Floral nectaries and nectar production in brown mustard (Brassica juncea) and white mustard (Sinapis alba) (Brassicaceae)

 The dynamics and abundance of nectar secretion as well as sugar productivity were studied in flowers of brown mustard (Brassica juncea) cv. Małopolska and white mustard (Sinapis alba) cv. Borowska. Moreover, floral nectaries were examined under LM and SEM. In both cultivars lateral and median pairs of nectaries secreted nectar. However, differences were found in morphology and activity of these pairs. The lateral nectaries produced more nectar than the median ones. Nectar secretion started at loose bud and peaked during anther dehiscence. Average amount of nectarsecreted by 100 flowers of cv. Małopolska and cv. Borowska were 119.9 mg and 134 mg. Mean concentration of nectar was 26.7% and 23.4%, respectively. One hundred flowers of cv. Małopolska and cv. Borowska secreted 28.4 mg and 24.9 mg of sugars in nectar. Estimated sugar productivity per 1 ha of crop was 65.5 kg and 71.2 kg, respectively. Received August 28, 2002; accepted November 2, 2002 Published online: June 2, 2003     

Sequence of the cryptic satellite DNA from the plant Sinapis alba

A satellite DNA with a buoyant density equal to that of main band DNA in neutral cesium chloride (‘cryptic satellite’) can be isolated from the DNA of mustard (Sinapis alba) nuclei by Ag⁺/Cs₂SO₄ density gradient centrifugation. This satellite is cleaved into 172 bp repeat units by HinfI, AluI or HaeIII. The HinfI fragments have been further cleaved by AluI, and seven AluI subfragments have been sequenced. As a result two versions of a basic 172 HinfI repeat have been found, one (A + B) with an additional HinfI site. These two sequences (A + B and C) are the most frequent versions of the basic repeat of mustard satellite DNA. The basic 172 bp unit does not contain subrepeats or palindromic sequences. It is not similar (at a criterion of 15 common bases) with any known satellite sequence. It is not unusually highly methylated in the native state.     

The nitrogen-sink is involved in the regulation of nitrogenase activity in white clover after defoliation

The objective of the present study was to develop an empirical cold hardiness model applicable to several taxa of deciduous trees. Cold hardiness expressed as lowest survival temperature of Acer rubrum, Betula nigra, Liquidambar styracifiua, Fraxinus pennsylvanica, Prunus serotina and Quercus alba was evaluated at approximately weekly intervals during the winters of three consecutive years. Plant samples and meteorological data were collected from Georgia Experiment Station, Griffin, Georgia. Maximum, minimum and average temperatures, hourly chill and heat accumulation. day length and time of year were used as input variables for model development. The statistical method of stepwise procedure of regression analysis was employed to select variables for the model. Based on the assumption that model components should be the same for all taxa included in this study and all three winters, the following independent model variables were selected as valid inputs: day length, number of accumulated hours with temperature above 20°C and number of accumulated hours with temperature below 10°C. Equation coefficients of species-specific models were determined for each species. Cold hardiness predictions were compared to actual observations for each species. The model components were interpreted as representing two processes: (1) internally regulated and independent of actual temperature, and (2) externally regulated and dependent on the amount of accumulated chill or heat. The model allowed for comparisons of cold hardening and dehardening between the studied taxa and between years.     

Photoacoustic spectra of needles as an indicator of the activity of the photosynthetic apparatus of healthy and damaged conifers

Photoacoustic spectra were measured at chopping frequencies of the excitation light at 22 and 515 Hz in order to detect differences between needles from healthy and damaged conifers ( Abies alba Mill, and Picea abies Karst.) with respect to pigment distribution and possibly also to photosynthetic activity. Fully green needles of healthy trees exhibit photoacoustic spectra at 22 Hz with a maximum in the red absorption region of the chlorophyll. This maximum is lost with increasing damage to needles and chlorophyll breakdown. The photoacoustic spectra at 22 Hz of the damaged needles therefore are characterized by a higher signal in the blue-light region as compared to that in the red-light region. This can be quantified by forming the ratio of the photoacoustic signals at 675 and 475 nm (ratio PA 675/475). The needles of the damaged trees possess a lower photosynthetic activity, as seen from the CO₂ fixation rate and the variable fluorescence (Rfd-values). It is assumed that the changes in the PA-spectra of the needles from damaged trees are the result of this decline of the photosynthetic apparatus and its function. In contrast to the PA-spectrum at 22 Hz the PA-spectra at 515 Hz, where the PA-signals primarily emanate from the epidermal layer, exhibit a different shape with a maximum near 550 nm. In the needles from the damaged trees the PA-signals are higher, particularly in this maximum range of the spectrum, than those of fully green needles from healthy trees.     

白环柄菇[Lepiota alba(Bresad.)Sacc]的生理学特性和栽培研究

白环柄菇是四川省菌物的一个新记录物种分类学地位为：担子菌亚门，层菌纲，伞菌目，伞菌科，环柄菇属。此菌无毒，可食。菌丝光锁状联合，形成大量菌核（Sclerotium），在伞菌目中是罕见的。详细报道了该菌的子实体、菌丝体的形态特征、生理特点和栽培技术。这是一种典型的高温性草菌。栽培出菇的培养料为草粉、牛粪、皮及食用菌栽培废料，瓶栽、袋栽、床栽均可，干菇生物学效率为4％-8％。     

Enhancement of the thermostability and hydrolytic activity of GH10 xylanase by module shuffling between <Emphasis Type="Italic">Cellulomonas fimi</Emphasis> Cex and <Emphasis Type="Italic">Thermomonospora alba</Emphasis> XylA

Two family GH10 xylanases with different thermostability, the Cex (optimum temperature 40°C) from Cellulomonas fimi and the XylA (optimum temperature 80°C) from Thermomonospora alba, were used to construct a chimeric xylanase by module shuffling for investigating the structural determinants responsible for the difference. The parent genes were shuffled by crossovers at selected module borders using self-priming Polymerase Chain Reaction (PCR)s. The shuffled construct, designated as CXC-X4,5, was cloned and its nucleotide sequence was confirmed. The chimera CXC-X4,5 showed activity against 4-O-methyl-d-glucurono-d-xylan–Remazol Brilliant Blue R (RBB-xylan) and over-expressed as His-tag fusion proteins. The homogeneous chimeric protein CXC-X4,5 showed significantly improved thermal profiles (optimum temperature 65°C) compared to those of one of the parents, Cex. This was apparently due to the influence of amino acids in the modules M4 and M5 inherited from thermophilic XylA. Measured K _m and k _cat values for the substrate p-nitrophenyl-β-d-cellobioside (PNP-G2) were closer to those of the other parent, Cex; however the K _m and k _cat values for the substrate p-nitrophenyl-β-d-xylobioside (PNP-X2) were between two parental xylanases. The ability of the chimeric enzyme to produce reducing sugar from xylan was enhanced in comparison with the parental enzymes. These results indicated that the amino acid residues in the modules M4 and M5 of XylA play an important role in determining enzyme characteristics such as thermal stability, and xylanases with improved properties can be prepared by manipulating this segment.     

Comparison of lag times in plant physiology

Abstract Comparison of lag (or latent) times is a useful tool in plant physiology for investigating potential mechanisms involved in a response. There are two main ways of deriving the lag time, but only one of these can be properly used for comparative purposes. The other method is biased by the faster responding plants and may not give a representative estimate for the lag time in the population. The fact that the two methods give different, non-comparable results has been widely overlooked. We suggest more care should be taken for their correct use, and propose two terms which can be used to describe the different estimates of the lag time to avoid confusion.