Optimal Local Estimates of Visual Motion in a Natural Environment.

Many organisms use visual signals to estimate motion, and these estimates typically are biased. Here, we ask whether these biases may reflect physical rather than biological limitations. Using a camera-gyroscope system, we sample the joint distribution of images and rotational motions in a natural environment, and from this distribution we construct the optimal estimator of velocity based on local image intensities.

Sparse but specific temporal coding by spikes in an insect sensory-motor ocellar pathway.

We investigate coding in a locust brain neuron, DNI, which transforms graded synaptic input from ocellar L-neurons into axonal spikes that travel to excite particular thoracic flight neurons. Ocellar neurons are naturally stimulated by fluctuations in light collected from a wide field of view, for example when the visual horizon moves up and down. We used two types of stimuli: fluctuating light from a light-emitting diode (LED), and a visual horizon displayed on an electrostatic monitor.

Growth characteristics and ion contents of non-selected and salt-selected callus lines of highbush blueberry (Vacdnium corymbosum) cultivars Blue Crop and Denise Blue.

Non-selected and sodium chloride selected callus lines of Vacdnium corymbosum L.cv Blue Crop and cv. Denise Blue were grown on media supplemented with 0-100 mM NaCl.

Longitudinal and transverse profiles of K and Cl concentration in 'low-' and 'high-salt' barley roots.

The concentrations of K and Cl in meristematic and differentiated cells of barley (Hordeum Vulgare. L. ev.

Maintenance of low cl concentrations in mesophyll cells of leaf blades of barley seedlings exposed to salt stress.

The concentrations of vacuolar Na(+) and Cl(-) in the epidermal and mesophyll cells of the leaf blade and sheath of Hordeum vulgare seedlings (cv California Mariout and Clipper) were measured by means of quantitative electron probe x-ray microanalysis. A preferential accumulation of Cl(-) in vacuoles of epidermal cells in both blade and sheath and a low level in mesophyll cells of the blade were evident in plants grown in full strength Johnson solution. The concentration of Cl(-) in the mesophyll cells of the blade remained at a low level after exposure to 50 or 100 millimolar NaCl for 1 day or to 50 millimolar for 4 days, while at the same time the concentration of Cl(-) in the epidermis and mesophyll of the sheath showed a dramatic increase.

Quantitative Estimates of Phosphorus Concentrations within Lupinus luteus Leaflets by Means of Electron Probe X-ray Microanalysis.

Phosphorus contents of epidermal vacuoles and mesophyll cells of Lupinus lutens leaflets were measured by electron probe x-ray microanalysis of fully hydrated, bulk frozen samples. Quantitation was achieved using standard solutions containing colloidal graphite to simulate cell contents and the derived nonlinear relationship between peak over background ratio and concentration improved the accuracy of the analytical procedure. Inorganic phosphate contents of mesophyll cells were shown to be highly dependent on phosphate nutrition.

The effect of abscisic acid on sugar levels in seedlings of Phaseolus vulgaris L. cv. redland pioneer.

Abscisic acid (ABA) caused an increase in total-sugar and a 3-fold increase in reducing-sugar content in the roots of intact bean seedlings. The level of reducing sugars was also increased in the stem but total sugar levels remained unaffected by ABA. ABA also increased reducing-sugar content of the root in seedlings with cotyledons removed but in this case the reducing- and total-sugar contents of the leaf were reduced.

Stimulation of volume flow and ion flux by abscisic acid in excised root systems of Phaseolus vulgaris L. cv. Redland Pioneer.

Abscisic acid (ABA) caused a 7-8-fold increase in volume flow in excised bean root systems and this was coupled with an increase in (42)K, (36)Cl and (24)Na flux into the xylem. The transport of (42)K and (36)Cl increased by a factor larger than the stimulation of volume flow, resulting in an increase in the concentration of those ions in the xylem exudate. Carbonyclcyanide-m-chlorophenyl hydrazone, on the other hand, eliminated ABA-stimulated (42)K transport and caused a further inhibition of (42)K flux, thus providing additional support for the proposition that ABA stimulation may involve an energised process of ion transport.

Rapid action of abscisic acid on photosynthesis and stomatal resistance.

(RS)-Abscisic acid, a natural plant hormone, has been found to inhibit photosynthesis in both detached and attached primary wheat leaves. The action occurs rapidly and is accompanied by large increases in stomatal diffusive resistance.