黄腐酸增强小麦抗旱能力的生理生化机制初探

叶面喷施黄腐酸可显著提高小麦幼苗的保水能力,表现为降低叶面蒸腾强度,增加气孔扩散阻力,提高幼苗的生物量,在干旱条件下尤为明显。喷施黄腐酸可使干旱条件下叶片内脯氨酸含量提高近一倍,并在水分充足时,也能使叶片脯氨酸含量增加78%。     

Adaptive phenology of desert and Mediterranean populations of annual plants grown with and without water stress

Summary The dynamics of vegetative and reproductive growth were compared in matched pairs of Mediteranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Brachypodium distachyon (L.) Beauv. and Bromus fasciculatus C. Presl., under high and low levels of water availability in a common-environment experiment. Plants of all desert populations showed earlier switches to reproductive development and to subsequent phenophases, and the transition to flowering occurred at smaller plant sizes. Water stress had no effect (E. hispanica) or slightly accelerated the transition to flowering in B. fasciculatus (by 1–2 days) and in B. distachyon (by 4–6 days). Plant senescence was strongly enhanced by water stress, and this enhancement was greater in desert populations than in corresponding Mediterranean ones. Duration of life cycle was greatly shortened by water stress in all three species. Desert and Mediterranean populations of the three species exhibited small differences in their relative response, i.e. phenotypic plasticity, to water stress for phenological and plant size parameters. In E. hispanica and B. fasciculatus the population x water regime interaction amounted to less than 3% of total variance. By contrast, the Mediterranean population of B. distachyon was much more plastic in its response to water stress than the desert population in its transition to plant senescence. Plants from the desert populations appeared to be adapted to shorter, more compact growth cycles, culminating in earlier dates of seed maturation and plant senescence. In addition, they showed larger phenotypic plasticity in the transition to plant senescence, which trait was enhanced or magnified by sustained or repeated lack of water. By contrast, plants from Mediterranean populations delayed switchover from one phenophase to the next, seeming thus to bet on more water being forthcoming.     

Molybdenum cofactor from the cytoplasmic membrane of Proteus mirabilis

Molybdenum cofactor was extracted from membranes of Proteus mirabilis by three methods: acidification, heat treatment and heat treatment in the presence of sodium-dodecylsulphate (SDS). Extracts prepared by the latter method contained the highest concentration of molybdenum cofactor. In these extracts molybdenum cofactor was present in a low molecular weight form. It could not penetrate an YM-2 membrane during ultrafiltration suggesting a molecular weight above 1000. During aerobic incubation of cofactor extracts from membranes at least four fluorescent species were formed as observed in a reversed-phase high performance liquid chromatography (HPLC) system. The species in the first peak was inhomogeneous while the species in the others seem to be homogenous. In water, all fluorescent products had an excitation maximum at 380 nm and an emission maximum at 455 nm. Their absorption spectra showed maxima at around 270 nm and 400 nm. Fluorescent compounds present in the first peak could penetrate an YM-2 membrane during ultrafiltration, whereas the compounds in the other peaks hardly did. Using xanthine oxidase from milk as source of molybdenum cofactor apparently identical cofactor species were found. Cytoplasmic nor membrane extracts of the chlorate resistant mutant chl S 556 of P. mirabilis could complement nitrate reductase of Neurospora crassa nit-1 in the presence of 20 mM molybdate. However, fluorescent species with identical properties as found for the wild-type were formed during aerobic incubation of extracts from membranes of this mutant.Non-common Abbreviations HPLC high performance liquid chromatography - I.D. internal diameter - SDS sodium dodecyl sulphate     

Cloning of alkaline phosphatase isozyme gene (iap) of Escherichia coli

In Escherichia coli three major alkaline phosphatase isozymes are formed by molecular conversions depending on physiological conditions. A chromosomal gene, iap, is responsible for alkaline phosphatase isozyme conversion and is assumed to code for a proteolytic enzyme removing the arginine residue(s) from the N-terminal position of alkaline phosphatase subunits. A chromosomal fragment which complemented the Iap^? phenotype was cloned into pBR322 by a shotgun method. Transducing phage λiap was constructed in vitro from the chromosomal fragment containing the iap gene and λtna DNA. The integration site of the phage on chromosome was identified as the iap locus by PI transduction, which meant that the cloned chromosomal DNA contained authentic iap gene.The restriction map of the hybrid plasmid was constructed. Based upon this information, several iap deletion plasmids as well as smaller iup⁺ plasmids were constructed. Analysis of the phenotypes conferred by these plasmids enabled us to locate iap gene within a 2-kb segment of the cloned DNA.The cells carrying the iap⁺ plasmid showed very efficient isozyme conversion even in medium containing arginine, an inhibitor for the isozyme conversion. This indicates overproduction of the iap gene product.     

Drought susceptibility of two tomato (Lycopersicum esculentum) varieties

The effects of three levels of moisture under greenhouse conditions and also identical moisture levels under field conditions, on the growth yield and water relations of two tomato cultivars, Fireball and Ife I, were investigated. The objective was to ascertain the drought susceptibility of these two tomato cultivars. The cultivar, Ife I, was more drought susceptible than Fireball and the drought susceptibility increased with the level of soil water stress. The drought tolerance, of Fireball is attributed to a lower leaf area, better root system development in terms of average root length and rooting depth, and a higher leaf water potential. The higher leaf stomatal resistances of Fireball variety suggest an inbuilt mechanism to regulate water vapour flow in times of stress.     

Varietal variation in uptake and utilization of potassium (rubidium) in high-salt seedlings of barley

Seedlings of eleven varieties of barley (Hordeum vulgare L.) showed differences in utilization of K⁺ from a full nutrient solution containing 3.0 mM K⁺. The K⁺ content of both roots and shoots was proportional to the fresh weights and dry weights after a week in the nutrient solution. The K⁺ use-efficiency ratio, which indicates the efficiency of nutrient utilization (mg dry weight produced per mg K⁺ absorbed), differed significantly among the varieties. There was no correlation between influx of Rb⁺ and the content of K⁺. It is suggested that there are wide varietal differences in such genetically-determined properties as ion influx and efflux and net ion transport to the shoot. Further-more, the influx of Rb⁺ was closely linked to transpiration, probably due to a variety-specific non-metabolic part of Rb⁺ influx. Varietal differences in influx of Rb⁺ were more pronounced in high-K⁺ roots than in low-K⁺ roots with maximum rate of Rb⁺ uptake, but the rank of varieties was the same in each case. – Criteria for the selection of K⁺ use-efficient varieties of barley are discussed.     

Cloning and sequencing of cDNA for mouse liver metallothionein-I

Metallothionein mRNA was purified from liver of mice injected with cadmium. The corresponding double-stranded cDNA was prepared and inserted into the PstI site of plasmid pBR322. The resulting recombinant DNA was used to transform the RR1 strain of $\text{Escherichia}\text{coli}$. Clones resistant to tetracycline and sensitive to ampicillin were screened for the presence of metallothionein-specific restriction fragments in their plasmids. One plasmid, called M135, contains a cDNA insert covering the entire length of the mRNA for mouse liver metallothionein-I, except for the first 18 bases at the 5′ end.     

The relative effectiveness of 6-thioguanine and 8-azaguanine in selecting resistant mutants from two V79 Chinese hamster cells in vitro

The frequency of surviving colonies in two V79 cell lines exposed to either 6-thioguanine or 8-azaguanine was dependent on initial plating density. Different degrees of metabolic-co-operation were found to occur in the two cell lines and the loss of both spontaneous and added mutants occurred at a lower cell density when 6TG was used for selection than when 8 AZ was used in both cell lines. Both analogues were degraded on incubation in medium plus serum in the absence of added cells. Variation in serum batch had little effect on the rate of degradation or on the frequency of colonies recovered after treatment of V79 cell lines with 8AZ. The reasons for preferring 8AZ to 6TG as a selective agent are discussed.     

Benthic macrofaunal communities in intermittent estuaries during a drought: Comparisons with permanently open estuaries

Drought conditions have prevailed in many areas of NSW since 2002. On the mid-north coast, below-average rainfall resulted in reduced riverine flows and the extended closure of intermittent estuaries within the Solitary Islands Marine Park. Patterns of structure of benthic infaunal communities were evaluated at the height of the drought to determine if they differed between closed, intermittent estuaries and permanently open estuaries within the region. Replicate van Veen grab samples were taken in the upper, mid- and lower reaches of six intermittent and three permanently open estuaries and sieved to retain the macrofauna. A range of physico-chemical measures was also taken at each sampling time. Multivariate analyses of assemblage data revealed a significant difference between the structure of the two estuary types and also among estuaries within each type. Differences between estuary types were attributable to small differences in the abundance of a number of taxa but also to the absence of the amphipod Urohaustorius metungi from most of the intermittent estuaries. In contrast, these small amphipods dominated communities in the lower reaches of the permanently open estuaries. Physico-chemical variables were highly variable among estuaries and were not strongly correlated with assemblage patterns. Correlations with catchment size were the strongest and, as most of the intermittent estuaries in the region are smaller than the permanently open estuaries, this confounds the interpretation of assemblage patterns in this preliminary study. In order to differentiate between the effects of catchment size and entrance status, the same estuaries need to be resurveyed during periods when at least some of the intermittent estuaries are open.     

Variation of cytosine methylation in response to water availability in two contrasting growth types of an amphibious plant Alternanthera philoxeroides

We used methylation-sensitive amplified polymorphisms (MSAP) to examine the alterations of cytosine methylation in two contrasting growth types of an amphibious plant Alternanthera philoxeroides in response to change of water availability. Using 34 pairs of selective primer combinations, we amplified 1026 and 1128 clear and reproducible bands in root and leaf of A. philoxeroides, respectively. When the aquatic types of plants were transplanted into drought culture, we found a decrease in the overall DNA methylation. When the terrestrial types of plants were transferred into flood culture, we detected a higher frequency of methylation than demethylation events. Alterations of DNA methylation were more evident in root than in leaf in response to change of water availability. When the confounding effects of variable environmental factors were removed, differences of cytosine methylation profiles were observed between two growth types of plants under common growth conditions.