Hormone Effects on the Membrane Potential and on Sucrose-Induced Depolarization of Young Citrus Leaves

The effect of IAA, GA₃ and ABA on transmembrane potential difference(Em) and on sucrose-induced depolarization has been studiedin young Citrus leaves. The addition of any of these hormonesto the perfusion solution (short-term experiments) did not affectEm or sucrose-induced depolarization. Hormonal treatments ofyoung leaves on the tree resulted, after 4 to 16 days (long-termexperiments), in an increase of Em for GA₃- and ABA-treatedleaves, while in IAA-treated ones no hyperpolarization was found.Only in ABA treated leaves this membrane hyperpolarization couldbe related to an enhancement of sucrose uptake. (Received April 28, 1992; Accepted September 21, 1992)     

17 beta-Hydroxysteroid dehydrogenase in the human prostate: properties and distribution between epithelium and stroma in benign hyperplastic tissue

In order to delineate differences in the mechanism of androgen action in epithelium (E) and stroma (S) of the human prostate, we studied the 17 beta-hydroxysteroid dehydrogenase (17 beta-HSDH) in these tissues of benign prostatic hyperplasia (BPH). Tissue was obtained by suprapubic prostatectomy. E and S were separated; samples were homogenized in buffer and incubated with [3H] steroids (4-androstenedione (Ae), estrone (E1), or dehydroepiandrosterone (DHEA] and NADH (4.2 mmol/l) as cosubstrate for 60 min at 37 degrees C. Separation and quantification of the metabolites were performed by TLC and LSC, respectively. The main results were: (1) Following incubation with DHEA and E1, only the metabolites 5-androstene-3 beta,17 beta-diol and estradiol, respectively, were found. Following incubation with Ae, testosterone, 5 alpha-dihydrotestosterone and 5 alpha-androstane-3 alpha-(beta),17 beta-diol were detected as metabolites (the sum of these metabolites were used for calculations). (2) The Michaelis constants were identical in E and S (mean +/- SEM (n), mumol/l, Ae 6.92 +/- 1.01, E1 7.84 +/- 0.69, DHEA 3.73 +/- 0.38). (3) The maximum velocity rate for the three substrates in E was 5-10-fold that in S (P at least less than 0.01), the value in the whole tissue homogenate (WT) being intermediate (pmol/mg protein h), for Ae: E 383 +/- 56, S 40 +/- 3, WT 75 +/- 13; for E1: E 362 +/- 71, S 33 +/- 4, WT 63 +/- 8; for DHEA: E 132 +/- 21, S 26 +/- 4, WT 36 +/- 4. On the basis of these results the role of 17 beta-HSDH in forming active androgens and estrogens from less potent precursors is discussed in the stromal and epithelial compartment of the human prostate.     

The Chlamydomonas cell cycle is regulated by a light/dark-responsive cell-cycle switch

Cultures of the unicellular green alga Chlamydomonas reinhardii can be synchronized by light/dark cycling not only under photoautotrophic but also under mixotrophic growth conditions. We observed that cultures synchronized in the presence of acetate continue to divide synchronously for one cell-cycle period when transferred to heterotrophic growth conditions. This finding enabled us to investigate the differential effects of light on cell growth and cell division. When cells were exposed to continuous light at the beginning of the growth period they entered the division phase earlier than dark-grown cells as a consequence of an increased growth rate. Illumination at the end of the growth period, however, caused a considerable delay in cell division and an extended growth period. The light-induced delay in cell division was also observed in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II. This finding demonstrates that cell division is directly influenced by a light/dard-responsive cell-cycle switch rather than by light/dark-dependent changes in energy metabolism. The importance of this light/dark control to the regulation of the Chlamydomonas cell cycle was investigated in comparison with other control mechanisms (size control, time control). We found that the light/dard-responsive cell-cycle switch regulates the transition from G1-to S-phase. This control mechanism is effective in cells which have attained the commitment to at least one round of DNA replication and division but have not attained the maximal cell mass which initiates cell division in the light.Abbreviations dCTP deoxycytidine 5-triphosphate - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Effects of light and acetate on the liberation of zoospores by a mutant strain ofChlamydomonas reinhardtii

In light-dark-synchronized cultures of the unicellular green algaChlamydomonas reinhardtii, release of zoospores from the wall of the mother cell normally takes place during the second half of the dark period. The recently isolated mutant ls, however, needs light for the liberation of zoospores when grown photoautotrophically under a 12 h light-12 h dark regime. The light-induced release of zoospores was found to be prevented by addition of the photosystem-II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Furthermore, light dependence of this process was shown to be abolished when the mutant ls was grown either photoautotrophically under a 14 h light-10 h dark regime or in the presence of acetate. Our findings indicate that the light-dependency of zoospore liberation observed in cultures of this particular mutant during photoautotrophic growth under a 12 h light-12 h dark regime might be attributed to an altered energy metabolism. The light-induced release of zoospores was found to be prevented by addition of cycloheximide or chloramphenicol, antibiotics which inhibit protein biosynthesis by cytoplasmic and organellar ribosomes, respectively. Actinomycin D, an inhibitor of RNA synthesis, however, did not affect the light-induced liberation of zoospores.Sporangia accumulate in stationary cultures of the mutant ls. Release of zoospores was observed when these sporangia were collected by centrifugation and incubated in the light after resuspension in fresh culture medium. Since liberation of zoospores was not observed after dilution of the stationary cultures with fresh culture medium, we suppose that components which interfere with the action of the sporangial autolysin are accumulated in the culture medium of the mutant ls.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea