The behaviour of the shoot apical meristem inChenopodium rubrum under conditions non-inductive for flowering

The results of different photoperiodic treatments preventing flowering and representing the control vegetative treatments in the studies of floral induction and differentiation were studied inChenopodium rubrum seedlings. A fully vegetative growth pattern of the meristem was maintained only in continuous light or after a photoperiodic treatment which consisted in a 15 min light break of the 8 h dark periods which themselves are a threshold for flowering inChenopodium. Light breaks applied to 10 h and longer dark periods did not prevent the changes resembling the early events of transition to flowering. Disappearance of zonal pattern, stimulation of apical growth, precocious initiation of leaf primordia and weakening of apical dominance have been observed. Flower formation did not follow. This work was supported by a grant from the Scientific Research Fund of SR Serbia.     

Changes in the Activity of the Chloroplastic and Cytosolic Forms of Dihydroxyacetone Phosphate Reductase during Maturation of Leaves

Young or mature rosette leaves from spinach (Spinacia oleracea L.) plants growing in the field, in the greenhouse, or in a growth chamber under a regimen of 8 hours light and 16 hours dark contained 15 to 50 nanomoles per minute per gram wet weight of NADH:dihydroxyacetone phosphate reductase activity. Of this activity, 75 to 87% was the chloroplastic isoform and 25 to 13% was the cytosolic form. When plants were induced to senesce, as measured by stem elongation and flowering, the percentage of the two reductase isoforms in rosette or stem leaves changed to about 12% as the chloroplastic and 88% as the cytosolic isoform. The change in enzyme activity of the rosette leaves occurred within 3 days, before phenotypic changes were observed. Likewise, when plants senesced in continuous darkness, the percentage of chloroplastic to cytosolic reductase changed from 80:20% to 25:75% after 62 hours before changes in total protein or chlorophyll occurred. The ratio of activities did not change in the first 16 hours of darkness or overnight. In each case the change in ratio resulted from about a 75% decrease in activity of the chloroplastic isoform and up to 14-fold increase in cytosolic isoform. In spinach leaves purchased at a local market primarily only the cytosolic isoform remained. When plants were returned to normal day-nights, after 62 hours in continuous darkness, the activity of the chloroplastic isoform increased, but not to control levels after 3 days, while the cytosolic enzyme decreased within 1 day to normal day-night values. Changes in activity were not due to changes during in vitro assays in activation by thioredoxin for the chloroplastic isoform or fructose 2,6-phosphate for the cytosolic isoform.     

Morphogenetic and diurnal variation of hypericin in some Hypericum species from Turkey during the course of ontogenesis

The genus Hypericum has received considerable interest from scientists, as it is a source of a variety of biologically active compounds including the hypericins. The present study was conducted to determine ontogenetic, morphogenetic and diurnal variation of the total hypericins content in some species of Hypericum growing in Turkey namely, Hypericum aviculariifolium subsp. depilatum var. depilatum (endemic), Hypericum perforatum and Hypericum pruinatum. The Hypericum plants were harvested from wild populations at vegetative, floral budding, full flowering, fresh fruiting and mature fruiting stages four times a day. Plants were dissected into stem, leaf and reproductive tissues, which were dried separately, and subsequently assayed for total hypericin content. The density of dark glands on leaves at full flowering plants was determined for each species. Floral parts had the highest hypericin content in all species tested. But diurnal fluctuation in the hypericin content of whole plant during the course of ontogenesis varied among the species. It reached the highest level at floral budding and tended to increase at night in H. aviculariifolium subsp. depilatum var. depilatum and H. pruinatum, whereas in H. perforatum hypericin content was the highest at full flowering and no diurnal fluctuation was observed. In general, hypericin content of leaves and whole plant was higher in H. aviculariifolium subsp. depilatum var. depilatum whose leaves had more numerous dark glands than those of the two other species.     

Metabolism of <Superscript>14</Superscript>C-glycine as a substrate for photorespiration of the leaf at different developmental stages of ephemeroides

The metabolism of ¹⁴C-glycine (a substrate for photorespiration) was studied in the light and in darkness under natural CO₂ concentration (0.03%) in the leaves of ephemeroides Scilla sibirica Haw. and Ficaria verna Huds. at different developmental stages. Using one and the same sample, potential photosynthesis (at 1% CO₂), true photosynthesis (at 0.03% CO₂), and leaf respiratory capacity were measured by the radiometric and manometric methods, respectively. All measurements were performed at 15°C, an average temperature during ephemer growth. It was found that, in the white zone of the Scilla leaf, the rate of CO₂ evolution resulting from metabolization of exogenous ¹⁴C-glycine was similar in the light and in darkness. In the green zone of the Scilla leaf and in the green leaf of Ficaria, both ¹⁴C-glycine absorption and ¹⁴CO₂ evolution were lower in the light as compared with darkness, which is explained by CO₂ reassimilation. In all treatments of both plant species, a specific inhibitor of glycine decarboxylase complex (GDC), aminoacetonitrile (5 mM) suppressed CO₂ evolution by 20–40%. It was concluded that in ephemeroides mitochondrial GDC, responsible for CO₂ evolution in photorespiration, is formed at the earliest stage of leaf development. This indicates that photorespiration can occur simultaneously with the development of the leaf photosynthetic activity. On the basis of the assumption that carbon losses in the form of CO₂ evolved during photorespiration comprise 25% of true photosynthesis, it was calculated that, in ephemer leaves, the highest rates of photorespiration and photosynthesis were attained during flowering when the leaf area was the largest and the rate of dark respiration was reduced by 1.5–2.0 times. The highest rates of dark respiration were observed in the beginning of growth. In senescing leaves by the end of the plant vegetation, potential photosynthesis and true photosynthesis were reduced, whereas dark respiration remained essentially unchanged. It is concluded that the high rates of potential and true photosynthesis are characteristic of ephemeroides when they complete their short developmental program in early spring (at 15°C); theoretically, photorespiration also occurs at a high rate during this period, when this process provides for a defense against the threat of photoinhibition at low temperature and high insolation.     

Metabolic regulation in the senescing tobacco leaf: I. Changes in pattern of p incorporation into leaf disc metabolites

Changes in phosphate metabolism were explored in discs from tobacco (Nicotiana tabacum) leaves of three contrasting types: green leaves which were fully expanded and attached to the plant, leaves which had yellowed following excision and dark starvation, and leaves which had yellowed while attached to the plant. 2,4-Dinitrophenol at 10⁻⁵m stimulated the respiration rate of discs from green and yellow-detached leaves only slightly, but markedly stimulated that of discs from yellow-attached leaves. Following a 10-minute uptake period the incorporation of ³²P-orthophosphate into phosphate esters and lipids of discs from yellow-detached leaves was resistant to 2,4-dinitrophenol, whereas in discs from green and yellow-attached leaves it was inhibited by 2,4-dinitrophenol. Incorporation into a salt-soluble fraction containing unidentified nucleotide material showed converse behavior in that it was stimulated by 2,4-dinitrophenol in discs from green and yellow-attached leaves; in discs from yellow-detached leaves it was resistant to 2,4-dinitrophenol. In discs from yellow-detached and yellow-attached leaves there was a shift in the labeling pattern of phosphate esters toward increased label in hexose phosphates at the expense of adenine nucleotides, 3-phosphoglycerate, and phosphoenolpyruvate. It is concluded that incorporation into phosphate esters in discs from yellow-detached leaves is by substrate level phosphorylation coupled to enhanced aerobic glycolysis. In discs from yellow-attached leaves, on the other hand, incorporation depends on oxidation phosphorylation, and it is suggested that the shift in labeling pattern is caused by senescence-induced changes in activity of glycolytic enzymes.     

Studies on Flowering Responses of Urena lobata

Urena lobata L. is a qualitative short-day plant with a critical dark period of about 12 hr. A minimum of 12 short days are required for floral initiation. Gibberellic acid (GA₃) sprayed onto the leaves promoted flowering. The growth retardant, (2-chloroethyl)-trimethylammonium chloride (CCC) markedly inhibited flowering and stem elongation. This inhibition was reversed by subsequent application of GA₃.     

Red light stimulates flowering and anthocyanin biosynthesis in American cranberry

Morphological responses of American cranberry (Vacciniummacrocarpon Ait, Ericaceae) to different light conditions (red,far-red, white light and sunlight) were examined. Root growth and development,stem elongation, leaf enlargement, de-etiolation of stem and leaf, flower budformation, and flowering of American cranberry were measured under each lightcondition and in the dark. It was found that red light promotes development ofroots and leaves, flowering, and de-etiolation of stem and leaf of Americancranberry. Stem elongation and etiolation of stem and leaf were shown infar-redlight and dark. Anthocyanin biosynthesis as phytochemical response in cranberryplants was most sensitive to red light. Estimation of anthocyanin levels indifferent parts of cranberry plant suggested that anthocyanins were presentonlyin red fruit skins, and not in peeled fruits, green fruits, green leaves, greenstems, roots and seeds.     

Succession of microfungal flora on Rodgersia podophylla plants at the forest side of Cryptomeria plantation

Microfungal flora on aerial parts of a forest floor plant, Rodgersia podophylla, were studied at the forest side of a Japanese cedar plantation. From May to October, Nigrospora spp. were dominantly isolated from leaves, whereas Acremonium spp. and Fusarium spp. were dominant on stems, suggesting that the aerial part of the plants about 1 m height can offer two different habitats for these dominant fungi. In September and October, we could easily discern different types of tissue on the withering leaves, i.e., brown (necrotic lesion), yellowish (border tissue between brown and green areas), and green (healthy tissue). Nigrospora spp. and Pestalotiopsis spp. were continuously isolated on the brown area as well as on green and yellowish areas. Pathogenicity of N. sacchari and P. neglecta on potted plant leaves was confirmed by inoculation. From these, the fungi of these two genera seemed to have changed from quiescent to pathogenic with leaf senescence. Sporulations by fungi of the two genera were recognized on overwintered stems. These fungi may overwinter in stems that are slow to decompose, and seem to go over to the leaves in the following spring. Thus, they could be candidates for parasites that may play an important role in decomposition of the plant.     

The microclimate under coloured hailnets affects leaf and fruit temperature, leaf anatomy, vegetative and reproductive growth as well as fruit colouration in apple

The purpose of this study was to investigate supposedly positive biological effects of coloured hailnets on microclimate, including photosynthetically active radiation (PAR), UV-B, air, soil, fruit and leaf temperature as well as humidity, which in turn may affect leaf anatomy, tree growth and fruit quality; apple was chosen as a model crop at Klein-Altendorf near Bonn, Germany; adjacent uncovered trees served as control. Red and green hailnets transmitted 3–6% more red or green light, without alteration of the red:far red (R–666 nm:FR–730 nm) ratio (0.99–1.01:1) and hence without affecting the phytochrome system. The microclimate was changed with a reduction by 12–23% in PAR and, to a larger extent, by 20–28% in UV, viz. shading. Light measurements at a 45° angle, to mimic the fruit or leaf position, showed that PAR was 90–210 µmol m⁻² s⁻¹ larger outside on a sunny summer day than under the white or red-white and 150–340 µmol m⁻² s⁻¹ larger than under red-black and green-black hailnets. Air temperature and relative humidity under coloured hailnets decreased by ca. 1.3°C and by ca 2% rh (cloudy) to 5% rh (sunny day), respectively, compared with outside; leaf temperature was decreased by up to 3°C and fruit temperature by up to 6°C. Soil temperatures at 5 cm depth were 0.5–1°C colder under red-black and green-black hailnets, but up to 0.9°C warmer under white and red-white hailnets compared with the uncovered control outside. Alternate bearing had a larger impact on vegetative growth in the affected year than the coloured hailnets; annual trunk diameter increments in cv. ‘Fuji’, i.e. the variety susceptible to alternate bearing, showed a larger variation than cv. ‘Pinova’ without alternate bearing. Reproductive growth, viz. return bloom and leaf anatomy were impaired by the coloured hailnets. Apple trees under dark hailnets developed thinner leaves with a thinner epidermis and fewer layers of palisade cells. These leaves were 3.5°C (dark hailnets) and 2.5°C (white hailnets) cooler than outside on a sunny day compared with ca. 1.5°C (dark hailnets) and 0.85°C (white hailnets) on a cloudy day. Transpirational cooling of cv. ‘Fuji’ leaves was 0.3–0.6°C outside and 1.4–1.6°C under the green-black hailnet on sunny days compared to <0.1°C on cloudy days. As a practical application, apple fruit colouration was dependent on light (PAR and UV-B) transmission of the respective hailnet colour.     

Chromis okamurai,a new damselfish from the Okinawa Trough,Japan

A new pomacentrid fish,Chromis okamurai, is described from a single specimen taken from the Okinawa Trough (25°53.4′N, 123°59.4′E), in 135–175 m. This species is most closely related to the deep-dwellingC. mirationis, sharing with it the same meristic data (in particular XIV dorsal spines and 2 upper and lower caudal spinules), large eye, and relatively deep body. It differs in having a small round posterior nostril (large and slit like inmirationis), longer second anal spine, shorter pelvic fins, and in color: two dark brown stripes on body and a pale pectoral-fin axil (mirationis has a single, midlateral, yellow to yellowish brown stripe which extends broadly onto lower part of caudal fin, and a black pectoral axil).     

Natural infections ofSisymbrium loeselii Jusl. with cabbage black ringspot and tobacco mosaic viruses

Investigating weeds for viruses in ruderal localities of Greater Prague two forms of mosaic diseases inSisymbrium loeselii Jusl. were demonstrated (green and yellowish-green mosaic). Transmission tests carried out on differential host plants showed that the green mosaic is caused by cabbage black ringspot virus (CBRV) and the yellowish green by mixed infection of CBRV and tobacco mosaic virus (TMV). TMV—isolate is characterized as an unusual necrotic strain; its capability to reproduce in cruciferous plant in nature is unique. It was ascertained that green mosaic was commonly spread overSisymbrium plants in ruderal ***DIRECT SUPPORT *** A01GP029 00004 associations on Prague territory; epidemiological significance of this discovery is discussed.     

Effects of cytokinin on adventitious root formation in callus cultures ofVigna unguiculata (L.) walp

Summary Yellowish compact callus, induced from cowpea hypocotyls on Murashige and Skoog(MS) medium (1962) containing 0.2 mg/l(0.93 μM) kinetin and 0.4 mg/l (1.81 μM) 2,4-dichlorophenoxyacetic acid (2,4-D), was subcultured on MS medium containing cytokinin alone, auxin alone, or auxins plus cytokinins in order to determine the effect of cytokinins on root organogenesis in callus cultures. The callus actively proliferated on the same medium but did not show any organogenic activity macroscopically as well as microscopically. On medium with N⁶-benzyladenine (BA) and 1-naphthaleneacetic acid (NAA), the yellowish compact callus first changed to pale green compact callus and then many green spots appeared on its surface under light culture. But the yellowsih compact callus remained yellowish and white spots appeared on its surface in dark culture. These spots gradually became white nodular structures. Adventitious root formation from the nodular structures occurred not only on the same medium, but also on medium with either auxin or cytokinin but not both. Yellowish compact callus on medium with auxin alone was transformed to yellowish friable callus, which did not develop adventitious roots. The yellowish friable callus could gain rhizogenic activity only after morphological modification to pale green compact callus on medium with auxin plus cytokinin. The modified callus did not form adventitious roots on medium with auxins but only with cytokinins. Therefore, it is suggested that cytokinins have stimulating effects on root formation from callus that previously did not show rhizogenic activity on medium with auxins alone. In addition, the rhizogenic potential of cowpea callus was discriminated from that of leaf explants, which formed adventitious roots directly on medium with auxin alone.     

Control of Flowering of Xanthium pensylvanicum by Red and Far-red Light

A study was made of the effects of various durations, intensities and combinations of red and far-red light interruptions on the flowering responses of Xanthium pensylvanicum Wallr. A dual response to treatments of far-red light was observed. In short dark periods, far-red light alone did not greatly affect flowering but was able to overcome the inhibition of flowering caused by red light. In dark periods longer than 15 hours, far-red inhibited flowering and added to rather than overcame the inhibition by red light. The dark period length required for far-red inhibition remained the same whether far-red was given at the start or at the eighth hour of darkness.

In 48-hour dark periods Xanthium showed 3 responses to additions of red and far-red light breaks: A) response to red light; B) response to far-red light; and C) response to red followed by far-red light. Red light given any time in the first 30 hours of darkness overcame the inhibitory effect of far-red light given at either the start or the eighth hour of darkness. Red light given later than the thirtieth hour did not overcome the far-red effect.

Approximately the same energy of red light was required to overcome the inhibitory effect of far-red at the second hour of darkness as was required to produce maximum red light inhibition at the eighth hour. Although far-red light was most inhibitory when given early in a long dark period, approximately the same energy of far-red light was required to saturate the far-red response at the fourth, eighth and sixteenth hours.

The results are discussed in relation to other reports of far-red inhibition of flowering in short-day plants.

     

Changes in Cotyledon mRNA during Ethylene Inhibition of Floral Induction in Pharbitis nil Strain Violet

Floral induction in seedlings of Pharbitis nil strain Violet, with one cotyledon removed, was manipulated by applying various ethylene treatments to the remaining cotyledon during a 16 hour inductive dark period. Exposure of cotyledons to ethylene (100 microliters per liter) for 4 hours at different times during the dark period inhibited flowering to some extent, with inhibition being greater towards the end of the dark period. RNA from cotyledons given a 16 hour dark period (induced) or exposed to 100 microliters per liter ethylene throughout the dark period, which completely inhibited flowering, was examined. The poly(A)⁺RNA was translated in vitro using a wheat germ system, and the resulting translation products were analyzed by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There were substantial qualitative and quantitative differences between the poly(A)⁺RNA extracted from induced cotyledons and that from those exposed to ethylene throughout the dark period. Some of these changes are similar to those observed when flowering was inhibited by photoperiodic treatments (M Lay-Yee, RM Sachs, MS Reid 1987 Planta. In press). The significance of these findings to our understanding of the molecular control of flower induction is discussed.     

The changes in the growth pattern of organs ofChenopodium rubrum photoperiodically induced to flowering

The relationship between photoperiodically changed growth of leaves, cotyledons, hypocotyl, roots and flowering has been investigated inChenopodium rubrum. It was found that all the growth characteristics recorded in leaves and cotyledons,i.e. length, area, dry weight and chlorophyll content, were inhibited during three inductive photoperiods (16 h darkness, 8 h light-SD) as compared with control plants grown under continuous illumination. Similarly, the cessation of root elongation and a decrease in root dry weight were observed. On the contrary, the elongation and dry weight of hypocotyl are stimulated by SD. The degree of the effect exerted by SD on the growth of different organs depends both on actual growth stage and the number of SD photoperiods. Increased relative rate of growth of roots and cotyledons was recorded in plants transferred after SD treatment to continuous illumination. However, this rise possesses only transitional character and the relative growth rate of treated plants equals that of control ones afterwards. The above growth changes are discussed as a possible modifying factor of floral differentiation.     

Purine Auxotrophic Mutants with Altered Spore Color in Streptomyces azureus. ATCC 14921

A purine auxotroph with pale purple spores and a derivative with yellowish orange spores were obtained from the wild-type strain of Streptomyces azureus ATCC 14921, which has bluish green spores. The changed color or pigmentation in the mutants was limited to the spores. They accumulated AIR (5′-phosphoribosyl-5-aminoimidazole) due to the lack of AIR carboxylase activity.     

Volatiles associated with different flower stages and leaves of Acacia cyclops and their potential role as host attractants for Dasineura dielsi (Diptera: Cecidomyiidae)

Acacia cyclops (Fabaceae) is an Australian species which was introduced into South Africa in the nineteenth century. Because of its invasive status in South Africa, a gall midge, Dasineura dielsi (Diptera: Cecidomyiidae), was released in 2001 in order to impact its reproduction by inducing galls on the flowers and thereby preventing seed set. Nothing is known about the cues used by D. dielsi for locating its host flowers. As part of an initial investigation into whether or not chemical cues might play a role in host finding, we analysed headspace samples of Acacia cyclops volatiles from leaves and reproductive parts at different stages (early bud, late bud, early flowering, and senescing flowering stages) using gas chromatography–mass spectrometry (GC–MS). In total, 72 different compounds were detected of which 62 were identified. The analyses showed that open flowers, the stage used by D. dielsi for oviposition, and yellow buds had similar odour compositions with (Z)-3-hexen-1-ol acetate, 4-oxoisophorone, (Z)-β-ocimene, an unknown aliphatic compound, heptadecane, and nonadecane dominating in open flowers. Leaf volatiles were distinct from those in the reproductive plant parts by their high relative amount of (Z)-β-ocimene. (Z)-3-Hexen-1-ol acetate had its maximum relative amount in the green bud samples and was much lower in the later floral stages. In contrast, 4-oxoisophorone peaked in yellow buds and open flowers with little or none of it found in younger or older stages. The volatile compounds of the different flower stages and leaves are discussed in relation to their potential role as attractants used by the biocontrol agent D. dielsi to locate its host plant.     

Fatty acid hydroperoxide lyase in tobacco cells cultured in vitro

Fatty acid hydroperoxide lyase (HPO lyase) was found in green and non-green tobacco cells cultured in vitro. The HPO lyase activity in non-green cells was $\text{1}\text{3}$-$\text{1}\text{2}$ of that in green cells. When the cells were transferred from the light to dark conditions or vice versa, cells turned non-green or green according to the light conditions. The HPO lyase activity also changed according to the light conditions, but the changes in HPO lyase activities were not proportional to the changes in chlorophyll contents. These results suggest that at least two types of HPO lyases are present in the green cells. One type of HPO lyase is perhaps common both to the green and non-green cells; another one is chloroplastic. The fatty acid compositions of cells and substrate specificities of HPO lyase differed between green and non-green cells.