Water In Petri Dishes Research Articles

Effects of salicylic acid application on germination, growth and development of rough lemon (Citrus jambhiri Lush.) under salt stress

Rough lemon (Citrus jambhiri Lush.) – RL, is used as a rootstock for citrus plants in saline conditions. NaCl causes an osmotic stress on plants mainly preventing the water uptake by the roots and thus reducing the plant growth. The objective of this study was to determine the effects of salicylic acid (SA) on germination of seeds and the growth and development of seedlings of RL rootstock under salt stress. For seed germination, a study was conducted in a completely randomized design in a 4 × 4 factorial scheme (SA at 0.00, 0.25, 0.50, or 1.00 mM and NaCl at 0, 50, 100, or 200 mM) with 4 repetitions, totaling 64 plots, of 25 seeds per plot. RL seeds were incubated in SA solutions for 24 h. Then, they were treated with NaCl-containing water in Petri dishes and incubated in the growth chamber at 25°C. For greenhouse experiment, a study was conducted in a randomized complete block in a 4 × 4 factorial scheme (SA at 0.0, 0.5, 1.0, or 2.0 mM and NaCl at 0, 50, 100, or 150 mM) with 3 repetitions, totaling 48 plots, of 2 plants per plot. Some morphological and physiological characteristics were determined. While germination time was extended, germination ratio and radicle extension were decreased in seeds under salt stress compared to control. Moreover, in these conditions the leaf membrane permeability and leaf falling were increased. In turn, plant height, diameter, root and shoot dry weight, leaf relative water content, and leaf chlorophyll were decreased in seedlings. Salt stress had negatively affected seed germination from 97.5% in control to 23.5% in 200 mM NaCl. However, SA treatments significantly decreased plant height to 67.8 cm in 2.0 mM compared to 80.1 cm in control in RL rootstock.

BIOTESTING OF THE ANTHROPOGENIC IMPACT ON AREAS OF THE R. ROS AND R. PROTOKA ON THE VIABILITY OF CARP FISH EGGS AND LARVAE

BIOTESTING OF THE ANTHROPOGENIC IMPACT ON AREAS OF THE R. ROS AND R. PROTOKA ON THE VIABILITY OF CARP FISH EGGS AND LARVAE

Responses of germination strategy of Agriophyllum squarrosum to rainfall pattern in the Tengger desert.

Agriophyllum squarrosum (L.) Moq. (Chenopodiaceae) is an annual pioneer psammophyte that is strictly distributed along desert margins. However, little is known about how this species adapts to shifting dunes. In this study, seeds bank was selected and germination behaviors of A. squarrosum were tested in laboratory. In addition, the effects of rainfall patterns on population dynamics were observed in field at the southeastern edge of the Tengger Desert. Soil seed bank density was significantly different in different depth of sand dunes. Under adequate water in Petri dishes, seeds began to germinate in less than 3 h and the germination peak was reached in seven days after watering. It showed that there is no innate dormancy of A. squarrosum. The buried experiments showed that the germination percentage decreased with increasing buried depth, and deeply buried seeds (10 cm) remained ungerminated. Population dynamics in different rainfall pattern of three years in field showed that germination, survival and deaths of A. squarrosum were extremely sensitive to rainfall variation. Our results suggest that precipitation is the key factor in determining population of A. squarrosum. The germination strategy of A. squarrosum ensures the efficiency use of unpredicted and scarce precipitation. The high disturbance of moving sand endowed persistence seed bank of A. squarrosum, which is essential for population continuation, avoiding population extinction under unpredicted precipitation.

Effect of Waterlogging Duration on Germination, Physiological Characteristics, and Yield of Mungbean (Vigna radiata L.)

The study was conducted to evaluate the germination, physiological responses, yield-related traits, and seed yield of three mungbean varieties, viz. DXVN7, DXVN5, and DX11, under waterlogging coditions in the 2019 Summer. In experiment 1, the seeds of the three mungbean varieties were immersed in distilled water in Petri dishes for 12, 24, 36, 48, and 72h. Afterwards, water was removed and the percentage of germinated seeds was calculated at 84h after sowing. In experiment 2, plants were waterlogged at the seedling stage (25 days after germination) for 3, 6, and 9 days. Waterlogging depth was maintained at 3cm above the soil surface. Physiological traits were determined at the recovery period after termination of waterlogging (45 days after germination). The results showed that waterlogging significantly decreased germination percentages, plant height, root dry weight, leaf relative water content (RWC), SPAD value, Fv/Fm index, leaf photosynthesis, total dry weight, and seed yield of all varieties. Germination percentages at 12 and 24h of waterlogging were not significantly affected, whereas germination was significantly reduced at up to 36h of waterlogging. Seventy-two hours of waterlogging caused failure in germination. Nine days of waterlogging at the seedling stage adversely affected the physiological traits and seed yield of the mungbean varieties with 31% of yield reduction. Meanwhile, plants grew better at 3 days of waterlogging. Among the three varieties, DXVN7 showed the best adaptability under waterlogging conditions, attaining the highest seed germination and yield.

First Report of Bacterial Leaf Spot of Cucurbita pepo Caused by Erwinia persicina in China.

In February 2020, the common symptoms of water-soaked spots on Cucurbita pepo L. cotyledon were observed in Guangrao county in Shandong province, China. Field investigation showed that 40% of the Cucurbita pepo cotyledons in an area of approximately 0.8 ha were infected. The disease resulted in a severe loss in seedling production. Samples of C. pepo with water-soaked leaf spots were collected and prepared for pathogen analysis. Symptomatic cotyledon tissue was surface disinfested in 75% ethanol for 30 sec, then rinsed three times in sterilized water. Bacteria were released in sterile water in Petri dish for 2 min by cutting symptomatic tissue into small sections and stirring the plant tissue mixture fully. The diffusate was streaked onto plates containing nutrient agar (NA) and plates were incubated at 28℃ for 2 days. Three representative isolates were purified eventually from each of the plates. Colonies on NA were small, round and with smooth margins. All bacterial isolates characterized as gram-negative, white to cream color, and pink pigment was formed on the plates over long-term culture. The isolates were positive for catalase, Voges-Proskauer, potato rot, methyl red, acetoin production, nitrate utilization and citrate utilization, and acid production from maltose, glucose, melezitose, sucrose, D-arabinose, D-trehalose, cellobiose, lactose, raffinose, mannitol, D-sorbitol, melibiose and xylitol. KOH production was demonstrated according to strand formation within the potassium hydroxide test (Suslow et al. 1982). Isolates were negative for oxidase, arginine dihydrolase, phenylalanine deaminase, gelatinase, esculine, indole production and H2S production. Total genomic DNA was extracted from isolate XHL2002230201 with TIANamp Bacteria DNA Kit (TIANGEN). Universal primers 27F and 1492R (Monciardini et al. 2002) were used in PCR to amplify a 1,307-bp DNA fragment of the 16S rRNA region for molecular identification. Furthermore, four additional housekeeping genes (gyrB, atpD, rho, and rpoS) were selected and amplified using specially designed primers. The amplification products of 16S rRNA were sequenced and submitted to GenBank under accession number (MT568607.1). Sequence analysis showed 99% similarity to Erwinia persicina strains B57 (LM651373.1) and B64 (CI789_17875) by BLAST search in GenBank database (Gálvez et al. 2015; Cho et al. 2019). A phylogenetic tree was constructed, and the taxonomic position of strain XHL2002230201 was determined from the multilocus sequence analysis (MLSA) on 16S rRNA and other four housekeeping genes with E. persicina and not with other closely related Erwinia species. Pathogenicity tests and re-isolation and re-identification of the bacteria were performed to confirm the isolate and fulfill the Koch' postulates. The strain XHL2002230201 suspensions (108 CFU ml-1) were spray inoculated onto fifteen Cucurbita pepo seedlings with two true leaves, and the same number of control plants were inoculated with water. Experiments were repeated three times. All inoculated plants were kept in a moist chamber placed in a greenhouse at 28℃. Initial symptoms were observed on leaves of inoculated plants at 5 days post-inoculation, whereas no symptoms appeared on the plants inoculated with sterile distilled water. Based on morphological and biochemical characteristics, phylogenetic analysis, and Koch's postulates, the bacterial isolates were identified as E. persicina. To our knowledge, this is the first report of E. persicina causing leaf spot disease on Cucurbita pepo in China.

Нова знахідка Vaucheria aversa Hass. (Ochrophyta, Xanthophyceae) в Україні

Vaucheria aversa (Xanthophyta) was recorded for the first time in Ukraine in Sula River, Hydrological Reserve «Artopolot», Poltava Region. It was found in benthos in spring (May 2020) in silty-sandy soil in shallow water. The material was collected and processed according to a common methodology. Sterile samples before the appearance of the gametengians were kept in natural water in petri dishes in well-lit places. This method of «coarse culture», in most cases, allowed to get gametangia within two weeks. The species identification was done with fertile filaments only. 4% formaldehyde solution was used for material fixation. Taxonomic identification of samples was done using a comparative and morphological methods, which includes analysis of morphological variability and verification of the consistency of the studied material with the diagnosis. Thalli of V. aversa are direct, branched, bisexual, 80–90 μm wide. Antheridia are cylindrical, tubular shape, pressed to the filament or slightly raised above it, 119–130 × 41–43 μm. Oogonia erect, sessile, ovoid to subspherical, sometimes placed in pairs, with a curved beak at the front, 190–230 × 140–163 μm. According to morphological characteristics this species is similar to another one from section Tubligerae Walz – V. fontinalis (Linnaeus) T.A. Christensen. Their distinctive and common features are as follows. Filaments of V. fontinalis are narrower (up to 75 μm) than V. aversa (up to 131 μm). Both species are characterized by oogonia grouped together in a row. Antheridia present in quantity 1 or 2 on both sides of oogonia. But the species are very different in size and shape of oogonia: in V. aversa they are sessile, located one at a time or less often two, extended near the base, sharply narrowed at the apex. The beak is directed straight or obliquely up, bent to the side of the oogonia body. In V. fontinalis oogonia are placed in one row, most often in the amount of 1-6, the beak tapers gradually. Anteridia are cylindrical, on short pedicel. V. aversa grew as a part of polyspecies complex of green algae together with representatives of such genera as Cladophora Kützing, Spirogyra Link and Mougeotia C. Agardh. V. aversa is widely distributed in continental water bodies of Europe, Asia and North America, Australia and New Zealand, but is firstly recorded in Ukraine.

Microbial Range Expansions on Liquid Substrates

Despite the importance that fluid flow plays in transporting and organizing populations, few laboratory systems exist to systematically investigate the impact of advection on their spatial evolutionary dynamics. To address this problem, we study the morphology and genetic spatial structure of microbial colonies growing on the surface of a nutrient-laden fluid $10^4$ to $10^5$ times more viscous than water in Petri dishes, the extreme but finite viscosity inhibits undesired thermal convection and allows populations to effectively live at the air-liquid interface due to capillary forces. We discover that S. cerevisiae (baker's yeast) growing on a viscous liquid behave like "active matter": they metabolically generate fluid flows many times larger than their unperturbed colony expansion speed, and that flow, in return, can dramatically impact their colony morphology and spatial population genetics. We show that yeast cells generate fluid flows by consuming surrounding nutrients and decreasing the local substrate density, leading to misaligned fluid pressure and density contours, which ultimately generates vorticity via a thresholdless baroclinic instability. Numerical simulations demonstrate that an intense vortex ring is produced below the colony's edge and quantitatively predict the observed flow. As the viscosity of the substrate is lowered and the self-induced flow intensifies, we observe three distinct morphologies: at the highest viscosity,compact circular colonies similar to those grown on hard agar plates except with a stretched regime of exponential expansion, intermediate viscosities give rise to compact colonies with "fingers" that are ripped away to break into smaller cell clusters, and at the lowest viscosity, the expanding colony breaks up into many genetically-diverse, mutually repelling, island-like fragments of yeast colonies.

Fertilizing ability of gametes at different post-activation times and the sperm-oocyte ratio in the artificial reproduction of pikeperchSander lucioperca

The time period during which oocyte and spermatozoa retain their fertilizing ability after contacting with water was evaluated in pikeperch (Sander lucioperca). In addition, success of in vitro fertilization was examined regarding to the sperm-to-oocyte ratio (SOR). In the first trial, oocytes were placed in Petri dishes containing 5 ml of the hatchery water, to which freshly collected and pooled sperm were added to each sample at 0, 15, 30, 60, 90, 120, 150 and 180 s post oocyte activation. The oocytes retained their fertility for at least 30 s after contacting with water. The second trial tested the maximum time period during which spermatozoa retained fertilizability after contacting with water. Milt (50 μl) was collected from each male and added to 5 ml of water in Petri dishes. Thereafter, oocytes were added at 0, 5, 15, 30, 60 and 75 s post-sperm activation. Delays exceeding 10 s affected negatively the fertilization success. The third trial examined the optimum SOR; in which was found that 100 × 103 spermatozoa per oocyte were the minimum ratio to ensure fertilization rates above 70%. Overall, the data clarified some biological interactions of gametes in the artificial propagation of pikeperch.

Comparison of germination abilities of Centaurea sp. under in vivo and in vitro conditions

In this study, in vivo and in vitro germination of endemic and under-threat Centaurea fenzlii and Centaurea derderifolia species were investigated. In in vivo germination, seeds were spread with forceps over the drying papers moisturized with distilled water in petri dishes. Then, petri dishes were closed and taken for germination in a climate chamber at 25°C and 16 hours light/8 hours dark photoperiods. In in vitro germination, following the sterilization period, seeds were cultured in MS, B5, SH and WH growth medium with 6 seeds in each in a climate chamber at 25°C under 16 hours light/8 hours dark photoperiod. Present findings revealed high germination rates for C. fenzlii and C. derderifolia seeds in WH growth medium.

Differential susceptibility of Hyalomma excavatum adults and nymphs to the entomopathogens Metarhizium anisopliae ARSEF 4556 and Steinernema carpocapsae

ABSTRACTThis study investigated the virulence of the entomopathogenic fungus, Metarhizium anisopliae strain ARSEF 4556, and the entomopathogenic nematode Steinernema carpocapsae against adult and nymphal stages of the tick Hyalomma anatolicum excavatum. The fungus was tested at three different concentrations, 106, 107, and 108 conidia ml−1. Ticks were exposed to 4000 IJs of S. carpocapsae in 0.5 ml distilled water in Petri dishes lined with 2 layers of moist filter paper. Adult ticks were not susceptible to M. anisopliae, whereas the nymphs were highly susceptible. Nymph mortality was dose dependent with all ticks being killed at the highest dose 96 hours post-inoculation. In contrast, S. carpocapsae was much more effective against engorged adults than unfed adults or nymphs. Tick susceptibility was not influenced by gender. The mean mortalities of the unfed adult males, females, and nymphs were 30% ± 9.2%, 40% ± 7.5%, and 36% ± 4.7%, respectively. Nymphal mortality was 36% and there was a significant difference between nematode treatment and control group (P < 0.05).

A simple method for diagnostic of Phytophthora infestans (Mont.) de Bary from potato agricultural fields of potato

A correct detection and appropriate identification of causal pathogens associated with crop plants or seeds are considered to be the most important issue in designing the proper management plans for plant diseases. This study was designed to detect Phytophthora infestans inoculum from potato grown soil. A high detection rate of P.infestans was obtained from the naturally infested soil of potato fields. Naturally soils were firstly moistened in a plastic pots and then pre-incubated at ±18°C for 3 days, baiting with potato tuber slice for 24, 48, and 72 h. The baits were then thoroughly washed, flooded with 10–15 ml of distilled water in Petri-dishes and incubated under continuous darkness in chamber ±18ºC. Sporangia started to emerge from the margins of potato tuber slice. They were easily observed under the stereomicroscope. Pure culture of the fungus was obtained by isolating from baited tubers on a Rye Agar medium. This is the first report of recovery of P. infestans from naturally infested potato growing soils using susceptible potato tuber (K. Bahar) as bait in India. All isolates were determined to be A2 mating type.

Repeating Crumley et al (1950)

Koch asked me in a comment to replicate an experiment done in 1950 by Helen A Crumley et al demonstrating Tobacco seed growth in deuterium oxide (D2O). The experiment is rather simple (and the figure from the paper is shown below) as Crumley placed 100 seeds in differing amounts of D2O (double distilled water, 33%, 66%, and 99.8% D2O) and analyzed the growth. Influence of ordinary water, 33%, 66%, and 99% deuterium oxide on tobacco seed germination. Counts made at daily intervals for 39 days. (From Crumley, Fig 3) So here I am planning the experiment. I will change some things from their experiment. First they placed the seeds on wet cloths (paper towels?), and I will submerge the seeds in the water amounts they used. They also used a variety of plant species (tobacco, clover, radish, Kentucky bluegrass), where I will just use tobacco seeds (but I will try two different species). Finally they talk about their results in terms of percent germination, but it isn’t clear from the paper if they mean number of plants that have exhibited germination, or if they are referring to some amount of growth exhibited by each plant. I will look for both possibilities and report the results as I find them. In a preliminary experiment I will submerge the plants in water in petri dishes and seal it with parafilm. I will be looking into a more airtight solution as time goes on. I also won’t do 100 seeds but probably on the order of 33 seeds per sample. And in the future I will look into figuring out a way to measure the seed growth. Original Crumley paper can be found here.

A simple method for detection of Phytophthora nicotianae from soybean soil

Abstract A high detection rate of Phytophthora nicotianae was obtained from the naturally infested soil of soybean fields. Air-dried soils were firstly moistened in a flask and then pre-incubated at 25 °C for 1-4 weeks before flooding with distilled water and baiting with soybean leaf disks for 6, 12, and 24 h. The baits were then thoroughly washed, flooded with 10-15 ml of distilled water in Petri-dishes and incubated under continuous fluorescent light for 72 h. Sporangia started to emerge from the margins of leaf disks. They were easily observed under the stereomicroscope. Pure culture of the fungus was obtained by spreading zoospore suspension on a 1.5% water-agar containing anti-bacterial antibiotics. This is the first report of recovery of P. nicotianae from naturally infested soybean soils using sensitive leaf disks of soybean (Williams cultivar) as bait in Iran. All isolates were determined to be A2 mating type.

Efeitos alelopáticos do exsudado radicular de &lt;I&gt;Amaranthus cruentus&lt;/I&gt; L. sobre sementes de &lt;I&gt;Glycine max&lt;/I&gt; (L.) Merril, &lt;I&gt;Zea mays&lt;/I&gt; L. e &lt;I&gt;Bidens pilosa&lt;/I&gt; L. DOI:10.5007/2178-4574.2011n40p13

Allelopathic effects of root exudates of Amaranthus cruentusL. on seed of Glycine max (L.) Merril, Zea mays L. and Bidens pilosa L.) The Amaranthus cruentus L. specie has great nutritional value because of its high protein content, and contain important minerals for alimentation. Consequently, the cultive of this cereal is extremely important, the consortium system is a way to guarantee the introduction of this species in the region cultivation. The objective was to know the allelopathic effects in consortium simulation of amaranth-soybean and amaranth-corn, besides the interaction between the invader beggarticks and the amaranth. For the exudate preparation, 50 amaranth seeds were germinated under moistened filter paper with 5mL of destilated water in Petri dishes, that were stored in germination chambers at 25ºC, with photoperiod of 12 hours of light. After five days, the seedings were removed and the same substrate was used to germinate the species studied. Also, the contrary was made, in which the germinated seeds of the agricultural species gave place to the amaranth seeds. The experimental design was entirely casualized, and the data was submitted to variance analysis and the means compared by the Tukey test (p&lt;0,05). None of the agricultural species showed sensitive to the amaranth effects, in the same conditions however, the beggarticks raised increased the length of the shoot. Only the corn exudate offers negative effects on the amaranth initial development. Therefore those consortium simulations must be field analyzed to prove such effects.

Tetranychus urticae (Acari: Tetranychidae) on Gerbera jamesonii Bolus and Hook (Asteraceae)

Gerbera (Gerbera jamesonii Bolus and Hook,) is an ornamental Asteraceae of great commercial value, and pests can affect adversely its cultivation. More than 20 species of arthropods cause economic damage on gerbera, among them the two spotted mite, Tetranychus urticae Koch, 1836 (Acari: Tetranychidae), considered a key pest for this and other ornamental plants. In this work, some life-cycle aspects of T. urticae on gerbera, considered important for the knowledge of its population dynamics and for pest management programs, were studied. Mites were reared on 3-cm diameter arenas of gerbera leaf discs maintained on distilled water in Petri dishes, under laboratory conditions of 25 masculineC, 70 +/- 10% RU and 14-hour photophase, with only one egg left per arena, in a total of 262 arenas. Egg viability was 96.5% and 97.1% for unmated and mated females, respectively. Unmated females originated larvae which lived for 3.2 days and the stages of protonymph and deutonymph, 1.9 and 1.6 days, respectively; those from mated females lived 3.5 days and for protonymphs and deutonymphs, 2.0 and 1.6 days, respectively. Except for the duration of one generation (T), with similar values, 18.6 and 19.7 days, respectively for unmated and mated females, the net reproductive rate of increase (R masculine), the innate capacity to increase in number (r m) and the finite rate of growth (lambda) were different for mated and unmated females, respectively 11.5 and 24.6 for R0; 0.12 and 0.17 for r m and 1.13 and 1.19 for lambda.

First Report of Foliar Infection of Starflower by Phytophthora ramorum.

In March 2002, Phytophthora ramorum S. Werres & A.W.A.M. de Cock was isolated from pacific or western starflower (Trientalis latifolia Hook.), an herbaceous perennial of the Primulaceae family, at Castro Canyon in Big Sur, Monterey County, California. Affected leaves had numerous necrotic lesions >5 mm in diameter surrounded by a yellow halo, and the lesions coalesced with time. Isolates were identified as P. ramorum by the large chlamydospores, caduceus, semipapillate sporangia, and sequences of the internal transcribed spacer (ITS) region of the rDNA (1,2). The same symptoms were observed on starflower in a second location at the Soquel Demonstration Forest, Santa Cruz County. Although P. ramorum was not isolated from symptomatic leaves on the plants in Santa Cruz County, the ITS region of the pathogen was amplified and sequenced using P. ramorum-specific primers. Both sites were mixed forests of coast redwood (Sequoia sempervirens), bay laurel (Umbellularia californica), and tanoak (Lithocarpus densiflorus), which are confirmed hosts of P. ramorum. To test for pathogenicity to starflower, asymptomatic plants were carefully excavated from the two forest locations, replanted in 15-cm paper cups in the original forest soil, and the foliage was inoculated with zoospores of P. ramorum isolate Pr-52, an isolate used in previous inoculations. The zoospores were produced by placing agar disks (1 cm in diameter) from the margin of 8- to 14-day-old colonies growing on V8 juice agar into 20 to 30 ml of sterile deionized water in petri dishes. After 2 days incubation at 20°C in the dark, zoospore release was induced by placing dishes at 4°C for 20 min and then to room temperature for 45 to 60 min. Three hundred μl of the zoospore suspension (approximately 2 × 104 zoospores/ml) was poured into 500-μl modified microcentrifuge tubes in which tips of leaves of starflower were submerged. Control leaves were dipped in sterile deionized water. Plants were placed in a humid-chamber consisting of moist paper towels placed on the tray and covered with a clear-plastic lid that was sprayed with sterile water. The chambers were maintained at 20 to 24°C in the laboratory. Two or three leaves were inoculated, and one leaf was left as the control on each of seven or eight plants in two separate trials. In both trials, water-soaked lesions were observed on the leaves 12 h after inoculation with P. ramorum. At 8 or 11 days after inoculation, necrotic lesions were present on all inoculated leaves starting from the leaf tips. Lesions averaged 29 mm (range 13 to 39 mm) and 45 mm (range 31 to 56 mm) in length in the respective trials. Some lesions covered entire leaves. P. ramorum was reisolated on Phytophthora-selective agar medium (1) from the lesions in both trials. Control leaves had no lesions, and P. ramorum was not reisolated. Infection of starflower and other understory species appears to occur under infested tree hosts such as bay laurel, which is known as a source of inoculum for P. ramorum. To our knowledge, this is the first report of an herbaceous host for P. ramorum and the first report of the disease on the Primulaceae. Previously, only woody hosts were known. Starflower is unlikely to play a major role in the natural spread of the disease, but the pathogen may be spread via movement of plants through the horticultural industry. Furthermore, Trientalis spp. in Europe where P. ramorum is present may also be potential hosts.

On the existence and stability of liquid water on the surface of mars today.

The recent discovery of high concentrations of hydrogen just below the surface of Mars' polar regions by Mars Odyssey has enlivened the debate about past or present life on Mars. The prevailing assumption prior to the discovery was that the liquid water essential for its existence is absent. That assumption was based largely on the calculation of heat and mass transfer coefficients or theoretical climate models. This research uses an experimental approach to determine the feasibility of liquid water under martian conditions, setting the stage for a more empirical approach to the question of life on Mars. Experiments were conducted in three parts: Liquid water's existence was confirmed by droplets observed under martian conditions in part 1; the evolution of frost melting on the surface of various rocks under martian conditions was observed in part 2; and the evaporation rate of water in Petri dishes under Mars-like conditions was determined and compared with the theoretical predictions of various investigators in part 3. The results led to the conclusion that liquid water can be stable for extended periods of time on the martian surface under present-day conditions.

Physical and chemical factors associated with the reduction or delay of seed germination and seedling emergence of bull thistle, Cirsium vulgare (Savi) Ten. under leaf litter1

Leaf litter can affect seed germination and seedling emergence by altering both the physical and chemical environment. A series of experiments were conducted to investigate litter effects on germination and emergence of Cirsium vulgare seeds and seedlings. Thin (2 layers) and thick (5 layers) of leaf litter of Acer saccharum, Quercus alba, and Juglans nigra reduced and delayed seedling emergence of bull thistle (C. vulgare) in two greenhouse experiments. Leaves of J. nigra were less effective than those of the other two species. In one experiment, removal of the litter after seedling emergence had ceased was followed by a second flush of emergence, but no further emergence occurred in the non-litter control. However, in a second experiment no further emergence was recorded after litter removal. Artificial litter, chemical-free cotton paper cut in leaf shapes, reduced and delayed seedling emergence but to a lesser extent than natural leaf litter. Germination in distilled water in Petri dishes was not affected within a pH range of 3-10. However, black walnut leaf extract reduced seed germination, and extracts of all three species slowed germination rates. There was no effect of leaf extracts on rates or percent emergence from soil in the greenhouse. We concluded that leaf litter can have an important role in determining patterns of seedling emergence of C. vulgare, possibly because of physical effects on the dormancy status of its seeds.

Anti-senescence Activity of Chemicals Applied to Kentucky Bluegrass

This study was conducted to determine the potential anti-senescence activity of certain chemicals by monitoring changes in gross. CO2 exchange with senescence of excised leaves of Kentucky bluegrass (Poa pratensis L.). One day following foliar applications of benzyladenine (BA), triadimefon, and propiconazole, with and without chelated Fe (8% Fe phosphate citrate), Kentucky bluegrass leaves were excised, floated on distilled water in petri dishes, and placed in a darkened growth chamber. Gross CO2 exchange rates (CER) were recorded 1, 4, 7, and 10 days after excision (DAE). Foliar applications of Fe, BA, triadimefon, or propiconazole applied alone induced an anti-senescence response. Combinations of Fe with the chemicals delayed excision-induced leaf senescence, but no significant increase in anti-senescence activity was obtained from the Fe and chemical combinations as compared to the materials applied alone. Chemical names used: N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); 1-(4-Chlorophenoxy)-3,3-dimethyl-1(1H-1,2,4-triazol-1yl)-2-butanone (triadimefon);1-[[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole (propiconazole).

Endogenous Sugar Levels and Their Effects on Root Formation and Petiole Yellowing of Detached Mustard Cotyledons

AbstractDetached cotyledons of Sinapis alba rooted readily in water in petri dishes in the light. The addition of (6 × 10−2M) galactose, mannose or 2‐deoxy‐D‐glucose to the culture medium proved toxic to cotyledon growth. Of the other sugars tested that were not toxic, sucrose was the most inhibitory to root formation and increased petiolar yellowing to the greatest extent. Glucose was more inhibitory than fructose which in turn increased petiolar yellowing more than methyl‐D‐glucose.Sucrose, glucose, or fructose at 6 × 10−2M in the culture medium gave rise to very substantial increases in the cotyledon petiole of reducing sugar and starch with smaller increases in sucrose. Methyl‐D‐glucose had much less effect on internal sugar levels. It was found that the higher the internal level of glucose the more rapid the rate and final extent of petiolar yellowing. In general, the degree of petiolar yellowing was inversely related to the ability of the cotyledon to root. Methyl‐D‐glucose differed from the other sugars in that it delayed and reduced root formation but had very little effect on petiolar yellowing.