Eri Nakajima

Isolation and identification of lateral bud growth inhibitor, indole-3-aldehyde, involved in apical dominance of pea seedlings

A lateral bud growth inhibitor was isolated from etiolated pea seedlings and identified as indole-3-aldehyde. The indole-3-aldehyde content was significantly higher in the diffusates from explants with apical bud and indole-3-acetic acid treated decapitated explants, in which apical dominance is maintained, than in those from decapitated ones releasing apical dominance. When the indole-3-aldehyde was applied to the cut surface of etiolated decapitated plants or directly to the lateral buds, it inhibited outgrowth of the latter. These results suggest that indole-3-aldehyde plays an important role as a lateral bud growth inhibitor in apical dominance of pea seedlings.

Leaching of the allelopathic substance, -tryptophan from the foliage of mesquite (Prosopis juliflora (Sw.) DC.) plants by water spraying

The allelopathic potential of -tryptophan in the leachate from the foliage of mesquite (Prosopis juliflora (Sw.) DC.) plants was investigated. Distilled water (500 ml) was sprayed on mesquite plants from above for 50 min and water passing through the foliage was collected. The content of -tryptophan in the sample (30 ml eq.) was analyzed using a physicochemical method and the concentration was shown to be 17.9 µM. The sample (30 ml eq.) caused 69.8% inhibition of the root growth of barnyard grass (Echinochloa crus-galli L.). The concentration of authentic -tryptophan required for 69.8% inhibition of the root growth of barnyard grass was estimated at 20.0 µM from the dose-response curve. Moreover, to establish the origin of -tryptophan in the leachate, the amount of -tryptophan in both the leaves and the leachates was determined. The amount of -tryptophan containing in the foliage significantly decreased by soaking with time, whereas in the leachates the amount increased. After 60 min, its content in the leachates was nearly equivalent to that of the leaves. These results suggest that -tryptophan leached from the foliage may play an important role in the allelopathy imposed by mesquite.

Quantification of Cyanamide Contents in Herbaceous Plants

Cyanamide (NH2CN) is found in nature, although it has long been recognized as an industrial product. Distribution of cyanamide in the plant kingdom was investigated using a direct quantitative determination method to detect and measure cyanamide by stable isotope dilution gas chromatography–mass spectrometry (the SID–GC–MS method). The SID–GC–MS method proved to be a robust way to quantify cyanamide contents in the extracts of 101 species of herbaceous plants. The average recovery of cyanamide from all plants tested was 55.6±20.3%. Vicia villosa and V. cracca contained cyanamide at 369–498 μg/gFW and 3,460–3,579 μg/gFW respectively, while the other 99 species contained no detectable cyanamide (<1 μg/gFW). This result suggests that distribution of cyanamide in the plant kingdom is limited and uneven.

Structure-activity relationships of alkaloids from mesquite (Prosopis juliflora (Sw.) DC.)

The structure–activity relationships of alkaloids (1–5) from mesquite were subjected to assessment of growth inhibition against the shoot and root growth of monocotyledonous plants, barnyard grass, rice and timothy, and dicotyledonous ones, amaranth, lettuce and cress. All alkaloids tested generally showed growth inhibitory against both monocotyledonous and dicotyledonous plants. Furthermore, these alkaloids exhibited higher activity against the growth of root than that of shoot of all plant species used, except that juliprosopine (5) showed higher activity against the shoot growth than the root growth of rice seedling. Among these alkaloids, the highest active compound appeared to be juliprosine (4), followed by a (1:1) mixture of 3-oxo- and 3′-oxo-juliprosine (3a and 3b), and juliprosopine (5). The activity of juliprosine (4) containing 2-methyl piperidine bearing hydroxyl groups at C-3 and C-3′ was higher than that of 3-oxo- and 3′-oxo-juliprosine (3a and 3b) containing 3-oxo- and 3′-oxo-2-methylpiperidine. Compound 3 and 4 containing dihydroindolizinium ring showed higher activity than compound 5 containing tetrahydroindolizine ring, whereas compound 1 containing tetrahydroindolizinone ring showed weaker activity. The activity of secojuliprosopinal (2) without indolizine ring was very weak. It was thus clarified that the active sites in the chemical structure of alkaloids from mesquite are the functional group at C-3 and C-3′ of piperidine and indolizine skeleton.

Effects of the auxin-inhibiting substances raphanusanin and benzoxazolinone on apical dominance of pea seedlings

The effects of the auxin-inhibiting substances raphanusanin ((3R*,6S*)-3-[methoxy (methylthio) methyl]-2-pyrrolidinethione, raphanusanin B)and benzoxazolinone (6-methoxy-2-bezoxazolinone, MBOA) on apical dominance of pea(Pisum sativum L. cv. Alaska) seedlings were studied.Application of raphanusanin B or MBOA to the apical bud, internode, or lateralbud of pea seedlings released apical dominance in either intact orindole-3-acetic acid (IAA )-treated, decapitated plants. These results suggestthat the auxin-inhibiting substances raphanusanin B and MBOA have activity inreleasing apical dominance. Conversely, the auxin transport inhibitors2,3,4-triiodobenzoic acid (TIBA) and 1-naphthylphthalamic acid (NPA) did notstimulate lateral bud growth when they were applied directly to the lateralbud,although application to the apical bud or internode released apical dominance.Therefore, the mode of action of raphanusanin B and MBOA in apical dominance isclearly different from that of auxin transport inhibitors. Raphanusanin B andMBOA may suppress the synthesis of growth-inhibiting factor(s) of the lateralbud induced by endogenous auxin transported from the apical bud or exogenouslyapplied auxin, and/or the action of the factor(s).

Evidence of cyanamide production in hairy vetch Vicia villosa

Cyanamide (NH2CN) has recently been isolated as a plant growth inhibitor from Vicia villosa, which is the first discovery of cyanamide from natural sources. To reveal the presence of the biosynthesized cyanamide in plants, 3.4 mM potassium (15N)nitrate was administered to 15- to 35-day-old plants of V. villosa, from which the cyanamide was purified and subjected to GC/MS analysis. The isotopic ratio 15N/(14N + 15N) of the cyanamide was calculated to be 0.143, while that of the cyanamide extracted from V. villosa grown in the presence of a natural N source was 0.0065. The 15N-enrichment proved de novo biosynthesis of cyanamide.