Plant responses to variable timing of aboveground clipping and belowground herbivory depend on plant age

Aims Plants use different types of responses such as tolerance and induced defense to mitigate the effects of herbivores.The direc-tion and magnitude of both these plant responses can vary with plant age.However,most studies have focused on aboveground herbivory,whereas important feeding occurs belowground.Here,we tested the hypothesis that plant tolerance and defense following shoot damage or root herbivory depends on plant age.Methods In order to test our hypothesis,we exposed the perennial grass spe-cies Holcus lanatus to defoliation and root nematode inoculation at three growth stages(young,intermediate and old plants),and exam-ined responses of plant traits related to tolerance(regrowth follow-ing defoliation)and defense(leaf and root nitrogen and phenolics).Important Findings Defoliation overall reduced plant shoot and root biomass as well as foliar concentrations of phenolics regardless of plant age at defoli-ation.In contrast,defoliation increased foliar N concentrations,but only when defoliation occurred at intermediate and old plant age.Inoculation with root-feeding nematodes reduced root N concentra-tions after a prolonged period of growth,but only when nematodes had been inoculated when plants were young.The relative shoot re-growth rate of plants increased immediately after defoliation but this was independent of the plant age at which defoliation occurred,i.e.was not stronger in plants that were defoliated at a more advanced age,as hypothesized.Similarly,relative root growth rates increased shortly after defoliation,but this was only observed for plants defoli-ated when they were young.We conclude that plant responses to aboveground and belowground herbivory in traits related to both defense and tolerance are affected by plant age,but do not gener-ally change with plant age.

Bolting and Flowering Response of <i>Lactuca georgica</i>, a Wild Lettuce Relative, to Low Temperatures

To learn about the phenological adaptation of Lactuca georgica Grossh., a wild relative of domesticated lettuce, we studied seed sampled accessions obtained from individual plants at 19 locations throughout six regions in Armenia, and from two natural populations in Dagestan (Russian Federation) collected as bulk samples. The effects of various vernalization treatments on time to bolting, flowering and seed production time were investigated during four successive years at different growth stages of L. georgica plants. We demonstrate that low temperatures play a major role in stimulating the reproduction process of L. georgica plants. Our results would suggest that for L. georgica: 1) There is an obligatory (or nearly so) vernalization requirement;2) Plant age, vernalization duration, and genotype of original sample have a role in bolting and flowering regulation;3) Some plants behaved as typical annuals, responding to vernalization treatment at the seedling stage, but, most did not;4) Four months of vernalization could be adequate to reach bolting in plants with a developed vegetative rosette, for most—but not all—samples;5) In order to find the best solution for stimulating the reproductive process of multiple genotypes, it seems that further study should focus on about 4 - 6 months of vernalization at 4°C applied to plants of about 10 - 22 months old vegetative rosettes, with controlled post-vernalization condition;6) L. georgica germplasm could be used as a source for delayed bolting in breeding of domesticated lettuce varieties.

DEVELOPMENT OF A MATERIALS RISK INFORMATION PLATFORM FOR A SAFE SOCIETY

A Materials Risk Information Platform is being developed under the cooperation of companies and academic societies with NIMS as project core. To combine safety and economy, which are sometimes contrary to each other, it is important to find an optimal solution using a new concept: risk based engineering. A 5-year project, the Materials Risk Information Platform, was started in 2001 in NIMS on the boilers of thermal power plants and the objectives of this project, research areas and its present state were outlined.