Shoot inversion-induced ethylene in Pharbitis nil induces the release of apical dominance by restricting shoot elongation

Shoot inversion induces outgrowth of the highest lateral bud (HLB) adjacent to the bend in the stem in Pharbitis nil. In order to determine whether or not ethylene produced by shoot inversion plays a direct role in promoting or inhibiting bud outgrowth, comparisons were made of endogenous levels of ethylene in the HLB and HLB node of plants with and without inverted shoots. That no changes were found suggests that the control of apical dominance does not involve the direction action of ethylene. This conclusion is further supported by evidence that the direct application of ethylene inhibitors or ethrel to inactive or induced lateral buds has no significant effect on bud outgrowth. The hypothesis that ethylene evolved during shoot inversion indirectly promotes the outgrowth of the highest lateral bud (HLB) in restricting terminal bud (TB) growth is found to be supported by the following observations: (1) the restriction of TB growth appears to occur before the beginning of HLB outgrowth; (2) the treatment of the inverted portion of the shoot with AgNO3, an inhibitor of ethylene action, dramatically eliminates both the restriction of TB growth and the promotion of HLB outgrowth which usually accompany shoot inversion; and (3) the treatment of the upper shoot of an upright plant with ethrel mimics shoot inversion by retarding upper shoot growth and inducing outgrowth of the lateral bud basipetal to the treated region.

Mechanical perturbation-induced ethylene releases apical dominance in Pharbitis nil by restricting shoot growth

Mechanical perturbation (MP, rubbing) or internodes of Pharbitis nil shoots initiates release of lateral buds (LB) from apical dominance within 48 h. Evidence is presented which suggests that MP promotion of LB outgrowth is mediated by ethylene-induced restriction of main shoot growth. Ethylene production in the internodes is stimulated by MP within 2 h. Effects of MP are mimicked by treatments with 1-aminocyclopropane-1-carboxylic acid (ACC) and are negated by the inhibitors of ethylene production or action, aminoethoxy vinylglycine (AVG) and AgNO3. The fact that effects of MP, ACC, and ethylene inhibitors are observed to occur on main shoot growth at least 24 h before they are observed to occur on LB growth suggests a possible cause and effect relationship. MP also causes an increase in internode diameter. MP stimulation of ethylene production appears to be mediated by ACC synthase. The results of this study and our previous studies suggest that apical dominance may be released by any mechanism which induces ethylene restriction of main shoot growth.

Production of cytokinin-like substances by mycorrhizal fungi of pine (Pinus sylvestris L.) in cultures with and without metabolites of actinomycetes

Studies on the effect of post culture liquids of actinomycetes on cytokinin-like substances production by mycorrhizal fungi have revealed that actinomycete metabolites inhibited or stimulated the synthesis of these compounds. The results of chromatographic analyses suggest, that substances stimulating the soybean callus are likely to be: riboside 6 (gamma, gamma-dimethylallylamino) purine and riboside zeatin. Using gas chromatography it was confirmed that both substances are produced by Rhizopogon luteolus. Paxillus involutus synthesizes probably besides the two substances also zeatin, as appears from the data obtained by column chromatography.

Investigations into the possible regulation of negative gravitropic curvature in intact Avena sativa plants and in isolated stem segments by ethylene and gibberellins

Using Avena sativa L. cv. Victory oat seedlings and excised p-1 stem segments (including the p-1 and p-2 internodes) the effect of exogenously supplied ethylene and the removal of ethylene on internodal extension and gravitropic bending was assessed. Similarly, the ability of the excised system to respond to gravistimulation was assessed in the presence of inhibitors of ethylene action (AgNO3) and ethylene synthesis (3,5-diiodo-4-hydroxybenzoic acid and benzyl isothiocyanate; BITC). The production of ethylene from both intact and excised systems was also measured from 0 to 48 h after gravistimulation, relative to vertical controls. Although gravitropic curvature is initiated, and indeed enters the most rapid phase of upward bending during the first 6 h, there is no difference in ethylene production between vertical and geostimulated plants during this period. The ethylene production of gravistimulated plants rises sharply to a maximum at 24 h, then decreases steeply to almost the control level by 48 h, at which time the rate of upward curvature is diminishing. Neither the addition nor removal of ethylene, nor the addition of inhibitors affecting ethylene-action (AgNO3) or synthesis (DIHB) influence gravitropic bending or internodal extension in excised segments. Although the ethylene synthesis inhibitor BITC slowed down the rate of upward bending, this effect could not be reversed by addition of ethylene. We conclude that the burst in ethylene production that develops in leaf-sheath bases (pulvini) after they have started to curve upwards is not primary to the induction of curvature. We further suggest that ethylene has no major effect or role in the induction of upward bending after gravistimulation. The metabolism of high specific activity gibberellin A1 ([3H]-GA1) in the excised system was assessed during 1, 2 and 4 h of gravistimulation. Changes in endogenous GAs and GA metabolism have been shown previously to be correlated (at the later stages) with gravistimulated bending in intact Avena shoots. The excised segments "leaked" free [3H]-GAs and [3H]-GA glucosyl conjugate-like substances into the bathing medium, and this was a confounding factor. Nevertheless, gravistimulated stem segments, and especially the bottom half of the segment, were significantly less leaky then vertical segments. Thus, just 1 h after gravistimulation, bottom segment halves retained 22% more precursor [3H]-GA1, 36% more free [3H]-GA-like metabolites, and 48% more [3H]-GA glucosyl conjugate-like metabolites than vertical segments. In contrast, the 1 h gravistimulated top halves retained slightly less (1-4%) precursor [3H]-GA1 and free [3H]-GA metabolites, but 21% more [3H]-GA glucosyl conjugate-like radioactivity than vertical segments.

Voltage transients elicited by sudden step-up of auxin

It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 microvolts and possessing risetimes (10-90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ ionophore.

Further studies of auxin and ACC induced feminization in the cucumber plant using ethylene inhibitors

The present study was designed to establish the role of an essential hormone controlling sex expression in cucumber. A potent anti-ethylene agent, AgNO3, completely inhibited pistillate flower formation caused by IAA, ACC or ethephon. Inhibitors of ethylene biosynthesis, AVG and CoCl2 also suppressed feminization due to exogenous IAA or ACC. Though AVG also suppressed ethephon-induced feminization, this may be due to the second effect of AVG rather than the effect on ACC biosynthesis. These results confirm that ethylene is a major factor regulating feminization and that exogenous auxin induces pistillate flower formation through its stimulation of ethylene production, rather than ACC production.

The effect of phytohormones produced by Arthrobacter sp. on the phosphatase activity in plant roots

Phytohormonal activity (auxins, gibberellins, cytokinins) was tested in the supernatant of a culture of Arthrobacter sp. Crude extract of the phytohormonal fraction was used as substrate for the growth of Lactuca sativa seedlings. Treating with bacterial hormones resulted in an increased plant develop- ment. Furthermore, a sharp increase of the acid phosphatase activity was observed in the roots.

Effects of interactions between different culture fractions of 'phosphobacteria' and Rhizobium on mycorrhizal infection, growth, and nodulation of Medicago sativa

Interactions between cell-free culture supernatants, cells, and the whole cultures of Rhizobium and phosphobacteria with endomycorrhizal fungi and their effects on growth and nutrition of Medicago sativa grown in a low-phosphate soil were studied. A satisfactory nodulation was greatly dependent on the mycorrhizal symbiosis. Cell-free supernatants of Rhizobium and phosphobacteria improved plant growth, nodulation and mycorrhiza formation. The activity of phosphobacterial culture seemed to be due mainly to the supernatant and the possibility of plant hormones contained in this culture fraction being involved in such interactions is discussed. An increase of the overall pool of soluble P in soil by the inoculated phosphobacteria cells was not found in the conditions of this experiment. It was noteworthy that the best positive effect was achieved by the treatment which consisted of the whole cultures of Rhizobium, phosphobacteria, and the mycorrhizal fungi applied all together.

[In vitro synthesis of cytokinins in isolated roots of lupin (Lupinus albus L.) treated with lectins extracted from cotyledons and leaves]

The synthesis of cytokinins in isolated roots of Lupinus albus L. cultured under sterile conditions, seems to be induced by leaf proteins and lectins extracted from the cotyledons. Immunochemical methods have been used to prove that the leaf proteins were lectins too, quite different from those coming from cotyledons, but having the same effect on the root cytokinins synthesis.

New microbial growth factor

A screening procedure was used to isolate from soil a Penicillium sp., two bacterial isolates, and a Streptomyces sp. that produced a new microbial growth factor. This factor was an absolute growth requirement for three soil bacteria. The Penicillium sp. and one of the bacteria requiring the factor, an Arthrobacter sp., were selected for more extensive study concerning the production and characteristics of the growth factor. It did not seem to be related to the siderochromes. It was not present in soil extract, rumen fluid, or any other medium component tested. It appears to be a glycoprotein of high molecular weight, and it has high specific activity. When added to the diets for a meadow vole mammalian test system, it caused an increased consumption of diet without a concurrent increase in rate of weight gain.

Products of soil microorganisms in relation to plant growth

A survey has been made of the range and activity of the organic products of soil microorganisms which have a direct influence on plant growth. Microbial metabolites which effect plants indirectly by the modification of the soil environment are also reviewed. The sources of substrates for the production of metabolites in soil and the farming practices which give rise to them are considered. It is stressed that an interdisciplinary approach is needed in the manipulation of microbiological activity in soil.

The effect of amitrole (3-amino-1H-1,2-4-triazole) on cytokinin activity and sexual reproduction in the yeast Schizosaccharomyces octosporus

Cytokinin activity in extracts from actively growing cultures of Schizosaccharomyces octosporus was greatly reduced by exposure to amitrole (5 X 10--3M). Amitrole treatment, at the same concentration, stimulated cell enlargment and ascus production in this organism. These data suggest that a relationship may exist between low levels of endogenous cytokinins, cell expansion in preference to cell division, and ascus formation.

Evidence for a sex hormone in Dictyostelium discoideum

A dialyzable sex hormone is produced by one strain of Dictyostelium discoideum (NC-4) that induces macrocyst formation (sexual stage) in its opposite mating type (V-12).

Morphological change in the early stages of the mating process of Rhodosporidium toruloides

The events which occur in the early stages of the mating process of the yeast Rhodosporidium toruloides between strains M-919 (mating type A) and M-1057 (mating type a) were investigated. In preliminary experiments we determined the frequency of mating by two newly designed methods: the liquid culture method and the membrane-filter microculture method. The mating frequencies of strains M-919 and M-1057 were 89% in the liquid culture method and 62% in the membrane-filter microculture method. The early stages in the mating process included the following events: (i) M-919 cells produce constitutively the extracellular inducing substance (A factor), (ii) M-1057 cells receive A factor, and in response to it they form mating tubes and secrete another inducing substance (a factor), (iii) M-919 cells receive a factor, and in response to it they form mating tubes, (iv) mating tubes elongate to the cells or the tubes of mating partner, (v) tips of the growing tubes recognize the opposite mating type cells or their tubes, followed by cell-to-cell fusion.

Stereochemical aspects of the formation of double bonds in abscisic acid

The stereochemistry of the hydrogen elimination that occurs during the formation of the Delta(4)- and Delta(2)'-double bonds of abscisic acid has been determined from the (14)C/(3)H ratios in abscisic acid biosynthesized by avocado fruit from [2-(14)C,(2R)-2-(3)H(1)]-, [2-(14)C,(2S)-2-(3)H(1)]- and [2-(14)C,(5S)-5-(3)H(1)]-mevalonate. Setting the (14)C/(3)H ratio at 3:3 for [2-(14)C,(2R)-2-(3)H(1)]mevalonate, the corresponding ratio in derived methyl abscisate was 3:2.28; the analogous ratio for methyl abscisate from [2-(14)C,(2S)-2-(3)H(1)]mevalonate was 3:1.63. Removal of the 3'-hydrogen atom of abscisic acid by base-catalysed exchange altered the ratios to 3:1.55 and 3:1.44 respectively. It was concluded that this 3'-hydrogen atom is derived from the pro-2R-hydrogen atom of mevalonate. Removal of the 4-hydrogen atom from methyl abscisate by formation of a derivative, a lactone, lacking this hydrogen atom changed the ratio to 3:1.04 for material derived from [2-(14)C,(2R)-2-(3)H(1)]-mevalonate and to 3:1.05 for [2-(14)C,(2S)-2-(3)H(1)]mevalonate, showing that this hydrogen atom also is derived from the pro-2R-hydrogen atom of mevalonate. These ratios of the lactones are consistent with their retaining one (3)H atom at the 6'-methyl position of abscisic acid from the [(2R)-2-(3)H(1)]- and [(2S)-2-(3)H(1)]-mevalonate. The presence of some label at positions 3' and 4 when [(2S)-2-(3)H(1)]mevalonate was the precursor is attributed to the action of isopentenyl pyrophosphate isomerase. The hydrogen atom at C-5 of abscisic acid is derived from the pro-5S-hydrogen atom of mevalonate.

Induction of adventitious roots by culture filtrates of the hairy root bacterium, Agrobacterium rhizogenes

Cell-free culture filtrates of Agrobacterium rhizogenes significantly increased adventitious root initiation in a mung bean hypocotyl bioassay. These filtrates were most active from cultures at their maximum cell density; the root-inducing activity declined rapidly after this time. The contents of cells disrupted by sonification were not active nor did they increase the activity of a 6-day-old culture filtrate. The root-inducing factor was heat stable, apparently dialyzable, and antagonized by kinetin. The 3-indole-acetic acid concentration of the culture filtrates was not high enough to account for the number of roots formed.

Conversion of 5-(1,2-epoxy-2,6,6-trimethylcyclohexyl)-3-methylpenta-cis-2-trans-4-dienoic acid into abscisic acid in plants

(+/-)-5-(1,2-Epoxy-2,6,6-trimethylcyclohexyl) -3-methyl[2-(14)C]penta-cis-2-trans-4-dienoic acid is converted into abscisic acid by tomato fruit in 1.8% yield (or 3.6% of one enantiomer if only one is utilized) and 15% of the abscisic acid is derived from the precursor. The 2-trans-isomer is not converted. The amounts of [2-(3)H]mevalonate incorporated into abscisic acid have shown that the 40-times higher concentration of (+)-abscisic acid in wilted wheat leaves in comparison with unwilted ones reported by Wright & Hiron (1969) arises by synthesis. The conversion of (+/-)-5-(1,2-epoxy-2,6,6-trimethylcyclohexyl) -3-methyl-[2-(14)C]penta-cis-2-trans-4-dienoic acid into abscisic acid by wheat leaves is also affected in the same way by wilting and it is concluded from this that the epoxide or a closely related compound derived from it is on the biosynthetic pathway leading to abscisic acid. The oxygen of the epoxy group was shown, by (18)O-labelling, to become the oxygen of the tertiary hydroxyl group of abscisic acid.

Tryptophan as an auxin precursor in cucumber seedlings

The conversion of tryptophan-(14)C to indoleacetic acid-(14)C in cucumber hypocotyls occurred under both sterile and non-sterile conditions. This conversion was not reduced under sterile conditions. The growth response of cucumber hypocotyl segments to exogenously supplied tryptophan was almost as great under sterile conditions as when contaminating micro-organisms were present. These data are consistent with the hypothesis that tryptophan is a normal precursor of indoleacetic acid in cucumber tissues. The conversions of tryptamine-(14)C and indoleethanol-(14)C to indoleacetic acid-(14)C also occurred under both sterile and non-sterile conditions. Indoleethanol-(14)C was formed from tryptamine-(14)C. Hypocotyl segment growth responses to tryptamine and to indoleethanol were not decreased under sterile conditions.

Zeatin and zeatin riboside from a mycorrhizal fungus

The puffball fungus Rhizopogon roseolus produces and releases three cytokinins when it is cultured in liquid media. Two of these compounds have been isolated in crystalline form from such media and were found to have properties identical to those of synthetic zeatin and zeatin riboside.