The structure of 180° supernumerary limbs and a hypothesis of their formation

The results of a detailed analysis of 100 supernumerary limbs generated by 180° ipsilateral rotation (on the same limb stump) of regeneration blastemas is presented. The limbs were analyzed in terms of their position of origin, frequency, cartilage structure by Victoria blue staining, and muscle structure by serial sections. Single, double, or triple supernumeraries can be produced at no unique position of origin, although the posterodorsal quadrant was preferred. Four classes of supernumerary limbs were generated by such operations—normal; double dorsal or double ventral; part normal/part mirror imaged; part normal/part inverted in approximately equal frequencies. After amputation of these supernumeraries the same muscle patterns are faithfully regenerated. A hypothesis to explain the production of these abnormal limbs is proposed based on the observed phenomenon of fusion of supernumerary blastemata, but their regenerative behaviour presents problems for current models of pattern formation. Similar results have been obtained with developing limb buds and the relation between development and regeneration is discussed.     

The Relationship between the Traits of the Two-Row Spike,the High Number of Thillers,and the High Regeneration Capacity in in vitro Culture in Barley

In barley (Hordeum vulgare L.), the traits of the two-row spike, the high rate of plant tillering, and the high capacity for multiple plant regeneration (MPR) in a callus culture of immature embryos were shown to correlate. When a dihaploid line (DH) obtained from cv. Golden Promise (two-row spike, high number of thillers) was crossed to a DH line from cv. Bruce (six-row spike, low number of thillers), the two-row trait dominated the F₁ generation, whereas, in F₂, the segregation ratio was 3 : 1. From F₃ progeny, we isolated the families comprising two-row homo- and heterozygotes and six-row homozygotes. In an F₃ hybrid population, the two-row plants manifested higher tillering and MPR rates as compared to the six-row plants. The correlation between the traits of the two-row spike, the high tillering, and the high MPR capacity may depend on the pleiotropic V gene, which controls the general mechanisms of meristem functioning essential for the development of these three traits.     

Field investigations of ammonia exchange between barley plants and the atmosphere. II. Nitrogen realiocation, free ammonium content and activities of ammonium-assimilating enzymes in different leaves

The activities of glutamine synthetase (GS) and glutamate synthase (GOGAT) in different leaves of field-grown spring barley were measured during the reproductive growth phase in 2 consecutive years. Concurrently, the contents of soluble ammonium ions and free amides in the leaves were determined. The studies were carried out to investigate the relationship between variations in these parameters and emission of NH3 from the plant foliage. GS and GOGAT activities declined very rapidly with leafage. The decline in enzyme activities was followed by an increase in soluble ammonium ions and amides in the leaf tissues. During the same period, about 75% of leaf and stem nitrogen was reallocated to the developing ear. The amount of NH₃ volatilized from the foliage during the reproductive growth phase amounted to about 1% of the reallocated nitrogen. The experimental years were characterized by very favourable conditions for grain dry matter formation and for re-utilization of nitrogen mobilized from leaves and stems. Ammonia volatilization occurring under conditions with declining GS and GOGAT activities and increasing tissue concentrations of NH₄⁺ may be useful in protecting the plant from accumulation of toxic NH₃ and NH₄⁺ concentrations in the tissues.     

The ability of nonspecific T-cell stimulators to induce helper-cell-dependent increases in either polyclonal or isotype-restricted Ig production in vivo

In order to delineate the various roles of T cells in B-cell activation, mice were exposed to a variety of specific or nonspecific T-cell stimuli including mitogens, e.g., concanavalin A, adjuvants, e.g., complete Freund's adjuvant, and colchicine plus nonimmunogenic doses of antigen, anti-lymphocyte serum, and pathogens and their spleens analyzed for total class-specific immunoglobulin-secreting cells as indicators of helper cell generation. The results demonstrate that, depending on the mode of stimulation, markedly different Ig-secreting cell response patterns were induced, differing with respect to their kinetics and the isotype induced. In contrast to polyclonal T-cell stimuli such as concanavalin A and 17X lethal malaria which induced increases in all classes of Ig-recruiting cells, injection of many T-cell-activating agents resulted in the selective production of IgG clones in particular IgG 1. Such findings are discussed in terms of the different mechanisms of T-cell help and provide further evidence for functional heterogeneity in the T-helper-cell pool.     

Epi- and intracuticular lipids and cuticular transpiration rates of primary leaves of eight barley (Hordeum vulgare) cultivars

The major constituents of the epi- and intracuticular lipids of primary leaves of 8 cultivars of barley ( Hordeum vulgare L.) have been studied together with cuticular transpiration rates. The total amount of analysed cuticular lipids ranged from 9.6 to 13.4 μg cm⁻² and was dominated by the epicuticular fraction, which made up 73–84% of the total. There were variations in the percentages of the analysed lipid classes, alkanes, esters, aldehydes, β-diketones and alcohols, between epi- and intracuticular lipids among individual cultivars, but no clear tendency in these variations, except for the aldehydes, was found. The epicuticular lipids were richer in aldehydes than the intracuticular lipids. The cuticular transpiration rates were poorly correlated with the levels or composition of epi-, intra- or total cuticular lipids. The cuticular transpiration rates were considerably altered as a response to a water stress treatment, but these changes could not be correlated with any changes in amount or composition of the cuticular lipids. From these results it is concluded that some property other than amount or composition of cuticular lipids is the most important in regulation of water diffusion through the cuticle.     

Structural and functional analysis of the reducing side of photosystem I

Structural analysis of the reducing side of photosystem I (PSI) has been carried out using chemical cross-linking and monospecific antibodies. Incubation of PSI isolated from barley (Hordeum vulgare L.) with the hydrophilic cross-linking agent N-ethyl-3-[3-(dimethylamino) propyl]-carbodiimide leads to cross-linking of the PSI-D subunit with the PSI-E and PSI-H subunits. In the presence of ferredoxin, cross-linking results in the formation of cross-linked products composed of PSI-D, PSI-E and ferredoxin and in a block in steady state NADP⁺ photoreduction. No cross-linking of ferredoxin occurs at elevated ionic strength or using heat-denatured ferredoxin. Cross-linking of ferredoxin does not inhibit electron transfer from plastocyanin to methyl viologen. Steady state NADP⁺ photoreduction was analyzed in PSI or thyla-koids incubated with antibodies against individual PSI subunits. Incubation with antibodies against PSI-C, -H, -I, or -L had no effect on PSI activity, whereas antibodies against PSI-D or PSI-E had similar effects and caused a large decrease in activity. The results provide evidence that the PSI-D and PSI-E subunits are localized on the reducing side of PSI, forming a barrier between PSI-C and the stroma as well as a docking site for ferredoxin. The PSI-H subunit has an exposed, stromal domain but this does not appear to contribute to the ferredoxin docking.     

Effects of Phosphorus Nutrient on the Hydraulic Conductivity of Sorghum （Sorghum vulgare Pers.） Seedling Roots Under Water Deficiency

Hydroponic experiments were conducted in a growth chamber and changes in the hydraulic conductivity of sorghum (Sorghum vulgare Pers.) roots (Lpr) at the three-leaf stage were measured using the pressure chamber method. Water deficiency was imposed with polyethylene glycol (PEG) 6000 and the phosphorus (P) levels were controlled by complete Hoagland solution with and without P nutrient. The objective of this study was to investigate the effect of P nutrition on root Lpr under water deficiency. The results showed that the Lpr in P deficiency treatments decreased markedly, but the Lpr recovered to the same value as that of control when sufficient P was supplied for 4-24 h. Water deficiency decreased Lpr, but the hydraulic conductivity of the roots with sufficient P supply was still higher than that of plants without P supply. When resuming water supply, the Lpr of the water-deficient plants under P supply recovered faster than that of plants without P supply, which indicates that plants with sufficient P nutrient are more drought tolerant and have a greater ability to recover after drought. The treatment of HgCl2 indicated that P nutrient could regulate the Lpr by affecting the activity and the expression levels of aquaporins.     

Activities of de-N-glycosylation are ubiquitously found in tomato plant

Activities of two de-N-glycosylation enzymes, PNGase (peptide N ⁴(N-acetyl-glucosaminyl)asparagine amidase) and ENGase (endo N-acetyl-β-D-glucosaminidase), involved in the release of N-glycans from N-glycoproteins, were monitored in several organs of tomato plants (Lycopersicon esculentum, Mill., cv. Dombito) with a fluorescence-HPLC procedure using a resofurin-labelled N-glycopeptide substrate. PNGase and ENGase activities were detected in every organ assayed but with quantitative differences. The highest activities were found in the youngest parts of the plant, i.e. apical buds, flowers and leaf blades. PNGase activities were consistently higher than ENGase activities (three-fold in average). Both de-N-glycosylation activities were associated with high levels of proteins and protease activities. During fruit growth and ripening, these three parameters decreased notably. The ubiquitous detection of these enzyme activities in the different organs is probably associated with the previously characterized unconjugated N-glycans in tomato. The possible role of PNGase and ENGase degradation products (i.e. unconjugated N-glycans) are discussed in relation with their biological functions in plant development.