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Biomedical subjects

A Lang

Publications and source records attributed to A Lang.

At least 217 records · Page 12Linked to original sources
PubMed1972

Comparison of endogenous gibberellins and of the fate of applied radioactive gibberellin a(1) in a normal and a dwarf strain of Japanese morning glory.

The effect of application of GA(3) on hypocotyl growth, the endogenous GAs, and the metabolism of applied (3)H-GA(1) were investigated in relation to dwarfism and light-mediated growth inhibition in the normal (tall) strain Violet and the dwarf strain Kidachi of Japanese morning glory (Pharbitis nil). GA(3) applied in a wide concentration range (10(-9) to 10(-3)m) to 4-day-old seedlings caused great extension of the hypocotyls in light-grown plants of both the normal and the dwarf strain. However, the dwarf strain did not attain the same length as the normal one at any given GA(3) concentration, even when saturation was reached. Dark-grown plants of the dwarf strain responded to GA(3), although relatively much less than light-grown ones; dark-grown plants of the normal strain showed no GA(3) response at all.The levels of free GAs in both strains remained more or less constant in both dark- and light-grown plants up to 18 days after germination. The levels of bound GA in dark- as well as light-grown plants of both strains increased after germination, reached a maximum at the 9th day after germination, and then rapidly declined again. The period of increase coincided with rapid elongation of the hypocotyl and the expansion of the cotyledons.The dwarf strain, Kidachi, contained less endogenous gibberellins, particularly bound gibberellins, than the normal strain, Violet. Dark-grown plants of both strains contained less bound GAs than light-grown plants.Applied (3)H-GA(1) was metabolized to the same extent in both dwarfs and normals, on the one hand, and in both dark- and light-grown plants, on the other. This metabolism involved binding as well as breakdown of the (3)H-GA(1).

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PubMed1968

Extractable and Diffusible Gibberellins From Light- and Dark-grown Pea Seedlings.

Gibberellins were obtained from light- and dark-grown peas by solvent extraction and agar diffusion. Both A(5)- and A(1)-like gibberellins were obtained by extraction; however, by diffusion only the A(1)-like gibberellin was found. There was no significant quantitative difference in the levels of diffusible or extractable gibberellin obtained from light- and dark-grown tall and dwarf peas. Several possible explanations for the discrepancy between diffusible and extractable gibberellin were investigated. Of these, only I was supported by experimental evidence, namely, that GA(5) can be converted to GA(1).

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PubMed1968

Contents and recovery of gibberellins in monoecious and gynoecious cucumber plants.

Diffusates from seedlings and root exudates from 6-week-old plants of a monoecious line of cucumber, Cucumis sativus L., contained considerably higher levels of gibberellin-(GA-) like substances than did those from plants of an isogenic gynoecious line. Most of the GA-like activity was found in a chromatogram region typical of GA(1) and GA(3); some activity, particularly in root exudates, appeared also at an R(F) similar to that of GA(4) and GA(7).When seedlings were treated with (3)H-labeled GA(1), more radioactivity was found in the diffusates from monoecious seedlings than from gynoecious ones. The same was true of biological activity in root diffusates from older plants which had been treated with gibberellin A(4+7).In conjunction with evidence present in literature, these results support the idea that endogenous GAs play a part in the regulation of sex expression in cucumber, relatively high levels favoring the formation of staminate flowers.

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PubMed1968

Fate of radioactive gibberellin a(1) in maturing and germinating seeds of peas and Japanese morning glory.

Radioactive gibberellin A(1) ((3)H-GA(1)) was injected into excised fruits of peas and Japanese morning glory. These were then grown in sterile culture to maturity and the label was followed in the seeds during further development and subsequent germination. During development of both pea and morning-glory seeds a large part of the radioactivity became associated with the aqueous fraction, while another part of the (3)H-GA(1) was converted into 2 new, acidic, biologically active compounds, designated X(1) and X(2). A relatively small part of the neutral compounds could be converted back to (3)H-GA(1), X(1), and X(2) by means of mild acid hydrolysis. During germination of pea and morning-glory seeds, part of the bound compounds was released in the form of (3)H-GA(1), X(1) and X(2) while, particularly during rapid seedling growth, a further conversion of (3)H-GA(1), mainly to X(1), took place. In pea seedlings, growth during the first 2 to 3 days after imbibition was not affected by Amo-1618, an inhibitor of gibberellin biosynthesis. This, in conjunction with the findings on the interconversions between free and bound (3)H-GA(1) suggests that, at least in peas, early seedling growth may at least partly be regulated by gibberellins released from a bound form which was formed during seed development.

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PubMed1968

Invertase activity and cell growth in lentil epicotyls.

The activity of invertase and its relation to growth were studied in the epicotyls of lentil seedlings incubated in the presence and absence of gibberellic acid (GA(3)).Invertase activity per epicotyl increases relatively more rapidly than does length, reaches a maximum during most active elongation, and declines upon cessation of growth.GA(3) enhances both growth and increase in invertase activity, without altering the kinetics of the 2 processes. If GA(3) is added during incubation invertase activity increases more rapidly than does elongation rate.Incubation of the seedlings in solutions of polyethyleneglycol inhibits the increase of both growth and invertase activity, the latter actually undergoing a decline, but causes no great change in the relative effect of GA(3). In presence of polyethyleneglycol GA(3) has however a relatively greater effect on invertase activity than on growth.Sugars in the incubation medium have no significant effect on growth and invertase activity in the epicotyl, except inhibition at relatively high concentrations.Cycloheximide, actinomycin D, and 5-fluorodeoxyuridine (FUDR) inhibit both growth and the increase in invertase activity. Added during incubation cycloheximide causes complete inhibition of growth and a decrease in invertase activity with no appreciable lag phase. With actinomycin D and FUDR the inhibition occurs after lag periods of 2 to 3 and of at least 10 hours, respectively. Thus the increase in enzyme activity is very probably based on de-novo synthesis, and the enzyme is in a state of turnover during growth.The enzyme is present in soluble form in the cytoplasm, not firmly bound to any cell structures.

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PubMed1966

DNA synthesis in the elongating nondividing cells of the lentil epicotyl and its promotion by gibberellin.

Two-day-old lentil seedlings, (Lens culinaris Med.) were incubated for a 48-hour period with and without gibberellin (GA) in the presence and absence of 5-fluorodeoxyuridine (FUDR). The number of cells per epicotyl did not increase during this period. Growth of the epicotyl was thus due to cell elongation alone.The elongating cells of this tissue synthesized DNA. GA promoted and FUDR inhibited cell elongation, DNA synthesis, and RNA synthesis in the tissue.FUDR promoted uptake of thymidine and thymidine incorporation into cellular DNA, presumably by inhibiting synthesis of endogenous thymidine. Presence of GA promoted thymidine incorporation into cellular DNA and uridine incorporation into cellular RNA. In either case, there was no effect on the uptake of the precursor into the tissue.Fractionation of thymidine-labeled nucleic acids on a MAK column showed that thymidine was exclusively incorporated into the DNA fraction. Presence of GA promoted thymidine incorporation into this fraction and also increased the amount of ribosomal RNA.The data provide direct evidence for the conclusion that DNA synthesis is necessary for elongation of certain plant cells.

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