Seasonal changes in chemical composition and construction costs of grapevine tissues

Modelling of the whole-vine carbon balance requires accurate estimates of tissue construction costs, i.e. the amount of glucose involved in the synthesis of a unit of biomass. In order to quantify construction costs during the vine's growth cycle, chemical compositions of leaves, stems, fruits, fine roots and trunk of 10-year-old grapevines (cv. Merlot) were determined in two seasons. Tissue construction costs were estimated using (i) an approach based on the quantification of the amount of glucose required for the synthesis of major chemical components of vine organs by the most probable metabolic pathways (coded as CCp) and (ii) a simpler technique in which costs were derived from tissue ash, carbon and nitrogen concentrations (coded as CCw). Both methods were well-correlated in all grapevine tissues despite CCp values were higher than CCwestimates. Grapevine leaves had higher concentrations of compounds with a high proportion of C and N atoms (proteins, lipids and phenolics) and higher CCw values throughout the season than other tissues. Small variation in CCw values however were observed seasonally in vegetative tissues despite their chemical composition varied considerably with plant development. Significant changes in CCw appeared in berry tissues between fruit set and maturity, reflecting a proportional increase in concentration of inexpensive metabolites (soluble sugars and organic acids)

Effects of nitrogen supply on must quality and anthocyanin accumulation in berries of cv. Merlot

Nitrogen supply to Merlot vines (Vitis vinifera L.), grown under controlled conditions, affected must quality and the anthocyanin content in berry skins irrespective of vegetative growth. High N supply delayed fruit maturation; berries had a higher arginine and a lower anthocyanin content with relatively more abundant acylated anthocyanins compared to berries of vines supplied with low N. During maturation the anthocyanin content in the skin of berries decreased; this was more significant in high-N vines. It is concluded that high nitrogen supply affects the metabolic pathway of anthocyanins in different ways, e.g. it delays the quantitative and qualitative biosynthesis and enhances their degradation during the final steps of berry maturation.

Interacting effects of soil fertility and atmospheric CO 2 on leaf area growth and carbon gain physiology in Populus × euramericana (Dode) Guinier

Two important processes which may limit productivity gains in forest ecosystems with rising atmospheric CO 2 are reduction in photosynthetic capacity following prolonged exposure to high CO 2 and diminution of positive growth responses when soil nutrients, particularly N, are limiting. To examine the interacting effects of soil fertility and CO 2 enrichment on photosynthesis and growth in trees we grew hybrid poplar ( Populus × euramericana ) for 158 d in the field at ambient and twice ambient CO 2 and in soil with low or high N availability. We measured the timing and rate of canopy development, the seasonal dynamics of leaf level photosynthetic capacity, respiration, and N and carbohydrate concentration, and final above- and belowground dry weight. Single leaf net CO 2 assimilation (A) increased at elevated CO 2 over the majority of the growing season in both fertility treatments. At high fertility, the maximum size of individual leaves, total leaf number, and seasonal leaf area duration (LAD) also increased at elevated CO 2 , leading to a 49% increase in total dry weight. In contrast, at low fertility leaf area growth was unaffected by CO 2 treatment. Total dry weight nonetheless increased 25% due to CO 2 effects on A. Photosynthetic capacity (A at constant internal p(CO 2 ), (( C 1 )) was reduced in high CO 2 plants after 100 d growth at low fertility and 135 d growth at high fertility. Analysis of A responses to changing C 1 indicated that this negative adjustment of photosynthesis was due to a reduction in the maximum rate of CO 2 fixation by Rubisco. Maximum rate of electron transport and phosphate regeneration capacity were either unaffected or declined at elevated CO 2 . Carbon dioxide effects on leaf respiration were most pronounced at high fertility, with increased respiration mid-season and no change (area basis) or reduced (mass basis) respiration late-season in elevated compared to ambient CO 2 plants. This temporal variation correlated with changes in leaf N concentration and leaf mass per area. Our results demonstrate the importance of considering both structural and physiological pathways of net C gain in predicting tree responses to rising CO 2 under conditions of suboptimal soil fertility.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65655/1/j.1469-8137.1995.tb04295.x.pd

Merkel Cells as Putative Regulatory Cells in Skin Disorders: An In Vitro Study

Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca2+-independent, as inhibition of Ca2+ channels or culture in the absence of Ca2+ failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated

Somatostatin Inhibits Cell Migration and Reduces Cell Counts of Human Keratinocytes and Delays Epidermal Wound Healing in an Ex Vivo Wound Model

The peptide hormone somatostatin (SST) and its five G protein-coupled receptors (SSTR1-5) were described to be present in the skin, but their cutaneous function(s) and skin-specific signalling mechanisms are widely unknown. By using receptor specific agonists we show here that the SSTRs expressed in keratinocytes are functionally coupled to the inhibition of adenylate cyclase. In addition, treatment with SSTR4 and SSTR5/1 specific agonists significantly influences the MAP kinase signalling pathway. As epidermal hormone receptors in general are known to regulate re-epithelialization following skin injury, we investigated the effect of SST on cell counts and migration of human keratinocytes. Our results demonstrate a significant inhibition of cell migration and reduction of cell counts by SST. We do not observe an effect on apoptosis and necrosis. Analysis of signalling pathways showed that somatostatin inhibits cell migration independent of its effect on cAMP. Migrating keratinocytes treated with SST show altered cytoskeleton dynamics with delayed lamellipodia formation. Furthermore, the activity of the small GTPase Rac1 is diminished, providing evidence for the control of the actin cytoskeleton by somatostatin receptors in keratinocytes. While activation of all receptors leads to redundant effects on cell migration, only treatment with a SSTR5/1 specific agonist resulted in decreased cell counts. In accordance with reduced cell counts and impaired migration we observe delayed re-epithelialization in an ex vivo wound healing model. Consequently, our experiments suggest SST as a negative regulator of epidermal wound healing

Protein and amino acid content in compatible and incompatible peach/plum grafts

Amino acid and soluble protein contents were studied in one compatible peach/plum graft (Prunus persica cv. Springtime/Prunus cerasifera cv. myrobalan P 2032) and one incompatible graft (Prunus persica cv. Springtime/Prunus cerasifera cv. myrobalan P 18) for three months after grafting. During a first period, between Days 57 and 78 after grafting, soluble proteins and free amino acids per tree were remobilized from the rootstock in both graft combinations. During a second period, between Days 78 and 89, soluble protein content per tree remained constant in the rootstock of both graft combinations, whereas total free amino acids per tree continued to decrease in the rootstock of the incompatible graft combination and stabilized in the compatible one. In the peach scion and the myrobalan rootstock, asparagine, aspartate, glutamate and arginine were the major free amino acids. Their concentration in the roots was unaffected or only little influenced by incompatibility. Free amino acid and soluble protein concentration in the incompatible rootstock was not indicative of nitrogen starvation or of carbohydrate starvation. In peach scions, at the end of the experiment, the soluble protein concentration was lower in all the organs in the incompatible grafts. The same pattern was found in scion for asparagine, aspartate and glutamate concentrations. This is indicative of nitrogen starvation in the aerial parts.Peer reviewe

Modeling Carbon Export Out of Mature Peach Leaves.

The characteristics of sorbitol and sucrose export out of mature leaves in seedlings of peach (Prunus persica L. Batsch cv GF 305) were investigated by simulating carbon fluxes through the leaf. Three treatments were employed: a control treatment and two treatments modifying leaf export, the latter using either shading or girdling. Photosynthesis and 14C partitioning into sorbitol and sucrose were measured during carbohydrate pool buildup at the beginning of the photoperiod, and the export rate of sorbitol and sucrose was modeled using a PSPICE (Simulation Program with Integrated Circuit Emphasis) simulator. The simulation allowed prediction of the resulting sorbitol and sucrose contents, which were compared to experimental carbohydrate contents. The apparent Km for sorbitol and sucrose phloem loading, estimated by carbon flux modeling, was 6.6 and 4 mol m-3, respectively. The predicted export capacity of the leaf, characterized by the estimated Vmax values for phloem loading of sorbitol and sucrose, was similar to the photosynthetic carbon flux measured under the leaf growth conditions. This export capacity was enhanced in plants in which all leaves except those studied were shaded. The mature leaf had a higher storage capacity for sorbitol than for sucrose in control plants, especially in the girdled treatment. Sucrose content appears to be tightly regulated