Aud Berglen Eriksen

Synthesis of 6-alkenyl- and 6-alkynylpurines with cytokinin activity

Abstract Analogs of the cytokinins trans -zeatin and benzylaminopurine have been prepared by Heck coupling on 6-vinylpurines or Sonogashira coupling on 6-halopurines as key-steps, and their cytokinin activity has been evaluated based on their ability to stimulate increased growth in radish cotyledons.

Visible foliar injury and infrared imaging show that daylength affects short-term recovery after ozone stress in Trifolium subterraneum

Tropospheric ozone is a major air pollutant affecting plants worldwide. Plants in northern regions can display more ozone injury than plants at lower latitudes despite lower ozone levels. Larger ozone influx and shorter nights have been suggested as possible causes. However, the effects of the dim light present during northern summer nights have not been investigated. Young Trifolium subterraneum plants kept in environmentally controlled growth rooms under long day (10 h bright light, 14 h dim light) or short day (10 h bright light, 14 h darkness) conditions were exposed to 6 h of 70 ppb ozone during daytime for three consecutive days. Leaves were visually inspected and imaged in vivo using thermal imaging before and after the daily exposure. In long-day-treated plants, visible foliar injury within 1 week after exposure was more severe. Multivariate statistical analyses showed that the leaves of ozone-exposed long-day-treated plants were also warmer with more homogeneous temperature distributions than exposed short day and control plants, suggesting reduced transpiration. Temperature disruptions were not restricted to areas displaying visible damage and occurred even in leaves with only slight visible injury. Ozone did not affect the leaf temperature of short-day-treated plants. As all factors influencing ozone influx were the same for long- and short-day-treated plants, only the dim nocturnal light could account for the different ozone sensitivities. Thus, the twilight summer nights at high latitudes may have a negative effect on repair and defence processes activated after ozone exposure, thereby enhancing sensitivity.

Copper resistance and genetic diversity inLychnis alpina (Caryophyllaceae) populations on mining sites

Copper mine populations ofLychnis alpina are shown to be significantly more resistant to increased copper concentrations compared to populations on normal soils. Data obtained from isozyme polymorphism analysis revealed that although the copper populations display considerable variation, they have lower genetic variability than the populations from normal soils, both on a local and a global scale, thus indicating a slight founder effect. Copper ecotypes inL. alpina have originated independently. The results are similar to what recently have been reported in heavy metal tolerant populations ofArmeria maritima.

Yield of tomato and maize in response to foliar and root applications of triacontanol

Triacontanol applied to tomato plants as a foliar spray caused a significant increase in total yield and yield per plant. When triacontantol was added to the growth medium, only a temporary increase in yield and number of fruits was observed. The yield of maize was unaffected by triacontanol, either applied to the leaves or to the growth substrate. These results support an earlier observation that a reduction in photorespiration is involved in the regulatory function of triacontanol, since only the yield of tomato, a C3 plant, was increased. The application method was an important factor in its effectiveness.

Effects of the Nordic Photoperiod on Ozone Sensitivity and Repair in Different Clover Species Studied Using Infrared Imaging

Abstract Plants in Nordic regions can be more ozone sensitive at a given ozone concentration than plants at lower latitudes. A recent study shows that the Nordic summer photoperiod, particularly the dim nighttime light, can increase visible foliar injury and alter leaf transpiration in subterranean clover. Effects of photoperiod on the ozone sensitivity of white and red clover cultivars adapted to Nordic conditions were investigated. Although ozone induced visible foliar injury and leaf transpirational changes in white clover, the effects were independent of photoperiod. In red clover, ozone combined with a long photoperiod with dim nights (8 nights) induced more severe visible injuries than with a short photoperiod. Furthermore, transpirational changes in red clover depended on photoperiod. Thus, a long photoperiod can increase ozone sensitivity differently in clover cultivars with different degrees of adaptation to northern conditions, suggesting that ozone indices used in risk analysis should take this effect into account.

6-Cyclopropylpurines as Novel Potent Analogs of Cytokinins

Abstract6-Alkynyl-, trans-6-alkenyl-, trans-6-cyclopropyl-and 6-alkylpurines structurally related to the cytokinin 6-benzylaminopurine (BAP) have been synthesized and examined with a radish cotyledon assay as plant growth stimulators. The growth stimulation obtained with the 6-alkylpurines trans-cyclopropylpurines was very close to that obtained with BAP, and the trans-styrylpurines were somewhat less effective. The fact that the conformationally locked cyclopropanes exhibit growth-stimulating effects comparable to the flexible 6-alkylpurines and to BAP, supports the hypothesis that the orientation of the NH-CH2 bond in “the active conformation” of BAP is close to anti, which means that the torsion angle C(6)-N(6)-CH2-C is approximately 180 degrees.

Synthesis of 6-substituted purin-2-ones with potential cytokinin activity

6-Substituted purin-2-ones have been prepared by completely regioselective addition of Grignard reagents to an N-protected purin-2-one followed by rearomatisation and deprotection. The target compounds may be regarded as analogues of the potent cytokinins trans-zeatin and benzylaminopurine (BAP), and most of the BAP analogues did induce increased weight growth in radish cotyledons. N-Protected (E)-6-styrylpurin-2-one underwent head to tail [2+2] dimerisation to the 1α,2α,3β,4β-substituted cyclobutane 15, when exposed to ordinary daylight. When irradiated with UV-light, the trans-compound isomerised to the corresponding cis-isomer. The structure of compound 15 was determined by single crystal X-ray diffraction methods at 150 K.