Seasonal and long-term soil water regime in West African tropical forest

Abstract. Variation of soil matric potential of a Wet Evergreen and a Moist Semi-deciduous West African forest were compared. The two forest types differed strongly in their soil water regime. Wet Evergreen forest experienced matric potentials below ?100 kPa only occasionally, while in Moist Semi-deciduous forest matric potentials were less than ?2.5 MPa for periods of several weeks or more each season. A water balance equation was used to simulate the soil water regime at both sites and predict severity and length of the dry period. The predictions showed good agreement with the field measurements of soil water potential over a 2-yr period. The methodology was used to estimate the occurrence and severity of droughts over longer periods at the two sites. The balance calculations suggest that droughts occur occasionally in the Wet Evergreen forest under study. The potential impact of droughts on species distribution and vegetation disturbance in tropical forests is discussed.     

The role of active oxygen in iron tolerance of rice (Oryza sauva L.)

Summary Iron tolerance of rice (Oryza sativa L.) was investigated using an oxygen depleted hydroculture system. Treatment with high concentrations of Fe²⁺ induced yellowing and bronzing symptoms as well as iron coatings at the root surface. Root and shoot growth were inhibited by increasing iron concentration in the medium. All symptoms were more pronounced in an iron sensitive cultivar (IR 64) compared to an iron tolerant one (IR 9764-45-2). Superoxide dismutase and peroxidase activity of root extracts of IR 97 were about twice that of IR 64 in untreated control plants. No significant increase of peroxidase activity was detected with increasing iron concentration in the medium. Catalase activity of IR 64 was slightly higher than that of IR 97, independent of iron concentration.Abbreviations SOD Superoxide dismutase (EC 1.15.1.1) - POD peroxidase (EC 1.11.1.7) - EDTA ethylenediamintetraacetic acid - fwt fresh weight - Hepes (N-[2-hydroxyethyl]piperazine-N-[2-ethanesulfonic acid]) - BSA bovine serum albumin - IR 97 IR 9764-45-2 an iron tolerant rice cultivar - IR 64 iron sensitive rice cultivar - PM plasma membrane     

A gene encoding a truncated large subunit of Rubisco is transcribed and salt-inducible in rice

Using the rice salt-tolerant mutant 20 as material, a cDNA library was constructed and two salt-inducible clones, SIR5.5 and SIR8.1, were isolated by differential screening. Homology analysis revealed that the two clones together constituted a chimeric rbcL which encoded a truncated large subunit of Rubisco with 337 amino-acids, plus 64 amino-acids of unknown origin. The expressions of both the normal and the chimeric locus appeared to be developmentally regulated and salt-inducible in shoots of the salt-tolerant mutant 20 and its original variety 77–170. In roots, their expressions were salt-inducible in the salt-tolerant mutant 20 whereas no, or only premature, forms were present in the salt-treated original variety 77–170. Higher concentrations of salt reduced the expressions of both normal rbcL and the chimeric locus. ABA showed no effect on their expression.     

BCL-2-Related Protein Expression in Apoptosis: Oxidative Stress Versus Serum Deprivation in PC12 Cells

Abstract: Expression of the BCL-2 protein family members, BAX, BAK, BAD, BCL-xL, BCL-xS, and BCL-2, was measured (by western blotting using specific antibodies) in PC12 cells before and during apoptosis induced by either H₂O₂ treatment or by serum deprivation and during rescue from apoptosis by nerve growth factor (NGF). H₂O₂-induced apoptosis, as measured by DNA fragmentation, caused: (a) a dose-dependent increase in BAX, (b) a dose-independent increase in BAK, and (c) a dose-dependent inhibition of BAD expression. By comparison, apoptosis induced by serum deprivation resulted in a time-dependent decrease in both BAX and BAK, along with a dramatic and sudden decrease in BAD expression. However, when PC12 cells were incubated in an apoptosis-sparing medium (i.e., NGF-supplemented serum-free medium), both BAX and BAK were increased significantly, whereas BAD expression remained inhibited. BCL-xL expression was increased by H₂O₂ but unaffected by serum deprivation or long-term NGF treatment. Neither BCL-2 nor BCL-xS expression could be detected in PC12 cells under the experimental conditions tested. Our results show that the expression of BAX, BAK, BAD, and BCL-xL is altered in a stimulus-dependent manner but cannot be used to define whether a cell will undergo or survive apoptosis. The similarity between changes in expression of BCL-2-related proteins induced by H₂O₂ exposure and NGF rescue could reflect activation in part of a common antioxidant pathway.     

Influence of elevated ambient temperature after breeding on plasma corticoids, estradiol and progesterone in gilts

Thirty Yorkshire gilts were used to determine the influence of elevated ambient temperature during days 8 to 16 after breeding on concentrations of progesterone, corticoids and estradiol in plasma. Gilts were mated to a boar between 0800 and 1000 hr of the first day (day 0) and each subsequent day of estrus. On day 5 or 6, 22 gilts were anesthetized and a cannula was placed in the anterior vena cava. Gilts were randomly allotted to either control (23+/-1 C) or hot (35+/-1 C for 12 hr and 32+/-1 C for 12 hr daily) environmental chambers on day 8. Gilts were bled twice daily (0800 and 2000 hr) on days 9 through 16, then once daily until day 28. A third group of noncannulated gilts was bred and assigned to the control chamber. All cannulated gilts were injected intravenously with 25 IU of ACTH on day 16, and frequent blood samples were collected. Concentrations of progesterone in plasma were similar for heat-stressed and control gilts that were pregant. However, progesterone in plasma was reduced during days 13 to 19 in nonpregnant heat-stressed gilts compared to the pregnant and nonpregnant control gilts. Concentrations of estradiol in plasma were greater in nonpregnant heat-stressed gilts than in nonpregnant control and all pregnant gilts on days 10, 11 and 12 after estrus. Concentrations of corticoids and progesterone in plasma after infusion of ACTH on day 16 after breeding were reduced in heat-stressed nonpregnant gilts compared to heat-stressed pregnant, control pregnant and control nonpregnant gilts. These data indicate that reduced reproductive performance which occurs after exposure of gilts to increased ambient temperature during days 8 to 16 after breeding may be related to altered endocrine function.     

Effect of soil moisture and clipping stresses on the nutrient (N,P and K) concentration,uptake and use efficiency in one temperate and two tropical grasses

Summary The concentration, uptake and element use efficiency of N, P and K in one C₃ annual (Polypogon monspeliensis) and two C₄ (Echinochloa colonum, an annual, andDichathium annulatum, a perennial) grasses were determined during winter and summer seasons in monocultures raised in field plots at three moisture levels,viz. full, half and one-fourth of field capacity. At each moisture regime the plants were clipped thrice at moderate and severe levels corresponding to 40 and 80% of live green. The concentration of these elements was characteristic of the growth habit of these plants;e.g. the build up of concentration was maximum in leaf of the annuals while it was comparable in crown and leaf of Dichanthium. The N level was maximum in Polypogon. The nutrient use effiency was comparable in the two annuals and maximum K and N use were obtained in Polypogon and Dichanthium, respectively.     

Resistenzphysiologische Grundlagen der evolutiven Kälteakklimatisation von Sproßpflanzen

Gradations in cold resistance of plants with different latitudinal and altitudinal distribution, and the various categories of chilling and freezing resistance are hypothesized to be evolutionary steps of adaptive responses to increasing low temperature stress and annual seasonality. The gradual lowering of the critical phase transition temperature of biomembrane lipids, the capacity of persistent supercooling of tissues, and the development of a dormancy linked freezing-tolerance are considered to be essential mechanisms resulting in improved acclimatation to low temperature climates.

     

Root-zone temperature and salinity: Interacting effects on tillering,growth and element concentration in barley

The effects of root-zone salinity (0, 30, and 60 mmol L^–1 of NaCl) and root-zone temperature (10, 15, 20, and 25°C) and their interactions on the number of tillers, total dry matter production, and the concentration of nutrients in the roots and tops of barley (Hordeum vulgare L.) were studied. Experiments were conducted in growth chambers (day/night photoperiod of 16/8 h and constant air temperature of 20°C) and under water-culture conditions. Salinity and root temperature affected all the parameters tested. Interactions between salinity and temperature were significant (p<0.05) for the number of tillers, growth of tops and roots, and the concentration of Na, K, P in the tops and the concentration of P in the roots. Maximum number of tillers and the highest dry matter were produced when the root temperature was at the intermediate levels of 15 to 20°C. Effect of salinity on most parameters tested strongly depended on the prevailing root temperature. For example, at root temperature of 10°C addition of 30 mmol L^–1 NaCl to the nutrient solution stimulated the growth of barley roots; at root temperature of 25°C, however, the same NaCl concentration inhibited the root growth. At 60 mmol L^–1, root and shoot growth were maximum when root temperature was kept at the intermediate level of 15°C; most inhibition of salinity occurred at both low (10°C) and high (25°C) root temperatures. As the root temperature was raised from 10 to 25°C, the concentration of Na generally decreased in the tops and increased in the roots. At a given Na concentration in the tops or in the roots, respective growth of tops or roots was much less inhibited if the roots were grown at 15–20°C. It is concluded that the tolerance of barley plant to NaCl salinity of the rooting media appears to be altered by the root temperature and is highest if the root temperature is kept at 15 to 20°C.     

Isolubimin: A possible precursor of lubimin in infected potato slices

Potato slices treated with spirovetiva-1(10),11-diene-2-one yield lubimin and rishitin within 24 hr. A vetispirane which has not been detected in fungally infected potatoes was also isolated. This compound, isolubimin, appears to be an intermediate in the conversion of the above spirovetivone to lubimin.