The current study reports the first comprehensive evaluation of a class of allelopathic terrestrial natural products as antifoulants in a marine setting. To investigate the antifouling potential of the natural dihydrostilbene scaffold, a library of 22 synthetic dihydrostilbenes with varying substitution patterns, many of which occur naturally in terrestrial plants, were prepared and assessed for their antifouling capacity. The compounds were evaluated in an extensive screen against 16 fouling marine organisms. The dihydrostilbene scaffold was shown to possess powerful general antifouling effects against both marine microfoulers and macrofoulers with inhibitory activities at low concentrations. The species of microalgae examined displayed a particular sensitivity toward the evaluated compounds at low ng/mL concentrations. It was shown that several of the natural and synthetic compounds exerted their repelling activities via nontoxic and reversible mechanisms. The activities of the most active compounds such as 3,5-dimethoxybibenzyl (5), 3,4-dimethoxybibenzyl (9), and 3-hydroxy-3′,4,5′-trimethoxybibenzyl (20) were comparable to the commercial antifouling booster biocide Sea-nine, which was employed as a positive control. The investigation of terrestrial allelopathic natural products to counter marine fouling represents a novel strategy for the design of “green” antifouling technologies, and these compounds offer a potential alternative to traditional biocidal antifoulants.

The physiological basis of thermoperiodic stem elongation is as yet poorly understood. Thermoperiodic control of gibberellin (GA) metabolism has been suggested as an underlying mechanism. We have investigated the influence of different day and night temperature combinations on GA levels, and diurnal steady-state expression of genes involved in GA biosynthesis (LS, LH, NA, PSGA20ox1, and PsGA3ox1) and GA deactivation (PsGA2ox1 and PsGA2ox2), and related this to diurnal stem elongation in pea (Pisum sativum L. cv Torsdag). The plants were grown under a 12-h light period with an average temperature of 17°C. A day temperature/night temperature combination of 13°C/21°C reduced stem elongation after 12 d by 30% as compared to 21°C/13°C. This was correlated with a 55% reduction of GA 1 . Although plant height correlated with GA 1 content, there was no correlation between diurnal growth rhythms and GA 1 content. NA, PsGA20ox1, and PsGA2ox2 showed diurnal rhythms of expression. PsGA2ox2 was up-regulated in 13°C/21°C (compared to 21°C/13°C), at certain time points, by up to 19-fold. Relative to PsGA2ox2, the expression of LS, LH, NA, PSGA20ox1, PsGA3ox1, and PsGA2ox1 was not or only slightly affected by the different temperature treatments. The sln mutant having a nonfunctional PsGA2ox1 gene product showed the same relative stem elongation response to temperature as the wild type. This supports the importance of PsGA2ox2 in mediating thermoperiodic stem elongation responses in pea. We present evidence for an important role of GA catabolism in thermoperiodic effect on stem elongation and conclude that PsGA2ox2 is the main mediator of this effect in pea.The ability of plants to discriminate between temperature during the day and night in their response to flowering, fruiting, and growth is referred to as thermoperiodism (Went, 1944). Erwin et al. (1989) showed that the effects of diurnal temperature alternation on stem length in Lilium longiflorum could best be described by the mathematical difference (DIF) between day temperature (DT) and night temperature (NT). Stem elongation thus increases with an increase in DIF, from a negative to a positive value. Stem elongation in many species is affected by the relationship between DT and NT, and the DIF concept is widely used for growth control in production of ornamental plants propagated in a greenhouse (Erwin and Heins, 1995;Myster and Moe, 1995;Moe and Heins, 2000). A negative DIF treatment (low DT and high NT) is a tool to produce compact flower plants and vegetable seedlings with short internodes without a delay in production time. Also, negative DIF treatments have largely replaced the use of chemical growth retardants in a number of commercial cultures.Thus, the use of such temperature regimes has substantial practical and economic implications in addition to representing an environmentally more sustainable method than chemical growth control. However, very little is known about the mechanisms underlying the thermoperiodic responses in plants. Such knowledge will be of gr...

Gibberellin (GA) is believed to be involved in thermoperiodic stem elongation. With this in mind, we studied the correlation between gibberellin A1 (GA1) levels and stem elongation affected by alternating day (DT) and night temperature (NT) in 5 genotypes of Pisum sativum differing in their degree of dwarfism. The endogenous GA content in the tissue of two of the genotypes was determined by combined gas chromatography and mass spectrometry. The wild genotype developed 40 to 50% shorter stems and internodes under a low DT and high NT combination (negative difference [DIF] between DT and NT, DT/NT 15.5/21.5 or 14/24°C) than under the opposite regime of high DT and low NT (positive DIF, DT/NT 22.5/16.5 or 24/14°C). The GA biosynthetic mutants ls and le, and the auxin and brassinosteroid mutant lkb responded in a similar way, but not as strongly as the wild type. The stem length of the GA‐insensitive slender mutant (la crys) was reduced by only 8% under negative compared to positive DIF. In the wild type endogenous GA levels decreased by 60% from positive to negative DIF in the upper part of the stem. Further, there was a corresponding decrease in the levels of precursors to GA1, i.e. GA53, GA44, GA19 and GA20, while 2β‐hydroxylated GA20 and GA1, GA29 and GA8, respectively, were unaffected by DIF. A similar increase in the ratios of GA29 to GA20 and GA8 to GA1 from positive to negative DIF was seen in the stem tissue of the le mutant as in the wild type. The temperature regimes affected the levels of GA1 and its precursors in combined leaf and petiole samples and in the shoot tip in a similar manner as in the stem tissue. However, the different temperature regimes did not affect the ratio of GA8/GA1 in the shoot tip. The results indicate that altered stem elongation of the pea plants in response to diurnal temperature alternations may be mediated by changes in endogenous levels of GA1. The GA1 levels may be controlled by an effect of DIF on both biosynthetic and inactivation steps.

Br å then V. T. Gonz á lez (victoria.gonzalez@uit.no), O. Junttila, B. Lindg å rd, R. Reiersen and A. Br å then, Batatasin-III (3,3-dihydroxy-5-methoxybibenzyl) is a phenolic compound associated with the allelopathic eff ect of the evergreen dwarf shrub Empetrum nigrum , and has been referred to as the causal factor for the species being successful in dominating extensive ecosystems. Yet, only a few plant species have been tested for their response to batatasin-III, and little is known about whether environmental factors modify this allelopathic eff ect. In this study, we tested the inhibitory eff ect of purifi ed batatasin-III through bioassays on 24 vascular plant species and, for certain species, we tested if this eff ect depended on growth substrate (mineral vs organic substrate), pH, and fertilization. Moreover, we tested if batatasin-III predicted the allelopathic eff ect of E. nigrum by analyzing the inhibitory eff ect of E. nigrum leaves and humus in relation to their batatasin-III content. Our results confi rmed batatasin-III as a stable compound capable of inhibiting germination and/or mean root elongation in all of the tested species, but this eff ect was modifi ed by growth substrate. Surprisingly, the measured batatasin-III content of E. nigrum leaves (mean value 19.7 Ϯ 10.8 (SE) mg g Ϫ1 ) and humus (mean value of 1 Ϯ 1.5 (SE) μ g g Ϫ1 ) did not predict the inhibitory eff ect on mean root elongation. Although batatasin-III was found to be phytotoxic to all the tested species, we conclude that this substance alone should not be used as a proxy for the allelopathic eff ect of E. nigrum .