Mg2+-, Ca2+-dependent unwinding of DNA by poly-L-glutamic acid

In order to examine a possibility that the high acidic amino acid region in the nonhistone protein HMG(1+2) is concerned with the Mg2+-, or Ca2+-dependent unwinding of DNA by the HMG(1+2) (1,2), poly-L-glutamic acid was employed as an acidic model peptide for thermal melting temperature analysis. The poly-L-glutamic acid bound to DNA either in the presence or absence of Mg2+. The poly-L-glutamic acid unwound DNA double-helix to a similar extent to HMG(1+2) in the presence of Mg2+ or Ca2+, but not in the absence of them. These results may suggest that the high acidic amino acid region in HMG(1+2) participates in Mg2+-, Ca2+-dependent unwinding of DNA double-helix.     

Specific photoperiodic stimulation of dry matter production in a high-latitude cultivar of Poa pratensis

Vegetative plants of Poa pratensis L. cv. Holt (origin 69°N) raised in short days gave large and significant increases in plant dry weight, plant height and leaf area upon exposure to continuous light, compared with 8-h short days, at essentially identical daily inputs of radiant energy (8-h summer daylight ± low intensity extension). For example, by the fourth harvest (after 26, 34 and 46 days at 21, 15 and 9°C, respectively), the dry weights of plants in long days were 81, 163 and 195% greater than those of the corresponding short-day controls at the respective temperatures. Plant leaf areas in long days were between two and four times as large as control values by the end of the experiment. This was mainly due to increased leaf length caused by long-day stimulation of cell extension and division. However, the photoperiod did not affect the partitioning of assimilates amongst leaves, culms and stolons. Most of these effects could also be brought about by exogenous gibberellin application to plants in short days. However, in contrast to the effect of long days, gibberellin treatment also induced stem internode elongation even in these vegetative plants. Examination by standard growth analysis procedures revealed that the observed increases in relative growth rate were due primarily to increased net assimilation rate followed, several days later, by increases in leaf area ratio when newly-emerged leaves began to constitute a significant proportion of the leaf area. It is concluded that these reactions are of great adaptive significance for growth at the marginal temperatures prevailing at high latitudes.     

The effects of time of seed production on the germination response of Spergularia marina

Germination studies were carried out with seeds of Spergularia marina L. Griseb produced over an interval of six months (June-November). The response of the seeds to light and dark, various constant and alternating temperature regimes, and salinity were determined. In addition, the effects of soil moisture status at the time of seed production on the subsequent germination response of seeds were also determined. Light was an absolute requirement for germination. While a constant temperature regime did not generally favour germination of seed of any month, alternating temperature greatly enhanced germination with an optimum at 5/15°C in all seeds. When imbibed in solutions of different salinities, seeds collected in July and October behaved like true halophyte seeds whereas those collected in June. August, September and November behaved like glycophyte seeds.
High concentration of gibberellic acid (3 000 μ M ) stimulated dark germination in the June and November seed lots, but in light, low GA3 concentration (300 μ M ) stimulated germination most. The addition of kinetin (30 μ M ) plus gibberellic acid enhanced germination in the dark in contrast to GA3 alone; kinetin alone stimulated a very low percentage germination.
The moisture status of the soil at the time seeds were produced did not affect the germination response of an early seed crop (July) but affected that of the later seeds (August).
Judging from the different germination responses, it appears that the seeds belong to at least two physiological groups, one which appears to need either a dark-wet or cold-wet pretreatmem for high germination to occur; and the other group which does not need pretreatmem. The ecological significance of these varied responses is discussed in relation to the survival of the species in its habitat.     

Effect of temperature on drought resistance and growth of cotton plants

In cotton plants ( Gossypium hirsutum L. cv. B.J.A.) the temperature of the roots affected both root and shoot growth, as did the temperature of the shoot. Drought resistance increased when the temperature imposed on roots (27°C) was lower than that imposed on shoots (17°C); the result was a decrease in both transpiration and flow of root sap. Stomatal characteristics as measured by density, index and resistance, depended only on shoot temperature. Differences in drought resistance, depended only on shoot temperature. Differences in drought resistance seem to be a result of changes in transpiration flow modulated by the amount of absorbed water.     

Influence of Planting Date on Damage to Soybean Caused by Heterodera glycines

Bragg soybeans were planted in nematicide-treated and nontreated plots on 15 May, 15 June, 1 July, and 15 July in 1980 and 1981 to determine the influence of planting date on damage caused by H. glycines. Although earlier studies showed the nematode was sensitive to high soil temperatures (> 34 C), late planting did not reduce damage caused by the nematode. Yields from plots treated with 1, 2-dibromo-3-chloropropane (57.5 kg a.i./ha) were 48, 118, 395, and 403% higher than yields from nontreated plots with planting dates of 15 May, 15 June, 1 July, and 15 July, respectively, when data were averaged over the 2 years. Increase in both seed size and number accounted for the yield increases in treated plots. Soil temperatures were highest during July in 1980, averaging 8.9 and 6.5 hours per day above 34 C at 10- and 20-cm depths, respectively. Larvae populations of H. glycines were reduced by the nematicide but not by late planting. These results indicate that damage caused by H. glycines may actually increase with later planting and that nematicides may be more beneficial when soybeans are planted late in a double-cropped production system.     

Effect of Aedes aegypti (Diptera:Culicidae) Age on Sex Ratios in Romanomermis culicivorax (Nematoda:Mermithidae)

First, second, third, early and late fourth-instar larvae, and pupae of Aedes aegypti were infected with Romanomerrais culicivorax and reared at 20, 25, and 30 C. An increase in the ratio of male to female nematodes was observed with increase in host age at the time of infection at each temperature. The number of pupal and late fourth-instar infections was low, but R. culicivorax continued to develop in adult A. aegypti. Since male nematodes were recovered from both male and female hosts infected as late fourth instars or pupae, the sex of the host did not influence the sex of the nematode.     

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C₃ and one C₄ species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO₂ and O₂, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.     

Ligation of highly modified bacteriophage DNA

After digestion by TaqI or nicking by DNAase I, five highly modified bacteriophage DNAs were tested as substrates for T4 DNA ligase. The DNAs used were from phages T4, XP12, PBS1, SP82, and SP15, which contain as a major base either glucosylated 5-hydroxymethylcytosine, 5-methylcytosine, uracil, 5-hydroxymethyluracil, or phosphoglucuronated, glucosylated 5-(4′,5′-dihydroxypentyl)uracil, respectively. The relative ability of cohesive-ended TaqI fragments of these DNAs and of normal, λ DNA to be ligated was as follows: $\text{λ}\text{DNA}\text{=}\text{XP}\text{12}\text{DNA}\text{>}\text{SP}\text{82}\text{DNA}\text{?}\text{nonglucosylated}\text{T}\text{4}\text{DNA}\text{>}\text{T}\text{4}\text{DNA}\text{=}\text{PBS}\text{1}\text{DNA}\text{?}\text{SP}\text{15}\text{DNA}$. TaqI-T4 DNA fragments were also inefficiently ligated by Escherichia coli DNA ligase. However, annealing-independent ligation of DNAase I-nicked T4, PBS1, and λ DNAs was equally efficient. We conclude that the poor ligation of TaqI fragments of T4 and PBS1 DNAs was due to the hydroxymethylation (and glucosylation) of cytosine residues at T4's cohesive ends and the substitution of uracil residues for thymine residues adjacent to PBS1's cohesive ends destabilizing the annealing of the restriction fragments. Only SP15 DNA with its negatively charged, modified base was unable to serve as a substrate for T4 DNA ligase in an annealing-independent reaction; therefore, its modification directly interfered with enzyme binding or catalysis.     

Temperature-related divergence in experimental populations of Drosophila melanogaster. II. Correlation between fitness and body dimensions

From a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18° C, a new population was derived and maintained at 28° C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two populations was estimated. Six body traits and reproductive fitness were taken into account. The third chromosome is responsible for the adaptive difference for temperature between the two lines. Temperature-selected genes which control body size are located on the second and third chromosomes, although the contribution of each chromosome depends on the environment in which the flies develop. The correlation between the chromosomal and cytoplasmic contributions to different traits and fitness, changes with temperature. At 28° C the correlation between fitness and each body trait is proportional to the response to selection exhibited by each of them, but this is not true at 18° C. Body size has, therefore, an adaptive significance in relation to temperature, which is expressed only in the environment where selection occurs. Cytoplasmic genes affect almost all characters to an extent similar to that of chromosomal genes. Inter-chromosomal and nucleo-cytoplasmic interactions are present and also change with temperature. In general, genes selected in a given environment produce greater phenotypic changes in that environment than in another. The population that experienced both temperatures is fitter in both environments, suggesting that the capacity to adapt to warm temperatures depends on genes other than those which are involved in the adaptation to cold.     

Induction of microspore embryogenesis inBrassica napus L. by gamma irradiation and ethanol stress

Summary Gamma irradiation and ethanol stress treatments redirected pollen development to an embryo formation pathway inBrassica napus. Less than 0.01% of microspores developed into embryos at 25°C compared to approximately 2% at 32°C. However, subsequent to gamma irradiation and ethanol treatments up to 1% and 0.7% of microspores formed embryos at 25°C, respectively. Gamma irradiation also enhanced embryogenesis at 32°C. The possible importance of these findings is discussed in relation to microspore embryogenesis.