Effects of boundary layer conductance on substomatal pressures of carbon dioxide

Abstract. Gas exchange measurements were made on single leaves of three C₃ and one C₄ species at air speeds of 0.4 and 4.0 m s⁻¹ to determine if boundary layer conductance substantially affected the substomatal pressure of carbon dioxide. Boundary layer conductances to water vapour were 0.4 to 0.5 mol m⁻² s⁻¹ at the lower air speed, and 1.2 to 1.5 mol m⁻² s⁻¹ at the higher air speed. Substomatal carbon dioxide pressures were about 5 Pa lower at low boundary layer conductance in the C₃ species, and about 3 Pa lower in the C₄ species when measurements were made at high and moderate photosynthetic photon flux densities. No evidence of stomatal adjustment to altered boundary layer conductance was found. Photosynthetic rates at high photon flux densities were reduced by about 20% at the low air speed in the C₃ species. The commonly reported values of substomatal carbon dioxide pressure for C₃ and C₄ species were found to occur only when measurements were made at the higher air speed.     

Reversing the inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus by GA3, ethephon or ACC

The germination of Amaranthus paniculatus seeds was inhibited by applying paclobutrazol, a specific inhibitor of gibberellin biosynthesis. This inhibition was markedly counteracted by gibberellin A₃ (GA₃), suggesting that endogenous gibberellins are required for germination in this species. The inhibitory effect of paclobutrazol was also overcome by ethephon (2-chloroethylphosphonic acid) or the precursor of ethylene biosynthesis, ACC (1-aminocyclopropane-l-carboxylic acid). Thus the physiological effect of gibberellin can be mimicked by ethylene released from ethephon or synthesised from exogenous ACC. It is suggested, that endogenous gibberellins are involved in germination of Amaranthus paniculatus seeds and that action of GA₃ can be substituted by ethylene.Abbreviations ACC 1-aminocyclopropane-l-carboxylic acid - AMO-1618 (2-isopropyl-5methyl-4-trimethylammoniumchloride)-phenyl-l-piperidinium-carboxylate - ancymidol -cyclopropyl--(4-methoxyphenyl)-5-pyrimidine methanol - chloromequat chloride (2-chloroethyl)trimethylammoniumchloride - ethephon 2-chloroethylphosphonic acid - GA gibberellin A₃ - paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-lyl)pentan-3-ol - Phosphon D 2,4,dichlorobenzyl-tributhylphosphoniumchloride - tetcyclacis 5,(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo)5,4,1,0,Z,6,0^8,11 dodeca-3,9-diene     

Host Status of Five Weed Species and Their Effects on Pratylenchus zeae Infestation of Maize

The host suitability of five of the most common weed species occurring in maize (Zea mays L.) fields in South Africa to Pratylenchus zeae was tested. Based on the number of nematodes per root unit, mealie crotalaria (Crotalaria sphaerocarpa) was a good host; goose grass (Eleusine indica), common pigweed (Amaranthus hybridus), and thorn apple (Datura stramonium) were moderate hosts; and khaki weed (Tagetes minuta) was a poor host. Only the root residues of khaki weed suppressed the P. zeae infestation of subsequently grown maize. When goose grass, khaki weed, and mealie crotalaria were grown in association with maize in soil infested with P. zeae, goose grass and khaki weed severely suppressed maize root development; this resulted in a low number of nematodes per maize root system and a high number of nematodes per maize root unit. Mealie crotalaria did not restrict maize root growth and did not affect nematode densities per maize root system or maize root unit. Special attention should be given to the control of mealie crotalaria, which is a good host for P. zeae, and goose grass, which, in addition to its ability to compete with maize, is also a suitable host for P. zeae.     

光对尾穗苋幼苗内苋红素合成的诱导

不同苗龄的尾穗苋黄化苗对10 min,15Wm~(-2)白光的反应能力不同。光诱导的苋红素合成始于播种后第 20h,至50h合成能力最大,82h以后幼苗对短时光照的反应能力趋于消失。苋红素合成的滞后期为3h,光处理后18h色素积累达到高峰。光调节苋红素合成符合红光—远红光可逆诱导反应等两个基本模式,确证光敏色素参与调控苋红素合成.     

尾穗苋茎的异常加厚

尾穗苋茎中多轮散生维管束的产生是由起源于原形成层的异常形成层连续活动的结果。异常形成层由１─２层细胞组成,在早期的活动中,通常以单向方式向内交替产生维管束原束和薄壁结合组织;而后期则以双向活动方式向内产生木质部和其间的厚壁结合组织,韧皮部较晚在异常形成层的外缘发生。原形成层束分化为具束中形成层的外韧维管束,但无束间形成层分化。中央维管束和各轮异常维管束中的束中形成层能产生一些次生维管组织。     

Diurnal changes in phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase properties in the natural environment: interplay of light and temperature in a C4 thermophile

Activities of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) were measured in leaf extracts of field grown Amaranthus paniculatus L. (C₄) during a natural diurnal irradiance and temperature pattern. Enzyme assays were run at both fixed (30°C) and the corresponding leaf temperature at the time of harvest. Light activation of PEP carboxylase (PEPCase) at fixed assay temperatures was expressed as a decrease in S_0–5 (PEP) after a threshold (> 330 μmol m^–2 s^–1) photon fluence rate was surpassed at noon. Earlier in the morning, increase in apparent enzyme affinity for PEP was observed when the assay was run at leaf temperature, indicating a physiologically meaningfull effect of temperature on S^0.5 (PEP). The 3.3-fold increase in PEPCase activity at low PEP and fixed assay temperature between the minimal and maximal irradiance and temperature hours of the day, became 12.8-, 11.5- and 7.4-fold when assays were run at the corresponding leaf temperature during three diurnal cycles with respective temperature differences (max minus min) of 9.0, 8.3 and 7.4°C. The extent of malate inhibition was the same for both day and night forms of PEPCase assayed at 35°C, but increased considerably with night enzyme at 25°C. The results indicate that light increases the apparent affinity of PEPCase for PEP and that at lower temperatures malate becomes more inhibitory. Pyruvate orthophosphate dikinase activity started to increase immediately after sunrise and the 10-fold increase at fixed temperature became 14.8-, 14.2- and 13.1-fold when assays were run at the above leaf temperatures. This indicates that the light effect predominates with pyruvate, orthophosphate dikinase, while with phosphoenolpyravate carboxylase, light and temperature co-operate to increase the day enzyme activities.     

Rapid recovery of photosynthetic cell suspension cultures following heterotrophic bleaching

Summary Seven suspension-cultured lines of five different species (Amaranthus powellii Datura innoxia, Glycine max, Gossypium hirsutum, andNicotiana tabacum × Nicotiana glutinosa fusion hybrid), which had been grown under photomixotrophic conditions, were placed under heterotrophic conditions (darkness and media with 3% sucrose or starch) where the chlorophyll levels declined to near zero. After three transfers over a 70-d period, the cells were placed back into photomixotrophic or photoautotrophic conditions where regreening occurred rapidly and continued growth was observed. This rapid adaptation to photosynthetic conditions contrasts with the original initiation process for these cultures, which required many months and an apparent selection since many of the original cells died. Thus, these seven photosynthetic cell suspension cultures appear to be different from the original cultures due possible to genetic or adaptive changes.     

微波法和超声波法提取绿穗苋多糖响应面优化研究

绿穗苋是一种药食兼用作物,其中多糖成份具有很高的药食价值。本研究以绿穗苋地上部分为材料,以微波和超声波两种方法对绿穗苋多糖进行提取,并通过响应面分析法对提取进行优化,确定最佳工艺,通过水提醇沉的方法得到绿穗苋粗多糖。综合比较两种提取工艺,提取效果最佳工艺为微波提取法。其条件为:提取时间41.42 min,提取功率211.65 W,料液比1:33.338 (g/mL),实际得率为13.25%。该研究结果促进绿穗苋资源的有效利用,为绿穗苋多糖的提取工艺及产品的开发利用提供理论依据。     

Sex expression, sex-specific traits, and the effects of salinity on growth and reproduction of Amaranthus cannabinus (Amaranthaceae), a dioecious annual

Amaranthus cannabinus was studied to investigate some of the ecological factors thought to be involved in the evolution of dioecy and to investigate the effects of salinity on sex expression and sex-specific selection. In the field portion of this study, sex ratios, stability of sex expression, spatial distribution, allocation strategies, and phenologies of the sexes were investigated in New Jersey freshwater and salt marsh populations of water hemp. To examine the effects of salinity on vegetative and reproductive development of males and females, plants were grown in the greenhouse at three salinity levels. Adult sex ratios were found to be 1:1. Temporal deviations from a 1:1 sex ratio varied by population and were due to differences in flowering phenology and mortality between the sexes. No plants were observed to change sex expression, and there was no evidence of spatial segregation of the sexes in the field. In both the field and the greenhouse, females allocated more resources to vegetative tissues and had a longer growing period than males. The results of this study suggest that increased reproductive efficiency through sex-specific growth patterns may have been an important selective factor involved in the evolution of dioecy in A. cannabinus.     

Mitigation of growth retardation effect of plant defense activator,acibenzolar-<Emphasis Type="Italic">S</Emphasis>-methyl,in amaranthus plants by plant growth-promoting rhizobacteria

Four rhizobacterial strains and acibenzolar-S-methyl (ASM), a chemical activator, which suppressed foliar blight of amaranthus (Amaranthus tricolor L.) caused by Rhizoctonia solani Kühn were evaluated for their effect on plant growth. The experiments were performed both under sterile and non-sterile soil conditions, in the presence or absence of the pathogen. In all cases, plants treated with ASM showed significant reduction in growth, as determined by shoot length, and shoot and root dry weight when compared to other treatments. The growth retardation effect of ASM was more profound with respect to shoot length. Reduction in shoot length was least when plants were treated with a combination of the chemical activator and Pseudomonas putida 89B61 under non-sterile soil conditions in the absence of the pathogen. Both under sterile and non-sterile soil conditions, in the presence of the pathogen, reduction in shoot length due to application of ASM was diminished significantly when plants were treated with rhizobacterial strain Pseudomonas fluorescens PN026R. Combined use of plant growth-promoting rhizobacteria (PGPR) and ASM was found to be beneficial as the growth retardation effect of the plant defense activator was reduced by the growth-promoting ability of the rhizobacteria.