Phototactic Orientation by the Marine Dinoflagellate Gyrodinium dorsum Kofoid.

SYNOPSIS. The phototactic orientation of the dinoflagellate Gyrodinium dorsum was examined using photomicrographic, cinematographic, and closed-circuit television technics. Particular emphasis was placed on examining the movements and possible roles of the flagella during orientation. The data suggest that the longitudinal flagellum is primarily responsible for phototactic orientation, while the lateral flagellum is involved in forward propulsion and cell rotation. A possible receptor mechanism is proposed by which light direction sensing is accomplished.     

Flagellar Activity of the Colony Members of Volvox aureus Ehrbg. during Light Stimulation*

SYNOPSIS. The flagellar behavior of the colonial Volvox aureus Ehrbg. was examined by placing 1.01 μ polystyrene particles in suspension with Volvox, and recording particle movement photomicrographically. When directional light stimulation was given, flagellar activity ceased in the anterior cells of the stimulated side. Such responses create unequal driving forces on the 2 sides of the colony, so that the colony turns toward the stimulated side. Dose response studies indicated a photoresponse gradient from front to rear in the colony, anterior cells being most responsive. The mechanism of gradient formation has yet to be determined.     

Characterization of simple sequence repeat markers derived in silico from Brassica rapa bacterial artificial chromosome sequences and their application in Brassica napus

A collaborative Brassica rapa genome sequencing project is currently in progress to aid the identification of agronomically important traits in Brassica species. As an initial stage, the ends of over 110 000 bacterial artificial chromosome clones were sequenced and mined for simple sequence repeats (SSRs). We present the characterization of 40 of these SSRs and their application in Brassica napus. The markers were screened against six Brassica species and Arabidopsis, and demonstrated reliable amplification, genome specificity, cross‐amplification and significant polymorphism. These SSRs will be useful for genetic analysis of Brassica germplasm.     

Integrated Analysis of Growth and Light Interception in Winter Lettuce I. Analytical Methods and Environmental Influences

Measurements on protected lettuce crops have been used to assesstwo new procedures for analysing the rate of dry-matter productionin crops or plant stands. ‘Integrated growth analysis’brings together two traditionally distinct treatments of growthanalysis by resolving crop growth rate (CGR) into stand biomassand the relative growth rate of individual plants. ‘Lightconversion analysis’ resolves CGR as the product of incidentlight receipt, efficiency of light interception by leaves, andefficiency of utilization of intercepted light in dry-matterproduction. Observations from winter lettuce trials were used to fit statisticalprogressions to the primary data and to obtain instantaneously-derivedestimates of all of the analytical components. Trials in threesuccessive years yielded similar patterns in time for the componentsof each of the analytical procedures, giving confidence in theirvalidity. In light conversion analysis, changes in CGR were due mainlyto incident light, which varied threefold, and to interceptingefficiency, which rose from a low initial value to full interceptionat hearting; the efficiency of utilization of light varied lessdramatically, with the value at hearting being about twice thatat planting. In integrated growth analysis a 30 per cent increasein CGR due to CO₂ enrichment, and a 5 per cent increase dueto lower daily minimum temperature, could each be coherentlyresolved into variations in biomass, leaf area ratio and netassimilation rate. In different ways it is concluded that both of these approachescan assist in analysing growth and in identifying the optionsavailable for improving crop yield. Lactuca sativa L., lettuce, growth analysis, crop growth rate, relative growth rate, light interception, light utilization     

Cereal aphids on maize in southern England

In 1978, 1979 and 1980, counts were made of the numbers of cereal aphids on a maize crop near Fordingbridge, Hampshire, England. Maize plants were selected away from the edge of the crop and the number, morph, species and feeding site of the aphids were recorded. Metopolophium dirhodum and Rhopalosiphum padi were found at densities that exceeded those found on small-grain cereals and grasses at the same time of the year. Sitobion avenae and Macrosiphum euphorbiae were found at relatively low densities, and Rhopalosiphum maidis and Metopolophium festucae were observed rarely. Unlike other species, the numbers of R. padi continued to increase throughout the summer and reached a peak in September/October; at this time of the year, R. padi constituted over 98% of the aphids found on maize. M. dirhodum and S. avenae were found mostly on the leaves whereas R. padi appeared to favour the cob until populations became too large to be supported. If the area of maize grown in the UK increases, the crop will probably play an important role in the life cycle of cereal aphids (especially R. padi ). It is suggested that further work should be carried out on the pest status of aphids on maize and on the role that maize may play in the ecology of cereal pests.     

Photosynthesis in Stands of Green Peppers. An Application of Empirical and Mechanistic Models to Controlled-environment Data

The photosynthetic response of stands of green peppers to lightand CO² is examined by means of various mathematical models.Several single leaf response equations are considered, fromthe simple and ubiquitous rectangular hyperbola, to more sophisticatedforms incorporating photorespiration and the oxygen effect.By making the usual assumptions about stand structure and lightpenetration, mechanistic crop response equations arc derivedfor each of the different leaf response equations. First, asa purely empirical approach, the leaf response equations areapplied directly to crop data, and it is concluded that therectangular hyperbola with a term for dark respiration [eqn(2)] gives an adequate summary of crop response to light andCO₂. Second, four mechanistic equations of crop response areapplied to the data, and, although the results are equivocal,it is suggested that the simpler crop equations [eqns (15) and(17)] are satisfactory at the present time, and it is not yetpossible to detect the results of photorespiration and the oxygeneffect directly in the crop data.     

Modelling Light Absorption and Canopy Net Photosynthesis of Glasshouse Row Crops and Application to Cucumber

A model of light absorption and photosynthesis applicable toglasshouse row crops is constructed and applied to cucumber.Light absorption is calculated using a method suggested fordiscontinuous canopies; photosynthesis is modelled with a non-rectangularhyperbola. The predictions of this model are compared with experimentaldata in the preceding paper. Here the model is used to simulateresponses to light and CO₂ concentration and especially to examinethe effects of varying the parameters of the crop that can becontrolled by the grower. These include the number of plantsin each row, the number and width of the rows, the gap betweenrows, and the height of the crop. For example, it is shown that,for high values of crop net photosynthesis, the number of rowsis more important at high light than at low light, whereas cropheight is more important at low light than at high light. Theimplications of these and other findings are discussed. Key words: Cucumis sativus L., glasshouse crops, cucumber, model, light absorption, photosynthesis, CO₂, row crops, simulation