[Characterization of root initiation and root senescence in callus- and organ-cultures of Daucus carota through determination of the specific activity of the glutamate-dehydrogenase (NAD)]

In callus tissues of Daucus carota rhizogenesis was influenced by addition to the cultures of solutions with different kinetin concentrations (0-0.1-0.5-2 mg/l) and a constant auxin content (1 mg/l). In these cultures the specific activity of glutamate-dehydrogenase (E.C. 1.4.1.2.), aspartate-aminotransferase (E.C. 2.6.1.1.), isocitrate-dehydrogenase (E.C. 1.1.1.42) and of acid phosphatase (E.C. 3.1.3.2.) was determined. Before root initiation can be seen morphologically in tissues grown on low kinetin concentrations, the specific activity of glutamate-dehydrogenase increases to more than three times the level found in cultures with no subsequent root initiation, whereas the specific activity of the other three enzymes changes far less. Total soluble protein measured as percentage of fresh weight remains nearly the same in all callus cultures. The activity of the same enzymes was measured in liquid grown roots of Daucus carota during a period of ageing of 130 days. During this time, the specific activity of glutamate-dehydrogenase is reduced to 1/10 of the value found in growing roots, whereas the activity of the other three enzymes is reduced only to 1/2 or to 1/3 of this value. Therefore, the state of senescence and the capacity for further growth can be characterized by the specific activity of the glutamate-dehydrogenase in the roots. The changes in the specific activity of glutamate-dehydrogenase in callus tissue and in the roots do not depend on inhibitory substances in the cell-free extracts.

[Studies on the role of silicic acid in the development of higher plants]

Germanium acid, a specific inhibitor of the silicic acid metabolism in diatoms, inhibits the growth of Sinapis alba, Lemna minor, Wolffia arrhiza, Nicotiana tabacum, Tradescantia spec, Zinnia elegans, and Secale cereale when applied in the same concentrations as those used in the case of diatoms (15-75 μg GeO2/ml medium). The growth of Aspergillus niger, Phycomyces blakesleanus, Escherichia coli K 12, Euglena gracilis and Pandorina morum is not influenced by these and higher concentrations of Germanium acid. By application of high concentrations of silicic acid, the growth inhibition produced by germanium acid in Lemna minor is partially reduced. Plants of Lemna minor which have been inhibited by germanium acid are essentially smaller than plants grown in a normal medium; their chlorophyll content is significantly decreased. The growth of the roots in Lemna is particularly inhibited. Isolated growing roots of Lycopersicon pimpinellifolium MILL. are inhibited by small concentrations of Ge(OH)4 (ca. 1,5×10(-4) M/l). In contrast to the growth of older plants, the germination of Secale cereale and Sinapis alba is not influenced by Ge(OH)4. The effects of germanium acid are discussed in relation to the physiological role of silicic acid. The results suggest that the element silicon, in the form of silicic acid, is generally essential for the normal development of higher plants.