Periods in Earth history characterized by extensive organic carbon deposition, so-called oceanic anoxic events (OAEs), are the subject of considerable scrutiny. Insight into the extent of anoxic conditions in the water column has been provided by the reported occurrence of derivatives of isorenieratene, a carotenoid found only in green sulphur bacteria and thus indicative of photic-zone euxinia (i.e. a water column containing free H 2 S), in North Atlantic deep-sea sediments deposited during the Cenomanian-Turonian boundary OAE2 (Bonarelli Event). In this study, we have used the distributions of chlorophyll and bacteriochlorophyll degradation products, maleimides (1-H-pyrrole-2,5-diones) and high molecular weight porphyrins, to examine further the Cenomanian-Turonian boundary OAE2 as well as other OAEs of the early Toarcian (Posidonienschiefer Event) and early Aptian (Selli Event). In particular, methyl isobutyl (Me,i-Bu) maleimide, on structural grounds, appears to be diagnostic of green sulphur bacteria. This compound occurs in five of seven examined marls that record the early Toarcian OAE (Marche-Umbria, Italy), further expanding the geographical range of Toarcian sediments where evidence for photic-zone euxinic conditions has been found. Me,i-Bu maleimide occurs in three of six black shales spanning the Livello Selli (Marche-Umbria, Italy), the type locality for the Aptian OAE1a, providing the first evidence for photic-zone euxinic conditions during this event. With respect to the Cenomanian-Turonian OAE, maleimide evidence for photic-zone euxinic conditions was found in all the North Atlantic sites investigated, including those characterized by relatively organic-lean sediments, several Tethyan sites and one site off western Australia. These data indicate that euxinic conditions were common in the water column during Mesozoic oceanic anoxic events.

SummaryThe gibberellin (GA) 20-oxidase (CmGA20ox1) from immature pumpkin seed produces predominantly inactive tricarboxylic acid GAs. We expressed CmGA20ox1 under the control of the CaMV 35S promoter in Solanum dulcamara to assess the usefulness of this gene for reducing GA content in transgenic plants. All transgenic plants obtained were semi-dwarfs with smaller, deep-green leaves and highly pigmented stems compared to the wild-type. Such transformants¯owered earlier than the wild-type plants and produced more fruit and more seeds per fruit. The transgene was ef®ciently expressed, producing high levels of CmGA20ox1 transcript and protein. Furthermore, the concentration of GA 1 was reduced in leaves of the transformants to approximately 20% or less of that in the wild-type and to about 40% or less in stems. The concentrations of other 13-hydroxylated GAs were also reduced, except for the tricarboxylic acid, GA 17 , which accumulated in the transformants due to 13-hydroxylation of GA 25 . By contrast, the concentrations of non-13-hydroxylated GAs, GA 4 and GA 34 , were not consistently reduced, indicating that the effect of expressing the pumpkin gene may not be predictable. Transcript abundance for a native GA 20-oxidase gene was higher in the leaves and stems of S. dulcamara transformed with the pumpkin gene than in wild-type, re¯ecting the feedback control of 20-oxidase gene expression that serves as a homeostatic mechanism for GAs.