Stephen J. Croker

Stomatal Closure in Flooded Tomato Plants Involves Abscisic Acid and a Chemically Unidentified Anti-Transpirant in Xylem Sap

We address the question of how soil flooding closes stomata of tomato (Lycopersicon esculentum Mill. cv Ailsa Craig) plants within a few hours in the absence of leaf water deficits. Three hypotheses to explain this were tested, namely that (a) flooding increases abscisic acid (ABA) export in xylem sap from roots, (b) flooding increases ABA synthesis and export from older to younger leaves, and (c) flooding promotes accumulation of ABA within foliage because of reduced export. Hypothesis a was rejected because delivery of ABA from flooded roots in xylem sap decreased. Hypothesis b was rejected because older leaves neither supplied younger leaves with ABA nor influenced their stomata. Limited support was obtained for hypothesis c. Heat girdling of petioles inhibited phloem export and mimicked flooding by decreasing export of [14C]sucrose, increasing bulk ABA, and closing stomata without leaf water deficits. However, in flooded plants bulk leaf ABA did not increase until after stomata began to close. Later, ABA declined, even though stomata remained closed. Commelina communis L. epidermal strip bioassays showed that xylem sap from roots of flooded tomato plants contained an unknown factor that promoted stomatal closure, but it was not ABA. This may be a root-sourced positive message that closes stomata in flooded tomato plants.

Function and transcript analysis of gibberellin-biosynthetic enzymes in wheat.

The enzymes gibberellin (GA) 20-oxidase and 3-oxidase are major sites of regulation in GA biosynthesis. We have characterised one member of each of the gene families encoding these enzymes that are highly expressed in elongating stems and in developing and germinating grains of wheat and are therefore likely to have prominent developmental roles in these tissues. We mapped the three homoeologues of the GA 20-oxidase gene TaGA20ox1 to chromosomes 5BL, 5DL and 4AL. TaGA20ox1 is expressed mainly in the nodes and ears of the elongating stem, and also in developing and germinating embryos. Expression in the nodes, ears and germinating embryos is predominantly from the A and D genomes. Each homoeologous cDNA encodes a functional enzyme that catalyses the multi-step conversions of GA12–GA9, and GA53–GA20. Time course and enzyme kinetic studies indicate that the initial oxidation steps from GA12 and GA53 to the free alcohol forms of GA15 and GA44, respectively, occur rapidly but that subsequent steps occur more slowly. The intermediate GA19 has an especially low affinity for the enzyme, consistent with its accumulation in wheat tissues. The three homoeologous cDNAs for the 3-oxidase gene TaGA3ox2 encode functional enzymes, one of which was shown to possess low levels of 2β-hydroxylase, 2,3-desaturase, 2,3-epoxidase and even 13-hydroxylase activities in addition to 3β-hydroxylase activity. In contrast to TaGA20ox1, TaGA3ox2 is expressed in internodes, as well as nodes and the ear of the elongating stem. It is also highly expressed in developing and germinated embryos.

Identification, quantitation and distribution of gibberellins in fruits of Pisum sativum L. cv. Alaska during pod development

In addition to the previously-reported gibberellins: GA1; GA8, GA20 and GA29 (García-Martínez et al., 1987, Planta 170, 130–137), GA3 and GA19 were identified by combined gas chromatography-mass spectrometry in pods and ovules of 4-d-old pollinated pea (Pisum sativum cv. Alaska) ovaries. Pods contained additionally GA17, GA81 (2α-hydroxy GA20) and GA29-catabolite. The concentrations of GA1, GA3, GA8, GA19, GA20 and GA29 were higher in the ovules than in the pod, although, with the exception of GA3, the total content of these GAs in the pod exceeded that in the seeds. About 80% of the GA3 content of the ovary was present in the seeds. The concentrations of GA19 and GA20 in pollinated ovaries remained fairly constant for the first 12 ds after an thesis, after which they increased sharply. In contrast, GA1 and GA3 concentrations were maximal at 7 d and 4–6 d, respectively, after anthesis, at about the time of maximum pod growth rate, and declined thereafter. Emasculated ovaries at anthesis contained GA8, GA19 and GA20 at concentrations comparable with pollinated fruit, but they decreased rapidly. Gibberellins a1 and A3 were present in only trace amounts in emasculated ovaries at any stage. Parthenocarpic fruit, produced by decapitating plants immediately above an emasculated flower, or by treating such flowers with 2,4-dichlorophenoxyacetic acid or GA7, contained GA19 and GA20 at similar concentrations to seeded fruit, but very low amounts of GA1 and GA3 Thus, it appears that the presence of fertilised ovules is necessary for the synthesis of these last two GAs. Mature leaves and leaf diffusates contained GA1, GA8, GA19 and GA20 as determined by combined gas chromatography-mass spectrometry using selected ion monitoring. This provides further evidence that vegetative tissues are a possible alternative source of GAs for fruit-set, particularly in decapitated plants.

Regulation of gibberellin biosynthesis in maize seedlings

Application of gibberellins (GAs) to seedlings of many plant species leads to increased growth, which would thus appear to be normally constrained by the concentration of endogenous GA. Mechanisms for regulating GA concentration, therefore, are important in controlling plant growth. There has been evidence for some years that environmental factors, such as day length, influence plant growth through changes in GA concentration. In rosette plants, for example, flowering in response to long days is preceded by rapid stem elongation that occurs as a result of an increased rate of GA biosynthesis (Zeevaart, 1971). In this case increased activity of enzymes which oxidise the GA skeleton at C-20 have been implicated (Gilmour et al. 1986). There is also evidence that the activity of GA20 313-hydroxylase is regulated by phytochrome in le pea (Campell and Bonner, 1986) and cowpea (Garcia-Martinez et al. 1987).

Gibberellins and α-amylase gene expression in germinating wheat grains

Gibberellins (GAs), GA8, GA17, GA19, GA20, GA29, and GA79 were identified by full-scan gas chromatography-mass spectrometry in a purified acidic fraction and GA8, GA20, GA79, and GA90 in a hydrolysed conjugate fraction from mature wheat grains. Gibberellin A20-13-O-glucoside was also quantified directly as the permethyl derivative in dry seed. The scutellum was identified as the major site of de novo GA biosynthesis by measuring ent-kaurene accumulation in vivo in grains treated with 2S,3S-paclobutrazol. Several GAs of the early 13-hydroxylation GA pathway began to accumulate in the axis and scutellum between 24 and 48 hours in untreated grains germinated at 15°C. Bioactive GA1 and GA3 also increased in the endosperm during this period, whereas abscisic acid contents of embryo and endosperm declined rapidly over 48 hours following imbibition. Treating grains with 2S,3S-paclobutrazol reduced GA1 plus GA3 content of scutella by 70–80% over 4 days without affecting significantly the steady-state pool of α-amylase mRNA transcripts. In contrast, a 50–80% reduction in the content of bioactive GAs in the endosperm was associated with a 70–78% decrease in transcripts for both α-amylase gene families in aleurones of paclobutrazol-treated grains. It was concluded that the initiation of α-amylase gene expression in wheat scutella was independent of de novo GA biosynthesis, whereas that in the aleurone was largely dependent on embryo-produced GAs.

OCCURRENCE IN HIGHER-PLANTS OF 1-(3-AMINOPROPYL)-PYRROLINIUM AND PYRROLINE - PRODUCTS OF POLYAMINE OXIDATION

Abstract The presence of 1-(3-aminopropyl)pyrrolinium (App) has been established in the leaves of oats, maize, barley and wheat seedlings. In oat leaves, concentrations of 1,3-diaminopropane (Dap), putrescine (Put) and App were greatest in the youngest plants. Changes in Dap and App could not be correlated with changes in polyamine oxidase activity. Concentrations of the amines were smaller in maize than in oats, and smallest in barley and wheat. Pyrroline, an oxidation product of Put in pea seedlings and of spermidine in oat and maize seedlings, has been demonstrated in extracts of these plants, and also in spinach leaves and in radish shoots, following distillation, derivatization with 2-aminobenzaldehyde, oxidation of the adduct and GC-MS. Piperideine was also identified in pea seedlings.

Identification of three C20-gibberellins: GA97 (2β-hydroxy-GA53), GA98 (2β-hydroxy-GA44) and GA99 (2β-hydroxy-GA19)

Abstract Three new C 20 -gibberellins, GA 97 (2β-hydroxy-GA 53 ), GA 98 (2β-hydroxy-GA 44 ) and GA 99 (2β-hydroxy-GA 19 ), have all been isolated from spinach, GA 97 also from tomato root cultures and pea pods, and GA 98 from maize pollen. The structures of these compounds were established by GC-mass spectrometric comparisons of the trimethylsilylated methyl esters with authentic samples prepared from gibberellic acid (GA 3 ).

THE DECOLORIZATION OF BETACYANIN BY POLYAMINES

Abstract The pigment betacyanin, the efflux of which has been used as a measure of membrane integrity in red beet discs, has now been shown to react with di- and polyamines with consequent decolorization.

3β,13-Dihydroxylated C20 gibberellins from inflorescences of Rumex acetosa L.

Abstract Using full scan GC–MS a wide range of gibberellins (GAs) was identified in the young inflorescences of the dioecious species Rumex acetosa L., consistent with the ubiquitous early 13-hydroxylation pathway in both male and female plants. In addition, R. acetosa is the first species in which all three 3β,13-dihydroxylated C 20 -GAs—GA 18 , GA 38 and GA 23 —have been identified in the same organism, suggesting an early 3β,13-dihydroxylation biosynthesis pathway in this species. Authentic GA 18 , GA 38 and GA 23 were synthesized and their effects and that of GA 1 , a GA common to both pathways, on the time to inflorescence emergence was investigated. GA 1 accelerated the emergence of inflorescences in both male and female plants. In addition some evidence for biological activity per se of the C 20 -GA 38 was obtained.

Coleoptile length, gibberellin sensitivity and concentrations in five non-allelic dwarf mutants of pearl millet — Pennisetum glaucum (L.) R. Br.

The concentrations of endogenous gibberellins (GAs) were determined by combined gas chromatography-mass spectrometry in shoots of five non-allelic dwarfs of pearl millet Pennisetum glaucum (L.) R. Br. One mutant (d3), with an extreme dwarf phenotype, was found to be deficient in all GAs measured; the others (d1, d2, d4 and the quantitatively inherited dwarf) had similar levels of GAs to the tall genotype. Only the GA-deficient dwarf recovered the tall phenotype in response to applying GA3 up to the adult stage, while the others showed slight to moderate responses at the seedling stage, depending on the season, and no response at later stages. The d1, d3 and d4 dwarfs had short coleoptiles. A wide range of coleoptile lengths with a normal distribution pattern was observed in the tall, d2 and the quantitatively inherited dwarf, suggesting that there is polygenic control of this trait.