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Raphanusanin is a light-induced growth inhibitor involved in inhibition of hypocotyl growth in response to unilateral blue light illumination in radish seedlings. To understand better the role of raphanusanin in growth inhibition, we randomly analyzed raphanusanin-induced genes using a modified DD-RT-PCR (differential display RT-PCR) approach. The differential expression RT-PCR approach resulted in identification of four known candidate genes, of which three encoded functional proteins known to be related to responsiveness to diverse environmental stimuli. One of these genes appeared to be an essential element in the inhibition of hypocotyl growth, and was named RsCSN3 (a homologue of subunit 3 of the COP9 signalosome). During the growth inhibition that was observed within minutes of irradiation, the expression of the RsCSN3 gene was increased by phototropic stimulation, as well as by raphanusanin treatment, suggesting that this gene is involved in light-induced growth inhibition. In addition, down-regulation of the RsCSN3 transcript, that is specifically expressed at 60 min after the onset of stimulation under blue light, green light, and raphanusanin treatment, shows a functional correlation with the phototropic response.

Polyacetylenes 1 and 2 were isolated from extracts of Japanese ivy (Hedera rhombea Bean) flower buds, with their chemical structures established on the basis of extensive 1D and 2D NMR and MS analyses. The absolute configurations of compounds 1 and 2 were determined by both chemical means, and by using the modified Mosher's method. Compound 1 is the first polyacetylene having an ester linkage between falcarindiol (3) and indole-3-acetic acid (IAA) moieties and 2 also had an unique substructure containing a conjugated diene adjacent to a hydroxy group. Polyacetylenes 1, 2, and 3 were also subjected to assessment of growth inhibition against the shoot and root growth of the monocotyledon plants, rice and perennial ryegrass, as well as the dicotyledons, cockscomb, lettuce, cress, and fenugreek. The most bioactive compound appeared to be compound 1, while 2 showed no activity. Compound 1 selectively showed growth inhibitory activity against dicotyledons.

In addition to (+)-, (-)- and (+/-)-heliannuol E, growth-inhibitory activities of five synthetic chromans and four tetrahydrobenzo[b]oxepins were examined against oat and cress. All heliannuol E isomers exhibited similar biological activities against cress, whereas when tested against oat roots, the unnatural optical isomer (+) showed no inhibitory activity. Four brominated chromans and two tetrahydrobenzo[b]oxepin derivatives also showed apparent inhibition against both cress and oat., (Copyright 2004 Elsiever Ltd.)

Plant growth inhibitory alkaloids were isolated from the extract of mesquite [Prosopis juliflora (Sw.) DC.] leaves. Their chemical structures were established by ESI-MS, 1H and 13C NMR spectra analysis. The I50 value (concentration required for 50% inhibition of control) for root growth of cress (Lepidium sativum L.) seedlings was 400 microM for 3''''-oxo-juliprosopine, 500 microM for secojuliprosopinal, and 100 microM for a (1:1) mixture of 3-oxo-juliprosine and 3'-oxo-juliprosine, respectively. On the other hand, the minimum concentration exhibiting inhibitory effect on shoot growth of cress seedlings was 10 microM for 3''''-oxo-juliprosopine, 100 microM for secojuliprosopinal, and 1 microM for a (1:1) mixture of 3-oxo-juliprosine and 3'-oxo-juliprosine, respectively. Among these compounds, a (1:1) mixture of 3-oxo-juliprosine and 3'-oxo-juliprosine exhibited the strongest inhibitory effect on the growth of cress 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.

Leaf-movement in nyctinastic plants has long been believed to be controlled by plant hormones that are common among all nyctinastic plants. We have identified several bioactive substances for nyctinasty, whose bioactivities were highly specific to the original plant, based on the bioassay using the original plant leaf, and have shown that nyctinastic leaf-movement is not regulated by plant hormones. Our present results are in accordance with Umrath et al. physiologically significant opinion.