H Thomas, J Archer, R Marggraf Turley. 2009. Evolution, physiology and phytochemistry of the psychotoxic arable mimic weed darnel (Lolium temulentum L). Progress in Botany (in press)

Abstract:
Darnel (Lolium temulentum L.), the subject of this review, is botanically and culturally significant because of its evolutionary origin as a mimic weed of cereals and its reputation as a source of potent psychoactive toxins. Evidence from molecular phylogeny, palaeontology and archaeology allows the source and spread of darnel in time and space to be reconstructed. Contemporaneously with the progenitors of wheat and barley, at the dawn of agriculture in the Fertile Crescent region of Mesopotamia and the Eastern Mediterranean, darnel was derived from a perennial ancestor that was subject to the same human-mediated selection pressures as the earliest cereal species, and shares with them the domestication traits of annuality, self-fertility, high harvest index and non-shattering grains. Because it combines the characteristics of cereals with those of forage species of the Lolium-Festuca complex, L temulentum is a useful experimental subject for the study of the physiology of temperate grasses. In particular it has been a model for research on the control of flowering by daylength, as well as investigations of vegetative development, resource allocation and responses to abiotic stresses. Recent studies of the chemical basis for darnel’s noxious reputation reveals a complex picture in which endophytic fungi, nematodes and pathogenic bacteria separately or in combination account for the toxicity of the darnel grain. The relationship, and frequent historical conflation, of darnel and ergot poisoning is considered in detail. Finally some examples are given of literary allusions to L temulentum, from Aristophanes to Shakespeare.

H Thomas. 2009. Leaf senescence and autumn leaf coloration. McGraw Hill 2010 Yearbook of Science and Technology (in press)

Abstract:
Autumn is visible from space.  Chlorophyll disappears during fall and leaves become yellow or red.  Color changes are the signs of complex biochemistry genetically programmed within senescing leaf cells.  If the process of chlorophyll removal goes wrong, as it does in certain mutants, leaves become vulnerable to damage by light.  Transformations in leaf color are indicators of biochemical defences against harmful photosensitivity, preserving the physiological integrity of senescing tissues necessary for the controlled recycling and redistribution of nitrogen and other essential nutrients.  There is also evidence that the distinctive colors of autumnal foliage signal the fitness status of the plant to potentially predatory insects.

H Thomas, H Ougham, LAJ Mur, S Jansson. 2009. Senescence and programmed cell death. In: Biochemistry and Molecular Biology of Plants. 2nd edition (eds B Buchanan, W Gruissem, R Jones). NY: Wiley (in press)

LAJ Mur, S Aubry, M Mondhe, A Kingston-Smith, J Gallagher, E Timms-Taravella, C James, I Papp, S Hörtensteiner, H Thomas, H Ougham. 2010. Accumulation of chlorophyll catabolites photosensitizes the hypersensitive response elicited by Pseudomonas syringae in Arabidopsis. New Phytologist (under review)

• The staygreen gene (SGR) encodes a chloroplast targeted protein which promotes chlorophyll degradation via disruption of light harvesting complexes (LHC). 
• Over-expression of SGR in Arabidopsis (SGR-OX) in a Col-0 background caused spontaneous necrotic flecking.  To relate this to the hypersensitive response (HR), Col-0, SGR-OX and RNAi SGR (SGRi) lines were challenged with Pseudomonas syringae pv. tomato (Pst) avrRpm1.  Increased and decreased SGR expression respectively accelerated and suppressed the kinetics of HR-cell death.  In Col-0, SGR transcript increased at 6 h following inoculation (hai) when tissue electrolyte leakage indicated the initiation of cell death. 
• Excitation of the chlorophyll catabolite pheophorbide (Pheide) leads to the formation of toxic singlet oxygen (¹O₂). Pheide was first detected at 6 hai with Pst avrRpm1 and was linked with ¹O₂ generation and correlated with reduced Pheide a oxygenase (PaO) protein levels.  Photosynthetic efficiency (F_v/F_m), quantum yield of electron transfer at photosystem II (fPSII), and photochemical quenching (qP), decreased at 6 hai in Col-0 but not in SGRi.  Disruption of photosynthetic electron flow will cause light-dependent H₂O₂ generation at 6 hai. 
• We conclude that disruption of LHC, possibly influenced by SGR, and absence of PaO, produces phototoxic chlorophyll catabolites and oxidative stress leading to the HR.

H Thomas, C Wyn Jones. 2009. Recapitulation, heterochrony and the war on the chord in jazz. In: Music and Evolutionary Thought (eds I Cross, B Zon). Cambridge University Press (in press)