亚硫酸氢钠对大蒜幼苗生长及细胞分裂的作用

研究SO2体内衍生物-亚硫酸钠与亚硫酸氢钠（分子比为3：1）混合液对大蒜幼苗生长和细胞分裂的效应。结果表明：低浓度（0.2mmol/L）的混合液促进幼苗生长,短时间（24h）作用时根尖细胞有丝分裂指数（MI）提高;高浓度（1.5与2.0mmol/L）处理抑制大蒜幼苗生长,细胞周期涎滞,大蒜根尖MI下降,并诱发细胞分裂异常,且呈明显的时间效应与剂量效应关系。     

DETERMINATE (det) MUTANT OF PISUM SATIVUM (LEGUMINOSAE: PAPILIONOIDEAE) EXHIBITS AN INDETERMINATE GROWTH PATTERN

Inflorescence ontogeny and morphology of the det mutant of Pisum sativum L. were investigated using scanning electron microscopy. This mutation causes the production of a limited number of axillary flowers followed by the formation of an apparent terminal flower slightly offset from the vertical. Our study indicates that the apparent terminal flower arises from an axillary meristem. The terminal meristem senesces and differentiates hairs, forming a rudimentary stub in the same manner as axillary meristems of conventional (Det) and det plants. Thus the dramatic effect of the det gene on inflorescence architecture results from early apical arrest rather than conversion of the terminal meristem to a flower as implied by the symbol det. This mutant will be valuable in elucidating regulation of apical arrest.     

CONTROL OF INTESTINAL EPITHELIAL REPLACEMENT: LACK OF EVIDENCE FOR A TISSUE-SPECIFIC BLOOD-BORNE FACTOR

The small intestine of rats was cut across in two places, about 14 and 50% of the length of the small intestine from the pylorus, and continuity was re-established by suturing the proximal and distal ends. The resulting sac of small intestine, averaging 36% of the total length of the small intestine, had its upper end closed off, and its lower end anastomosed, either to the intestine-in-continuity (an ‘intestine-sac’), or to the skin of the abdominal wall (a ‘skin-sac’). On the ninth post-operative day, the cell production rate in squashes of micro-dissected whole crypts of Lieberkühn was measured by mitotic blockade with Colcemid. The rate of cell production in unoperated and sham-operated rats was 30 cells/crypt/hr, throughout the length of the small intestine. In the intestine in continuity, the rate increased to an average of 46 cells/crypt/hr above the anastomosis, and to 54 cells/crypt/hr below it. At the lower end of the ‘intestine-sac’, which drained into the intestine-in-continuity, the rate was 39 cells/crypt/hr, while in the lower end of the sac which drained to skin the rate of cell production was only 16 cells/crypt/hr. This significantly lower cell production rate in intestine which was not in contact with ingesta is taken to be evidence of the importance of local, rather than blood-borne factors in the control of epithelial replacement.     

FLEXURAL STIFFNESS ALLOMETRIES OF ANGIOSPERM AND FERN PETIOLES AND RACHISES: EVIDENCE FOR BIOMECHANICAL CONVERGENCE

Evidence for convergence in biomechanical and anatomical features of leaves (elastic modulus E, second moment of area I, taper of petioles, the longitudinal distribution of petiolar and laminar weight, and volumes of tissues) is presented based on a survey of 22 species (distributed among dicots, monocots, and ferns). In general, regardless of taxonomic affinity, petioles were found to be mechanically constructed in one of two ways: Type I petioles—as cantilevered, end-loaded beams with relatively uniform flexural stiffness (EI) (simple and palmate leaves); and Type II petioles—as tapered cantilevered beams whose static loadings (biomass) and EI increase basipetally (pinnate leaves). In general, collenchyma and sclerenchyma were found to be peripherally located in transections through Type I and II petioles, respectively. Statistical analyses within each species and among species with either type of petiole indicated that EI ≈ k₁Lp^2.98 and EI ≈ k₂Lp^2.05 for Type I and II petioles, respectively, where k₁ and k₂ are dimensional constants and Lp is petiolar length. The data are interpreted to indicate that Type I and II petioles mechanically operate to deal with static loadings in two distinct ways, such that Type II petioles function in an analogous manner to branches supporting separate leaves (leaflets). The convergence in mechanical “designs” among taxonomically distinct lineages (angiosperms and ferns) is interpreted as evidence for selection on mechanical attributes of load supporting structures (petioles).     

N-METHYL-N'-NITRO-N-NITROSOGUANIDINE AS A MUTAGEN FOR BLUE-GREEN ALGAE: EVIDENCE FOR REPAIR1

Survival and mutagenesis have been examined in the marine coccoid blue-green alga, Agmenellum quadruplicatum, after treatment with the chemical mutagen, N-methyl-N'-nitro-N-nitrosoguanidine (NTG). When cells were immediately returned to growth conditions following NTG treatment, the survival level was consistently low and essentially independent of the treatment conditions. The types of mutants found paralleled those previously described in the freshwater coccoid, Anacystis nidulans. If, however, cells were kept under very low light intensity, a nongrowth condition, following NTG treatment, viable cell recovery was dramatically increased. This “dim light” repair in A. quadruplicatum has characteristics similar to those reported for the dark repair systems of bacteria and yeast.     

THE SPECTRAL SENSIBILITY OF THE SUN-FISH AS EVIDENCE FOR A DOUBLE VISUAL SYSTEM

1. An extension of a previously described method makes possible the measurement of the visibility function of Lepomis at high intensities of spectral illumination. This is accomplished by determining the relative energies of various spectral beams which will just produce a visual orienting response by the animal to the movement of a pattern composed of fine lines. 2. The function so determined is different from that obtained with a pattern composed of wide bars and spaces at a lower intensity level. 3. This difference furnishes direct and quantitative proof that the eye of Lepomis is a physiologically duplex visual system and parallels the known anatomical distinctions between the rods and cones. 4. A comparison of the visibility curves of the two systems indicates that both functions are similar in shape but that the cone curve is shifted to the red. 5. It is suggested that this relation between the two systems, which is also found in the human and the fowl, indicates that the photosensory substance is the same in each case for the rods and cones. According to this hypothesis, the shift of the cone curve is due to a common physical cause which depends on differences in the properties of the solvent media in the cones and in the rods.     

GLUCOCORTICOIDS AS A REGULATORY FACTOR FOR BRAIN TRYPTOPHAN HYDROXYLASE

—The normal developmental rise of tryptophan hydroxylase levels in neonatal rat brain was blocked by adrenalectomy. Similarly, adrenalectomy prevented the rescrpine-induced elevation of tryptophan hydroxylase activity in brain stem of adult mice. In both cases, the effects of adrenalectomy could be reversed by replacement injections of corticosterone. Repeated injections of corticosterone (5 mg/kg daily) in fact induced a rise of brain tryptophan hydroxylase levels in neonatal brain. However, neither adrenalectomy nor repeated injections of large doses of the hormone (20 mg/kg, daily) was found to be effective in affecting the normal enzyme levels in adult brain. Apparent K_m of the enzyme for substrate was unchanged by corticosterone in vivo or in vitro. These results indicate that glucocorticoids have a significant role in the regulation of brain tryptophan hydroxylase: possibly as an inducing signal during neonatal development and as a permissive factor at adult age.     

EVIDENCE FOR PREDATION AS A FACTOR IN DETERMINING SHELL COLOR FREQUENCIES IN A MANGROVE SNAIL LITTORINA SP. (PROSOBRANCHIA: LITTORINIDAE)

It was hypothesized that in Littorina populations living on Avicennia marina in Moreton Bay, Queensland, yellow shelled individuals are at a selective advantage over other shell colors and that this advantage is due to differential selection by predators. Yellow shelled individuals were more likely to be recaptured than others, indicating a higher survival rate of yellows. When predation was restricted on ten mangrove trees, the apparent advantage of yellow shells was removed. After 18 months, the relative frequency of yellow shelled individuals was significantly lower on experimental trees than on control trees. A combination of selection for crypsis and for the less common morph is suggested as the mechanism maintaining the high levels of variation in this species.     

MEASUREMENT OF ACETYLCHOLINE TURNOVER WITH GLUCOSE USED AS PRECURSOR: EVIDENCE FOR COMPARTMENTATION OF GLUCOSE METABOLISM IN BRAIN

The turnover of acetylcholine in whole mouse brain in vivo has been determined using [U-¹⁴C]glucose as a precursor of the acetyl moiety. The standard requirements for the measurement of turnover were met: the injection did not change the concentrations of precursor or product, the amount of radioactivity in the brain was proportional to the amount injected, and the relationship between the specific activity of glucose and that of acetylcholine was typical of a precursor and a product. The value for acetylcholine turnover was 64 pmol/min per mg protein, approx 6.4 nmol/min per g brain. Treatment with amobarbital (0.16 mmol/kg) decreased the incorporation of glucose into acetylcholine by 73 × 7%, and treatment with atropine increased it by 18 × 6%. These values agree with those using choline as a precursor, supporting the validity of the values for turnover obtained with either labelled precursor. The specific activity of acetylcholine was higher than that of pyruvate at all times in mouse brain in vivo and in rat brain slices in vitro. These observations demonstrate compartmentation of glucose metabolism with respect to acetylcholine synthesis in the brain. They agree with observations by others of compartmentation of acetyl metabolism. They provide an explanation for the close linkage which has been observed between carbohydrate catabolism and acetylcholine synthesis in the CNS.