Defence Is a Priority in Female Juveniles and Adults of Taxus baccata L.

Female individuals of dioecious plants invest their resources more in storage and defence, and the males have higher nitrogen content invested in the production of pollen grains. An unresolved problem is whether this strategy occurs only in sexually mature plants or can also occur in juvenile plants. To answer this, Taxus baccata (L.) needles from the mature plants and rooted cuttings (juveniles) in a pot experiment were compared for the content of carbon, nitrogen, starch, total non-structural carbohydrates (TNC), and total phenolic compounds (TPhC). The results indicate that the differences between sexes occurred mainly in sexually mature plants, where the starch content was higher in females and nitrogen in males. However, the novelty of the results is that TPhC was generally higher in females than males in both adults and juveniles, suggesting that defence is a priority for females from an early age. We do not know if this is an innate trait because the strobili production (albeit at a very low level) of juveniles was observed in all individuals after the autumn of the first year. We found no effect of fertilization on sex-specific response in the pot experiment, which may be related to the lower reproductive effort of juveniles

Growth hormone exerts no effect on the timing of the first zygotic cleavage in cattle

v2010o

Expression of abscisic and gibberellic acid signalling factors in Fagus sylvatica L. seeds during dormancy breaking and germination

European beech seeds are characterised by deep physiological dormancy and to germinate, they require several weeks of stratification at 3°C. Seed dormancy is under hormonal regulation, but the de- tails of how hormones regulate deep dormancy in trees remain not yet well elucidated. We hypothesised that the mechanism of seed dormancy breaking is differentially regulated according to depth of dormancy. Expression of ABI5 and 14-3-3, members of the abscisic acid pathway, and RGL2, a member of gibberel- lic acid pathways, were examined at the protein and mRNA levels during dormancy alleviation of beech seeds. Unlike in non-deep dormant seeds, ABI5, 14-3-3 and RGL2 were present during nearly all periods of cold stratification in beech seeds, but during dormancy breaking and germination these proteins nearly disappeared. Relative abundances of ABI5 and 14-3-3 transcripts were the highest in dormant dry seeds, and during stratification it decreased gradually. We suppose that during stratification, de novo translation of proteins on the basis of deposited mRNA occurred. On the base of our research we can conclude that the seed dormancy breaking mechanism differs according to seed’s dormancy dept

Postglacial migration dynamics helps to explain current scattered distribution of Taxus baccata

Taxus baccata L. has a scattered distribution and the decline of yew woodlands is observed across the entire species range. Passively protected populations in the central and northern part of their distribution are declining without human intervention. However, the establishment of new yew populations is observed in habitats that have been significantly transformed by humans. The following question need to be answered: why do yews find better in environmental conditions that have been strongly modified by humans compared to natural systems? The Quaternary history might be the key to understand the current yew situation. As suggested by palaeobotanical studies, pollen of T. baccata was observed at optima of the interglacials, but in subsequent periods, it has been displaced by that of other shade-tolerant species. Pollen diagrams indicate that after the last glaciation, the yew did not appear earlier than other shade-tolerant species and did not have the opportunity to become common in occurrence, as in previous interglacial periods. As a result, yews occur only as relict populations within environmental islands where the competition with other shade-tolerant species is low. The negative human impact on yew is well-documented, but limitations resulting from the biology of this species are also very important. T. baccata is a species whose current scattered distribution may explain the Quaternary history. Yew situation is better in artificial conditions because people reduce competition from other trees species and deer pressure. Possible positive impact of human on yew distribution in the past is also discussed. The current biological condition of this species suggests the need for active protection

Cross-talk between singlet oxygen- and hydrogen peroxide-dependent signaling of stress responses in Arabidopsis thaliana

Upon a dark-to-light shift, the conditional fluorescent (flu) mutant of Arabidopsis releases singlet oxygen ((1)O(2)) within the plastid compartment. Distinct sets of nuclear genes are activated that are different from those induced by superoxide (O(2)(•−)) and/or hydrogen peroxide (H(2)O(2)), suggesting that different types of reactive oxygen species activate distinct signaling pathways. It is not known whether the pathways operate separately or interact with each other. We have addressed this problem by modulating noninvasively the level of H(2)O(2) in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX). The overexpression of the H(2)O(2)-specific scavenger reduced strongly the activation of nuclear genes in plants treated with the herbicide paraquat that in the light leads to the enhanced generation of O(2)(•−) and H(2)O(2). In the flu mutant overexpressing tAPX, the intensity of (1)O(2)-mediated cell death and growth inhibition was increased when compared with the flu parental line. Also, the expression of most of the nuclear genes that were rapidly activated after the release of (1)O(2) was significantly higher in flu plants overexpressing tAPX, whereas in wild-type plants, overexpression of tAPX did not lead to visible stress responses and had only a very minor impact on nuclear gene expression. The results suggest that H(2)O(2) antagonizes the (1)O(2)-mediated signaling of stress responses as seen in the flu mutant. This cross-talk between H(2)O(2)- and (1)O(2)-dependent signaling pathways might contribute to the overall stability and robustness of wild-type plants exposed to adverse environmental stress conditions