S236 Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S235–S242

The compartmentalization of the two types of CK species in long-range translocation implies the action of a selective transportsystem of CK. There are several lines of evidence that somemembers of the purine permease and equilibrated nucleosidetransporter families can mediate the translocation of CKnucleobase and nucleoside, respectively. We will outline recentprogress in the regulation of CK biosynthesis and translocation.

doi:10.1016/j.cbpa.2007.01.538

P3.4Systemic regulation of cytokinin transport and metabolism

in branching mutants of Arabidopsis

C. Turnbull, H. Wang, N. Young, (Imperial College London)

Cytokinins participate inmany developmental processes, but theirrole as long-distance signals remains unclear. Previous work onpea ramosus (rms) mutants showed that branching shootphenotypes result in down-regulated xylem cytokinin exportfrom roots, strongly indicating the existence of a long-distancefeedback signal (FS) transported from shoot to root that regulatesxylem cytokinin. Here, we show that the FS operates similarly inorthologousmaxmutants of Arabidopsis. Xylem cytokinin levelsof all max mutants were severely depleted, and highly branchedmax2 mutant shoots down-regulated xylem cytokinin exportfrom grafted wild-type rootstocks. We are also generating acytokinin ‘budget’ for shoots and roots, by quantifying cytokininimport, export, synthesis and degradation. To complement thexylem data, cytokinins were measured in phloem exudates ofArabidopsis which revealed opposite patterns – increased levelsof several cytokinins in max mutants. To shed light on regulationof cytokinin metabolism, crosses were made between maxmutants and lines carrying either promoter–GUS fusions fordifferent cytokinin oxidase (CKX) genes, or constitutively over-expressing CKX (CKXox) to generate plants globally depleted incytokinin. We show that CKX expression is differentiallyregulated in max backgrounds in a tissue- and gene-specificmanner, and that max CKXox double mutant phenotypes areessentially additive. On this basis we propose that at least part ofthe FS function acts directly or indirectly on CKX expression, andthat low xylem cytokinin and low whole-plant cytokinin levelshave very different developmental consequences.

doi:10.1016/j.cbpa.2007.01.539

P3.5Soil: Plant signalling networks and the control of water useand plant productivity

B. Davies, I. Dodd, (Lancaster University); A. Belimov, V.Safranova, (ARRIAM)

Soil drying and other stresses commonly limit plant productiv-ity through an impact on both gas exchange and canopy

development. This limitation occurs via the influence ofchemical and hydraulic signals moving from the root to theshoot. We review the identity of signals limiting leafconductance and leaf growth and consider prospects formanipulation of signalling, with special reference to the impactof changes in sap pH, modified fluxes of abscisic acid (ABA)and of the ethylene precursor ACC (1-aminocyclopropane-carboxylic acid). ABA delivery to the sites of action in theshoots may be influenced by both synthesis and degradation ofthe hormone and its compartmentalization in the leaf as afunction of pH variations in different cellular compartments.ACC signalling, which can have an important influence on leafgrowth of plants in drying soil as well as in plants subjected to arange of other stresses, can be altered if we use genotypes withaltered ACC status. In addition, certain bacteria occurring on theroot surface containing the enzyme ACC deaminase can beshown to modify the sensitivity of root and leaf growth to soildrying, apparently by influencing ethylene signalling. Thepaper highlights the importance of soil to plant signalling androot to shoot signalling in modifying the plant's response toenvironmental stress and shows how endogenous signalingcascades may be modified to agricultural advantage.

doi:10.1016/j.cbpa.2007.01.540

P3.6Computer simulations of auxin transport: From technique

to discipline

E. Kramer, (Simon's Rock College)

Computer models have recently been applied to a wide range oftopics in plant growth and development. The talk will begin witha relatively nontechnical introduction to the parts of a computermodel, then move on to discuss some common techniques andtheir limitations.Wewill conclude with a brief survey of the stateof the field, with reference to recent work in wood grain patternformation, phyllotaxis, and root gravitropism.

doi:10.1016/j.cbpa.2007.01.541

P3.7Do brassinosteroids undergo long-distance transport inplants?

G. Symons, C. Jager, J. Ross, J. Reid, (University of Tasmania)

It is widely accepted that brassinosteroids (BRs) are importantregulators of plant growth, and are involved in processes asdiverse as cell elongation, stress responses and fruit ripening.Significant progress has been made in our understanding of BRbiosynthesis, perception and signal transduction. However, incomparison with other plant hormones, especially auxin (IAA),there has been very little focus on the transport of BRs and itspotential role in regulating endogenous BR levels. Several