The Extraction and Assay of 1-Kestose:Sucrose Fructosyl Transferase from Leaves of Wheat

Isolating the enzymes responsible for fructan synthesis in plants has been hampered by unsuitable assays used during purification. It is believed that there are two enzymes necessary for fructan synthesis in higher plants, one initiating synthesis utilizing sucrose as donor and the other elaborating the polymer using fructan oligomers as donor. In this paper, a rapid quantitative assay is described to measure the latter fructosyl transfer. The activity was absent from leaves that were not synthesizing fructan. Activity in crude extracts showed a hyperbolic dependence upon sucrose concentration. Activity against 1-kestose showed a pronounced optimum, suggesting that self-transfer also occurred.     

Conditioning of Parsley (Petroselinum crispum L.) Suspension Cells Increases Elicitor-Induced Incorporation of Cell Wall Phenolics

The elicitor-induced incorporation of phenylpropanoid derivatives into the cell wall and the secretion of soluble coumarin derivatives (phytoalexins) by parsley (Petroselinum crispum L.) suspension cultures can be potentiated by pretreatment of the cultures with 2,6-dichloroisonicotinic acid or derivatives of salicylic acid. To investigate this phenomenon further, the cell walls and an extracellular soluble polymer were isolated from control cells or cells treated with an elicitor from Phytophthora megasperma f. sp. glycinea. After alkaline hydrolysis, both fractions from elicited cells showed a greatly increased content of 4-coumaric, ferulic, and 4-hydroxybenzoic acid, as well as 4-hydroxybenzaldehyde and vanillin. Two minor peaks were identified as tyrosol and methoxytyrosol. The pretreatment effect is most pronounced at a low elicitor concentration. Its specificity was elaborated for coumarin secretion. When the parsley suspension cultures were preincubated for 1 d with 2,6-dichloroisonicotinic, 4- or 5-chlorosalicylic, or 3,5- dichlorosalicylic acid, the cells exhibited a greatly increased elicitor response. Pretreatment with isonicotinic, salicylic, acetylsalicylic, or 2,6-dihydroxybenzoic acid was less efficient in enhancing the response, and some other isomers were inactive. This increase in elicitor response was also observed for the above-mentioned monomeric phenolics, which were liberated from cell walls upon alkaline hydrolysis and for "lignin-like" cell wall polymers determined by the thioglycolic acid method. It was shown for 5-chlorosalicylic acid that conditioning most likely improves the signal transduction leading to the activation of genes encoding phenylalanine ammonia lyase and 4-coumarate: coenzyme A ligase. The conditioning thus sensitizes the parsley suspension cells to respond to lower elicitor concentrations. If a similar mechanism were to apply to whole plants treated with 2,6-dichloroisonicotinic acid, a known inducer of systemic acquired resistance, one can hypothesize that fungal pathogens might be recognized more readily and effectively.     

Water Relation Alterations Observed during Hypersensitive Reaction Induced by Bacteria

Upon exposure to pathogenic bacteria, resistant and nonhost plants undergo a hypersensitive reaction (HR) that is expressed as rapid plant cell death. If sufficient concentrations of these bacteria are inoculated to such plant tissue, then that portion of the tissue rapidly collapses and becomes necrotic. As the tissue collapses the water relations of inoculated tissues become markedly disturbed. We measured a decline in the relative water content (RWC) in the leaf-like cotyledons of cotton (Gossypium hirsutum cv Immune 216) within the first 4 h (cut at 1 h) after inoculation with Pseudomonas syringae pv tabaci. However, the decrease in RWC was not caused by a decrease in initial fresh weight but by increased water uptake during incubation in water. By 8 h after inoculation, cotyledons still on the plant had lost turgidity, and their area decreased. K+ efflux was also observed concurrently with the decrease in RWC, providing a reason for the loss of turgidity in the tissue. These observations suggest that cells lose turgor and change shape from cylinders with large intercellular spaces to those of a more tabular shape. During this change cell walls come closer together, providing an avenue for increased water uptake through capillary action. The stomatal diffusive resistance of intact cotyledons increased; hence, water loss through stomata is not the cause of the observed wilting and RWC decline. An increase in K+ per dry weight suggests that phloem loading or movement may also be impaired during bacterially induced HR.     

'Concealed' antigens: expanding the range of immunological targets

For many parasites, the interaction between the immunogenicity of the parasite and the immunological response of the host is a dynamic equilibrium that allows both to survive, albeit often with severe consequences for the host. Vaccines, if intended as a means of parasite control, are unlikely to be generally successful if they do no more than mimic an immunological equilibrium that would be reached after natural exposure to the parasites. The situation must be tipped in favour of the host. It has been difficult to find ways around this impasse. One approach has been receiving practical attention over recent years, an approach that Peter Willadsen, Craig Eisemann and Ross Tellam have called vaccination against 'concealed' antigens.     

Evolution and development of the vertebrate skull: The role of pattern formation

The vertebrate skull is anatomically complex and phylogenetically diverse; it presents unique opportunities to examine the role of developmental processes in evolutionary change. Previous studies have largely examined phylogenetic trends in tissue composition or change in the timing of developmental events (heterochrony). Additional important insights may be gained if skull evolution and development are viewed from the standpoint of pattern formation. Contemporary models of pattern formation offer the possibility of linking developmental mechanisms of cranial morphogenesis from the level of genes, through cell biology, to adult form.     

Chitinase: a novel target for blocking parasite transmission?

In many species of blood-sucking arthropod, the internal tissues are covered by chitinous material that may hinder parasite invasion. To circumvent this potential barrier, therefore, parasites have developed mechanisms that involve the enzyme chitinase. In this review, Mohammed Shohobuddin and David C. Kaslow examine the relationship between chitinase and parasite transmission.     

Female control of paternity

Of the two components of sexual selection, female choice is much less obvious than male-male competition, and hence has always been considered to be of secondary importance. However, recent field observations and new theory have brought about a radical change of emphasis. It now appears that although a female's choice of who fathers her offspring often occurs in a subtle manner, it may be widespread and take place through a variety of behavioural and physiological mechanisms, including the manipulation of male behaviour and the selection of sperm within the female reproductive tract.