Defence reactions of mature Norway spruce (Picea abies) before and after inoculation of the blue-stain fungus Endoconidiophora polonica in a drought stress experiment

We performed an inoculation experiment using the blue-stain fungus Endoconidiophora polonica at the Rosalia Roof study site, which was set up to study drought effects on Norway spruce susceptibility to attacks by the European spruce bark beetle Ips typographus. Tree resistance parameters such as resin flow rate and extent of hypersensitive wound reaction in the phloem were investigated prior to and after fungal infection. Sample trees with different drought treatments (trees fully covered or semi-covered by roofs, control trees) were inoculated with E. polonica in July 2014. In order to check for areas of phloem necrosis, the outer bark around the inoculation holes was scratched off 6 weeks later. We recorded the amount of resin exudation within 12 hours overnight in August and September 2013 and 2014. Although wound reaction zones did not differ in size between tree collectives of the various treatments, fully covered trees tended to exhibit larger necrotic areas compared to control trees. The least water supplied trees showed lowest resin flow rates prior to fungal inoculation, but were the only group to show significantly enhanced resin flow five weeks after the evaluation of defence reactions. Our results agree with earlier findings that wounding and few fungal inoculations can increase tree resistance in the medium term given not too severe water stress. Further investigations will clarify how water stress affects the availability of non-structural carbohydrates for secondary metabolism, when depletion of resources eventually occurs, and at which point trees are most susceptible to bark beetle attack.

The Formation of Traumatic Rows of Resin Ducts in Larix Decidua and Picea Abies (Pinaceae) as a Result of Wounding Experiments in the Dormant Season

Wounding experiments, imitating the impact of geomorphic processes such as rock fall, were performed on Larix decidua Mill. and Picea abies (L.) Karst., before the beginning and at the end of the growing season. This was done to evaluate the timing and spread of traumatic rows of resin ducts (TDs) as a result of wounding during dormancy, when most mass movements occur. All treatments were successful in inducing TDs. However, a high inter- and intra-species variability concerning the timing and position of the TDs was noted. In larch, TDs were formed as first cells after wounding (immediate reaction) only in the vicinity of the wound. In contrast, none of the spruce trees exhibited immediate reactions. Neither larch nor spruce formed continuous TDs around the stem. TDs in larch were more extensive if, in addition, stems were bent before the growing season. In contrast, spruce showed this reaction when bent at the end of the growing season. The results indicate that the varying lengths of the growing seasons at different geographical locations need to be taken into account before an immediate wound reaction can be clearly defined, if an increase of the reliability and accuracy of process reconstructions is aimed for.

TEM Survey of the Cytoplasmic wound reaction of Caulerpa prolifera

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Accumulation of mansonones in callus cultures of Ulmus americana L. in the absence of a fungal-derived elicitor

The Dutch elm disease pathogens Ophiostoma ulmi (Buism.) Nannf. and Ophiostoma novo-ulmi Brasier elicit the production of phytoalexins called mansonones in the American elm (Ulmus americana L.). As part of a larger investigation, it was revealed that mansonone elicitation in callus culture does not require the Dutch elm disease pathogens, as has been reported in other studies. The objective of this study was to determine the nature and timing of the nonfungal elicited mansonone accumulation in U. americana callus. Initially, 7-week-old calli were subjected to inoculations with various fungal growth medium components. Mansonone production occurred in all treatments, indicating that it was stimulated prior to the addition of the medium components. Next, cotyledons and calli at various stages of development were analysed for the production of mansonones to determine the timing of its production. Mansonone production appeared to be correlated with the initiation of callus production and may be related to the callus wound reaction. As the callus aged, its colour changed from white–green to brown possibly as a result of phytoalexin accumulation. Additional experiments in which the cotyledon source, agar source, and type of plant tissue culture media were modified resulted in no change to the mansonone accumulation ability of the callus. The discrepancy between our results and those of other researchers could be due to differences in the method of mansonone quantification, namely, that our method is more sensitive and led to the detection of mansonones where previously none had been found. Further research must be done in this area to investigate this mansonone accumulation. Key words: phytoalexin, Dutch elm disease, mansonone, Ulmus americana, callus.

Wound healing in whole potato tubers: a cytochemical, fluorescence, and ultrastructural analysis of cut and bruise wounds

Healing was investigated in whole tubers wounded by cuts and bruises and compared with core, disc, and slice wounds. Bright-field, fluorescence, and transmission electron microscopy were used in conjunction with cytochemical analyses. Wound reaction cells bordering a wound site responded to wounding initially with deposition of callose at the primary pit fields followed by intussusception of lignin in the middle lamellae and primary walls and suberization along the inner surfaces of the primary walls. Suberization was initially detected by the presence of a prosuberin lamella in which suberin lamellae subsequently developed. Both lignin and the prosuberin lamella were first detected in wound reaction cells of the cortex at 4 h in cut, core, disc, and slice wounds and at 8 h in bruise wounds. Healing was completed with formation of a continuous wound cork cambium beneath the wound site. With lignification and suberization, wounded potato tubers apparently develop specialized barriers against potential pathogens and water loss. The overall healing process proceeds more slowly in bruise wounds than in cut wounds. Moreover, the capacity for wound healing decreases with increasing age of the tuber, or time in storage. Key words: lignin, prosuberin lamella, Solanum tuberosum, suberin, suberization, wound healing.