OXIDATION OF PHLORIDZIN BY ISOLATED CHLOROPLASTS

Phloridzin was shown to be oxidized by chloroplast fragmentsfrom swiss-chard. From inhibitor studies, kinetics and affinitytoward oxygen, it was inferred that the oxidation was mediatedby a phenolase in a "cresolase" type reaction. Atebrin was foundto inhibit the enzymatic oxidation of phloridzin and of 4-methylcatechol. (Received November 2, 1966; )     

Seasonal variation in ribulose bisphosphate carboxylase activity in Pinus silvestris

Ribulose bisphosphate carboxylase activity was examined in Pinus silvestris L. during successive seasons. The enzyme activities were studied both in seedlings, kept under controlled conditions in a climate chamber, and in needles from a 15-year-old tree in a natural stand. The enzyme activities were analysed in cell-free extracts prepared with Tween 80 as protective agent. The carboxylase activity fluctuated periodically both in the seedlings and in the natural stand. In the seedlings, the weight-related activity in the older needles increased 50–100% (in the cotyledons c. 200%) in the beginning of the “summer”. It decreased as the new shoot developed. The specific activity increased c. 100%. With chlorophyll as base, the activity usually decreased during “summer”. In the developing current needles the carboxylase activity increased when expressed on a weight or on a protein basis. The decrease in weight-related carboxylase activity in the older needles was preceded by, or simultaneous with, loss of total protein. It is suggested that protein, including the carboxylase, is utilized as nitrogen reserve for the new shoot. During hardening by combined photoperiod and thermoperiod, the carboxylase activity decreased when expressed relative to dry weight and protein. Calculated on a chlorophyll basis, the activity was rather constant. In the natural stand the activity in the one- and two-year-old needles increased during spring and summer and decreased during autumn and winter. Even at severe winter stress substantial carboxylase activity remained in the needles. The activity of the enzyme in vivo is discussed with respect to electron transport and net photosynthesis.     

Conditions for rooting of leafy cuttings of Alnus incana

The rooting of softwood cuttings of Alnus incana (L.) Moench in nutrient solution was studied under controlled conditions. Cuttings consisting of one internode with the leaf and axillary bud attached rooted easily and more rapidly than shoot tip cuttings. Light was necessary for rooting but good rooting was obtained in photon flux densities of both 40 and 190 μmol m^-2s^-1. Root number and root length was reduced when light reached the base of the cuttings. Treatment with indolebutyric acid (10^-6–10^-4M) increased the number of roots but 10^-4M delayed rooting and decreased the root length. Debudded internode cuttings rooted as well as intact cuttings, and detached leaves also contained sufficient substances for rooting.     

Effects of altered α‐ and β‐branch carotenoid biosynthesis on photoprotection and whole‐plant acclimation of Arabidopsis to photo‐oxidative stress

Functions of α‐ and β‐branch carotenoids in whole‐plant acclimation to photo‐oxidative stress were studied in Arabidopsis thaliana wild‐type (wt) and carotenoid mutants, lut ein deficient (lut2, lut5), n on‐p hotochemical q uenching1 (npq1) and s uppressor of z eaxanthin‐l ess1 (szl1) npq1 double mutant. Photo‐oxidative stress was applied by exposing plants to sunflecks. The sunflecks caused reduction of chlorophyll content in all plants, but more severely in those having high α‐ to β‐branch carotenoid composition (α/β‐ratio) (lut5, szl1npq1). While this did not alter carotenoid composition in wt or lut2, which accumulates only β‐branch carotenoids, increased xanthophyll levels were found in the mutants with high α/β‐ratios (lut5, szl1npq1) or without xanthophyll‐cycle operation (npq1, szl1npq1). The PsbS protein content increased in all sunfleck plants but lut2. These changes were accompanied by no change (npq1, szl1npq1) or enhanced capacity (wt, lut5) of NPQ. Leaf mass per area increased in lut2, but decreased in wt and lut5 that showed increased NPQ. The sunflecks decelerated primary root growth in wt and npq1 having normal α/β‐ratios, but suppressed lateral root formation in lut5 and szl1npq1 having high α/β‐ratios. The results highlight the importance of proper regulation of the α‐ and β‐branch carotenoid pathways for whole‐plant acclimation, not only leaf photoprotection, under photo‐oxidative stress.     

Infestation of commercial bumblebee (Bombus impatiens) field colonies by small hive beetles (Aethina tumida)

Abstract.  1. The small hive beetle, Aethina tumida , is a parasite of honeybee ( Apis mellifera ) colonies native to sub-Saharan Africa and has become an invasive species. In North America the beetle is now sympatric with bumblebees, Bombus , not occurring in its native range. Laboratory studies have shown that small hive beetles can reproduce in bumblebee colonies but it was not known whether infestations occur in the field.
2. For the first time, infestation of bumblebee colonies by small hive beetles was investigated in the field. Commercial Bombus impatiens colonies ( n = 10) were installed in proximity to infested apiaries. Within 8 weeks, all colonies that were alive in the 5-week observation period ( n = 9) became naturally infested with adult small hive beetles and successful small hive beetle reproduction occurred in five colonies.
3. In four-square choice tests, the beetles were attracted to both adult bumblebee workers and pollen from bumblebee nests, suggesting that these odours may serve as cues for host finding.
4. The data indicate that bumblebee colonies may serve as alternative hosts for small hive beetles in the field. To foster the conservation of these essential native pollinators, investigations on the actual impact of small hive beetles on wild bumblebee populations are suggested.     

Ancient DNA reveals traces of Iberian Neolithic and Bronze Age lineages in modern Iberian horses

Multiple geographical regions have been proposed for the domestication of Equus caballus . It has been suggested, based on zooarchaeological and genetic analyses that wild horses from the Iberian Peninsula were involved in the process, and the overrepresentation of mitochondrial D1 cluster in modern Iberian horses supports this suggestion. To test this hypothesis, we analysed mitochondrial DNA from 22 ancient Iberian horse remains belonging to the Neolithic, the Bronze Age and the Middle Ages, against previously published sequences. Only the medieval Iberian sequence appeared in the D1 group. Neolithic and Bronze Age sequences grouped in other clusters, one of which (Lusitano group C) is exclusively represented by modern horses of Iberian origin. Moreover, Bronze Age Iberian sequences displayed the lowest nucleotide diversity values when compared with modern horses, ancient wild horses and other ancient domesticates using nonparametric bootstrapping analyses. We conclude that the excessive clustering of Bronze Age horses in the Lusitano group C, the observed nucleotide diversity and the local continuity from wild Neolithic Iberian to modern Iberian horses, could be explained by the use of local wild mares during an early Iberian domestication or restocking event, whereas the D1 group probably was introduced into Iberia in later historical times.