A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

Abscisic Acid may Mediate the Rapid Thermal Acclimatization of Photosynthesis in Wheat

Exposing cold-grown (6°C) plants of a winter cultivar (Avalon)and a spring cultivar (Highbury) of wheat to a single warm night(18 h and 25°C) significantly increased the photosyntheticrate and stomatal conductance of fully-expanded leaves withoutaffecting the calculated, substomatal CO₂ pressure. Prior to the warm-night treatment net photosynthesis and stomatalconductance in Avalon were very small at high leaf temperaturesduring measurement (25–30°C). Such high temperatureinhibitions were not observed in Highbury. Exposure to the warm-nighttreatment alleviated these inhibitions in Avalon. Consequently,the temperature response of photosynthesis was similar in theleaves of the treated cultivars and showed a relatively broadoptimum. The application of exogenous abscisic acid in the transpirationstream to the leaves of treated plants caused a reduction ofsimilar proportions in the steady-state rate of photosynthesisand in stomatal conductance and essentially reversed the effectsof the warm-night treatment in a manner which depended on thecultivar. The endogenous abscisic acid content of leaves declinedby 50% during the warm-night treatment. In conjunction, thesedata suggest that changes in the content of abscisic acid inthe leaf may regulate the observed temperature acclimatizationof apparent photosynthesis in the fully-expanded leaves of cold-grownwheat. Key words: Abscisic acid, photosynthesis, stomatal conductance, temperature, acclimatizatio     

The Uptake and Transport of 14C in Cells of Conocephalum conicum L. in Light

Dissolved inorganic ¹⁴carbon, fed to a small portion of thetissue of Conocephalun conicum, travelled along the tissuesfrom cell to cell at rates of about 2.0 to 1.7 µm 5^–1,which is of the same order of magnitude as streaming rates inthese cells. Trans-cellular transport can take place againsta pressure gradient, but pressure gradients of 200 kPa or morein either direction reduced the trans-cellular transport significantlywithout reducing streaming rate and are, therefore, thoughtto have induced ‘valving’ effects at the plasmodesmata.Ammonium ion reduced or inhibited transport without reducingstreaming rates and is, therefore, thought to have inhibitedan active component in the plasmodesmata. Thus the results obtainedfrom tandem cells of Nitella can be transferred to tissues. Key words: Conocephalum, transport, plasmodesmata     

Calcium Antagonist TMB-8 Inhibits Cell Wall Formation and Growth in Pea

The effects on auxin-stimulated growth and cell wall formationof 8-(N, N-diethylamino)-octyl-3, 4, 5-trimethoxybenzoate.HCI(TMB-8), an intracellular Ca²⁺ antagonist, were investigatedin abraded stem segments from aetiolated seedlings of Pisumsativum L. cv. Alaska. Incubation of segments at pH 6.0 with200 mmol m^–3 TMB-8 resulted in a 50% inhibition of auxin-stimulatedgrowth. Added Ca²⁺ did not restore normal auxin-stimulated growth,presumably because of its well-known stiffening effect on thecell wall. In segments incubated at a pH (7–2) which preventedelongation, auxin promoted the incorporation of [³H]glucoseinto the cell wall relative to total uptake of label. TMB-8abolished about 60% of the total incorporation of label intocell walls in the presence of auxin, but was not effective inthe absence of auxin. Exogenous CaCl₂ reversed the inhibitoryeffect of TMB-8 on relative cell wall incorporation in a parabolicmanner, with a 50% reversal at about 100 mmol m^–3 andcomplete reversal at 1.0 mol m^–3 Ca²⁺. Other ions tested(Mg²⁺, Mn²⁺, Cu²⁺, Zn²⁺) were without substantial effect atconcentrations of 0.5 mol m^–3. Both apparent uptake ofCa²⁺ and consequent reversal of TMB-8 inhibition of cell wallincorporation were blocked by the Ca²⁺ channel blockers verapamiland La³⁺. The data provide further evidence that auxin-stimulatedgrowth is dependent upon continued cell wall incorporation,and suggest that a Ca²⁺ messenger system may be involved inthe promotory actions of auxin on cell wall synthesis and long-termgrowth. Key words: Auxin, calcium, cell wall synthesis     

Action of Sorghum Proteinase on the Protein Bodies of Sorghum Starchy Endosperm

Protein bodies isolated from the starchy endosperm of ungerminatedsorghum exhibited some autolytic activity but seemed incapableof significant self-hydrolysis. Enzyme assay, transmission electronmicroscopy, sodium dodecyl sulphate—polyacrylamide gelelectrophoresis and amino acid analysis revealed that a proteinaseextract from germinated sorghum could degrade the protein bodiesin a manner resembling that which takes place in vivo. The proteinbodies were degraded mainly from the periphery. Glutelin (matrixprotein) was first hydrolysed, followed by the prolamin proteinbody protein. Proteinase extracts from both the germ and endospermof germinated sorghum were capable of degrading the proteinbodies. This finding is consistent with the concept that theproteinase is synthesized in the germ and then secreted intothe starchy endosperm during germination. Key words: Sorghum bicolor, protein body degradation, proteinase.     

Potential Increase in Photosynthetic Efficiency from the Redistribution of Solar Radiation in a Crop

The efficiency of the conversion of photosynthetically activeradiation by C₃ plants falls off with increasing intensity.Hypothesis: an increase in the productivity of direct solarenergy will be achieved if, by redistribution, it is interceptedat a more uniform and lower intensity by a greater proportionof the leaf area of a crop. A model is developed which usesestimates of the proportions of clear and overcast conditionsfrom site records of solar radiation to calculate the resultantphotosynthetic productivity. The amounts of diffuse light anddirect light are estimated for clear conditions. The model predictsthat redistributing direct solar radiation over twice the leafarea at half the intensity would give an increase of 22% inannual productivity. The model gives reasonable values for theproductivity reductions reported for two shading regimes. Tomato plants were grown for 21 d in three cabinets under regimesthat differed from each other only in the distribution of PARenergy over the daily photoperiod: (a) 103 W m^–2 for halfthe photoperiod followed by 13 W m^–2, (b) 13 W m^–2followed by 103 W m^–2 and (c) 58 W m^–2 for the wholephotoperiod. The dry matter increase of plants under the uniformregime was 33% greater than the average of those in the twoasymmetric regimes. It is suggested that, in protected cultivation, screens of partiallyreflective material could be used to redistribute solar radiationfrom leaves exposed to high intensities on to shaded leavesand so raise the photosynthetic efficiency. Assuming an absorptionof direct light by the screens of 0.10, the increase in productivityis estimated to be 17%. Key words: Photosynthesis, C₃, canopy, solar energy, solar redistribution, light interception, partial reflection, growth cabinet, glasshouse, tomato     

Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain

Griffis, K. & Chapman, D. J. 1990 10 15: Modeling Cretaceous-Tertiary boundary events with extant photosynthetic plankton: effects of impact-related acid rain. Lethaia , Vol. 23, pp. 379–383. OSIO. ISSN 0024–1164.
An acid rain phenomenon has previously been proposed as one of the consequences of a bolide impact contributing to the extinctions at the Cretaceous-Tertiary boundary. This hypothesis has been tested by observing the growth responses of four organisms under simulated acid rain conditions. Two of these phytoplankton, Ditylum (a diatom) and Thoracosphaera (a dinoflagellate). are genera that persisted through the boundary, while the other two, Coccolithus (a coccolithophorid) and Gonyaulax (a dinoflagellate), are post-boundary genera. Ditylum and Coccolithus survive the acid rain simulation. but with the loss of scales in Coccolithus . The two dinoflagellate are sensitive to acid rain simulations. with Gonyaulax unable to survive beyond seven days. The results indicate that acid rain may have contributed to the Cretaceous-Tertiary boundary extinctions. but that the changes resulting from the acid rain were not as severe as postulated or were short-lived and quickly dissipated. ▭ Acid rain, coccolithophorids. Cretaceous/Tertiary extinctions, diatons, dinoflagellates, phytoplankton .     

Development of Amblyospora campbelli (Microsporida: Amblyosporidae) in the Mosquito Culiseta incidens (Thomson)

The complete life cycle of Amblyospora campbelli (Kellen and Wills, 1962) (Microsporida: Amblyosporidae) requires a two-host system involving the mosquito host, Culiseta incidens (Thomson), and an obligatory intermediate copepod host. The parasite has dimorphic spore development producing meiospores (haploid condition) and binucleated spores (diploid condition), either as an exclusive infection or simultaneously (within females only). This is the 1st known report of concurrent spore development within an adult mosquito host, and, therefore, shows the Amblyospora campbelli system to be uniquely different from other Amblyospora spp. cycles previously described. The significance of dimorphic spore development is discussed. In females, diplokaryotic meronts may invade oenocytes, causing a benign-type of infection. A blood-meal is required to initiate sporulation of the binucleate spore. The binucleate spore contains the sporoplasm involved in transovarial transmission. A 2nd sporulation sequence, primarily in adipose tissue, may involve both males and females. In this sequence, repeated merogonic division greatly increased the density of diplokaryotic meronts and generally involved most of the body of the host. Production of meiospores, unlike that for the binucleate spore, appeared to be spontaneous (i.e. no obligatory blood meal). Survivorship of male and female larval mosquitoes was nearly equal. Adult females spread the parasite in three ways: transovarial, transovum, and by meiospore deposition.     

CHEMICAL COMMUNICATION IN INSECT COMMUNITIES: A GUIDE TO INSECT PHEROMONES WITH SPECIAL EMPHASIS ON SOCIAL INSECTS

• 1 Chemical communication plays an important part in the lives of insects, and particularly in lives of those that live in groups or social organizations.
• 2 Chemicals which are used in communication in the general sense are called semiochemicals, and there are a number of subdivisions recognized under this title.
• 3 Pheromones are a category of semiochemicals which are used for communication between individuals of the same species.
• 4 Pheromones are in turn subdivided into primer and releaser pheromones. The former produce a relatively long-lasting physiological change in the receiver, and the latter stimulate the receiver to some immediate behavioural response.
• 5 Far more is known about releaser pheromones at present because they are easier to study.
• 6 Nine categories of releaser pheromone are recognized here, used by both social and non-social insects.
• 7 Sex pheromones are widely used to bring the sexes together for mating, and they have been extensively studied in Lepidoptera.
• 8 Invitation pheromones, encouraging the species to feed or oviposit at an explored site, are not extensively known.
• 9 Aggregation pheromones are designed to bring individuals together into groups which may be temporary in sub-social insects, or permanent in social insects.
• 10 Dispersal or spacing pheromones are used by other species to reduce intraspecific competition for scarce resources.
• 11 Alarm pheromones are a broad and sometimes unclearly defined group which communicate alarm or attack, chiefly in colonial species.
• 12 Trail pheromones, applied to a surface by an individual, to be followed by another, are confined to Hymenoptera, Isoptera and a few Lepidoptera as far as is known.
• 13 Territorial and home range pheromones may be widely distributed, but as yet few of them have been recognized.
• 14 Surface and funeral pheromones are even less well known. Surface pheromones may play a large part in species or colony recognition.
• 15 We can expect the number and complexity of pheromones to be much greater in social insects, a part of the subject which until now has received relatively less attention.
• 16 As our understanding of the subject grows we may expect other categories to be added to this list.