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Xylem anatomy may change in response to environmental or biotic stresses. Vascular occlusion, an anatomical modification of mature xylem, contributes to plant resistance and susceptibility to different stresses. In woody organs, xylem occlusions have been examined as part of the senescence process, but their presence and function in leaves remain obscure. In grapevine, many stresses are associated with premature leaf senescence inducing discolorations and scorched tissue in leaves. However, we still do not know whether the leaf senescence process follows the same sequence of physiological events and whether leaf xylem anatomy is affected in similar ways. In this study, we quantified vascular occlusions in midribs from leaves with symptoms of the grapevine disease esca, magnesium deficiency and autumn senescence. We found higher amounts of vascular occlusions in leaves with esca symptoms (in 27% of xylem vessels on average), whereas the leaves with other symptoms (as well as the asymptomatic controls) had far fewer occlusions (in 3% of vessels). Therefore, we assessed the relationship between xylem occlusions and esca leaf symptoms in four different countries (California in the USA, France, Italy and Spain) and eight different cultivars. We monitored the plants over the course of the growing season, confirming that vascular occlusions do not evolve with symptom age. Finally, we investigated the hydraulic integrity of leaf xylem vessels by optical visualization of embolism propagation during dehydration. We found that the occlusions lead to hydraulic dysfunction mainly in the peripheral veins compared with the midribs in esca symptomatic leaves. These results open new perspectives on the role of vascular occlusions during the leaf senescence process, highlighting the uniqueness of esca leaf symptoms and its consequence on leaf physiology.

Riparian alder forests are threatened by Phytophthora across Europe. Comparative studies of the pathogenicity of Phytophthora species are crucial for developing effective management strategies. Although only a limited number of species, particularly P. × alni, lead to tree decline in natural environments, many species demonstrate pathogenicity in inoculation trials. Phytophthora species vary in their ability to infect different tissues, such as phloem and xylem, and trigger defence responses in the host through the formation of tyloses and callose. By comparing the histological responses of alder to various Phytophthora species, we can gain insights into the success of P. × alni and the potential damage that could be caused by other species. To investigate the defence strategies of black alder (Alnus glutinosa) against attack by Phytophthora and Halophytophthora species present in Catalonia (NE Spain), we conducted inoculation trials on saplings using nine potentially pathogenic species and compared the histological responses. Phytophthora × alni and P. plurivora were the most aggressive species followed by other exotic species such as P. × cambivora and P. cactorum. Phytophthora × alni and P. plurivora were equally damaging despite the higher prevalence of P. × alni in declining alders in natural settings. Although P. × alni mainly invaded the phloem, P. plurivora also invaded the xylem and triggered the production of tyloses. Histological analyses revealed a diverse range of plant responses to infection by Phytophthora species, providing a better understanding of their adaptability in natural environments compared with solely observing lesions. The low level of callose production in saplings inoculated with P. × alni compared with callose production in saplings inoculated with less pathogenic species suggests that P. × alni can evade recognition by the host and, hence, could partially explain its success.

The purpose of this paper was to confirm the influence of pulsive pressure waves on the liquid penetration into wood in the semi-opened container. Wood block sample was irradiated by the pulsive pressure waves in the semi-opened container filled with water used as a liquid. The irradiation was also performed in the closed container for the comparison. The water penetration into the sample was promoted by the pressure-wave irradiation. There was little difference in the degree of the penetration between the closed and the semi-opened containers. It was presumed from the measured hydraulic pressure that the pressure-wave energy irradiated on the sample in the closed container was higher than that in the semi-opened container. It was also presumed that the cavitation generation was promoted in the semi-opened container. This indicates that the cavitation as well as the pressure waves themselves affected the liquid penetration into wood. The compressive deformation of the sample irradiated in the semi-opened container was slightly smaller than that in the closed container. This indicates that the pulsive pressure-wave irradiation in the semi-opened container promoted the liquid penetration into wood with less compressive deformation.

The name jarrah dieback has been used for two different disorders, leading to considerable confusion. It was coined in the 1940s to describe the sudden death of groups of jarrah (Eucalyptus marginata) trees in south western Western Australia, which occurred on poorly drained sites, following exceptionally heavy rainfall. In the 1960s these sites were shown to be infested by Phytophthora cinnamomi and jarrah deaths were attributed to it, even though it was only isolated from 5 % of sampled trees. Also the definition of jarrah dieback was expanded to include deaths of many other plants on infested sites, from which P. cinnamomi was more readily isolated. Jarrah trees die from severe water deficiency, indicating problems with water conduction through roots. Xylem vessel diameters vary along roots, being narrow at the root collar, while distally they are larger, providing water storage. Jarrah transpires vigorously during summer, accessing water at depth on sites with deep soil, but being more dependent on internally stored water when root systems are shallower. Following waterlogging, sapwood vessels become blocked with tyloses, reducing both conductivity and potential water storage; such trees may have insufficient water reserves for summer survival. In jarrah P. cinnamomi is unlikely to cause water deficiency because sapwood invasion is rapidly contained in healthy roots. Recent investigations into P. cinnamomi invasion and host responses in other plants show that it can potentially cause a vascular wilt in Banksia spp. and chronic, symptomless infections in herbaceous plants. Susceptibility to waterlogging damage, and/or mortality resulting from infection by P. cinnamomi can only be clarified by detailed knowledge of the hosts and their vulnerabilities. This is essential for making diagnoses, devising management strategies, and avoiding the confusions of the past.

The article presents the results of the study of the effect of thermochemical pretreatment on the struc-ture of conductive elements of oak wood and me-chanism of convective drying process

Pectin methylesterases (PMEs) catalyze the demethylesterification of cell wall polygalacturonans, and this is thought to play important roles in cell wall extensibility and intercellular adhesion. In addition, PMEs influence many physiological processes, such as stem elongation, root development, fertilization, fruit softening, and xylogenesis. This study focuses on establishing gene expression profiles for transgenic poplar (Populus tremula L. x P. tremuloides Michx.) lines, over-expressed (PME 2B and PME 7) and suppressed (PME 5 and PME 6N), in the expression of PME1. Employment of a transcriptomic approach; spotted poplar cDNA 25 K microarrays, allowed for a simultaneous analysis of about 17,000 genes, gaining insight into effects on plant cell metabolism. A concluding remark of the outcome of the microarray experiment was rejection of the hypothesis that lignin biosynthesis is regulated on a transcriptional level, even though the lignin content was altered, as demonstrated by previous molecular characterizations. Thus, to connect lignification with pectin modification machinery, alternative hypothesis were tested and revealed a higher abundance of H2O2 and peroxidases in the PME over-expressing lines, compared to wild-type line, confirming a positive correlation between the lignin content, H2O2, and peroxidase activity. Furthermore, the up-regulation of a callose synthase gene in the xylem of one suppressed line; in addition to formation of tyloses, as a reaction of PME suppression, indicated a putative defense response. Many other genes involved in oxidative stress responses were observed significantly affected in transgenic lines. This unexpected result implicated activation of signaling cascades and signal transduction through critical stress pathways such as the salicylic acid, jasmonate and ethylene pathways. It might be speculated that the stress signaling was triggered by the elicitor oligogalacturonic acid (OGA), derived from the cell wall, as a result o, Pektinmetylesteras (PME) catalyserar demetylesterifieringen av cellväggspolygalakturons, vilket anses spela viktiga roller i bl. a. cellväggens utsträckningsmöjligheter och intercellulär vidhäftning. Dessutom påverkar PME åtskilliga fysiologiska processer, såsom stamförlängning, rotutveckling, befruktning, fruktuppmjukning och xylogenes. Denna studie fokuser på att etablera genuttrycksprofiler for transgena poppellinjer (Populus tremula L. x P. tremuloides Michx.), överuttryckta (PME 2B och PME 7) och underuttryckta (PME 5 och PME 6N), i uttrycket av PME1. Användandet av ett transkriptomiskt tillvägagångssätt; 25 K cDNA mikromatriser, tillät en samtidig analys av ca 17 000 gener, vilket gav en inblick i inverkan på växtcellmetabolismen. En slutsats av mikromatrisexperimentet var förkastandet av hypotesen att ligninbiosyntesen är reglerad på en transkriptionell nivå, trots det faktum att lignininnehållet faktiskt förändrats, vilket kunnat påvisas av tidigare molekylär karaktärisering. Följaktligen, för att anknyta lignifiering med pektinmodifieringsmaskineriet, alternativa hypoteser testades vilka påvisade en högre förekomst av H2O2 och peroxidaser i PME-överuttryckta linjer kontra vildtypslinje, vilket bekräftade en positiv korrelering av lignininnehåll, H2O2 och peroxidasaktivitet. Vidare, överuttrycket av en kallossyntasgene i xylemet hos en underuttryckt linje, samt uppkomst av tyloser som en reaktion på PME-underuttryck, indikerade på en trolig försvarsreaktion. Slutligen, flera andra gener involverade i oxidativ stress respons observerades som signifikant påverkade i transgena linjer. Detta oväntade resultat antydde aktivering av signaleringskaskader och signalförmedlingar via kritiska stressvägar, såsom salicylsyra-, jasmonat- och etylenvägar. Man kan spekulera i huruvuda stresssignalleringen var framkallad av stresssignalmolekylen oligogalakturonsyra (OGA), vars ursprung förmodlingen finns beläget i cellväggen, vilket återspeglar dess förändrade kemiska samma