Environmental Control of Flowering in some Northern Carex Species

The environmental control of flowering in some arctic-alpineCarexspecies has been studied in controlled environments.Carex nigra,C. brunnescens, C. atrata, C. norwegica andC. serotina all hada dual induction requirement for flowering. In all exceptC.nigra either low temperature (12 °C or lower) or short days(SD) over a wider range of temperatures were needed for primaryfloral induction and inflorescence formation. InC. nigra primaryfloral induction took place in SD only (9–21 °C),8–10 weeks of exposure being required for a full response.In all these species long days (LD) were required for, or stronglypromoted, culm elongation and inflorescence development (secondaryinduction). Quantitative ecotype differences in both primaryand secondary induction were demonstrated. Unlike the otherspecies,C. bicolor proved to be a regular LD plant which requiredLD only for inflorescence initiation and development. In allspecies leaf growth was strongly promoted by LD, especiallyin the higher temperature range (15–21 °C). In SDand temperatures below 15 °C the leaves became senescentand the plants entered a semi-dormant condition which was immediatelyreversed by LD. The results are discussed in relation to growthform and life history of shoots. Carex ; dual induction; ecotypic diversity; flowering; growth; photoperiod; sedges; temperature     

Evidence for Reversible Tyrosine Protein Phosphorylation in the Okadaic Acid-Producing Marine Dinoflagellate Prorocentrum lima

ABSTRACT. The protist Prorocentrum lima , a primary producer of the tumour promoter okadaic acid, is a member of the dinoflagellate class of marine microorganisms. Herein, we have identified and characterized a protein tyrosine kinase (designated PLIK 1A) in P. lima that autophosphorylates almost exclusively on tyrosine residues. PLIK 1A was shown to have an approximate molecular mass of 38 kDa by SDS-PAGE and a native molecular mass within the range of 47–55 kDa by Superdex-75 gel filtration. Phosphoamino acid analysis of autophosphorylated PLIK 1A revealed the presence of phosphotyrosine and autophosphorylated PLJK 1A reacted with monoclonal anti-phosphotyrosine antibodies in a Western immunoblot. In addition, two protein tyrosine phosphatases were identified in P. lima that had apparent molecular masses within the ranges of 150–168 kDa and 73–82 kDa as determined by Superdex-200 gel filtration. These P. lima phosphatases, termed PLPTP-I and PLPTP-II, efficiently dephosphorylated tyrosine phosphorylated myelin basic protein. owever, only PLPTP-I was capable of dephosphorylating the tyrosine phosphorylated substrate angiotensin. Both PLPTP-I and PLPTP-II were able to dephosphorylate tyrosine autophosphorylated PLIK 1A. These data provide the first evidence for reversible tyrosine protein phosphorylation in P. lima by protein tyrosine kinases and phosphatases     

Growth and Dormancy in Norway Spruce Ecotypes (Picea abies) I. Interaction of Photoperiod and Temperature

Growth and dormancy as affected by photoperiod and temperature have been studied in Norway spruce ecotypes of different latitudinal and altitudinal origin. First-year seedlings were used. In all ecotypes apical growth cessation and terminal bud formation occurred within 2 weeks after exposure to SD at temperatures of 18 to 24°C. At lower temperatures or at near-critical photoperiods the response was delayed. The critical photoperiod for apical growth cessation varied from 21 hours in ecotype Steinkjer, Norway (64°N) to about 15 hours in ecotype Lankowitz, Austria (47°04′N). High-elevation ecotypes also had longer critical pholoperiods than low-elevation ecotypes from the same latitude. A detectable growth depression resulted from as little as 1 or 2 SDs of 10 hours, and with 4 or more SDs apical growth cessation took place. In contrast to the situation in the shoot, root growth was not affected by photoperiod. Accordingly, the top:root ratio is drastically affected by photoperiod. The critical photoperiod for cambial growth was shorter than that for apical growth in all ecotypes and cambial growth cessation was delayed for several weeks compared with cessation of apical growth. A transition to formation of late-wood tracheids with thick walls and narrow lumens took place upon exposure to SD. The photoperiodic effects were significantly modified by temperature, but the critical photoperiods were only slightly changed by temperature in the range of 12 to 24°C. However, a 10-hour “night” at 4°C caused growth cessation in continuous light in four ecotypes tested. Temperature optimum for apical growth under non-limiting photoperiods (24 hours) was 21°C in all ecotypes, but with little difference among 18,21 and 24°C. The Q₁₀ for apical growth was 3.5 in the temperature range 12 to 18°C. The growth potential as determined in 24-hour photoperiods was not significantly different among the various ecotypes except for one northern eco-type which was clearly inferior to the others. However, the growth of ecotype Steinkjer (64°N) was greatly suppressed even by the long midsummer days at 59°40′N, thus demonstrating the misleading impression one gets of the growth potential of northern ecotypes when they are moved southwards.     

Growth and Dormancy in Norway Spruce Ecotypes

Height and radial growth of spruce in years n+ 1, n+ 2, and n+ 3 as affected by photoperiod and temperature in year n have been studied in controlled environments and in the field. In agreement with common opinion apical shoot growth in year n+ 1 was strongly dependent on the temperature conditions prevailing in the period following budset in year n. This was found mainly to be a direct effect upon the differentiation of the shoot and needle primordia for next year's growth. A similar, although less pronounced effect, was found also on radial growth, possibly an indirect effect elicited through the effect on apical growth. A rather wide temperature optimum of 18 to 24°C was found in three Norwegian ecotypes and a somewhat lower optimum (15 to 18 C) in an Austrian high altitude ecotype. The shorter the bud differentiation period, the higher was the temperature optimum in all ecotypes (heat sum effect). Photoperiod which is the main factor controlling the time of budset, thus had a great after-effect. The after-effect was strongly modified by photoperiod and to a lesser extent also by temperature in the current growing season. It is concluded that in second-year or older spruce plants the important effect of photoperiod in the current growing season is to control quantitatively and qualitatively the amount of secondary (lammas) shoot formation, and to modify shoot extension in the main growth flush. Longer photoperiods were needed for continuation or resumption of growth in second-year plants than for maintenance of uninterrupted growth in first-year seedlings. Delayed flushing was observed in plants maturing at high temperatures, indicating that these plants had entered a deeper state of dormancy than those maturing at lower temperatures. Also in years n+ 2 and n+ 3 apical and radical growth was significantly related to photoperiod and temperature conditions in year n. This effect gradually became an indirect one through the effects on general plant size (leaf and root area). The results are discussed in the light of previous work in the field.     

Photoperiod and Temperature Interactions in Growth and Flowering of Strawberry

Growth and flowering of strawberry cultivars were studied in controlled environments. Early cultivars adapted to marginal growing areas in Scandinavia initiated flower buds in all photoperiods including continuous light at temperatures of 12 and 18°C. At 24°C they remained vegetative in photoperiods above 14 or 16 h. The later cultivars ‘Senga Sengana’ and ‘Abundance’ did not initiate flower buds in 24-h photoperiods at any of these temperatures. Their critical photoperiod changed from above 16 h at 12°C to about 14 and 13 h at 18 and 24°C, respectively. It is concluded that at high latitudes temperature is as important as photoperiod in controlling flowering in the strawberry. Stolon formation, petiole elongation, and leaf area growth were stimulated by high temperature and long days, usually with optima at 16 h and 18°C for petiole elongation and 16 h and 24°C for stolon formation. Although growth and flowering responses in general were opposite, the results indicate that they are to some extent independent. The photoperiodic growth responses were mainly of morphogenetic nature. Dry weight of stem and leaves was little influenced by photoperiod when the irradiance was kept constant.     

Activity of Various Growth Substances in the Avena First Internode Test

The elongation growth of the Avena first internode segments was studied in the presence of one or several of the following growth substances: indoleacetic acid (IAA), 6-fur-furylamino purine (FAP, kinetin), 6-benzylamino purine (BAP), gibberellin A₃ (GA₃) and A₄₊₇ (GA₄₊₇), and abscisic acid (ABA). The cytokinins at concentrations of 10^?7 to 10^?6M stimulated growth with 4 to 6 per cent but this effect was not statistically significant. Concentrations higher than 5 × 10^?6M inhibited growth. FAP and BAP (from 10^?8M to 10^?6M) had no significant interaction with any other growth substance used. The two-factor interactions of IAA × ABA, IAA × GA₃, and GA₃× ABA, as well as the three-factor interaction IAA × ABA × GA₃ were significant. However, the IAA × ABA interaction was significant only when high concentration (10^?6M) of ABA was used. The growth inhibition produced by 10^?7 and 10^?6M ABA was overcome by about equimolar concentrations of IAA. The stimulation of growth by GA₃ and GA₄₊₇ (10^?9 to 10^?7M) was prevented by simultaneous application of ABA, and it was reduced significantly by application of IAA (10^?7 to 10^?8M). GA3 at 10^?8M combined with different concentrations of IAA gave slightly higher elongation than IAA alone but the observed values were significantly lower than expected assuming independent additive action.     

Effects of phosphorus and nitrogen enrichment on the yield of some strains of Stigeoclonium Kütz. (Chlorophyceae)

SUMMARY.

• 1 The combined effect of nitrate and phosphate concentrations on the yields of five selected strains of Stigeoclonium is demonstrated in a synthetic medium as well as in natural waters.
• 2 Increase of yield after addition of one nutrient depends on the concentration of the other. A graphic growth model based on the experiments in synthetic medium is presented, which allows prediction of yields at different combinations of nitrate and phosphorus concentrations.
• 3 In general, yields in natural waters before and after addition of nitrate and/or phosphate agree with the model. In some cases, other limiting factors appear to be involved.
• 4 The possible effects of nitrogen and phosphorus limitation on the phosphorus and nitrogen metabolism of the alga are discussed.
• 5 Neither an exponential model (Baule-Mitscherlich) nor a hyperbolic model adequately describe the interaction demonstrated between nitrogen and phosphorus limitation.

     

Experiments with duckweed–moth systems suggest that global warming may reduce rather than promote herbivory

1. Wilf & Labandeira (1999) suggested that increased temperatures because of global warming will cause an increase in herbivory by insects. This conclusion was based on the supposed effect of temperature on herbivores but did not consider an effect of temperature on plant growth. 2. We studied the effect of temperature on grazing pressure by the small China‐mark moth (Cataclysta lemnata L.) on Lemna minor L. in laboratory experiments. 3. Between temperatures of 15 and 24 °C we found a sigmoidal increase in C. lemnata grazing rates, and an approximately linear increase in L. minor growth rates. Therefore, an increase in temperature did not always result in higher grazing pressure by this insect as the regrowth of Lemna changes also. 4. At temperatures below 18.7 °C, Lemna benefited more than Cataclysta from an increase in temperature, causing a decrease in grazing pressure. 5. In the context of global warming, we conclude that rising temperatures will not necessarily increase grazing pressure by herbivorous insects.     

Dual Floral Induction Requirements in Phleum alpinum

Flowering requirements of four Norwegian populations of Phleumalpinum were studied in controlled environments. A dual inductionrequirement was demonstrated in all populations. Inflorescenceinitiation had an obligatory requirement for short days (SD)and/or low temperature, while culm elongation and heading wereenhanced by long days (LD) and higher temperatures. At 3 and6 °C primary induction was almost independent of photoperiod,whereas SD was more effective than LD at higher temperatures.The critical temperature for primary induction was about 15°C in SD and 12 °C in LD. Saturation of induction required12 weeks of exposure to inductive conditions, although someheading and flowering took place with 6 weeks exposure to optimalconditions (9 °C/SD). Inflorescence development also tookplace in 8 h SD although it was delayed and culm elongationwas strongly inhibited compared with LD conditions. Only smalldifferences in flowering response were found between the populations. Phleum alpinum L., alpine timothy, dual floral induction, flowering, photoperiod, temperature