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Texbot 7: Transport in Cuticles and Periderms

Texbot 7 is a collection of papers previously published in the Journal of Experimental Botany as a special focus section on transport in cuticles and periderms.

When conquering dry land some 4X10 8 years ago, plants had to solve two major problems: establishing mechanical stability of the plant body, and protection from desiccation. Specific modifications of primary carbohydrate cell walls by chemically different, extracellular biopolymers represented evolutionary stable and successful solutions to both of these problems. Deposition of the aromatic biopolymer lignin to primary cell walls of carbohydrates renders plants mechani-cally stable, allowing height growth of 30 m and more. Deposition of the aliphatic biopolymers cutin and suberin to epidermal and peridermal cell walls protects plants from desiccation, allowing survival even in deserts.

Exactly how plants achieve this feat has long remained largely unresolved. One person who has immensely improved our understanding of such transport barriers is Professor Jörg Schönherr. Since the 1970s he has been investigating the transport properties of cutinized and suberized barriers at the plant/air interface. From an initial focus on ecophysiological questions, primarily dealing with water permeability, he later turned to the ecotoxicological and agronomic questions of the uptake of xenobiotics and agrochemicals into leaves. More recently, he has made a large contribution to our under-standing of the foliar uptake of polar compounds, i.e. ions and hydrophilic organic molecules.

On the occasion of his 65th birthday and retirement in March 2005, he assembled a group of former students and colleagues, now working on various aspects of transport across cutinized and suberized barriers in groups located in Germany, Switzerland, and the UK, for a week-long symposium held near Izmir in Turkey. It was the aim of the meeting to review the larger group’s achievements in the past, to assess the current level of knowledge, and to identify central topics and open questions for future research in the field of cutinized and suberized transport barriers of plants. The review papers in this TEXBOT originate from that meeting. The contributors are sincerely grateful to the Journal of Experimental Botany for providing the opportunity to publish the reviews as one unit and to the people behind it for their help in making it a reality.

Picking up from nearly forgotten work dating from the middle of the last century and adding new and unequivocal results, Schönherr demonstrates in the opening paper that lipophilic plant cuticles of certain species contain polar paths, aqueous pores that allow penetration of foliar applied ions and charged molecules into leaves. This network of localized pathways complements the lipophilic path across the cuticle, which consists of random diffusion steps. An update of recent achievements in understanding the penetration of water, which as a small and uncharged but polar molecule is likely to use both types of pathway across cuticles to some extent, is given in the second paper by Kerstiens. Without doubt the most comprehensive set of data for cuticular transport is available for lipophilic organic molecules (either xenobiotics or agrochemicals). In the third and fourth contributions, Buchholz reviews cuticular transport of these compounds and its acceleration by plasticizers and Schreiber discusses similar issues for isolated and subsequently recrystallized cuticular waxes. Following on from this, different predictive models of cuticular uptake of lipophilic and other chemicals are compared by Kerstiens. Lendzian discusses similarities and differences in transport properties between suberized and cutinized barriers in the sixth contribution.

Finally, Kerstiens et al. suggest a method for the future quantification of changes in leaf or stem surface barrier properties of transgenic plants with modified cutin and/or wax biosynthesis.

The present set of papers documents the large advances in understanding barrier properties of cutinized and suberized barriers of plants that have been achieved within the last couple of decades. It also demonstrates the tremendous experi-mental and intellectual input by Jörg Schönherr. Without his permanent motivation, constant support of co-workers and former students, and continuous interest in their research, all this would not have been possible, and that is what we are thankful for.

Lukas Schreiber
Bonn University
Gerhard Kerstiens
Lancaster University