Photosynthetic Electron Transport During Senescence of the Primary Leaves of Phaseolus vulgaris L.: III. KINETICS OF CHLOROPHYLL FLUORESCENCE EMISSION FROM INTACT LEAVES

The kinetics of 685 nm chlorophyll fluorescence emission weremeasured at 20 °C following illumination of primary leavesof P. vulgaris. During foliar senescence, a large reductionwas observed in the maximal level of fluorescence emission (P)of the induction curve, normalized with respect to the minimallevel (O), and in the time taken to reach P. This suggests thatfewer plastoquinone (PQ) molecules were able to accept electronsfrom each photosystem two (PS II) reaction centre in older leaves.Measurements of fluorescence emission at 77 °K indicatedthat the primary photochemical quantum yield of the PS II reactioncentres remained constant during senescence. The redox stateof the PQ pool was estimated throughout the induction curveat 20 °C. In both mature and senescent leaves PQ was highlyreduced at P. There followed a reoxidation of PQ in the matureleaves, but in the old leaves the PQ pool remained reduced.This indicates that the rate of electron flow from PQ to photosystemone (PS I) decreased considerably during senescence. Fluorescencewas quenched from P to a steady state level (T) in leaves ofall ages, and this was associated with a redistribution of excitationin favour of PS I. Since, in senescent leaves, changes in theredox state of PQ were absent, it is suggested that quenchingresulted from the generation of proton and ion gradients acrossthe thylakoid membranes, and the synthesis of ATP.     

Form and function within a phylogenetic framework: locomotory habits of extant predators and some Miocene Sparassodonta (Metatheria)

In this study, we analysed locomotory habits in extant predators and Sparassodonta species through geometric morphometric techniques and discriminant analyses of the distal humerus in anterior view, proximal ulna in lateral view, and tibia in proximal view. We included a wide sample of extant predators, and considered the phylogenetic and allometric structure in the data sets. We also included some Sparassodonta, a group of carnivorous metatherians that inhabited South America during the Cenozoic, and inferred their locomotory habits. Results suggest the presence of a close relationship between shape and locomotory habits, even after removing the shape component explained by phylogeny in the three postcranial elements. Terrestrial habits were inferred for Arctodictis sinclairi, Borhyaena tuberata, ‘Lycopsis’ longirostrus, and Thylacosmilus atrox. Some degree of cursoriality was highlighted in B. tuberata and T. atrox, and climbing abilities in ‘L.’ longirostrus, and to a lesser degree in B. tuberata. Scansorial habits were inferred for Cladosictis patagonica, Sipalocyon gracilis, Prothylacynus patagonicus, and Pseudonotictis pusillus, and in the case of C. patagonica, some digging ability was also tentatively inferred. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 224–251.     

The Role of Leaves in the Perception of Vernalizing Temperatures in Sugar Beet

Annual and biennial sugar beet varieties require long days toinduce flowering but the biennial genotypes additionally requirevernalization. Previous research has suggested that the inabilityof non-vernalized biennial plants to flower can be explainedby a lack of competence of the leaves to respond to long days.In this study defoliation experiments were used to investigatewhich leaves could perceive long daylengths and, in particular,whether leaves initiated from a non-vernalized shoot apicalmeristem could perceive vernalizing temperatures and producea floral stimulus in long days. Annual and vernalized biennialplants flowered if young leaves (i.e. those formed during orafter vernalization) were kept on the plants, but they did notflower if only older expanded leaves (including those expandedprior to vernalization) were present. No evidence was obtainedto indicate that the older leaves contained inhibitors of floweringand it seems most likely that there is a decline in responsivenessto daylength with increasing leaf age. Exposure to vernalizingtemperatures accelerated flowering of the annual and was essentialfor flowering of the biennial. The presence of a single leafinitiated, but not expanded, prior to the transfer of biennialplants to vernalizing temperatures was sufficient to induceflowering. This indicates that expanding leaves do not needto be initiated from a vernalized apical meristem to becomecompetent to produce a floral stimulus in long days. Key words: Beta vulgaris L., sugar beet, vernalization, flowering     

Modelling power‐line collision risk for the Blue Crane Anthropoides paradiseus in South Africa

The Overberg wheatbelt population of Blue Cranes Anthropoides paradiseus in the Western Cape of South Africa is approximately half the global population of this vulnerable species. Blue Cranes are highly susceptible to collisions with overhead power lines, and a spatial model was developed to identify high‐risk lines in the Overberg for proactive mitigation. To ground‐truth this model, we surveyed 199 km of power lines. Although Blue Cranes were the most commonly killed birds found (54% of all carcasses), the model was unable to predict lines with high collision risk for Blue Cranes. Further Geographic Information System (GIS) modelling was undertaken to test a wider range of landscape and power‐line variables, but only the presence or absence of cultivated land could usefully identify lines posing a collision risk. Modelling was limited by a lack of detailed spatial habitat data and recent information on Crane numbers and distributions. We used recent carcass counts to estimate a Blue Crane collision rate, corrected for sample biases, of 0.31/km power line per year (95% CI 0.13–0.59/km/year), which means that approximately 12% (5–23%) of the total Blue Crane population within the Overberg study area is killed annually in power‐line collisions. This represents a possibly unsustainable source of mortality. There is urgent need for further research into risk factors and for mitigation measures to be more widely implemented.     

Importance of pre‐anthesis anther sink strength for maintenance of grain number during reproductive stage water stress in wheat

Reproductive stage water stress leads to spikelet sterility in wheat. Whereas drought stress at anthesis affects mainly grain size, stress at the young microspore stage of pollen development is characterized by abortion of pollen development and reduction in grain number. We identified genetic variability for drought tolerance at the reproductive stage. Drought‐tolerant wheat germplasm is able to maintain carbohydrate accumulation in the reproductive organs throughout the stress treatment. Starch depletion in the ovary of drought‐sensitive wheat is reversible upon re‐watering and cross‐pollination experiments indicate that the ovary is more resilient than the anther. The effect on anthers and pollen fertility is irreversible, suggesting that pollen sterility is the main cause of grain loss during drought conditions in wheat. The difference in storage carbohydrate accumulation in drought‐sensitive and drought‐tolerant wheat is correlated with differences in sugar profiles, cell wall invertase gene expression and expression of fructan biosynthesis genes in anther and ovary (sucrose : sucrose 1‐fructosyl‐transferase, 1‐SST; sucrose : fructan 6‐fructosyl‐transferase, 6‐SFT). Our results indicate that the ability to control and maintain sink strength and carbohydrate supply to anthers may be the key to maintaining pollen fertility and grain number in wheat and this mechanism may also provide protection against other abiotic stresses.