The effects of calcium ions on lysine transport Into cultured Wisconsin-38 tobacco cells were examined. In the presence of calcium, lysine was transported at a relatively low rate for 30 to 40 minutes followed by a period of increasing rates and subsequent st tion at a higher rate after 2 to 3 hours. In the absence of calcium, transport was uniformly low.

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Dihydrodipicolinic acid reductase, an enzyme which catalyzes the pyridine nucleotide-linked reduction of dihydrodipicolinic acid to tetrahydrodipicolinic acid in the biosynthetic pathway leading to L-lysine, has been partially purified from maize (Zea mays cv Pioneer 3145) kernels. The crude maize extract and the partially purified enzyme were assayed for dihydrodipicolinic acid reductase by their ability to restore the capability of crude extracts of a mutant Escherichia coli (CGSC 4549; defective in dihydrodipicolinic acid reductase) to synthesize diaminopimelic acid from aspartic acid and pyruvic acid.

Arginine transport in suspension-cultured cells of Nicotiana tabacum L. cv. Wisconsin-38 was investigated. Cells that were preincubated in the presence of Ca(2+) for 6 h prior to transport exhibited stimulated transport rates. After the preincubation treatment, initial rates of uptake were constant for at least 45 min. Arginine accumulated in the cells against a concentration gradient; this accumulation was not the result of exchange diffusion. Arginine uptake over a concentration range of 2.5 μM to 1 mM was characterized by simple Michaelis-Menten kinetics with a Km of 0.1 mM and a Vmax of 9,000 nmol g(-1) fresh weight h(-1). Transport was inhibited by several compounds including carbonylcyanide-m-chlorophenylhydrazone, 2,4-dinitrophenol, N,N'-dicyclohexylcarbodiimide, and N-ethylmaleimide. Inhibition by these compounds was not the result of increased efflux resulting from membrane damage. A variety of amino acids and analogs, with the exception of D-arginine, inhibited transport, indicating that arginine transport was mediated by a general L-aminoacid permease. Competition experiments indicated that arginine and lysine exhibited cross-competition for transport, with Ki values similar to respective Km values. Arginine transport and low-affinity lysine transport are probably mediated by the same system in these cells.

Incorporating activated charcoal (AC) in culture media has been shown to affect growth and development of various organisms. Since AC stimulates the development of tobacco haploid plantlets from cultured anthers, research was conducted to determine the effect of activated charcoal on pith-derived callus growth and shoot development in Nicotiana tabacum cv. Wisconsin 38. Our results indicate that the hormones required for callues growth and shoot development in Wisconsin-38 tobacco are adsorbed by AC, thereby inhibiting callus growth and prohibiting shoot development. This effect was observed even when AC was removed from the medium by filtration prior to culturing the callus.

Callus was induced in different somatic organs of Oryza sativa L. Specific minimum 2,4‐dichlorophenoxyacetic acid (2,4‐D) concentrations in the medium were necessary for the induction of callus from different organs while high levels of 2,4‐D (6–10 mg/l) induced callus formation in each organ tested. The optimum 2,4‐D concentration for callus induction and growth for root‐derived calli was 2 mg/l and for leaf‐derived 6 mg/l. Root and shoot organogenesis were induced in both root‐ and leaf‐derived calli by sub‐culturing to a medium lacking 2,4‐D. Root organogenesis occurred at a higher frequency than shoot organogenesis. Shoot organogenesis rarely occurred in calli without differentiated roots. Increased age of callus cultures almost completely inhibited shoot development. The addition of the cytokinin 6‐γ,γ‐dimethylallyl‐amino purine partially restored the potential for shoot organogenesis. Whole plants were easily recovered from the calli and grown to maturity with some plants exhibiting phenotypic abnormalities.

Plants of Mimulus cardinalis Douglas (Scrophulariaceae) were grown in axenic culture from seed for 28 days on a minimal salts medium supple-mented with L-lysine, L-methionine, L-threonine, L-isoleucine, DL-or L-homoserine or DL-homocysteine, alone or in combinations ranging from 5 to 1000 μM. Abnormal growth was observed at the higher concentrations of all these aminoacidsexcept homocysteine. The lysine inhibition was significantly reduced by methionine, homocysteine or isoleucine. The threonine inhibition was significantly reduced by methionine or homocysteine. A combination of lysine and threonine at 1 MM was lethal. This synergistic effect was prevented when methionine, homoserine or homocysteine were added to the lysine-threonine combination. These results can be explained in terms of end-product control of aspartokinase and homoserine dehydrogenase by lysine and threonine, respectively, in the biosynthetic pathway to these aspartic-acid-derived amino acids.

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