莴苣大孢子发生过程中钙的分布动态

莴苣胚囊发育为蓼型,减数分裂形成的4个大孢子中只有合点端的一个大孢子可继续发育,其余3个大孢子从珠孔端依次退化.大孢子母细胞中的钙沉淀颗粒很少,减数分裂后的四分体中的钙沉淀颗粒稍有增加.以后,4个大孢子中的钙沉淀颗粒在数量上有明显差异:即将退化的大孢子中钙明显减少,而未退化大孢子细胞质中则保持有较多的细小钙沉淀颗粒.大孢子的退化是一种细胞程序死亡现象,细胞中的钙浓度降低时可能启动了大孢子细胞的程序性死亡过程,而细胞中的钙浓度高时则保持大孢子细胞的继续发育.文章首次揭示了大孢子发生过程中钙的分布特征.     

What are the effects of nitrogen deficiency on growth components of lettuce?

Relationships between nitrogen (N) content and growth are routinely measured in plants. This study determined the effects of N on the separate morphological and physiological components of plant growth, to assess how N-limited growth is effected through these components. Lettuce ( Lactuca sativa ) plants were grown hydroponically under contrasting N-supply regimes, with the external N supply either maintained continuously throughout the period of study, or withdrawn for up to 14 d. Richards' growth functions, selected using an objective curve-fitting technique, accounted for 99.0 and 99.1% of the variation in plant dry weight for control and N-limited plants respectively. Sublinear relationships occurred between N and relative growth rates under restricted N-supply conditions, consistent with previous observations. There were effects of treatment on morphological and physiological components of growth. Leaf weight ratio increased over time in control plants and decreased in N- limited plants. Shoot:root ratio followed a similar pattern. On a whole-plant basis, assimilation of carbon decreased in N-limited plants, a response paralleled by differences in stomatal conductance between treatments. Changes in C assimilation, expressed as a function of stomatal conductance to water vapour, suggest that the effects of N limitation on growth did not result directly from a lack of photosynthetic enzymes. Relationships between plant N content and components of growth will depend on the availability of different N pools for remobilization and use within the plant.     

Screening of RAPD Markers Linked to the Photoperiod-Sensitivity Gene in Rice Chromosome 6 Using Bulked Segregant Analysis

Bulked segregant analysis was used to determine randomly amplifiedpolymorphic DNA (RAPD) markers in a specific interval in themiddle of chromosome 6 of rice for tagging the photoperiod sensitivitygene.Two pools of F₂ individuals (japonica cv. Nipponbare and indicacv. Kasalath) were constructed according to the genotypes ofthree restriction fragment length polymorphism (RFLP) markerslocated at both ends and the middle of the targeted interval.Then another pair of pools were constructed based on the "graphicalgenotype," which was made with our high density linkage map.RAPD analysis was performed using these DNA pools as templates,and polymorphic fragments were detected and mapped. Using 80primers, either singlyor pairwise, we tested 2,404 primer pairsand established 14 markers tightly linked to the photoperiodsensitivitygene. The obtained RAPD markers were converted intosequence-tagged sites bycloning and sequencing of the polymorphicfragments and they can be used directlyfor construction of physicalmaps. This bulked segregant method can be applied for any speciesand any region of interest in which detailed linkage maps orphysical maps are needed.     

DNA pooling strategy for saturation mapping in outbred crosses

We present a method to identify molecular markers linked to a genomic interval in outbred pedigrees. Using information from fully informative RFLP markers on a single linkage group containing a quantitative trait locus for wood specific gravity, we constructed four DNA pools from nonrecombinant progeny of a three-generation outbred pedigree. The four pools were screened to identify linked RAPD markers. The phase and zygosity of a linked RAPD marker could be determined directly from the array of RAPD bands present or absent in the four pools. Two hundred fifty-six primers were tested on the four DNA pools, revealing 61 putatively linked loci. Nine RAPD loci were linked to the genomic interval. The approach developed here could be generally applied to saturation mapping in outbred pedigrees where fully informative markers have previously been mapped.     

Stomatal conductance of lettuce grown under or exposed to different light qualities

BACKGROUND AND AIMS: The objective of this research was to examine the effects of differences in light spectrum on the stomatal conductance (Gs) and dry matter production of lettuce plants grown under a day/night cycle with different spectra, and also the effects on Gs of short-term exposure to different spectra. METHODS: Lettuce (Lactuca sativa) plants were grown with 6 h dark and 18 h light under four different spectra, red-blue (RB), red-blue-green (RBG), green (GF) and white (CWF), and Gs and plant growth were measured. KEY RESULTS AND CONCLUSIONS: Conductance of plants grown for 23 d under CWF rose rapidly on illumination to a maximum in the middle of the light period, then decreased again before the dark period when it was minimal. However, the maximum was smaller in plants grown under RB, RGB and GF. This demonstrates that spectral quality during growth affects the diurnal pattern of stomatal conductance. Although Gs was smaller in plants grown under RGB than CWF, dry mass accumulation was greater, suggesting that Gs did not limit carbon assimilation under these spectral conditions. Temporarily changing the spectral quality of the plants grown for 23 d under CWF, affected stomatal responses reversibly, confirming studies on epidermal strips. This study provides new information showing that Gs is responsive to spectral quality during growth and, in the short-term, is not directly coupled to dry matter accumulation.     

Identification of peanut (Arachis hypogaea L.) RAPD markers diagnostic of root-knot nematode (Meloidogyne arenaria (Neal) Chitwood) resistance

DNA markers linked to a root-knot nematode resistance gene derived from wild peanut species have been identified. The wild diploid peanut accessions K9484 (Arachis batizocoi Krapov. & W. C. Gregory), GKP10017, (A. cardenasii Krapov & W. C. Gregory), and GKP10602 (A. diogoi Hoehne) possess genes for ressitance to Meloidogyne arenaria. These three accessions and A. hypogaea cv. Florunner were crossed to generate the hybrid resistant breeding line TxAg-7. This line was used as donor parent to develop a BC₄F₂ population segregating for resistance. Three RAPD markers associated with nematode resistance were identified in this population by bulked segregant analysis. Linkage was confirmed by screening 21 segregatingh BC₄F₂ and 63 BC₅F₂ single plants. Recombination between marker RKN410 and resistance, and between marker RKN440 and resistance, was estimated to be 5.4±1.9% and 5.8±2.1%, respectively, on a per-generation basis. These two markers identified a resistance gene derived from either A. cardenasii or A. diogoi, and were closely linked to each other. Recombination between a third marker, RKN229, inherited from A. cardenasii or A. diogoi, and resistance was 9.0±3.2% per generation. Markers RKN410 and RKN229 appeared to be linked genetically and flank the same resistance gene. All markers were confirmed by hybridization of cloned or gel-purified marker DNA to blots of PCR-amplified DNA. Pooled data on the segregation of BC₅F₂ plants was consistent with the presence of one resistance gene in the advanced breeding lines. Different distributions of resistance in the BC₅F₂ progeny and TxAG-7 suggest the presence of additional resistance genes in TxAG-7.     

A molecular marker associated with the H21 Hessian fly resistance gene in wheat

Near-isogenic lines in conjunction with bulked segregant analysis were used to identify a DNA marker in wheat (Triticum aestivum L.) associated with the H21 gene conferring resistance to biotype L of Hessian fly [Mayetiola destructor (Say)] larvae. Near-isogenic lines were developed by backcross introgression BC3F3:4 (Coker 797 * 4 / Hamlet) and differed by the presence or absence of H21 (on 2RL) derived from Chaupon rye (Secale cereale L.). Bulked DNA samples were prepared from near-isogenic lines and BC3F2 population individuals segregating for reaction to Hessian fly biotype L and screened for random amplified polymorphic DNA markers using 46 10mer primers. Random-amplified polymorphic DNA markers from resistant and susceptible individuals and parental lines were scored and these data were used to identify a 3 kb DNA fragment that was related to the occurrence of H21. This fragment was amplified from DNA isolated from Hamlet, a near-isogenic line carrying 2RL, and bulked DNA from resistant BC3F2 individuals, but not from the recurrent parent Coker 797 or DNA bulks from susceptible BC3F2 plants. Analysis of 111 BC3F2 segregating individuals and BC3F2:3 segregants confirmed the co-segregation of the 3 kb DNA marker with the H21 resistance gene to Hessian fly. Use of this marker could facilitate more rapid screening of plant populations for Hessian fly resistance and monitoring the introgression of H21.     

An efficient mutational method for photosynthetic bacteria

The pigment and auxotrophic mutants of Rhodobacter sphaeroides Y6 were obtained by treatment with ethyl methanesulfonate (EMS) followed by lithium chloride (LiCl). Treatment with 0.081 MEMS and subsequent treatment with 0.071 M LiCl resulted in 12% higher frequency og than that by 0.081 mol/L EMS alone, and the same frequency of pigment mutations than application of 0.081 M EMS alone; the frequency of auxotrophic mutations increased 2.5-fold when treatment with lithium chloride was applied. A blue shift by 10 nm was recorded in the absorption spectrum of carotenoids form YM5-3 green mutant; considerable accumulation of neurosporine was revealed by HPLC and mass spectrometry. The method is efficient for isolating the mutants of photosynthetic bacteria. Published in Russian in Mikrobiologiya, 2006, Vol. 75, No. 6, pp. 758–764. The text was submitted by the authors in English.