Se Morris

Auxin Dynamics after Decapitation Are Not Correlated with the Initial Growth of Axillary Buds

One of the first and most enduring roles identified for the plant hormone auxin is the mediation of apical dominance. Many reports have claimed that reduced stem indole-3-acetic acid (IAA) levels and/or reduced basipetal IAA transport directly or indirectly initiate bud growth in decapitated plants. We have tested whether auxin inhibits the initial stage of bud release, or subsequent stages, in garden pea (Pisum sativum) by providing a rigorous examination of the dynamics of auxin level, auxin transport, and axillary bud growth. We demonstrate that after decapitation, initial bud growth occurs prior to changes in IAA level or transport in surrounding stem tissue and is not prevented by an acropetal supply of exogenous auxin. We also show that auxin transport inhibitors cause a similar auxin depletion as decapitation, but do not stimulate bud growth within our experimental time-frame. These results indicate that decapitation may trigger initial bud growth via an auxin-independent mechanism. We propose that auxin operates after this initial stage, mediating apical dominance via autoregulation of buds that are already in transition toward sustained growth.

Rapid increases in cytokinin concentration in lateral buds of chickpea (Cicer arietinum L) during release of apical dominance

Abstract. We examined the role of cytokinins (CKs) in release of apical dominance in lateral buds of chickpea (Cicer arietinum L.). Shoot decapitation or application of CKs (benzyladenine, zeatin or dihydrozeatin) stimulated rapid bud growth. Time-lapse video recording revealed growth initiation within 2 h of application of 200 pmol benzyladenine or within 3 h of decapitation. Endogenous CK content in buds changed little in the first 2 h after shoot decapitation, but significantly increased by 6 h, somewhat later than the initiation of bud growth. The main elevated CK was zeatin riboside, whose content per bud increased 7-fold by 6 h and 25-fold by 24 h. Lesser changes were found in amounts of zeatin and isopentenyl adenine CKs. We have yet to distinguish whether these CKs are imported from the roots via the xylem stream or are synthesised in situ in the buds, but CKs may be part of an endogenous signal involved in lateral bud growth stimulation following shoot decapitation. To our knowledge, this is the first detailed report of CK levels in buds themselves during release of apical dominance.

Feedback regulation of xylem cytokinin content is conserved in pea and Arabidopsis

Increased-branching mutants of garden pea (Pisum sativum; ramosus [rms]) and Arabidopsis (Arabidopsis thaliana; more axillary branches) were used to investigate control of cytokinin export from roots in relation to shoot branching. In particular, we tested the hypothesis that regulation of xylem sap cytokinin is dependent on a long-distance feedback signal moving from shoot to root. With the exception of rms2, branching mutants from both species had greatly reduced amounts of the major cytokinins zeatin riboside, zeatin, and isopentenyl adenosine in xylem sap compared with wild-type plants. Reciprocally grafted mutant and wild-type Arabidopsis plants gave similar results to those observed previously in pea, with xylem sap cytokinin down-regulated in all graft combinations possessing branched shoots, regardless of root genotype. This long-distance feedback mechanism thus appears to be conserved between pea and Arabidopsis. Experiments with grafted pea plants bearing two shoots of the same or different genotype revealed that regulation of root cytokinin export is probably mediated by an inhibitory signal. Moreover, the signaling mechanism appears independent of the number of growing axillary shoots because a suppressed axillary meristem mutation that prevents axillary meristem development at most nodes did not abolish long-distance regulation of root cytokinin export in rms4 plants. Based on double mutant and grafting experiments, we conclude that RMS2 is essential for long-distance feedback regulation of cytokinin export from roots. Finally, the startling disconnection between cytokinin content of xylem sap and shoot tissues of various rms mutants indicates that shoots possess powerful homeostatic mechanisms for regulation of cytokinin levels.

Students’ experiences of supervision in academic and industry settings: results of an Australian study

The joint supervision of Research Higher Degree (RHD) students by an industry and university supervisor is likely to increase in forthcoming years with a rise in the number of university–industry collaborations. Research students may become involved in these collaborative arrangements for a variety of reasons and may launch into their RHD without considering how they will serve two masters, and how this complex relationship will affect their RHD experience. Moreover, little research has been conducted to assess the impact of these arrangements on current RHD students’ experiences. The experiences of students with academic and industry supervisors were, therefore, explored in a survey of confirmed RHD students at an Australian research‐intensive university. This paper investigates whether RHD students conducting research in traditional academic settings have a different experience to students working on industry‐related projects in industry settings, specifically in regards to supervision and institutional access and engagement.

Problem-based learning in clinical education: the next generation

Bridges, McGrath and Whitehill, from The University of Hong Kong, are the editors of this eighth volume in the Springer ‘Innovation and Change in Professional Education’ series. The book contains articles from practitioners and researchers in the problembased learning (PBL) field and contains contributions from research conducted in Australia, Canada, Germany, Hong Kong, Japan, Sweden and the USA. The research reported is from traditional PBL areas such as biology, dentistry, medicine, pharmacology and speech/language pathology; it also includes several interdisciplinary approaches to PBL such as Howe and Schnabel’s dentistry/architecture collaboration in Chapter 8. The editors assert that this book provides research-driven new methodologies to enable teachers and practitioners to support student learning and PBL program development. By providing empirical research that reflects studies on ‘how to do PBL’, the editors claim they have positioned the book away from the stance of other publications, which feature articles on ‘why PBL’. Taking this slant, the chapters in the book have been organised into three research themes: student learning outcomes in PBL, new technologies for PBL curriculum design and exploring ‘inside’ the PBL process. I was fascinated by Jin’s study, which takes ‘a sociocultural and critical perspective in examining the roles of silence within the interactional dynamics of PBL tutorials’ (p. 173). In many contexts, silence can be taken to mean inaction or misunderstanding. However, many communication theorists believe that silence is actually an aspect of effective communication (Grice, 1989). Jin’s work provides an in-depth qualitative analysis on students’ silence in PBL tutorials in English-as-a-second-language settings, with the specific research question ‘What are the roles of silence in spoken English interaction in PBL tutorials?’ Jin reports that, from the students’ perspective, silence in PBL tutorials can be categorised into five themes:

Publishing Short-Cuts and Their Potential Career Impact

One essential element to a successful research career is your ability to produce quality, peer-reviewed publications. In the process of learning how to do research and write publications based on your findings, most doctoral students and early career researchers will be faced with decisions that may impact on their burgeoning careers. You may come across many freeways and roadblocks on your research journey and the temptation to take short-cuts to ‘get that paper published’ is attractive to some. To illustrate the importance of basic ethical considerations when publishing, this article explores the story of Cindy and will raise your awareness of publishing short-cuts and their potential impact on your career. This article will also provide you with suggested places to seek guidance to develop your ethical responsibility as a researcher.