified as follows: after germination in the dark for 2 days, (21-22°), the seedlings were laterally illunminated before a bank of fluorescent lights at an intensity of 4300 ft-c for 3 more days (22-25°).This research w-as supported by Public Health Research Grant GM 09086 from the National Institutes of Healtlh.ion Absorption Procedure. The preparation of root tips and the conditions for the uptake of selenate and selenite were identical with the procedures de-scribed earlier (15).Fractionation of Radioactive Tissues. At the end of thle uptake period, roots were blotted on filter paper and weighed rapidly. For nleasurement of the total radioactivity abs,orbed, roots were prepared as described earlier (15). For measurement of the ethanol insoluble fraction, the weighed roots were suiccessively extracted with 70 % (v/v) ethanol 6 to 8 times until the radioactivity in the ethanol extract was approximately 1 % of the radioactivity in the first extraction. The acid digestion mixture was slowly added to the extracted roots to avoid foaming, and the extracted roots were digested as described earlier (15). A precipitate which formed in the digest of the ethanol-extracted roots had no effect on the counts. Samples for total and ethanol-insoluble radioactivity were run in triplicate.For biochemical analysis of soluble radioactive components, weighed roots from 24 colanders were pooled and extracted with 48 ml of 70 % ethanol.Column Chromatography. The use of Dowex-1-Cl coltumns for identification of selenite and selenate has been described previously ( 12).Paper Chromatographiy. XVhatman No. 1 was used throughout. The following solvent systems were used: No.

A bstract. Absorption of selenate and selenite by excised roots of A stragalus Crotalariae, a selenium accumulator, and of A. lentiginosus, a non-accumulator, was favored by CaCl, and a pH of 4.0. The uptake of selenate and possibly selenite, is metabolically linked. Roots of a number of Astragalus species were examined, and in all cases selenate entered the roots muoh faster than selenite. In these short-term experiments there was no relation between uptake of the 2 ions and classification of a species as selenium-accumulator or non-accumulator.

No abstract

Cryoprotection of suspension cultures of sugarcane cells (Saccharum sp.) during freezing to various temperatures was tested using glucose, dimethylsulfoxide, and ethylene glycol at various concentrations, alone and in combinations. Viability of the thawed cells was assessed by triphenyltetrazolium chloride reduction, cell growth, and microscopic examination. Enhanced cryoprotection-as much as a doubling in viability value-was achieved by employing glucose and dimethylsulfoxide in mixtures, as compared with the lesser cryoprotective effect of either compound alone, at 1.9 molar total concentration in all cases; the mixture was most effective at a concentration of about 1.9 molar, with a molar ratio of the two components of about 1:3, respectively. Much of the increase in viability value arose from a decrease in toxic effect that came about through mixing the cryoprotective agents. Binary mixtures containing ethylene glycol and either glucose or dimethylsulfoxide were less effective and more toxic than comparable glucose-dimethylsulfoxide mixtures. Use of the optimized latter mixture allowed freezing of these tropical cells to -23 C with little decrease in survival, or to -40 C, still with the capability for delayed growth.Many benefits, experimental and practical, are to be expected from the viable, low temperature frozen storage of plant tissues (1,14,26). In attempting to attain this goal, investigators have examined and attempted to understand or imitate the yearly adaptation undergone by temperate zone plants during their natural freeze-hardening process (8,9).During freeze-hardening, a large number of physical and chemical changes take place within the plant. These include tissue dehydration and the degradation and resynthesis of whole classes of chemical compounds of both low and high mol wt, whose cryoprotective roles are poorly understood (8,15). In studying the protection of cultured plant cells against freezing damage in vitro, investigators have added chemical agents, singly or sometimes in arbitrary appearing combinations (4,7,12,13,17,22 -4, 7, 9, 11-13, 17, 22), the results in this paper support the positive findings. They offer quantitative evidence of more than additive cryoprotection when sugarcane cells are treated with a combination of cryoprotective compounds. MATERIALS AND METHODSThe cell cultures used were Saccharum cv. H50-7209 (trispecific hybrid) obtained from Dr. P. H. Moore, USDA, Honolulu. All suspensions were subcultured weekly and maintained on a rotary shaker (150 rpm) at 28 C. The medium for growing cane cells consisted of a modified Murashige-Skoog formula containing 2,4-D (3 mg/liter) and 10lo coconut water (6).Actively growing cells were usually harvested for freezing experiments 6 to 9 days after inoculation. The cell suspension was concentrated to a convenient cell density by decanting supernatant medium, after allowing the heterogeneous mixture of cell clump sizes to settle for 10 min. Aliquots (1-2 ml) from the gently stirred suspension were then distributed into gr...

No abstract