Photoinhibition Of Hardened And Non-hardened Rye (secale Cereale L Cv Musketeer) Studied With Isolated Thylakoids, Isolated Mesophyll Cells, And Intact Leaves

Photoinhibition of photosynthesis has been shown to be more severe when combined with other stresses. This suggests a possible correlation between the capacity to grow at low temperature and an increased resistance to photoinhibition at low temperature. Previous work has shown with chlorophyll a fluorescence that rye plants (Secale cereale L. cv Musketeer) acclimated to low temperature were more resistant to photoinhibition than non-hardened rye plants. The goal of the present study was to assess whether the morphological changes observed at the leaf level and the structural changes observed at the thylakoid level during the cold hardening process were responsible for the increased resistance of cold hardened rye to photoinhibition.;Photoinhibition was monitored in hardened and non-hardened winter rye at the leaf level, with isolated mesophyll cells, and with isolated thylakoids. They were exposed to high photon fluxes at 20 and at 5{dollar}\sp\circ{dollar}C and recovery from photoinhibition was assessed upon return to lower photon fluxes. Room temperature chlorophyll a fluorescence, light limited CO{dollar}\sb2{dollar} fixation rates, electron transport rates, photoacoustic spectroscopy and atrazine binding were measured during and following photoinhibition.;Cold-hardened isolated rye cells were more resistant to photoinhibition when monitored with chlorophyll a fluorescence. However, CO{dollar}\sb2{dollar} fixation rates showed similar extent of photoinhibition in cold hardened and non-hardened isolated rye cells. Photoinhibition was similar at 5 and at 20{dollar}\sp\circ{dollar}C but the recovery from photoinhibition was slower when occurring at 5{dollar}\sp\circ{dollar}C. Both groups of cells showed similar rates of recovery. In contrast, cold hardened isolated rye thylakoids were more susceptible to photoinhibition which mainly affected Photosystem II activity.;Leaf morphological differences and structural changes occurring at the thylakoid level during cold hardening of winter rye are not responsible for its increased resistance to photoinhibition. Photoinhibition as monitored with chlorophyll a fluorescence showed different trends and different kinetics compared to CO{dollar}\sb2{dollar} fixation. CO{dollar}\sb2{dollar} fixation data showed that regulatory mechanisms also play a role during photoinhibition and subsequent recovery. Therefore, CO{dollar}\sb2{dollar} fixation should be monitored in intact leaves before the increased resistance of cold hardened winter rye is conclusively proven

Cloudberry cultivation in cutover peatland : improved growth on less decomposed peat.

La culture de la chicouté est sérieusement évaluée comme une option de réhabilitation des tourbières après récolte de la tourbe à des fins horticoles. Outre le gain en termes de valeur écologique et économique de ces sites, la culture de la chicouté pourrait augmenter le rendement en fruits et faciliter la récolte des fruits par rapport à la récolte en tourbières naturelles. Des études antérieures ont montré une croissance initiale lente qui a été provisoirement attribuée aux caractéristiques du substrat. Des expériences sur le terrain et en serres ont donc été mises en place pour mieux caractériser l'effet de différents substrats combinée aux techniques de restauration, sur la croissance des clones mâles et femelles. La chicouté a présenté une meilleure croissance en tourbe fibrique moins décomposée (H1–H3) qu'en tourbe mésique plus décomposée. La restauration devrait donc précéder la mise en culture de la chicouté de quelques années, afin de planter les rhizomes dans la couche de tourbe fibrique nouvellement accumulée. Les clones mâles produisent des feuilles plus grandes et plus de ramets par rhizome que les clones femelles en conditions communes de croissance. Les différences observées entre les sexes sont donc d'ordre génétique plutôt qu'environnemental. De plus, nous avons observé que les clones semblent particulièrement sensibles à la présence d'aluminium. En conclusion, le niveau de décomposition de la tourbe apparaît comme un des facteurs déterminant le succès de plantations de chicouté.Cloudberry cultivation is being seriously considered as a rehabilitation option for industrial peatlands after horticultural peat extraction has ceased. Besides increasing the ecological and economic values of these sites, cloudberry cultivation could improve fruit yield and facilitate fruit harvesting compared to picking in natural peatlands. Previous studies reported slow establishment that was tentatively associated with substrate characteristics. Field and greenhouse experiments were thus conducted to better characterize the impact of different peat substrates in combination with restoration techniques on the growth of male and female clones. Cloudberry grew much better in less-decomposed fibric peat (H1-H3) than in more-decomposed mesic peat. Restoring the moss layer of the former peat field would thus need to precede cloudberry planting by a few years, in order to plant the rhizomes in a newly formed fibric peat layer. Male clones produced larger leaves and more ramets per rhizome than female clones under common greenhouse conditions, which indicated that differences between sexes are most likely genetic rather than environmental. Furthermore, we found cloudberry clones may be very sensitive to aluminium toxicity. In conclusion, the degree of peat decomposition appears to be one of the key factors determining the success of cloudberry plantations

Sustainable leaf harvesting and effects of plant density on wild leek cultivation plots and natural stands in Southern Quebec, Canada

Overharvesting reduces the populations of wild leek in deciduous temperate forests of North America. Forest farming relying on planted bulbs that are fertilized and selectively harvested could enhance and sustain wild leek production. Density reduction following bulb harvest could improve yield in natural wild leek stands that reach growth-limiting densities. Limiting the harvest to leaves may also provide an alternative form of exploitation, but could slow growth by reducing both carbon and nutrient reserves depending on the timing and intensity of such harvest. Our objectives were to assess the effects of (1) planting density and post-harvest density reduction, and (2) the timing and intensity of leaf harvest on subsequent growth and reproduction of wild leek. Three experiments were established. Bulbs were planted at densities from 44 to 356 bulbs m-2 , covering the range surveyed in natural populations. Plots in dense populations were subjected to up to 40 % bulb harvest. In cultivated plots, either half or all the leaves on each plant were harvested, from 15 to 25 days after unfolding. Plants growing in higher density plots exhibited slower growth and reproduction rates, but greater productivity per cultivated area. A similar effect, albeit marginal, was obtained following bulb harvests in natural populations. Harvesting leaves did not affect survival, but delaying the harvest and harvesting only half of the leaves favored subsequent plant growth. We recommend harvesting down to a fixed bulb density rather than harvesting a percentage of bulbs, and harvesting leaves only as ways to ensure sustainable exploitation of leeks

Invader disruption of belowground plant mutualisms reduces carbon acquisition and alters allocation patterns in a native forest herb

Invasive plants impose novel selection pressures on naïve mutualistic interactions between native plants and their partners. As most plants critically rely on root fungal symbionts (RFSs) for soil resources, invaders that disrupt plant–RFS mutualisms can significantly depress native plant fitness. Here, we investigate the consequences of RFS mutualism disruption on native plant fitness in a glasshouse experiment with a forest invader that produces known anti‐fungal allelochemicals. Over 5 months, we regularly applied either green leaves of the allelopathic invader Alliaria petiolata, a nonsystemic fungicide to simulate A. petiolata's effects, or green leaves of nonallelopathic Hesperis matronalis (control) to pots containing the native Maianthemum racemosum and its RFSs. We repeatedly measured M. racemosum physiology and harvested plants periodically to assess carbon allocation. Alliaria petiolata and fungicide treatment effects were indistinguishable: we observed inhibition of the RFS soil hyphal network and significant reductions in M. racemosum physiology (photosynthesis, transpiration and conductance) and allocation (carbon storage, root biomass and asexual reproduction) in both treatments relative to the control. Our findings suggest a general mechanistic hypothesis for local extinction of native species in ecosystems challenged by allelopathic invaders: RFS mutualism disruption drives carbon stress, subsequent declines in native plant vigor, and, if chronic, declines in RFS‐dependent species abundance

Source–sink imbalance increases with growth temperature in the spring geophyte Erythronium americanum

Spring geophytes produce larger storage organs and present delayed leaf senescence under lower growth temperature. Bulb and leaf carbon metabolism were investigated in Erythronium americanum to identify some of the mechanisms that permit this improved growth at low temperature. Plants were grown under three day/night temperature regimes: 18/14 °C, 12/8 °C, and 8/6 °C. Starch accumulated more slowly in the bulb at lower temperatures probably due to the combination of lower net photosynthetic rate and activation of a ‘futile cycle’ of sucrose synthesis and degradation. Furthermore, bulb cell maturation was delayed at lower temperatures, potentially due to the delayed activation of sucrose synthase leading to a greater sink capacity. Faster starch accumulation and the smaller sink capacity that developed at higher temperatures led to early starch saturation of the bulb. Thereafter, soluble sugars started to accumulate in both leaf and bulb, most probably inducing decreases in fructose-1,6-bisphosphatase activity, triose-phosphate utilization in the leaf, and the induction of leaf senescence. Longer leaf life span and larger bulbs at lower temperature appear to be due to an improved equilibrium between carbon fixation capacity and sink strength, thereby allowing the plant to sustain growth for a longer period of time before feedback inhibition induces leaf senescence

Disruption of AP1S1, Causing a Novel Neurocutaneous Syndrome, Perturbs Development of the Skin and Spinal Cord

Adaptor protein (AP) complexes regulate clathrin-coated vesicle assembly, protein cargo sorting, and vesicular trafficking between organelles in eukaryotic cells. Because disruption of the various subunits of the AP complexes is embryonic lethal in the majority of cases, characterization of their function in vivo is still lacking. Here, we describe the first mutation in the human AP1S1 gene, encoding the small subunit σ1A of the AP-1 complex. This founder splice mutation, which leads to a premature stop codon, was found in four families with a unique syndrome characterized by mental retardation, enteropathy, deafness, peripheral neuropathy, ichthyosis, and keratodermia (MEDNIK). To validate the pathogenic effect of the mutation, we knocked down Ap1s1 expression in zebrafish using selective antisens morpholino oligonucleotides (AMO). The knockdown phenotype consisted of perturbation in skin formation, reduced pigmentation, and severe motility deficits due to impaired neural network development. Both neural and skin defects were rescued by co-injection of AMO with wild-type (WT) human AP1S1 mRNA, but not by co-injecting the truncated form of AP1S1, consistent with a loss-of-function effect of this mutation. Together, these results confirm AP1S1 as the gene responsible for MEDNIK syndrome and demonstrate a critical role of AP1S1 in development of the skin and spinal cord

Fertilizers stimulate root production in cloudberry (Rubus chamaemorus) rhizomes transplanted in a cutover peatland

Cloudberry has good economic potential for Canada, but crop practices must be improved before commercial production can be established. Transplants usually consist of rhizome segments collected in natural populations; however, the very low root density of these transplants might partly explain their initial slow growth and high mortality. The objective of this study was to determine the effects of mineral fertilization and auxin applications on root initiation and elongation. Three N–P–K fertilization treatments were applied at the planting of bare rhizomes in peatlands, while auxin applications were tested in both greenhouse and field experiments. Roots of fertilized plants were two to four times longer and more numerous than those of control plants after one complete growing season but fertilization did not lead to early rooting. Rhizome segments produced new shoots before investing in root production, suggesting that rhizome carbohydrate reserves are not sufficient to allow both the shoot and root to be produced at the same time. Auxin applications to the rhizomes incurred high mortality and did not stimulate root production in both the field and greenhouse experiments. We conclude that fertilizers applied at planting can improve cloudberry initial survival rate, rooting, and early shoot growth, which could eventually lead to improved plant cover and fruit yield.La chicouté présente un bon potentiel économique pour le Canada, mais il faut en améliorer la culture avant qu’on puisse la produire commercialement. Les boutures sont habituellement des segments de rhizome, recueillis dans des peuplements naturels. La densité très faible des racines chez les boutures pourrait expliquer en partie la croissance anémique initiale et le taux de mortalité élevé. Cette étude devait établir les effets d’un amendement minéral et de l’application d’auxine sur la production et l’élongation des racines. Trois engrais N–P–K ont été appliqués lors de la plantation de rhizomes nus dans une tourbière. L’application d’auxine a été teste en serre et sur le terrain. Les racines des plants fertilisés étaient deux à quatre fois plus longues et plus nombreuses que celles des plants témoins après une saison de croissance, mais la fertilisation n’accélère pas l’enracinement. Les segments de rhizome produisent de nouvelles pousses avant de produire des racines, signe que les réserves d’hydrates de carbone du rhizome ne suffisent pas à la genèse simultanée des organes aériens et souterrains. L’auxine appliquée au rhizome entraîne une mortalité élevée et ne stimule pas la formation de racines sur le terrain ni en serre. Les auteurs en déduisent que l’application d’engrais à la plantation peut rehausser le taux de survie initial de la chicouté, son enracinement et la croissance des pousses, ce qui pourrait mener à une meilleure couverture végétale et un rendement fruitier supérieur. [Traduit par la Rédaction