Onset Of Regrowth Research Articles

Impact of root C and N reserves on shoot regrowth of defoliated alfalfa cultivars differing in fall dormancy

AbstractKey determinants of regrowth rate following harvest in alfalfa (Medicago sativa L.) are the levels of root carbon (C) and nitrogen (N) reserves. This study was undertaken to assess the impact of alfalfa cultivars differing in fall dormancy on regrowth potential in relation to the quantitative changes in root C and N reserves at the onset of regrowth. Five contrasting alfalfa cultivars were grown in the field and were harvested three times. Shoot regrowth dry weight increased significantly with decreasing fall dormancy. Alfalfa cultivars with less dormancy tended to have higher concentrations of root C and N reserves, whereas significantly greater pools of root C and N reserves were found in roots at each harvest time because of greater root dry weight. Shoot regrowth was positively correlated to the pools of root soluble sugar, starch and total non‐structural carbohydrates, but not correlated to their concentrations at each harvest time. Shoot regrowth was also linearly related to the pools of root total N and soluble proteins, but not consistently related to their concentrations. Our results suggest that the total amount of C and N organic reserves in alfalfa roots rather than their concentrations are determining factors of shoot regrowth.

Comparing chamber and eddy covariance based net ecosystem CO2 exchange of fen soils

AbstractDue to their high emission potential, the reporting of CO2 emissions from peatlands requires exact emission factors for different land use categories. Recently used emission factors are mainly based on CO2 flux measurements by chamber techniques or the micrometeorological eddy covariance (EC) method. However, evidence about the reliability and comparability of annual CO2 balances based on these methods is scarce. Therefore, manual chamber measurements of ecosystem respiration (RECO) and net ecosystem exchange (NEE) were conducted for two years (March 2012–April 2014) to model annual balances of two sites on fen soils with different land use intensity in northern Germany: an unutilized and rewetted grassland (UG) and an intensively utilized wet grassland (GW). Simultaneously, EC measurements of NEE were conducted on the sites. Two reasons for occasionally great deviations in NEE between the methods could be observed: (1) the accordance of both methods was most hampered during transition periods such as the beginning of the growing season and the onset of regrowth after a grassland defoliation due to different spatial scales of EC and chamber measurements and (2) RECO and gross primary production (GPP) partitioned from EC NEE measurements were systematically lower than those from the chamber‐based model, which could be a result of the EC energy balance gap. Differences were more pronounced for the managed site GW as a result of more frequent regrowth periods. It is concluded that the EC and chamber method can show comparable results for the CO2 exchange of grasslands on fen soils when the limitations of both methods are known and considered for the reporting of emission factors. These limitations are due to energy balance closure and potentially biased footprints for EC and a restricted representativeness especially during early stages of plant development for the chamber method.

Nitric Oxide as a Switching Mechanism between Axon Degeneration and Regrowth during Developmental Remodeling

During development, neurons switch among growth states, such as initial axon outgrowth, axon pruning, and regrowth. By studying the stereotypic remodeling of the Drosophila mushroom body (MB), we found that the heme-binding nuclear receptor E75 is dispensable for initial axon outgrowth of MB γ neurons but is required for their developmental regrowth. Genetic experiments and pharmacological manipulations on ex-vivo-cultured brains indicate that neuronally generated nitric oxide (NO) promotes pruning but inhibits regrowth. We found that high NO levels inhibit the physical interaction between the E75 and UNF nuclear receptors, likely accounting for its repression of regrowth. Additionally, NO synthase (NOS) activity is downregulated at the onset of regrowth, at least partially, by short inhibitory NOS isoforms encoded within the NOS locus, indicating how NO production could be developmentally regulated. Taken together, these results suggest that NO signaling provides a switching mechanism between the degenerative and regenerative states of neuronal remodeling.

Assessment of genetic fidelity of encapsulated microshoots of Picrorhiza kurrooa

In vitro grown microshoots of Picrrhiza kurrooa were encapsulated in the alginate beads. Regrowth of encapsulated microshoots, using alginate encapsulation, of P. kurrooa reached 89.33% following 3 months of storage. Amongst developing plantlets, 42.66% exhibited formation of multiple shoots at the onset of regrowth and 21.43% demonstrated simultaneous formation of shoots and roots. Healthy root formation was observed in plantlets following 2 weeks of their transfer to half-strength Murashige and Skoog medium containing 1 μM α-naphthalene acetic acid. Plants were transplanted to the greenhouse in three batches with 95% frequency of survival. The genetic fidelity of P. kurrooa plants growing out after storage in encapsulated form was ascertained by random amplified polymorphic DNA (RAPD) analysis. Molecular analysis of randomly selected plants from each batch was conducted using 45 random decamer primers. Of 45 primes tested, 14 produced scorable amplified products. Total 68 bands were observed amongst them 7.35% bands were polymorphic. Cluster analysis of the RAPD profile revealed an average similarity coefficient of 0.966 thus confirming genetic stability of plants derived from encapsulated microshoots following 3 months of storage.

An evaluation of genetic fidelity of encapsulated microshoots of the medicinal plant: Cineraria maritima following six months of storage

Regrowth of encapsulated microshoots, using alginate encapsulation, of Cineraria maritima reached 82.35% following 6 months of storage. Amongst developing plantlets, 33.33% exhibited formation of multiple shoots at the onset of regrowth and 11.76% demonstrated simultaneous formation of shoots and roots. Healthy root formation was observed in plantlets following 2 weeks of their transfer to half-strength Murashige and Skoog medium containing 1.0 mg l−1 α-naphthalene acetic acid. Plants were transplanted to the greenhouse in three batches with 90% frequency of survival. Molecular analysis of randomly selected plants from each batch was conducted using 20 random amplified polymorphic DNA (RAPD) markers. Of 20 primers tested, 14 produced amplification products, and a total of 69 bands with an average of 4.93 bands per primer were observed. Of these 69 scorable bands, only 20% of bands were polymorphic. Cluster analysis of the RAPD profiles revealed an average similarity coefficient of 0.944 thus confirming molecular stability of plants derived from encapsulated microshoots following 6 months of storage.

Analysis of Leakage Currents in AlGaN/GaN Current Aperture Vertical Electron Transistors (CAVETs)

AbstractA complete analysis of leakage currents in AlGaN/GaN Current Aperture Vertical Electron Transistors (CAVETs) with regrown aperture and source regions was carried out. The total observed leakage current was found to be a combination of both gate leakage and source leakage. Two paths for source leakage have been identified; electrons passing directly through the insulating layer to the drain region as well as electrons traveling through the aperture but underneath the 2DEG at the AlGaN/GaN interface. Source leakage through the insulating layer resulted from pits formed at the onset of regrowth, as the sample was heated to growth temperature, and was successfully eliminated by optimizing regrowth conditions. Source leakage underneath the 2DEG occurred when the unintentionally doped (UID) GaN layer above the insulating layer was not fully depleted and could be eliminated by reducing the thickness of the UID GaN layer. Gate leakage has been attributed to the enhanced incorporation of n-type impurities inside as well as above the aperture region during regrowth, resulting in a narrowing ofthegateSchottkybarrier.

Hair cycle and alopecia.

Male pattern alopecia is the outcome of profound modifications in the duration, succession and frequency of hair cycles. These phenomena were studied by phototrichogram in 10 male subjects, with or without alopecia, over a period of 15 years. Almost 10,000 hair cycles were accounted for, yielding a detailed picture of the alopecia condition: (1) A decrease in the duration of anagen for a certain proportion of hairs, a proportion which increases in size, the more advanced the alopecia; the result of this premature transformation from anagen to telogen is an increase in the rate of hair loss. (2) A parallel decline in hair diameter. (3) Longer latency periods between the fall of a hair and the onset of regrowth, leading to a reduction in the number of hairs present on the scalp surface. The shorter finer hairs are absent more frequently and absent for longer periods and this contributes to the effect of alopecia.

A Cold Environment Is a Prerequisite for Formation of “Plastid Initials” in Winter Buds of Poplar

The "plastid initial," the presumed precursor of eoplasts and proplastids, is present in the cells of the apical meristem of winter buds of poplar (Populus euramericana). The formation of the plastid initial in the cells of winter buds is initiated soon after the breaking of the innate or resting stage of dormancy, even in winter under nongrowing conditions in mid-January or early February. From this stage to March, the conglomeration of the plastid initial and the formation of prolamellar bodies is evident. In contrast to the poplar samples kept outdoors, the cells of the apical meristem of the indoor winter buds did not show any indication of the formation of the plastid initial and the buds of the latter sample did not flush even at the end of May. These results suggest that the sequence of reactions involved in the onset of regrowth may be closely related to the formation of the plastid initial.

Macromolecular synthesis during recovery of the marine Vibrio sp. S14 from starvation

The recovery of Vibrio sp. S14 cells from energy- and nutrient-starvation was monitored after the addition of glucose minimal medium. Upshift experiments were done throughout a starvation period of 200 h to determine whether cells were more responsive to nutrient addition at the onset of starvation, or if the previously described programme of starvation-induced cellular reorganization had to be completed before cells could become committed to recovery following nutritional upshifts. The kinetics of macromolecular synthesis (RNA, protein and DNA), the rate of respiration and changes in median cell volume in response to nutritional upshifts at different times of starvation were examined. The relative rates of RNA and protein synthesis increased immediately upon addition of glucose minimal medium; the increase in protein synthesis was not dependent on a parallel increase in RNA synthesis, indicating that the starved cells may have an excess of protein synthesizing machinery, including stable RNA and functional ribosomes. The subsequent increase in the rate of DNA replication was initiated approximately 60 min before the first apparent cell division at approximately one doubling of the theoretical minimal cell volume (Vu). Two-dimensional gel electrophoresis was used to demonstrate the fate of starvation-specific proteins during the upshift, and also the synthesis of recovery-induced proteins that were not found in starving cells. Most starvation-inducible proteins were repressed immediately at the onset of the nutritional upshift, while 11 of the 21 recovery-induced proteins identified were expressed exclusively during the maturation phase and were subsequently repressed at the onset of regrowth. The possible role of such maturation-specific proteins in the rapid formation of a reproductive cell committed to growth and division is discussed.

Liposomes as drug carrier system for cis-diamminedichloroplatinum (II). II. Antitumor activity in vivo, induction of drug resistance, nephrotoxicity and Pt distribution.

In this study we have investigated the use of liposomes as a drug carrier system for cis-diamminedichloroplatinum(II) (cis-DDP) in order to reduce the nephrotoxicity with preservation of antitumor activity. Liposomes (PC/PS/Chol 10:1:4) were prepared using hydration media containing no or a relatively low concentration of NaCl. It was found that cis-DDP containing liposomes (lip cis-DDP) injected i.v. to IgM immunocytoma-bearing LOU/M rats at a dose of 1 mg cis-DDP/kg (cumulative dose 7 mg cis-DDP/kg) showed less antitumor activity than the free drug. The optimal cumulative dose of free cis-DDP for induction of antitumor activity in this tumor system is 7 mg/kg (7 X 1 mg/kg). At a dose of 2 mg lip cis-DDP/kg (cumulative dose 14 mg cis-DDP/kg) the antitumor activity could not be increased by choosing another phospholipid composition of the liposomes [DPPC/DPPG/Chol (10:1:10)]. cis-DDP incorporated in DPPC/DPPG/Chol liposomes showed a similar antitumor activity to cis-DDP incorporated in PC/PS/Chol liposomes. After an i.v. dose of 2 mg lip cis-DDP/kg (PC/PS/Chol) kidney damage was less compared to the treatment with free cis-DDP (1 mg/kg). However, after a single dose of 2 mg cis-DDP/kg or a cumulative dose of 8 or 16 mg cis-DDP/kg, kidneys of rats treated with lip cis-DDP contained twice as much Pt as after treatment with free cis-DDP. Moreover, after treatment with lip cis-DDP, a twofold increase of the amount of Pt in tumor tissue was measured. In vitro studies with Pt recovered from spleens obtained from rats treated with lip cis-DDP i.v. showed that based on the equal amounts of Pt recovered the antitumor activity of the recovered Pt was reduced, indicating inactivation of cis-DDP in vivo. As during treatment with free cis-DDP, recurrence of the tumor was observed during the continued treatment with lip cis-DDP. It was found that these recurrent tumors were resistant to further therapy with cis-DDP. In conclusion, cis-DDP encapsulation into liposomes decreased the nephrotoxicity. The antitumor activity of cis-DDP is preserved by liposome encapsulation when it was used at a dose of 2 mg/kg, but it was reduced in terms of earlier onset of regrowth.

The effect of irradiation on the oxygen removal rate of the SSBIa rat fibrosarcoma

Changes in the oxygen uptake of the SSB 1a rat fibrosarcoma following exposure to single doses of radiation have been measured by a technique which also enables the spatial distribution of oxygen uptake rate to be determined. The oxygen uptake rate is measured at 91 sampling positions within an area approximately 5 mm in diameter on a cut surface of recently excised tissue. A first minimum in oxygen uptake per unit volume occurs 3 days after irradiation, during a period of radiation-induced growth inhibition, and this may correspond to improved oxygenation of the tumour. A second decline in oxygen uptake rate coincides with the onset of regrowth and is associated with a change in the pattern of subsequent cell proliferation within the tumour. The changes in oxygen uptake rate are discussed in relation to various models for the processes of tumour reoxygenation.