The effect of oxygen on nitrate and nitrite assimilation in leaves of Zea mays L. under dark conditions

The assimilation of nitrate under dark-N₂ and dark-O₂ conditions in Zea mays leaf tissue was investigated using colourimetric and ¹⁵N techniques for the determination of organic and inorganic nitrogen. Studies using ¹⁵N indicated that nitrate was assimilated under dark conditions. However, the rate of nitrate assimilation in the dark was only 28% of the rate under non-saturating light conditions. No nitrite accumulated under dark aerobiosis, even though nitrate reduction occurred under these conditions. The pattern of nitrite accumulation in leaf tissue in response to dark-N₂ conditions consisted of three phases: an initial lag phase, followed by a period of rapid nitrite accumulation and finally a phase during which the rate of nitrite accumulation declined. After a 1-h period of dark-anaerobiosis, both nitrate reduction and nitrite accumulation declined considerably. However, when O₂ was supplied, nitrate reduction was stimulated and the accumulated nitrite was rapidly reduced. Anaerobic conditions stimulated nitrate reduction in leaf tissue after a period of dark-aerobic pretreatment.     

Leaf hydrocarbons of Phacelia species (hydrophyllaceae)

Whole leaf hydrocarbons of six species of Phacelia were investigated for their variability among natural Californian populations, and for adaptive     

Volatile constituents of the leaves of Cupressus dupreziana and Cupressus sempervirens

The essential oils of the leaves of Cupressus dupreziana and Cupressus sempervirens were compared. The composition of the hydrocarbon fraction showed a great similarity between the two species.     

Epidermis effects on spectral properties of leaves of four herbaceous species

The spectral properties of the leaves of the herbaceous species Brassica oleracea L. var. botrytis L., Cerastum tomentosum L., Petunia hybrida Vilm., and Talinum paniculatum (Jacq.) Gaertn. were examined to see what effect the epidermis had on leaf absorptance, reflectance and transmittance. Removal of the epidermis from the side of the leaf surface being illuminated resulted in increases in leaf absorptance and transmittance, and a decrease in reflectance in the 400–800 nm waveband. Removal of the epidermis from the opposite side of an illuminated leaf (effect was similar in both abaxial and adaxial surfaces) resulted in small decreases in both absorptance and reflectance, and corresponding increases in transmittance. Removal of both the upper and lower epidermis resulted in a marked increase in transmittance, while both leaf reflectance and absorptance were decreased. The results suggest that the presence of the epidermis significantly increases leaf absorptance in the photosynthetic wavebands.     

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.     

Localization of Glyoxylate Cycle Enzymes in Glyoxysomes in Euglena*

SYNOPSIS. We demonstrated previously microbodies in Euglena gracilis grown in the dark on 2-carbon substrates. We have now established in Euglena the particulate nature of enzymes known in other organisms to be localized in microbodies (glyoxysomes and leaf peroxisomes). On a linear sucrose gradient the glyoxylate cycle enzymes band together at a nigner equilibrium density (1.20 g/cm3) than mitochondrial marker enzymes (1.17 g/cm3), establishing the existence in Euglena of glyoxysomes similar to those of higher plants. Glyoxylate (hydroxypyruvate) reductase and, under certain conditions, also glycolate dehydrogenase co-band with the glyoxylate cycle enzymes, suggesting that Euglena glyoxysomes, like those of higher plants, may contain peroxisomal-type enzymes. Catalase, an enzyme characteristic of microbodies from a variety of sources, was not detected in Euglena.     

Application ofVerticillium lecanii for the control ofAphis gossypii by a low-volume electrostatic rotary atomiser and a high-volume hydraulic sprayer

Verticillium lecanii (Fungi: Deuteromycete) blastospores were applied to a chrysanthemum crop by an ULV electrostatically charged rotary atomiser (APE-80). The deposition of spores and subsequent control ofAphis gossypii were compared to high volume hydraulic application. A full rate treatment (2×10¹³ blastospores per ha.) was applied by the APE-80 at week 1 and reduced spore rates of 1/6^th and 1/12^th applied by both the APE-80 and the hydraulic sprayer once and twice a week respectively for weeks 1 to 6. Untreated plots served as controls. Initial deposits of spores were higher with the electrostatic sprayer and better distributed with respect to the position of the target aphids. Significantly lower aphid populations were recorded on the electrostatically treated plots in week 4. The single full rate treatment had significantly fewer aphids than the untreated plots from week 3 and all treatments had significantly fewer aphids than the untreated plots from week 5 onwards. The proportion of the aphid population killed byV. lecanii was higher on the electrostatically treated plots until week 6.      

蚕豆叶片发育与衰老过程中超氧物歧化酶活性与丙二醛含量变化

蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.     

Plant resistance, plant traits, and host plant choice of the leaf-folding sawfly on the arroyo willow

Abstract. 1. The hypotheses that genetic variation in host plant resistance of the arroyo willow affected leaf folder ( Phyllocolpa sp.) (Hymenoptera: Tenthredinidae) density and that genetic variation in shoot length and leaf length was correlated with resistance were tested.
2. Willows grown in pots and exposed to ovipojsition by the leaf folding sawfly in cages had significantly different densities among clones, indicating variation in resistance caused by genetic differences among conspecific host plants.
3. There was a general correspondence between leaf folder density on potted cuttings and on the plants in the field that were the sources of cuttings.
4. In behavioural choice experiments, susceptible clones (with highest leaf fold densities) had the highest oviposition activity of female leaf folders compared to clones that were resistant to the leaf folder.
5. Clones differed significantly in shoot length and leaf length among clones grown in pots, among clones in the field, and between shoots with galls and shoots without galls on clones in the field.
6. Leaf folder density was significantly positively correlated with mean shoot length on field clones in 1985 and 1986, but was not correlated with leaf length, although leaf length and shoot length were correlated.
7. Leaf length variation among willow clones accounted for a significant portion of the variation in resistance of potted willows, but shoot length was unimportant.     

A micromorphological study of some representative genera in the tribe Saturejeae (Lamia ceae)

HUSAIN, S. Z., MARIN, P. D., ŠILIĆ, Č., QAISER, M. & PETCOVIĆ, B., 1990. A micromorphological study of some representative genera in the tribe Saturejeae (Lamiaceae). The Old World genera in the tribe Saturejeae are usually distributed either in Europe and North Africa or in the temperate parts of Asia. The centres of distribution of investigated genera are mainly in the Mediterranean region. In taxonomic revisions very little reference is made to micromorphological characters, in particular, to nutlets and leaf indumentum, in spite of the stability of these characters. Scanning electron microscopy of nutlet surface and patterns of leaf indumentum show a wide range of variation, not only among genera, but also at lower levels of classification. In view of this, nutlet surface and leaf indumentum structure, as seen with the SEM, of representative species of eight genera in the tribe Saturejeae provides useful additional character combinations in delimiting these closely related genera. This study also supports Boissier's delimitation of sections Micromeria and Pseudomelissa.