Physiological Responses to Drought of Lolium perenne L.: Measurement of, and Genetic Variation in, Water Potential, Solute Potential, Elasticity and Cell Hydration

Thomas, H. 1987. Physiological responses to drought of Loliumperenne L.: Measurement of, and genetic variation in, waterpotential, solute potential, elasticity and cell hydration.—J.exp. Bot. 38: 115–125. Clonally-replicated genotypes of Loiium perenne L. were grownin a controlled environment. Leaf water potential (_w) osmoticpotential (_s), turgor potential (_p = _w – _s), elasticity(E), leaf hydration (g water per g dry matter, H) and numberof green leaves per tiller (N_GL) were measured before and duringa 42 d drought treatment. A simplified method of estimating E (at _w < 1?0 MPa) usingonly six measurements was developed to permit a measurementrate of 8 leaves per hour. Measurement errors in all characterswere 3% or less. During drought, _w and _s (at _w = 0?5 MPa) decreased significantly,_p and E increased significantly, and H decreased slightly. Plantsize during drought was negatively correlated with _s, and ^Hand positively correlated with _p, osmotic adjustment, E andN_GL. Measurements made on the genotypes before draughting didnot give a reliable indication of their physiological conditionafter adaptation to drought. Genetically controlled variation (‘broad sense heritability’)of drought-adapted plants for E was 15%, _w 23%, _s, 34%, _p, 35%,H 34% and N_GL 64%. The possibilities for, and effectivenessof, divergent selection of genotypes with high and low expressionof the characters are discussed. Key words: Water relations, Lolium, genetic variation     

The use of experimental palaeontology in reproducing the effects of diagenetic flattening on graptolites

The detailed effects of diagenetic flattening on the graptolitc rhabdosomc have been investigated experimentally. The initial procedure, to test the effects of flattening on cylinders constructed from a variety of semi-brittle to plastic materials when compressed in a plaster 'matrix', demonstrates that a degree of rigidity is necessary to prevent lateral spread on diagenetic compression, even when lateral confining pressures are present. A second experiment demonstrates conclusively that the effects of flattening on the thecal style of Dicellograptus complanatus proposed by Briggs & Williams (1981; Lethaia 14) can be simulated. A model of an aseptate diplograptid produced a median depression when compressed but no preservational 'median septum', which is considered to be produced in several diplograptid taxa. It is shown that some diplograptids spread laterally along a median line when flattened in scalariform orientation although this has not yet been achieved experimentally owing to the high degree of compression required. □ Graptolithina, diagenesis, flattening,     

Blepharisma seculum, sp. nov., a Member of the Subgenus (Compactum)

SYNOPSIS. Blepharisma seculum sp. nov. is described as a small-sized blepharisma with a compact, spheroid macronucleus and a distinct curvature of the body anteriorly. A comparison of this form with other species of the genus Blepharisma subgenus ( Compactum ) is given.     

An association of carbohydrates with particles of arabis mosaic virus retained within Xiphinema diversicaudatum

Sections through the odontophore of Xiphinema diversicaudatum showed two types of staining for carbohydrates using the periodic acid - thiosemicarbazide -silver proteinate (PA-TSC-SP) reaction. The first consisted of thin, localised, intensely-stained patches on the lining of the food canal of all the specimens examined. The second type, found only in nematodes exposed to AMV-infected plants, revealed cloud-like areas of carbohydrate - containing material associated with the stained patches on the lining of the food canal. By staining alternate sections with uranyl acetate/lead citrate, these carbohydrate clouds were shown to contain virus particles. Although the cloud material could have originated from either the plant or the nematode, sections through a pellet of partially purified virus particles prepared from plants did not stain for carbohydrate. The possible role of carbohydrate in virus retention and transmission is discussed.