Apical control of branch growth and angle in woody plants

Apical control is the inhibition of a lateral branch growth by shoots above it (distal shoots). If the distal shoots are cut off to remove apical control, the lateral branch can grow larger and may bend upwards. Apical control starts when new lateral buds grow after passing through a period of dormancy. Buds initially break and produce leaves, then apical control is exerted and the lower (proximal) laterals stop growing. Apical control also inhibits growth of large, old branches. Gravimorphism and restricted water and nutrient transport can inhibit branch growth, but they are not primary mechanisms of apical control. Apical control may reduce branch photosynthesis. Under apical control allocation of branch-produced assimilate to the stem is relatively high, so low assimilates in the branch may limit branch growth even though hormone levels are adequate for growth. Hormones appear to be involved in apical control, but it is not known how. One role of hormones may be to maintain the strength of the stem sink for branch-produced assimilate. Upward bending of a woody branch after release from apical control requires both new wood production and production of wood cells that can generate an upward bending moment. Apical control inhibits radial growth of branches and, in some species, may regulate the production of wood with an upward bending moment.     

Suppression of the source activity affects carbon distribution and frost hardiness of vegetating winter wheat plants

Effect of suppression of the source activity on some physiological characteristics of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) was studied on plants grown in water culture. The plants were examined at the mixotrophic stage of growth period, during their transition from vegetative state to relative dormancy in autumn. The average temperature over 10 days of the experiment was 6°C at 9-h photoperiod and illuminance of 8–20 klx. The source strength was suppressed successively with a series of treatments: intact control plants (V1); plants with the seed endosperm removed (V2); plants with photosynthesis inhibited (V3); plants with the seed endosperm removed and photosynthesis inhibited (V4); plants with the seed endosperm removed, photosynthesis inhibited, and the root nutrient medium replaced with distilled water (V5). On the 6th–10th day of the experiment, the relative growth rate (RGR) was determined from dry weight increments. At the same time, the distribution of biomass among organs, the CO₂ exchange rates (photosynthesis and dark respiration), the content and proportions of sugars (sucrose, glucose, and fructose), the total content of phenolic compounds and flavonoids, the index of membrane stability (IMS) in leaves, and frost hardiness of plants were measured. Frost hardiness of vegetating plants was shown to be inversely related to RGR (R = ?0.906), dark respiration rate (R = ?0.789), the percentage of sucrose in total sugar content (R = ?0.737), leaf IMS (R = ?0.390), and the rate of apparent photosynthesis (R = ?0.288); it was directly proportional to the content of flavonoids (R =0.973), total phenols (R = 0.743), and sugars (R = 0.385). The role of modified source-sink relations in frost hardiness of vegetating plants at the stage of their transition to cold hardening is discussed. The differences between plants undergoing this transition and cold-hardened plants are considered, as well as the importance of phenolic compounds for the development of frost hardiness.     

植物的顶端优势和水分上升机理新说

植物体有一个能量系统,由植物顶端、由植物顶端、形成层及其初生韧皮部和木质部、传递细胞等组成。这些细胞含线粒体量多质好,摘顶等刺激这些地方ＡＴＰ复合酶能产生大量能量,通过胞间连丝引起连锁反应并刺激和激活激素、营养物质等而产生生命活动、项端优势等。植物细胞的原生质是一种液晶,只需极少能量便能产生很大的作用。除去顶芽,刺激线粒体能产生大量能量供给侧芽,激活侧芽激素等而使侧芽生长,由于能量作功,逐渐减少,     

Structural changes in brucella chemical vaccine after gamma-irradiation

It was shown that gamma-irradiation of Brucella strain chemical vaccine stimulated phospholipid peroxidation therein: the content of extractable total phospholipids in the exposed vaccine decreased mainly due to diminution of phosphatidylcholines and phosphatidyl-ethanolamines. A relative content of high- and low-molecular weight protein components increased in the gamma-irradiated vaccine.     

pH changes in Chinese hamster cells after gamma-irradiation

Intracellular pH (pHin) changes after gamma-irradiation of Chinese hamster fibroblasts have been studied by a fluorescence method using the ratio of fluorescence intensities after excitation at 488 and 458 nm and measurement at emission wavelength of 515 nm. Irradiation with doses inducing reproductive death (2.5-20 Gy) causes a pHin shift towards the alkaline region by 0.4-0.5 pH units, but this shift is transient. Irradiation with a 500 Gy dose, inducing interphase death, causes a more pronounced (pHin greater than or equal to 8.0) alkalization of the intracellular medium which is retained for more than 1.5 hours post-irradiation. It is proposed that the observed alkalization of the internal medium of irradiated cells is possibly due to a change in the functional state of mitochondria. These changes are probably one of the causes of interphase cell death after irradiation with high doses.     

Unpaired bases in phage DNA after gamma-irradiation in-situ and in-vitro

Summary Phage Lambda DNA, gamma-irradiated in-situ and in-vitro, has been analyzed for unpaired bases by melting, reannealing, and cleavage with Sl nuclease which is specific for single-stranded DNA. DNA, irradiated in-situ, i.e., in the phage particle, contained sites being sensitive to Sl nuclease. These single-stranded lesions were passed over and conserved during reannealing, whereas adjacent DNA regions reannealed specifically. Complementary base-pairing was restored after Sl nuclease treatment. Comparison of the T_m,-data before and after Sl nuclease treatment indicated that the single-stranded regions were removed by the enzyme. In contrast, DNA irradiated in-vitro, i.e., gamma-irradiated in aqueous solution, failed to match complementarily and was not sensitive to Sl nuclease. Thus it appears that lesions leading to unpaired bases were randomly distributed in DNA irradiated in-vitro, but occurred in clusters after irradiation in-situ. Most probably these clusters contain damaged bases which in turn caused localized disruption of the hydrogen bonds between complementary base pairs.     

S1-sensitive sites in DNA after gamma-irradiation

DNA from gamma-irradiated T1 bacteriophages was analyzed for "single-stranded" sites by cleavage with S1 nuclease from Aspergillus oryzae as lesion probe. The ratio of "S1-sensitive sites" to the amount of radiation-induced single-strand breaks was about one. Presumably these "denatured" sites were associated with single-strand breaks. The subsequent check for the persistence of "single-stranded" sites within the DNA molecule by thermokinetics demonstrated a strong affinity of the nuclease to its substrate, the single-stranded lesion, and a perfect excision. It is assumed that the direct absorption of radiation energy in the DNA gives rise to the formation of such bulky lesions.     

Apical stem cells sustaining prosperous evolution of land plants

Journal of Plant Research -     

Curcumin treatment enhances the repair and regeneration of wounds in mice exposed to hemibody gamma-irradiation

Hemibody irradiation in multiple fractionated doses is frequently used for the treatment of various neoplastic disorders. It produces both acute and late effects on the skin and subcutaneous tissues that have profound implications in the healing of surgical wounds. Because of the crucial practical importance of hemibody radiation exposure associated with skin wounds, it is imperative to investigate the efficacy of cost-effective herbal products in the reconstruction of irradiated wounds. Therefore, the effect of pretreatment of curcumin was studied on the healing of excision wound in mice exposed to 2, 4, 6, or 8 Gy of hemibody gamma-radiation. A full-thickness skin wound was created by removing the skin flap of the dorsum of 8- to 10-week-old Swiss albino mice partially (lower half, below the rib cage) exposed to 2, 4, 6, or 8 Gy of gamma-radiation. The progression of wound contraction was monitored periodically by capturing video images of the wound, where the first image of each wound from different groups was obtained 1 day after wounding and that day was considered as day 0. Eight animals were used in each group at each exposure dose for wound contraction studies. Furthermore, the effect of curcumin on mean healing time after exposure of mice to 2, 4, 6, or 8Gy of hemibody gamma-radiation was also evaluated, where eight animals were used in each group at each exposure dose. Collagen, hexosamine, DNA, nitric oxide, and histologic profiles were also evaluated during the course of healing of excision wounds at days 4, 8, and 12 after irradiation treated or not with curcumin before exposure to 0 or 6 Gy of gamma-radiation. Six animals were used in each group at each interval for each biochemical parameter studied, except for histologic evaluations, where four animals were used in each group at each interval. Exposure of mice to different doses of gamma-radiation resulted in a dose-dependent delay in contraction and wound-healing time of excision wound, whereas curcumin pretreatment caused a significant elevation in the rate of wound contraction and a decrease in the mean wound-healing time. Treatment with curcumin before irradiation enhanced the synthesis of collagen, hexosamine, DNA, nitrite, and nitrate, and histologic assessment of wound biopsy specimens revealed improved collagen deposition and an increase in fibroblast and vascular densities. The authors' study demonstrates that curcumin pretreatment has a conducive effect on the irradiated wound and could be a substantial therapeutic strategy for ameliorating radiation-induced delay in wound repair in cases of radiation-induced skin injuries.     

Changes in synapses after gamma-irradiation of the rat head

High reactivity and, at the same time, flexibility of interneuronal contacts were observed after exposure of rat head to 2-100 Gy radiation. At high doses (200-400 Gy) radiation-induced changes played a major role in the development of the cerebral form of radiation sickness. A complete asynapsis is probably one of the causes of the animals death "under the ray" (irradiation of the head with a dose of 1000 Gy).     

Catalytic properties of testicular hyaluronidase after gamma-irradiation

The effect of gamma-irradiation on ovine testicular hyaluronidase was studied in aqueous solution. Following irradiation, hyaluronidase is inhibited, and the kinetics of inhibition follow a pattern in which Km and Vmax decline as radiation dose is increased. It was indicated that the binding affinity of the residual activity of hyaluronidase with substrate is enhanced and depends upon radiation damage. Effects of various agents such as pH, salts, PCMB and glutathione on irradiated hyaluronidase have been compared with non-irradiated enzyme. The irradiated hyaluronidase was more sensitive to inhibition by CuSO4 than the non-irradiated enzyme. The residual activity after irradiation is less refractory to FeCl3 inhibition and less sensitive to NaCl stimulation compared to non-irradiated hyaluronidase. pH response curves of ovine testicular hyaluronidase show two maxima which become more evident after irradiation.     

Agrobacterium-mediated transformation and regeneration of cotton plants

Cotton (Gossypium hirsutum L.) was transformed by the EHA101 strain of Agrobacterium tumefaciens harboring a binary vector pGA482GG plasmid carrying the marker genes for neomycin phosphotransferase II (nptII) determining resistance to kanamycin and β-glucuronidase (GUS). The cotyledons, hypocotyls, shoot meristem tissue, and its segments taken from in vitro growing seedlings were used as explants. Explants were cultured in a Murashige and Skoog (MS) medium containing various hormone combinations to induce shoot regeneration. The highest frequency of shoot formation was obtained from the shoot meristem. After selection in the MS medium containing kanamycin (50 mg/l), these tissues were tested by histochemical GUS assay. Shoots regenerated from excised shoot meristems or their halves were cultured for 4–6 weeks to obtain rooted plants, which then produced fully-developed plants and seeds in pots. Genomic integration of the kanamycin-resistance gene was detected by the PCR analysis. Seed germination percentage was 95% after the F1 seeds of transgenic cotton plants were cultured on half-strength MS medium supplemented with 50 mg/l kanamycin. Thus, a protocol for effective Agrobacterium-mediated genetic transformation of cotton was optimized. Published in Russian in Fiziologiya Rastenii, 2006, Vol. 53, No. 3, pp. 462–467. The text was submitted by the authors in English.     

Somatic embryogenesis and regeneration of flowering plants in rose

Summary Somatic embryos of the cut rose cultivars Domingo and Vickey Brown were obtained from callus derived from leaf explants on half strength Murashige and Skoog medium with low concentrations of kinetin and 1-naphthyl acetic acid or 2-naphthyloxyacetic acid. Somatic embryos were first observed after 6 to 12 weeks of culture on callus formed at the basis or midrib of the leaf. Embryos could be grown to phenotypically true to type greenhouse plants.Abbreviations IAA 3-indole-acetic acid - IBA indole-3-butyric acid - NAA 1-naphthylacetic acid - NOA 2-naphthyloxyacetic acid - BAP 6-benzylaminopurine - KIN 6-furfurylaminopurine - MS Murashige and Skoog