E.G. Groenewald

Prostaglandins and related substances in plants

Prostaglandins (PGs) have been detected in many different plants and certain microorganisms.A few prostaglandin-like compounds have also been shown to occur in plants such as flax,Chromolaena morii, and aquatic sedge; and direct precursors (arachidonic acid, di-homo-γ-linolenic acid and eicosapentaenoic acid) have been detected in a variety of plants and microorganisms, including certain red algae, brown algae, green algae, and saltwater diatoms. Furthermore, arachidonic acid has been found in mosses and a liverwort. It has also been reported that arachidonic acid occurs in certain angiosperms, namely, poplar (Populus balsamifera), wheat germ oil,Aloe vera, andAllium sativum (garlic).In our studies on the possible physiological effects of prostaglandins we found that a PG possibly has an effect on the flowering of the short-day plantPharbitis nil. It has hastened flower formation by 28 days as compared with controls under inductive conditions (short days), and certain inhibitors of PG-biosynthesis inhibited flowering to a greater or lesser extent.In other physiological studies of prostaglandins, it was found that they have an effect on such aspects as GA3-controlled responses in barley endosperm, inhibition of crown gall tumor formation on potato discs, and certain electron-flow reactions in isolated chloroplasts. In corn leaf segments it has an effect on photosynthesis, nucleic acid metabolism, and protein synthesis. The effect on four plant bioassay systems was negligible. It has also been reported that PGs play a role in the regulation of cell membrane permeability.ZusammenfassungProstaglandine (PGs) wurden in vielen verschiedenen Pflanzen und in gewissen Mikroorganismen entdeckt.Auch ein paar prostaglandinenverwandte Verbindungen wurden im Flachsextrakt und in aquatischer Binse nachgewiesen; direkte Vorläufer (Arachidonsäure, dihomo-γ-Linolensäure und Eicosapentaensäure) wurden in einer Vielzahl von Pflanzen und Mikroorganismen entdeckt, auch in gewissen Rot-, Braun- und Grünalgen und Salzwasserdiatomeen. Darüberhinaus wurde Arachidonsäure in Moosen und in einem Lebermoos nachgewiessen. Aufgrund von Berichten kommt Arachidonsäure in gewissen Angiospermen, nämlich der Pappel (Populus balsamifera), im Weizenkeim — Oel,Aloe vera undAllium sativum (Knoblauch) vor. In unseren Studien über mögliche physiologische Effekte von Prostaglandinen fanden wir, dass ein Prostaglandin möglicherweise das Blühen der KurztagpflanzePharbitis nil bewirkt. Es beschleunigt die Blütenbildung um 28 Tage im Vergleich zu einer Kontrollgruppe bei induzierenden Bedingungen (Kurztage), während gewisse Hemmstoffe der PG-Biosynthese die Blütenbildung mehr oder weniger hemmten.Beim Studium der physiologischen Wirkung der Prostaglandine zeigte sich ein Effekt auf von GA3 kontrollierte Reaktionen im Gerstenendosperm, auf die Hemmung der Bildung von Wurzelhalsgallentumor auf Kartoffelscheiben und auf die Auslösung des Elektronenflusses in isolierten Chloroplasten. In Maisblattstücken zeigte sich eine Wirkung von PG auf Photosynthese, Nukleinsäure-Metabolismus und Proteinsynthese. Die Wirkung auf vier Biotestsystemen ist minimal. Berichten zufolge spielen PGs bei der Regulation der Zellmembranen Permeabilität eine Rolle.

Root formation and attempts to establish morphogenesis in callus tissues of beans (Phaseolus vulgaris L.)

Callus growth and subsequent root formation were obtained from radicle starting material using kinetin or [2-isopentenyl] adenine and 2,4-D. Substituting NAA for 2,4-D resulted in poor callus growth and no root formation. Gibberellic acid, c-AMP and c-GMP as supplements tended to reduce callus growth. When KNO3 and NH4NO3 of the Murashige and Skoog medium were replaced by ammonium citrate as nitrogen source no callus growth was observed.

The Effect of Various Lipids on Flowering of Pharbitis nil in in vitro Culture

The effect of applied arachidonic acid, prostaglandin (PGE1) and various sterols and combinations of arachidonic acid + sterols, on flowering of Pharbitis nil were ascertained by using a tissue culture technique. It was found that arachidonic acid, PGE1 stigmasterol, testosterone, cholesterol, stigmasterol + arachidonic acid, β-sitosterol + arachidonic acid and cholesterol + arachidonic acid all caused earlier flowering. Four inhibitors of prostaglandin biosynthesis (gentisic acid, acetylsalicylic acid, salicylic acid and oleic acid), inhibited flowering completely. The results confirm that the compounds tested could possibly play a role in the flowering of P. nil.

The metabolism of inhibitor of flowering and prostaglandin biosynthesis, acetylsalicylic acid, in Pharbitis nil cotyledons

Acetylsalicylic acid, which applied to cotyledons of the short day plant Pharbitis nil prior to an inductive 16-h dark period inhibits flowering by 90 %, is converted to salicylic acid and to a lesser extent to gentisic acid in the cotyledons during this 16-h dark period. Our results confirmed that salicylic acid and gentisic acid are responsible for the inhibition of flowering. They also inhibit prostaglandin biosynthesis.

The effect of applied arachidonic acid on the formation of prostaglandins in plantlets from excised apices of the short-day plant, Pharbitis nil

The effect of arachidonic acid (AA) application to excised apices of Pharbitis nil and the subsequent production of prostaglandins (PGs) were examined. The detection of the PGs was done by means of a radioimmunoassay (RIA) and tritium labelling techniques. Both PGE 2 and PGF 2α were detected and quantified by RIA after AA application. This suggests the synthesis of PGs from AA. These results were confirmed using tritium labelled AA. This experiment was done in connection with the fact that Pharbitis nil is a short-day plant. Arachidonic acid, a possible precursor of PGs, possibly promotes flowering of this plant. Arachidonic acid might be converted by cyclo-oxygenases to PGs which are involved in flowering.

The florigen mystery

In order to obtain flowering, different applications of chemicals on plants were tested by several researchers. Substances that were tested were, amongst others, auxin, gibberellin, cytokinin, abscisic acid, prostaglandin; melatonin. All had an effect on flowering. With the aid of molecular-genetic research it was established that the product of certain genes, namely CONSTANS (CO) and FLOWERING LOCUS T (FT) could be the flowering stimulus. It could be a peptide or mRNA.

A few aspects of the physiology of flowering in photoperiodic sensitive plants

Drie verskillende aspekte van die fisiologie van blomvorming by fotoperiodies sensitiewe plante word bespreek, naamlik die florigeenhipotese, fitochroom en die tydmetingsmeganisme van blomvorming en geneties molekulere studies. Daar is baie bewyse dat die hipotetiese verbinding, florigeen, in plante voorkom, maar dit is nog nooit gekarakteriseer nie. Daar is ’n familie fitochrome in plante ontdek en sommige is gemoeid met die sirkardiese horlosie en dus met die tydmetingsmeganisme van blomvorming. Geneties molekulere studies, alhoewel nog in ’n vroee stadium, is besig om die molekulere netwerke, wat onderling werksaam is op te klaar. Alhoewel florigeen met behulp van hierdie studies nog nie opgespoor kon word nie, is die toekoms rooskleurig.