Rates of Drying and Survival of Rhizobium meliloti Strains During Storage at Different Relative Humidities

An investigation was made of the survival of six strains of Rhizobium meliloti filtered on membrane filters and held in atmospheres of controlled relative humidities (RH) of from 0 to 100% at 30°C in the presence of air. The rate of water loss in the desiccator was determined by the humidity-controlling solution used. Drying was accelerated by a mild evacuation of the desiccator during the drying step. Survival rates of R. meliloti strains were much higher after slow drying to 0% RH than immediately after rapid drying. Fast drying (drying period less than 3.4 h) was shown to adversely affect the tolerance to storage at all RH values tested (no survival after 2 to 5 days of storage). When survival during storage was measurable (after slow drying), the optimum RH values for storage were 43% for strains A145 and Wu498, 22 to 43% for strains RCR2011, Wu499, and Ar16, and 83% for strain RCR2004. The most favorable drying periods were 8, 9.2, 14.2, and 50.1 h for the subsequent storage of strain RCR2011 at RH values of 0, 22, 43, and 83%, respectively. The damaging effects of rapid drying on the tolerance of strain RCR2011 to storage at different RH values could be prevented either by rehydration and subsequent slow redrying or incomplete rapid drying followed by slow drying. It is suggested that R. meliloti strains are susceptible to desiccation stresses. However, the quantitative differences among strains appear to be large enough to permit selection with regard to tolerance to desiccation and storage in dried states.     

Survival of root‐lesion nematodes (Pratylenchus thornei) after wheat growth in a vertisol is influenced by rate of progressive soil desiccation

The root‐lesion nematode (Pratylenchus thornei) is a major pathogen of wheat in the subtropical grain region of eastern Australia. Experiments were conducted to learn whether soil desiccation can account for the rapid fall in peak P. thornei population densities noted in the field after wheat matures. The decline in population densities of P. thornei after growth of wheat was measured on progressive desiccation of soil with roots by fast and slow drying methods. The vertisolic soil of initial moisture content 45% w/w (or matric potential of pF 3.3) was dried in 5% decrements to an air‐dried gravimetric moisture content of 15% (pF 5.6) taking 10.7 h for fast drying and 91.5 h for slow drying. After drying, live nematodes were extracted with Whitehead trays for 2 and 7 days and counted in four life stages (adults and juvenile stages J2, J3 and J4). Fast drying resulted in a sigmoidal decline in total P. thornei with only 5% of the population alive in soil at 15% moisture content, but slow drying had no significant effect on the population density. The percentage of nematodes extracted at 2 days compared with the total extracted over 7 days in undried soil (～89% of total) declined quadratically on desiccation to be 48% (fast drying) and 78% (slow drying) at 15% moisture content. With fast drying, the proportion of adults and J2 decreased whereas the proportion of J4 increased as the soil dried. With slow drying, the proportion of J2 and J3 stages decreased while the proportion of J4 increased. Thus the J4 or pre‐adult was the life stage most tolerant of soil desiccation. Time is required for P. thornei to go into a state of anhydrobiosis as a soil dries and this information can be used to model P. thornei survival in the field based on environmental parameters.     

INCORPORATION OF H3-THYMIDINE IN LEAF NUCLEI OF XANTHIUM PENNSYLVANICUM

The basic kinetics and the pattern of incorporation of H³-thymidine was studied in the leaf lamina of Xanthium pennsylvanicum. A method of foliar absorption was used to incorporate the radioisotope into leaf nuclei. The autoradiographic techniques employed provided data on the amount of the isotope incorporated. It was determined that 10 μc/ml (sp. act. 6.7 c/mmole) of H³-thymidine with 1–8 hr of isotopic growth and 4 hr of postisotopic growth gave the most satisfactory results. The percent of labelled nuclei and the number of grains per nucleus were presented as functions of isotopic and postisotopic growth periods. Distribution of grains in the nuclei approximated the Poisson distribution at 1 hr of isotopic growth. Increased time of isotopic growth changed the pattern of grain distribution. No deleterious effects were observed using an 8-hr period of isotopic growth, but prolonged incubation time significantly decreased the proportion of mitotic figures in the lamina. The amount of incorporation of the DNA precursor expressed as percent of labelled nuclei was linear to about 16 hr of isotopic growth and thereafter decreased gradually. As indicated by the average number of grains per nucleus, H³-thymidine incorporation increased to about 16 hr, and soon after reached a saturation level. The percent of labelled nuclei and the number of grains per nucleus decreased as a function of the postisotopic growth period. However, they were significantly greater in the lamina near the vein than in the lamina region at some distance from the vein. The radioactive precursor was initially absorbed by the cells of the lamina and was subsequently translocated into the vascular system. There it was circulated and made available to the dividing cells near veins of the lamina. This region may be a metabolically distinct part of the lamina with significantly higher rates of incorporation and mitotic turnover.     

Abscisic acid and ethylene interact in wheat grains in response to soil drying during grain filling

Grain filling is an intensive transportation process regulated by soil drying and plant hormones. This study investigated how the interaction between abscisic acid (ABA) and ethylene is involved in mediating the effects of soil drying on grain filling in wheat (Triticum aestivum). Two wheat cultivars, cv. Yangmai 6 and cv. Yangmai 11, were field-grown, and three irrigation treatments, well-watered, moderately soil-dried (MD) and severely soil-dried (SD), were imposed from 9 d post anthesis until maturity. A higher ABA concentration and lower concentrations of ethylene and 1-aminocylopropane-1-carboxylic acid (ACC) were found in superior grains (within a spike, those grains that were filled earlier and reached a greater size) than in inferior grains (within a spike, those grains that were filled later and were smaller), and were associated with a higher filling rate in the superior grains. An increase in ABA concentration and reductions in ethylene and ACC concentrations in grains under MD conditions increased the grain-filling rate, whereas much higher ethylene, ACC and ABA concentrations under SD conditions reduced the grain-filling rate. Application of chemical regulators gave similar results. The results did not differ between the two cultivars. The grain-filling rate in wheat is mediated by the balance between ABA and ethylene in the grains, and an increase in the ratio of ABA to ethylene increases the grain-filling rate.     

Hormonal changes in the grains of rice subjected to water stress during grain filling

Lodging-resistant rice (Oryza sativa) cultivars usually show slow grain filling when nitrogen is applied in large amounts. This study investigated the possibility that a hormonal change may mediate the effect of water deficit that enhances whole plant senescence and speeds up grain filling. Two rice cultivars showing high lodging resistance and slow grain filling were field grown and applied with either normal or high amount nitrogen (HN) at heading. Well-watered and water-stressed (WS) treatments were imposed 9 days post anthesis to maturity. Results showed that WS increased partitioning of fixed (14)CO(2) into grains, accelerated the grain filling rate but shortened the grain filling period, whereas the HN did the opposite way. Cytokinin (zeatin + zeatin riboside) and indole-3-acetic acid contents in the grains transiently increased at early filling stage and WS treatments hastened their declines at the late grain filling stage. Gibberellins (GAs; GA(1) + GA(4)) in the grains were also high at early grain filling but HN enhanced, whereas WS substantially reduced, its accumulation. Opposite to GAs, abscisic acid (ABA) in the grains was low at early grain filling but WS remarkably enhanced its accumulation. The peak values of ABA were significantly correlated with the maximum grain filling rates (r = 0.92**, P < 0.01) and the partitioning of fixed (14)C into grains (r = 0.95**, P < 0.01). Exogenously applied ABA on pot-grown HN rice showed similar results as those by WS. Results suggest that an altered hormonal balance in rice grains by water stress during grain filling, especially a decrease in GAs and an increase in ABA, enhances the remobilization of prestored carbon to the grains and accelerates the grain filling rate.     

G2 sub-population in mouse liver induced into mitosis by lead acetate

A single intracardiac dose of lead acetate (40 microgram lead/g body weight) induced a 25-fold increase in mitosis of mouse hepatocytes 5 hr after injection, as determined by autoradiography. The prompt appearance of a mitotic wave and the relatively large number of mitoses suggest that the mitotic cells were derived from a hepatocyte sub-population arrested in the G2 phase. The injection of lead also stimulated a small increase in labeled hepatocytes within 6 hr. Analysis of grain counts gave no evidence for unscheduled DNA synthesis. The incremental labeled cells may have originated from a small fraction of the G1 population that was ready to enter the S phase without the usual pre-synthetic delay.     

Absolute quantitative autoradiography of low concentrations of [125I]-labeled proteins in arterial tissue

We developed a method for absolute quantitative autoradiographic measurement of very low concentrations of [125I]-labeled proteins in arterial tissue using Kodak NTB-2 nuclear emulsion. A precise linear relationship between measured silver grain density and isotope concentration was obtained with uniformly labeled standard sources composed of epoxy-embedded gelatin containing glutaraldehyde-fixed [125I]-albumin. For up to 308-day exposures of 1 micron-thick tissue sections, background grain densities ranged from about two to eight grains/1000 micron 2, and the technique was sensitive to as little as about one grain/1000 micron 2 above background, which correspond to a radioactivity concentration of about 2 x 10(4) cpm/ml. A detailed statistical analysis of variability was performed and the sum of all sources of variation quantified. The half distance for spatial resolution was 1.7 micron. Both visual and automated techniques were employed for quantitative grain density analysis. The method was illustrated by measurement of in vivo transmural [125I]-low-density lipoprotein [( 125I]-LDL) concentration profiles in de-endothelialized rabbit thoracic aortic wall.     

The response of alpha-amylase activity during wheat grain development to nitrogen fertiliser

The aim of this study was to test whether the effect of nitrogen fertiliser on Hagberg falling number of winter wheat (Triticum aestivum) grain in the absence of sprouting is mediated by pre-maturity alpha-amylase activity and is related to grain drying rate. A field experiment with two cultivars (Avalon and Mercia) in 1990 and 1991 compared four application rates of nitrogen. Samples of grain were taken at intervals during development for moisture determination and alpha-amylase assay. Grains from plots given nitrogen dried faster in both years, but alpha-amylase activity and Hagberg falling number responded differently to nitrogen in the two years. In the warmer and drier year of 1990, alpha-amylase activity declined throughout development leading to very high Hagberg falling number at harvest, with little effect of nitrogen. In the cooler and wetter year of 1991, alpha-amylase activity declined until about 30% moisture. After this stage, alpha-amylase activity increased in the absence of sprouting in grain from plots receiving little or no nitrogen. This resulted in a linear increase in Hagberg falling number in response to nitrogen fertiliser. Electrophoresis of alpha-amylase isozymes indicated that the increase in Hagberg falling number in response to nitrogen was not mediated by a decrease in retained pericarp alpha-amylase activity, but by a reduction in pre-maturity alpha-amylase activity. These results support the hypothesis that slow grain drying enhances pre-maturity alpha-amylase formation, and also support the hypothesis that an additional environmental factor varying between seasons is involved in pre-maturity alpha-amylase formation.     

Abscisic acid in developing wheat grains and its relationship to grain growth and maturation

Summary During the later stages of growth of grains of wheat (Triticum aestivum L. cvs. WW15 and Gabo) there is a dramatic increase (up to 40fold) in the content of abscisic acid (ABA) to 4–6 ng per grain. This level remains high from 25 to 40 days after anthesis. Then, in association with natural or forced drying of the grain, there is a rapid drop (5–10 fold) in the ABA content and a brief increase in the content of bound ABA. The bulk of ABA in an ear was in the grain (95%) and although the embryo contributed 19% of this ABA it was less than 5% of the grain by weight. There was no clear relationship between ABA content and the growth of grains in various spikelet or floret positions. Application of (±)-ABA to the ear had no effect on grain growth rate but led to an earlier cessation of grain growth and hastened the drying of the grain. Isolated embryos and whole grains were capable of germinating during the mid grain growth period (15–25 days), but germination capacity declined subsequently as ABA accumulated. Later, still, with grain drying and loss of ABA, embryo and grain became germinable again. At this time there was also a dramatic increase in the ability of the grain to synthesize -amylase. It is suggested that the accumulation of ABA at the later stages of grain growth prevents precocious germination and premature hydrolysis of starch reserves of the morphologically mature but still unripe grain. An inevitable consequence of such action may be in triggering grain maturation.     

Automated quantitative analysis of single and double label autoradiographs.

A method for the analysis of silver grain content in both single and double label autoradiographs is presented. The total grain area is calculated by counting the number of pixels at which the recorded light intensity in transmission dark field illumination exceeds a selected threshold. The calibration tests included autoradiographs with low (3H-thymidin) and high (3H-desoxyuridin) silver grain density. The results are proportional to the customary visual grain count. For the range of visibly countable grain densities in single labeled specimens, the correlation coefficient between the computed values and the visual grain counts is better than 0.96. In the first emulsion of the two emulsion layer autoradiographs of double labeled specimens (3H-14C-thymidin) the correlation coefficient is 0.919 and 0.906. The method provides a statistical correction for the background grains not due to the isotope. The possibility to record 14C tracks by shifting the focus through the second emulsion of the double labeled specimens is also demonstrated. The reported technique is essentially independent of size, shape and density of the grains.     

G2 Sub-Population In Mouse Liver Induced Into Mitosis By Lead Acetate

A single intracardiac dose of lead acetate (40 μ lead/g body weight) induced a 25-fold increase in mitosis of mouse hepatocytes 5 hr after injection, as determined by autoradiography. the prompt appearance of a mitotic wave and the relatively large number of mitoses suggest that the mitotic cells were derived from a hepatocyte sub-population arrested in the G₂ phase. the injection of lead also stimulated a small increase in labeled hepatocytes within 6 hr. Analysis of grain counts gave no evidence for unscheduled DNA synthesis. the incremental labeled cells may have originated from a small fraction of the G₁ population that was ready to enter the S phase without the usual pre-synthetic delay.     

Slowly developing drought stress increases photosynthetic acclimation of Catharanthus roseus

Our understanding of plant responses to drought has improved over the decades. However, the importance of the rate of drought imposition on the response is still poorly understood. To test the importance of the rate at which drought stress develops, whole-plant photosynthesis (P(net) ), respiration (R(dark) ), daily carbon gain (DCG), daily evapotranspiration (DET) and water use efficiency (WUE) of vinca (Catharanthus roseus), subjected to different drought imposition rates, were investigated. We controlled the rate at which the substrate dried out with an automated irrigation system that allowed pot weight to decrease gradually throughout the drying period. Fast, intermediate and slow drying treatments reached their final pot weight [500 g, substrate water content (θ) ≈ 0.10 m3 m(-3) ] after 3.1, 6.6 and 10 days, respectively. Although all drying treatments decreased P(net) and R(dark) , slow drying reduced P(net) and R(dark) less than fast drying. At a θ < 0.10 m3 m(-3) , DCG and DET in the slow drying treatment were reduced by ≈50%, whereas DCG and DET in the fast drying treatment were reduced by 85 and 70% at a θ of 0.16 m(3) m(-3) . Plants exposed to slow drought imposition maintained a high WUE, even at θ < 0.10 m3 m(-3) . Overall, physiological responses to low θ were less severe in plants subjected to slow drying as compared with fast drying, even though the final θ was lower for plants exposed to slow drying. This suggests that the rate at which drought stress develops has important implications for the level of acclimation that occurs.     

Hormones in the grains in relation to sink strength and postanthesis development of spikelets in rice

Inferior spikelets usually exhibit a slower grain filling rate and lower grain weight than superior spikelets in a rice (Oryza sativa L.) panicle. This study investigated whether the variations in grain filling between the two kinds of spikelets were attributed to their sink strength and whether the sink strength was regulated by the hormonal levels in the grains. Using two field-grown rice genotypes, the division rate of endosperm cells, hormonal levels in the grains, and grain weight of both superior and inferior spikelets were determined during the grain filling period. The results showed that superior spikelets had dominance over inferior spikelets in endosperm cell division rate and cell number, grain filling and grain weight. Changes in zeatin (Z) and zeatin riboside (ZR) contents paralleled and were very significantly correlated with the cell division rate and cell number. Cell division rate and the content of indole-3-acetic acid (IAA) in the grains were also significantly correlated. Gibberellin (GAs; GA₁+ GA₄) content of the grains was high but ABA levels were low at the early grain filling stage. ABA increased substantially during the linear phase of grain growth and was very significantly correlated with grain dry weight during this period. Application of kinetin at 2 through 6 days post anthesis (DPA) significantly increased cell number, while spraying ABA at 11 through 15 DPA significantly increased the grain filling rate. The results suggest that differences in sink strength are responsible for variations in grain filling between superior and inferior spikelets. Both cytokinins and IAA in the grains may mediate cell division in rice endosperm at early grain filling stages, and therefore regulate the sink size of the grain, whereas ABA content correlates with sink activity during the linear period of grain growth.     

Double Emulsion Autoradiography for Identifying Tritium-Labelled cells in sections

The sensitivity of tissue autoradiography can be doubled and the number of false negative cells nearly eliminated by interposing thin tissue sections between two layers of photographic emulsion. A mouse was given 50 μc of tritiated thymidine (SA 2,500 c/M) intraperitoneally and killed 1.5 hr later. A portion of the small bowel was removed, fixed and embedded in methacrylate in the usual way. Sections 2 μ thick were cut and allowed to flatten on water at 40° C. Some sections were used to make conventional single emulsion auto-radiographs and other sections were interposed between two layers of emulsion by first coating slides with NTB 3 emulsion, picking up the sections from a water bath at 18° C, drying, soaking 1 min in benzene, drying, and then dipping again in NTB 3 emulsion. They were exposed at 4° C in a low humidity, 100% CO₂ atmosphere for 10 days, developed and covered in the usual way. There was an average of 20.16 ± 1.4 grains per labelled cell in the double emulsion group compared with 10.6 ± 0.9 grains in the single emulsion group. In the double emulsion autoradiographs there were 55.1 ± 1.65 labelled cells per unit area as compared with 39.8 2 2.0 in the single emulsion group.     

Seasonal variation in the response of Hagberg falling and liquefaciton numbers to propiconazole fungicide in wheat

The hypothesis was tested that seasonal differences in the response to propiconazole fungicide of hagberg failling and liquefaction numbers are related to grain drying rate, as indicated by potential evaportranspiration. The response of Hagberg failling and liquefaciton numbers to late-season applicaitions of propiconazole was calculated using data from a field experiments in each of the years 1981 to 1990 on winter wheat (Triticum aestivum) cv. Agalong grown with similar husbandry at one site. Cumulative potential evapotranspiration was calculated over seven different periods during grain ripening. No visible sprouting occurred in any experiment and Hagberg falling number was above 250 s in nine of the 10 years. Disease severity on the flag leaf was less than 7% in nine of the 10 years, and diseases were generally controlled well by propiconazole. There were no significant relationships between the response of Hagberg falling number and any of the potential evapotranspiration variables. The response of liquefaction number was exponentially related to each of three cumulative potential evapotranspiration variables which covered periods before the estimated date of 40% moisture content. Years with lower cumulative potential evapotranspiration gave the greater responses, but the relationships were considerably influenced by the two lowest potential evapotranspiration years. It was concluded that these data provide indirect evidence that the response of Hagberg falling number (when transformed to liquefaction number) to fungicide is mediated through grain drying rate, and furthermore that the results are compatible with the hypothesis that pre-maturity alpha-amylase activity is stimulated by slow grain drying.     

Nongraded Dehydration and Low-Pressure Infiltration for Rapid Celloidin Embedding of Brain Tissue

Various ways of shortening single steps in the celloidin process have been combined to form a routine method which may be completed, for tissues of average size, within a week following fixation. Fixed, washed tissue slices 5 mm thick are dehydrated in 1 or 2 changes of absolute ethanol and acetone, 1:1. This requires 24 hr in an incubator at 37 C, or 12-16 hr if a magnetic stirrer is used. After ether-alcohol for 4 hr. the tissues are transferred to 5% celloidin and infiltrated in a vacuum desiccator attached to a filter pump. When the volume of celloidin is reduced to half the original amount (about 2 hr), the tissues are removed from the infiltrating fluid and embedded in 10% celloidin. The blocks are hardened in chloroform and cleared by suspending them in 2 or 3 changes of terpineol agitated by a magnetic stirrer. Sections are cut in terpineol, using any type of microtome. After washing in 95% alcohol, they are mounted on albumenized slides for staining.     

黑藻花粉粒形态结构的观察

为了研究沉水植物特殊的生物学特性,观察了水鳖科黑藻(Hydrilla verticillata)花粉粒的光学显微镜和电子显微镜的形态与结构,其花粉粒的壁极薄且极易破裂,无萌发孔,内含许多淀粉粒。在自然状态下,无法完整保存其干燥的花粉粒。     

黑藻花粉粒形态结构的观察

为了研究沉水植物特殊的生物学特性 ,观察了水鳖科黑藻 (Hydrillaverticillata)花粉粒的光学显微镜和电子显微镜的形态与结构 ,其花粉粒的壁极薄且极易破裂 ,无萌发孔 ,内含许多淀粉粒。在自然状态下 ,无法完整保存其干燥的花粉粒。     

Running and shipping elevate plasma levels of beta-endorphin-like substance (B-END-LI) in thoroughbred horses

A specific RIA for beta-endorphin (B-END) was developed to measure horse plasma levels of B-END-like material (B-END-LI) during exercises and shipping. Three exercise speeds and durations were: trot at 260-300 m/min for 10 min; slow gallop at 390-420 m/min for 5 min and fast gallop at 700-800 m/min for 2 min. Blood samples were taken from 4 horses before, immediately after, 30 and 60 min after exercise. Trotting increased plasma B-END-LI from a basal level of 109 +/- 7 pg/ml to 172 +/- 22 at the end of exercise and returned to 127 +/- 17 and 107 +/- 10 pg/ml at 30 and 60 min after exercise. Similar results were obtained in slow gallop (121 +/- 6 to 210 +/- 17 then 155 +/- 8 and 131 +/- 11 pg/ml). However, fast gallop caused the greatest increase (352%) in B-END-LI to concentrations of 544 +/- 93 pg/ml and 276 +/- 74 pg/ml at 5 and 30 min after exercise. Plasma B-END-LI returned to 199 +/- 46 pg/ml in 1 hr. Sequential exercises of trot, slow and fast gallop were conducted in 6 horses. Plasma B-END-LI were 116 +/- 19 pg/ml (pre-exercise), 198 +/- 21 (trot), 361 +/- 51 (slow gallop), 500 +/- 57 (fast gallop) and 248 +/- 29, 171 +/- 24, 143 +/- 20 and 139 +/- 21 pg/ml at 0.5, 1, 2 and 3 hr, respectively, following exercises. Transportation in horse trailer also significantly increased plasma levels of B-END-LI from a basal level of 138 +/- 12 to 196 +/- 24 pg/ml within 30 min and this levels were maintained at 45 min (177 +/- 3 pg/ml). Plasma levels of B-END-LI began to decline at 60 min of shipping. These results showed that plasma B-END-LI was increased in all speeds of exercise and by shipping and returned to pre-exercise and pre-shipping level in 30 min except fast gallop which returned to pre-exercise level in 1 hr.     

Post-anthesis alternate wetting and moderate soil drying enhances activities of key enzymes in sucrose-to-starch conversion in inferior spikelets of rice

This study tested the hypothesis that a post-anthesis moderate soil drying can improve grain filling through regulating the key enzymes in the sucrose-to-starch pathway in the grains of rice (Oryza sativa L.). Two rice cultivars were field grown and two irrigation regimes, alternate wetting and moderate soil drying (WMD) and conventional irrigation (CI, continuously flooded), were imposed during the grain-filling period. The grain-filling rate and activities of four key enzymes in sucrose-to-starch conversion, sucrose synthase (SuSase), adenosine diphosphate-glucose pyrophosphorylase (AGPase), starch synthase (StSase), and starch branching enzyme (SBE), showed no significant difference between WMD and CI regimes for the earlier flowering superior spikelets. However, they were significantly enhanced by the WMD for the later flowering inferior spikelets. The activities of both soluble and insoluble acid invertase in the grains were little affected by the WMD. The two cultivars showed the same tendencies. The activities of SuSase, AGPase, StSase, and SBE in grains were very significantly correlated with the grain-filling rate. The abscisic acid (ABA) concentration in inferior spikelets was remarkably increased in the WMD and very significantly correlated with activities of SuSase, AGPase, StSase, and SBE. Application of ABA on plants under CI produced similar results to those seen in plants receiving WMD. Applying fluridone, an indirect inhibitor of ABA synthesis, produced the opposite effect. The results suggest that post-anthesis WMD could enhance sink strength by regulating the key enzymes involved, and consequently, increase the grain-filling rate and grain weight of inferior spikelets. ABA plays an important role in this process.