Endopeptidase Isoenzyme Characteristics in Cucumis sativus Leaves During Dark-induced Senescence

The changes and characteristics of endopeptidase （EP） isoenzymes in cucumber （Cucumis sativus L.） leaves during dark-induced senescence were investigated by activity staining after gradient-polyacrylamide gel electrophoresis （G-PAGE） containing co-polymerized gelatin as substrate. The results showed that both the chlorophyll and the protein contents of leaves were decreased, and the protein degradation was correlated with the increase of proteolytic activity during the course of leaf senescence. Meanwhile, nine cucumber endopeptidases isoenzymes （CEP） with 140, 120, 106, 94, 76, 55, 46, 39 and 35 kDa molecular weights were detected. Four of these, CEP2, 3, 4 and CEP9 appeared all the time, but the changes of the activity were different during incubation. Another four CEPs （CEP5, 6, 7 and CEP8） whose activities increased with dark-induced time were only detected in senescent leaves. Furthermore, the biochemical properties of these nine CEP were also characterized. All the CEPs had high activities from 35 ℃ to 45 ℃, and the optimum temperature was found to be 40 ℃. However, the activities of CEPs were not detected below 25 ℃ or over 60 ℃. The activity bands appeared at a wide range of pH from 5.0 to 9.0, but the optimum pH was found at 7.0. No CEPs were detected at pH 4 or pH 10. By inhibition analysis we concluded that CEP2, 3, 4 and CEP9 were serine endopeptidases and CEP6 was a kind of cysteine protease. It is suggested that serine endopeptidases might play a major role in cucumber leaf senescence, and for the first time, six senescencerelated endopeptidases （CEP1, 5, 6, 7, 8 and 9） were found in cucumber leaves.     

Structural-functional changes in detached cucumber leaves, and modelling these by hormone-treated leaf discs

Senescence and rejuvenation were investigated in detached cucumber (Cucumis sativus L.) leaves after cultivation in nutrient solution for one week or four weeks. Rooting of the petiole (visible generally from the 7th day) elicited a combination of different morphological, anatomical, and physiological changes in the lamina. Extensive growth in area and thickness, extreme regreening, changes of chloroplast structure and activity, as well as the pattern of Chl-protein complexes were observed and compared either to the corresponding parameters of young detached leaves or mature attached leaves. These responses could be provoked separately by treating excised leaf discs with kinetin, benzyladenine, or indolylacetic acid. The hormones showed mutuality in their effects, benzyladenine being responsible for the growth of cells, while indolylacetic acid and kinetin promoted an increase in chlorophyll content. However, none of the treatments resulted in the growth of the chloroplasts in the leaf discs, which was only prominent in the rooting leaves.     

多胺对离体黄瓜子叶花芽构建的影响

研究了外源多胺对离体黄瓜(CucumissativusL.)子叶内在多胺含量和花芽构建的影响。在MS培养基中添加5×10-2mmol·L-1亚精胺(Spd)、精胺(Spm)能明显提高子叶内Spd含量和SpdPut值,子叶成花率也明显高于对照组,而添加5×10-2mmol·L-1Put、5mmol·L-1环己胺硫酸盐(CHAS)培养的结果则相反。表明子叶内Spd含量和SpdPut与成花率呈正相关关系。在添加5mmol·L-1D精氨酸(DArg)处理后,子叶内SpdPut高于Spd处理,但子叶成花率低于对照组,表明Put、Spd含量也影响离体子叶花芽的构建。在实验中添加CHAS处理后子叶内Spm含量高出对照组10倍,子叶成花率却为0,其它各处理与对照组的内源Spm变化基本一致,成花率却差别明显,表明子叶内Spm含量与黄瓜子叶花芽构建之间无明显相关性。     

Progress in Wheat Resistance to Spot Blotch in Bangladesh

Spot blotch, caused by Cochliobolus sativus, is considered one of the most destructive diseases of wheat (Triticum aestivum) in the warm areas of South Asia. Over the past 20 years, wheat breeding efforts in the region have improved spot blotch resistance in susceptible commercial cultivars. This study assessed resistance and spot blotch‐induced yield losses in newly released wheat cultivars developed in Bangladesh since the release of the landmark wheat variety ‘Kanchan’. Replicated field studies were conducted during the 2003 and 2004 wheat seasons at two sites: a farmer's field and a research station in a warm region of Bangladesh where spot blotch has been a serious problem. Spot blotch affected 60% of the crop and caused yield losses of from 2% to 22%. Disease severity and disease‐induced grain yield reductions were less in wheat genotypes developed since 1983, with a corresponding trend towards higher yield in newly developed varieties. The level of resistance to spot blotch in the new cultivars and advanced breeding lines represents considerable progress in breeding for resistance over the past two decades.     

3种不同皮色萝卜种质染色体核型分析

本研究采用根尖压片法,对3种不同肉质根皮色的萝卜种质进行染色体数目和核型分析,以获得准确的细胞遗传学信息.研究结果表明,Nau-dqp08,Nau-txbyw07和Nan-chhong108这3种不同皮色萝卜的染色体数目均为18,核型公式分别为2n=2x=18=14m+4sm,2n=2x=18=18m和2n=2x=18=16m+2sm,且核型都属于1A型;核不对称系数分别为59.48%、55.39%与58.08%;核型不对称性大小为Nau-dqp08＞Nan-chhong108＞Nau-txbyw07,其中Nau-txbyw07核型较为原始.本研究结果可为萝卜种质鉴定、遗传变异和亲缘关系分析提供细胞学依据.     

同源四倍体萝卜雄配子体发育

利用爱氏苏木精染色-冬青油透明"技术,首次报道了同源四倍体萝卜(2n=4x=36)雄配子体的动态发育过程.结果表明:同源四倍体萝卜小孢子核经一次有丝分裂产生营养核与生殖核,生殖核再经一次有丝分裂形成两个精核,最终形成3-细胞型成熟花粉,与相应的二倍体雄配子体的整个发育过程相似;四倍体花粉具2个、3个或4个萌发孔,二倍体多为3孔花粉;四倍体雄配子体发育过程中异常频率为32%,比二倍体高20%,败育主要发生在四分体时期和单核期.     

黄瓜中CBF1基因的克隆及其表达分析

以黄瓜中RNA为模板,RT-PCR扩增出CBF1基因cDNA序列的部分片段。测序表明此基因与黄瓜CBF1基因的同源性达99．44％。RT-PCR方法检测结果显示,CBF1基因在低温和盐胁迫下的黄瓜中表达,而在干旱和ABA胁迫下则不表达。     

Biochemical changes associated with in vivo RbcL fragmentation by reactive oxygen species under chilling-light conditions

During physiological stress, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) degradation is accelerated, which is considered to be one of the key factors responsible for photosynthetic decline. A recent study has shown that the large subunit (RbcL) of Rubisco is directly fragmented by hydroxyl radicals in Cucumis sativus leaves under chilling-light conditions. In the present study, we investigated biochemical aspects associated with this in vivo RbcL fragmentation by reactive oxygen species. RbcL fragmentation was observed in C. sativus and Phaseolus vulgaris , but not in Solanum lycopersicum , Glycine max , Oryza sativa , Triticum aestivum , Spinacia oleracea or Arabidopsis thaliana . In C. sativus and P. vulgaris , RbcL fragmentation followed the fragmentation of PsaB, while in the other species, PsaB fragmentation did not occur. In C. sativus and P. vulgaris , the activities of antioxidant enzymes decreased dramatically under chilling-light conditions, and the proportion of uncarbamylated Rubisco increased. These data suggest that in vivo RbcL fragmentation under chilling-light conditions is associated with a combination of events, namely, inactivation of antioxidant enzymes, destruction of photosystem I and an increase of uncarbamylated Rubisco, which can produce hydroxyl radicals via the Fenton reaction at the catalytic site of RbcL.     

Characterization of repeat arrays in ultra‐long nanopore reads reveals frequent origin of satellite DNA from retrotransposon‐derived tandem repeats

Amplification of monomer sequences into long contiguous arrays is the main feature distinguishing satellite DNA from other tandem repeats, yet it is also the main obstacle in its investigation because these arrays are in principle difficult to assemble. Here we explore an alternative, assembly‐free approach that utilizes ultra‐long Oxford Nanopore reads to infer the length distribution of satellite repeat arrays, their association with other repeats and the prevailing sequence periodicities. Using the satellite DNA‐rich legume plant Lathyrus sativus as a model, we demonstrated this approach by analyzing 11 major satellite repeats using a set of nanopore reads ranging from 30 to over 200 kb in length and representing 0.73× genome coverage. We found surprising differences between the analyzed repeats because only two of them were predominantly organized in long arrays typical for satellite DNA. The remaining nine satellites were found to be derived from short tandem arrays located within LTR‐retrotransposons that occasionally expanded in length. While the corresponding LTR‐retrotransposons were dispersed across the genome, this array expansion occurred mainly in the primary constrictions of the L. sativus chromosomes, which suggests that these genome regions are favourable for satellite DNA accumulation.