Morphology and Anatomy of the Haustorium of the Root Hemiparasite Olax phyllanthi (Olacaceae), with Special Reference to the Haustorial Interface

Gross morphology and internal structure of haustoria of Olaxphyllanthi are described in parasitism with a range of hosts,including roots of woody and herbaceous dicotyledons and certainmonocotyledons, and occasional instances of autoparasitism andhaustorial formation on monocotyledon rhizomes. Successful penetrationto xylem occurs on virtually all hosts across broad diameters,ages and anatomies of host root, but anatomical impedimentsto haustorial establishment and penetration are recorded forcertain host taxa. Each haustorium is a comparatively simpleand ephemeral structure. Its developing sucker (endophytic regionof the haustorium) spreads laterally around the surface of thehost xylem, yet never completely encircles the host stele. Damageto hosts is minimal and secondary thickening (of hosts) continueson the side of a host root opposite to a haustorium. The haustorialsucker lacks phloem and its interface with host xylem is comprisedalmost entirely (more than 98.7%) of parenchyma. The few terminatingtracheids at an interface lie in very close proximity to oroccasionally directly against exposed xylem vessels, but lumento lumen continuity between tracheary elements of the partnersis not achieved. Three dimensional reconstructions based onserial transverse sectioning indicate that well defined filesof tracheids connect back from an interface to the core of graniferoustracheary elements in the external body of the haustorium, andthence to the xylem of the parent parasite root. The findingsare discussed in relation to existing studies on haustorialanatomy. Root parasite, Olacaceae, haustorial anatomy, host specificity     

Growth, Resource Allocation and Haustorial Biology of the Root Hemiparasite Olax phyllanthi (Olacaceae)

Olax phyllanthi was found to parasitize a wide range of taxain the native habitat in coastal heath, South-West Australia.All major life and growth forms were regularly exploited, includingmost woody dicotyledons (except members of the Myrtaceae), afew monocotyledons and cohabiting root hemiparasites. Initiationof haustoria occurred mostly in autumn (southern hemisphere),with some senescing the following summer, and others survivinguntil replaced by a new generation of haustoria the followingautumn. Seedlings increased in dry matter and contents of N,P, K, Mg and Ca during preparasitic development, but did notsurvive beyond 6 months if failing to establish haustoria ona suitable host. Plant dry matter, mineral content and haustorialnumber increased exponentially during subsequent parasitic development.Mean shoot:root d. wt ratios of 1st to 3rd-year plants lay withinthe range 1.2–1.4. Root systems were laterally extensiveand restricted to the top 40 cm of rooting substrate. Mean totalroot lengths of 2nd- and 3rd-year plants were 7.1m (n = 5) and60.9 m (n = 5), respectively. Haustoria comprised 0.7–3.5%of plant d. wt, with a mean of 7.9 haustoria (n = 10, 2nd- and3rd-year plants) per metre of root length. Comparisons of mineralconcentrations in dry matter of O. phyllanthi and of a rangeof commonly parasitized hosts showed the parasite to be muchricher on average than its hosts in K, P, and to a lesser extentin N, but not noticeably different in Mg and Ca. Olax, root hemiparasite, mineral nutrition, haustoria, resource allocation     

Effect of Light on Cell Division in Developing Callus Cultures

Explants removed from the Jerusalem artichoke tuber and exposedto white light in the presence of 2, 4-D, when cultured in liquidmedia, exhibit much smaller dividing populations than similartissue not exposed to light. White light, which is effectiveonly in the presence of 2, 4-D and during the period beforethe onset of DNA replication, is required only in small amountsto promote a maximum effect, although inhibition of cell divisionwas never complete Light does not interfere with the timingof the cell cycle but exerts an influence on the size of thedividing population. The results presented are consistent witha hypothesis which postulates that a substance or substancesessential for cell division is reduced in amount by exposureto light. The extent of the first synchronous division is probablytherefore determined by the supply of this substance.     

Sclerotic plates or circumorbital bones in early jawed fishes?

Abstract: Circumorbital dermal bones are found in most groups of early vertebrates that have dermal bony plates on the head. Taxonomic distribution of dermal sclerotic plates on the eye itself is less clear, partly because the eyeball is rarely preserved and sometimes because sclerotic bones have been misinterpreted as circumorbital bones. Based on the examination of climatiid Climatius plus mesacanthid, cheiracanthid and acanthodid acanthodiform acanthodians, we conclude that most, if not all, acanthodiforms and climatiids had sclerotic rings. Presence and number of these elements should be included as a character in phylogenetic analyses of early jawed vertebrates.     

Combining contemporary ecology and palaeolimnology to understand shallow lake ecosystem change

1. Palaeolimnology and contemporary ecology are complementary disciplines but are rarely combined. By reviewing the literature and using a case study, we show how linking the timescales of these approaches affords a powerful means of understanding ecological change in shallow lakes. 2. Recently, palaeolimnology has largely been pre‐occupied with developing transfer functions which use surface sediment‐lake environment datasets to reconstruct a single environmental variable. Such models ignore complex controls over biological structure and can be prone to considerable error in prediction. Furthermore, by reducing species assemblage data to a series of numbers, transfer functions neglect valuable ecological information on species’ seasonality, habitat structure and food web interactions. These elements can be readily extracted from palaeolimnological data with the interpretive assistance of contemporary experiments and surveys. For example, for one shallow lake, we show how it is possible to infer long‐term seasonality change from plant macrofossil and fossil diatom data with the assistance of seasonal datasets on macrophyte and algal dynamics. 3. On the other hand, theories on shallow lake functioning have generally been developed from short‐term (<1–15 years) studies as opposed to palaeo‐data that cover the actual timescales (decades–centuries) of shallow lake response to stressors such as eutrophication and climate change. Palaeolimnological techniques can track long‐term dynamics in lakes whilst smoothing out short‐term variability and thus provide a unique and important means of not only developing ecological theories, but of testing them. 4. By combining contemporary ecology and palaeolimnology, it should be possible to gain a fuller understanding of changing ecological patterns and processes in shallow lakes on multiple timescales.