Thermal Dissection of Lentil Seedling Amine Oxidase Domains by Differential Scanning Calorimetry

The relationships between the structural and energetic domains of lentil seedling amine oxidase (LSAO) were investigated using modifiers that target the active site and the carbohydrate moiety of the enzyme. An irreversible inhibitor, aminoguanidine, specifically modified the active site of the lentil enzyme, whereas sodium metaperiodate cleaves carbohydrate moieties covalently bound to the native enzyme. Differential scanning calorimetry (DSC) measurements were made on the modified LSAOs. Deconvolution of the reversible thermal DSC profiles of the modified enzyme gave three subpeaks (energetic domains), each of which was assigned to one of the three structural domains of the native protein. Our results led us to conclude that deglycosylation of LSAO has no effect on thermal stability, whereas binding of the inhibitor imparts more stability to the enzyme.     

Photolysis of 3-Hydroxyisoxazoles

Photolysis of 3-hydroxy-5-phenylisoxazole in methanol with a low-pressure mercury lamp afforded 5-phenyl-4-oxazolin-2-one, together with small amounts of benzoic acid and benzoylacetamide. Similarly, 3-hydroxy-5-methylisoxazole in distilled water afforded 5-methyl-4-oxazolin-2-one as the major product. Both isoxazoles were stable in sunlight for up to 20 days.     

Purification and Properties of a Pectin trans-Eliminase in Erwin aroideae Formed in the Presence of Nalidixic Acid

A strain of Erwinia aroideae produces a remarkable amount of pectolytic enzyme when the organism was induced by nalidixic acid for the bacteriocin production. This pectolytic enzyme was purified approximately 60-fold from the induced medium by carboxymethyl-cellulose and Sephadex G–75 gel column chromatographies after batchwise treatment with carboxymethyl- and diethylaminoethyl-celluloses. The purified enzyme was almost homogeneous on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, a molecular weight of about 28,000 to 32,000 was determined for this enzyme. The optimum pH of the enzyme activity was about 8.0 to 8.2. The purified enzyme produced reaction products from pectin and methoxylated pectic acid which had a strong absorption at 235 nm indicating a trans-eliminase reaction. Pectin or pectic acid with higher methoxyl content was a good substrate for this enzyme, while no significant activity was observed when pectic acid was a substrate. The limit of degradation of pectin and pectic acid with higher methoxyl content (90% esterified) by the enzyme were 6.5% and 43%, respectively. It was concluded that the enzyme is a new endo-pectin trans-eliminase from bacterial origin.     

Carpology,germination and seedling performance in Digitalis thapsi L. (Scrophulariaceae)

Summary

We analyse the fruiting phase of the life cycleof Digitalis thapsi L. We studied the production and size of seeds and capsules, and the interpopulational variability and inter-relationships of these parameters. The capsule volume, number of seeds per capsule, of seeds per individual, and of capsules per individual were inter-related and fairly affected by the medium, whereas seed weight was found to bea more independent character. A germination study showed that the species has agreat germinative capacity and has positive photoblasty. It is non-dormant especially if incubated under experimental conditions close to the climatic conditions of the site of provenance of the samples. An increase in temperature speeds up the process without increasing germinability. The morphological and biometric characteristics of the first stages of development of the species following germination were analysed. It was found that seed weight is not positively correlated with cotyledon length nor with any of the other parameters con-sidered, and that the length of the fifth leaf is a useful parameter to express inter-populational genetic variability. Seedling production in spring seems to be influenced more by physical than by chemical factors.     

There's no place like home: seedling mortality contributes to the habitat specialisation of tree species across Amazonia

Understanding the mechanisms generating species distributions remains a challenge, especially in hyperdiverse tropical forests. We evaluated the role of rainfall variation, soil gradients and herbivory on seedling mortality, and how variation in seedling performance along these gradients contributes to habitat specialisation. In a 4‐year experiment, replicated at the two extremes of the Amazon basin, we reciprocally transplanted 4638 tree seedlings of 41 habitat‐specialist species from seven phylogenetic lineages among the three most important forest habitats of lowland Amazonia. Rainfall variation, flooding and soil gradients strongly influenced seedling mortality, whereas herbivory had negligible impact. Seedling mortality varied strongly among habitats, consistent with predictions for habitat specialists in most lineages. This suggests that seedling performance is a primary determinant of the habitat associations of adult trees across Amazonia. It further suggests that tree diversity, currently mostly harboured in terra firme forests, may be strongly impacted by the predicted climate changes in Amazonia.     

Frequency‐dependent selection for rare genotypes promotes genetic diversity of a tropical palm

Negative frequency‐dependent selection among species is a key driver of community diversity in natural systems, but the degree to which negative frequency‐dependent selection shapes patterns of survival and genetic diversity within species is poorly understood. In a 5‐year field experiment, we show that seedlings of a tropical palm with rare genotypes had a pronounced survival advantage over seedlings with common genotypes, with effect sizes comparable to that of light availability. This ‘rare genotype advantage’ led to an increase in population‐wide genetic diversity among seedlings compared to null expectations, as predicted by negative frequency‐dependent selection, and increased reproductive success in adult trees with rare genotypes. These results suggest that within‐species negative frequency‐dependent selection of genotypes can shape genetic variation on ecologically relevant timescales in natural systems and may be a key, overlooked source of non‐random mortality for tropical plants.     

农林废弃物混配基质的理化性质及其对油茶幼苗生长效应的综合评价

以腐熟的甘蔗渣( SB)、木薯皮( CP)、花生壳( PS)和火炭灰( BA)及园土( GS)为原料,按照不同体积比配制成9种混配基质,并以等体积比泥炭和园土混配基质为对照,对各基质的理化性质及基质中油茶( Camellia oleifera Abel)幼苗的生长状况进行比较;在对基质理化指标和油茶幼苗的壮苗指数进行线性回归分析和通径分析的基础上,采用主成分分析和综合评价法对各基质的育苗效果进行综合评价。结果表明：9种农林废弃物混配基质的容重、总孔隙度和毛管孔隙度分别为0.23~0.47 g·cm-3、60.90%~67.23%和46.53%~58.27%, pH 6.72~pH 7.14,各基质的速效氮含量、速效磷含量、速效钾含量、pH值、电导率和通气孔隙度均高于或显著高于对照,容重则显著低于对照。在不同基质中油茶幼苗的茎粗、单株叶片数、叶长、叶宽、叶绿素相对含量( SPAD)、单株茎叶干质量、单株根干质量和壮苗指数均存在一定差异,而株高和根冠比却无显著差异;其中S9混配基质也V( SB)：V( CP)：V( BA)=2：1：1页中幼苗的大部分生长指标较高,表现出明显的生长优势。线性回归和通径分析结果显示：除通气孔隙度外,基质的其他8个理化指标基本涵盖了影响幼苗壮苗指数的关键因素;其中,速效钾含量是对壮苗指数直接影响最大的负相关因子,而速效磷含量、电导率和总孔隙度对壮苗指数则有较大的正向直接作用,并且三者通过速效钾含量对壮苗指数产生较大的负向间接作用;此外,基质容重对壮苗指数也有一定的负向直接作用。综合评价结果显示：S9和S7混配基质也V( SB)：V( BA)：V( GS)=4：3：3页对油茶育苗效果的综合得分较高,分别为14.363和14.337,建议将S9混配基质作为油茶育苗的首选替代基质,S7混配基质作为备选基质。     

籼粳稻杂交衍生RIL系的苗期抗旱性评价

为鉴定籼粳稻杂交衍生系的苗期抗旱性,以课题组自育的高代抗逆品系ZD15为母本、籼稻品种IR29为父本,以及杂交衍生的重组自交系群体120份为试验材料,利用PEG-6000对各材料苗期进行干旱胁迫处理,测定根长、根冠比、地上部鲜重、地下部鲜重、地上部干重和地下部干重;利用PEG-6000对各材料芽期进行干旱胁迫处理,测定芽鞘长和芽长。采用主成分分析和隶属函数法对各材料的抗旱性进行综合评价,根据综合抗旱D值可将122份材料分成3类,D值在0.201～0.400之间的有33份,属于不抗旱材料;D值在0.401～0.600之间的有79份,属于中等抗旱材料;D值在0.601～0.800之间的有10份,属于抗旱材料。利用D值进行逐步回归分析,结果表明根长、根冠比、地上部鲜重、地下部鲜重、地上部干重、地下部干重、芽鞘长和芽长8个性状均可作为水稻苗期抗旱性的评价指标。本研究筛选出的抗旱材料,可作为育种中间材料进一步培育,或作为育种资源加以利用,以丰富本区水稻育种的资源库。     

Seasonal distribution of increased precipitation in maternal environments influences offspring performance of Potentilla tanacetifolia in a temperate steppe ecosystem

Aims Precipitation is predicted to increase in arid and semiarid regions under climate change, with greater changes in intra- and inter-annual distribution in the future. As a major limiting factor in these regions, changes in precipitation undoubtedly influence plant growth and productivity. However, how the temporal shifts in precipitation will impact plant populations are uncertain.