Hormonal Changes Associated with Growth and Development of Red Raspberries

Analysis for gibberellin-like substances (GA) and cytokinins in cold and non-cold treated fall-bearing and cold treated June-bearing cultivars of red raspberries (Rubus idaeus L.) was made at the 10 and 20 node stages of growth (at 10 nodes, all plants were vegetative; at 20 nodes, only cold treated plants of fall-bearing cultivars were flower induced). Quantitative changes in GAs, as analyzed by the lettuce hypocotyl bioassay, were observed only in flower induced plants. In fall-bearing cultivars at the 20 node stage of growth, there was a 100% greater activity in cold than non-cold treated plants. Likewise, cold treated plants had a 60% greater activity at the 20 than at the 10 node stage of growth. Major qualitative differences in GAs were observed between the 10 and 20 node stage of growth in cold treated fall-bearing cultivars but not in cold treated plants of June-bearing cultivars. Changes in compounds at R_f 0.3 and 0.5 accounted for 35 to 54% of the total increase in GA activity between flower induced and non-induced stages of growth. Cytokinin activity tested by the tobacco callus bioassay was greater at the 20 than at the 10 node stage of growth in all cultivars and treatments. However, cold treated plants of the fall-bearing type had 70% greater cytokinin activity than non-cold treated plants at both stages of growth. It is suggested that gibberellins, possibly acting synergistically with cytokinins, are involved inflower induction in red raspberries.     

Subfossil Cladocera in relation to contemporary environmental variables in 54 Pan-European lakes

1. Changes in cladoceran subfossils in the surface sediments of 54 shallow lakes were studied along a European latitude gradient (36–68°N). Multivariate methods, such as regression trees and ordination, were applied to explore the relationships between cladoceran taxa distribution and contemporary environmental variables, with special focus on the impact of climate. 2. Multivariate regression tree analysis showed distinct differences in cladoceran community structure and lake characteristics along the latitude gradient, identifying three groups: (i) northern lakes characterised by low annual mean temperature, conductivity, nutrient concentrations and fish abundance, (ii) southern, macrophyte rich, warm water lakes with high conductivity and high fish abundance and (iii) Mid‐European lakes at intermediate latitudes with intermediate conductivities, trophic state and temperatures. 3. Large‐sized, pelagic species dominated a group of seven northern lakes with low conductivity, where acid‐tolerant species were also occasionally abundant. Small‐sized, benthic‐associated species dominated a group of five warm water lakes with high conductivity. Cladoceran communities generally showed low species‐specific preferences for habitat and environmental conditions in the Mid‐European group of lakes. Taxon richness was low in the southern‐most, high‐conductivity lakes as well as in the two northern‐most sub‐arctic lakes. 4. The proportion of cladoceran resting eggs relative to body shields was high in the northern lakes, and linearly (negatively) related to both temperature and Chl a, indicating that both cold climate (short growing season) and low food availability induce high ephippia production. 5. Latitude and, implicitly, temperature were strongly correlated with conductivity and nutrient concentrations, highlighting the difficulties of disentangling a direct climate signal from indirect effects of climate, such as changes in fish community structure and human‐related impacts, when a latitude gradient is used as a climate proxy. Future studies should focus on the interrelationships between latitude and gradients in nutrient concentration and conductivity.