Combined effect of light and temperature on triacylglycerol accumulation in Dicranum elongatum

In the subarctic moss Dicranum elongatum Schleich & Schwaegr., the level of total lipids and triacylglycerols (TAG) was high in late winter and spring and low in autumn and winter. Four-week exposure of field material to continuous light (135μmol m⁻²s⁻¹) at 1°C resulted in a considerable increase in the amount of TAG in the autumn material acclimated to low temperatures and rhythmic light in the field. In contrast, the same treatment did not cause any increase in TAG in the spring material, acclimated to low temperatures and continuous light in the field. Results from experiments, in which moss cultivated for 4 months at 9°C on 12-h photoperiods (135μmol m⁻²s⁻¹) was kept for 3 weeks at low temperatures (9°C and −3°C) either in continuous light (135 or 70 μmol m⁻²s⁻¹) or with 12-h photoperiods (135 μmol m⁻²s⁻¹), indicated that the TAG level was higher at higher light intensity. At 9°C it was also higher in continuous light of both intensities than in rhythmic light. These results strongly suggest that decreasing irradiance and decreasing daylength limits the accumulation of TAG in D. elongatum during autumn in the subarctic.     

Characterization of prolamellar bodies, from dark-grown seedlings of Scots pine, containing light- and NADPH-dependent protochlorophyllide oxidoreductase

Cotyledons of conifers have a light-independent pathway for chlorophyll biosynthesis. To investigate whether the prolamellar body of Scots pine ( Pinus sylveslris L.) is similar to the better known prolamellar body of wheat, etioplast membrane fractions were isolated from cotyledons of dark-grown Scots pine. Dark-grown cotyledons contained both chlorophyll and protochlorophyllide, 158 and 10 nmol (g fresh weight)'respectively, and had a chlorophyll a to b ratio of 4.2. The content of glyco- and phospholipids was 7.1 μmol (g fresh weight)¹. About 40 mol % of these lipids were the specific plastid lipids – monogalactosyl diacylglycerol. digalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol in the relative amounts 50, 35 and 7 mol %. The mol ratio of monogalactosyl diacylglycerol to digalactosyl diacylglycerol was 1.7. Low temperature fluorescence emission spectra of intact cotyledons and homogenate showed maxima at 633, 657, 686, 696 nm and a broad peak at 725–735 nm. The maxima at 633 and 657 nm represented different forms of protochlorophyllide and the other emission maxima represented chlorophyll protein complexes. The 657 nm form of protochlorophyllide was phototransformable both in vivo and in the isolated membranes. The phototransformable protochlorophyllide was substantially enriched in the prolamellar body fraction.
The specific activity of light dependent protochlorophyllide oxidoreductase in the prolamellar body fraction was found to be 2 nmol chlorophyllide formed [(mg protein)⁻¹ min⁻¹]. The molecular weight of the enzyme polypeptide was determined as 38 000 dalton with sodium dodecylsulphate-polyacrylamide gel electrophoresis.     

Use of allele-specific sequencing primers is an efficient alternative to PCR subcloning of low-copy nuclear genes

Direct Sanger sequencing of polymerase chain reaction (PCR)-amplified nuclear genes leads to polymorphic sequences when allelic variation is present. To overcome this problem, most researchers subclone the PCR products to separate alleles. An alternative is to directly sequence the separate alleles using allele-specific primers. We tested two methods to enhance the specificity of allele-specific primers for use in direct sequencing: using short primers and amplification refractory mutation system (ARMS) technique. By shortening the allele-specific primer to 15-13 nucleotides, the single mismatch in the ultimate base of the primer is enough to hinder the amplification of the nontarget allele in direct sequencing and recover only the targeted allele at high accuracy. The deliberate addition of a second mismatch, as implemented in the ARMS technique, was less successful and seems better suited for allele-specific amplification in regular PCR rather than in direct sequencing.     

Use of Avermectins for the Control of Meloidogyne incognita on tomatoes

The efficacy of avermectins B₁ and B₂ for control of Meloidogyne incognita on tomato was studied in pots and field plots for two seasons. Avermectins were applied as granules and liquid in furrows or by low pressure drip irrigation systems, at rates ranging from 0.093 to 0.34 kg a.i./ha, as single or multiple applications. Levels of control comparable to those obtained by oxamyl and aldicarb at 3.36 kg a.i./ha were achieved by the avermectin with only 1/10 the volume of chemicals applied to the environment. Avermectin protection of the roots remained constant throughout the first 5 weeks giving slightly longer protection than oxamyl or aldicarb.     

Exothermic responses of dormant Salix stems during exposure to subzero temperatures

Differential thermal analysis (DTA) was used to determine the exothermic responses in dormant stems and excised lengths of stem of Salix dasyclados Wimmer subjected to artificial freezing treatments.
The presence of ice on the surfaces of intact stems restricted the mechanism of freezing avoidance to temperatures above –4°C. In contrast, excised lengths of stem started to freeze as soon as the ambient temperature fell below –2°C, demonstrating that extracellular ice formation takes place earlier if cut surfaces are present. Exposure of dormant excised lengths of stem to subfreezing temperatures for more than 8 weeks did not alter their nucleation temperature not their exothermic differential responses. Early extracellular crystallisation of freezable cellular water provides conditions that allow dormant Salix dasyclados stems or excised lengths of stem to survive extreme freezing stress.
Crystallisation of extracellular and cellular water took place in the cortex, and did not result in visual damage or reduced survival. This nucleation of extracellular water took place over the same temperature range whether the excised dormant lengths of stem were partly (bark only) or completely thawed. Exposure of dormant tissue to 20°C for up to 24 h did not alter the level of freezing tolerance, nor did it increase the susceptibility of excised lengths of stem to damage by extreme temperature fluctuations.