Molecular and Subunit Heterogeneity of Legumin of Pisum sativum L. (Garden Pea)-- A Multi-Dimensional Gel Electrophoretic Study

Pisum sativum legumin has been shown to be heterogeneous withrespect to the existence of different molecular forms, the molecularweights of subunit pairs, and the molecular weights and isoelectricpoints of constituent subunits. Disulphide-bonded subunit pairswith mol. wt. 54 000 constitute a major part of total legumin.In addition, subunit pairs varying in mol. wt. from 35 000 to58 000 have been observed which associate in various ways togive rise to at least three distinct molecular forms of leguminseparable on non-dissociating gels. ‘Three-dimensional’gel electro-phoresis has been employed to understand the consitutionof these forms in detail.     

The Onset of Germination Ability in Developing Wheat

The ability of primary wheat grains (cv. Sappo) to germinatewas determined at different times from anthesis. Fresh, prematurelyharvested grains germinated best at low temperatures (<10°C). The temperature range over which appreciable germinationtook place broadened and the maximum percentage germinationachieved increased with lengthening time between anthesis andharvest. Chilling and exogenous applications of GA₃ each affectedthe rate of germination and the maximum percentage germinationof grains in their own ways. The results are discussed in relationto the identification of ‘dormancy’ in wheat grains.     

Reversed animal-plant interactions: the evolution of insectivorous and ant-fed plants

Insectivorous plants and ant-fed plants represent the two ways in which plants have evolved to utilize directly nutrients derived from animals. This paper addresses the limitations under which selection acts to favour the evolution of one or the other of these nutrient-gathering tactics. Both tactics have evolved independently at least six times under similar ecological conditions, indicating that the evolutionary solutions to ecological problems are limited by the historical make-up of communities and are, to some extent, predictable. Both insectivorous and ant-fed plants evolve in environments with very low levels of availability of nutrients in the substrate; the primary use of the animal-food is probably nitrogen; the vast majority of species are perennial, and most species are tropical or subtropical, although some insectivorous genera are primarily temperate.
Although these two nutrient-gathering tactics evolve in response to similar ecological problems, whether plants evolve an insectivorous habit or the ant-fed habit depends on the growth forms of the plants and the habitats in which they grow. Most insectivorous plants evolve as herbs in wet, sterile soils or in sterile aquatic habitats; ant-fed plants evolve as epiphytes on trees in open-canopied habitats. These kinds of animal-plant interactions are relatively rare because the environments in which they are favoured by selection are uncommon.     

Activity profiles of enzymes involved in glutamine and glutamate metabolism in the apple during autumnal senescence

Seasonal changes in glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), and glutamate dehydrogenase (EC 1.4.1.3) were measured in both senescing leaf and bark tissues of ‘Golden Delicious’ apple trees (Malus domestica Borkh.). From the measured enzyme activities we attempted to estimate the in vivo catalytic potentials of the enzymes with special reference to nitrogen mobilization and conservation of senescing apple trees. The cumulative glutamine synthetase activity of leaf tissue was about three times higher than that of bark. The estimated catalytic potential of leaf glutamine synthetase was 800-fold higher than the actual protein nitrogen loss of senescing leaves. The cumulative glutamate synthase activity of bark was about six times higher than that of leaf. The estimated catalytic potential of bark glutamate synthase was 160-times higher than the actual protein nitrogen gain in that tissue. The cumulative glutamate dehydrogenase activities in leaf and bark tissue were approximately the same. However, the catalytic potential of leaf glutamate dehydrogenase was twice that of leaf glutamate synthase. It is thus concluded that the physiological role of glutamine synthetase in senescing leaf tissue is to furnish the amide(s) prior to mobilization of nitrogen to storage tissue. The higher activity of glutamate synthase in bark tissue could provide a mechanism to transform the imported amide nitrogen to amino nitrogen of glutamate for storage protein synthesis. The possible regulatory factors upon the activity of these enzymes in the tissues of senescing apple trees are discussed.     

Efficiency and regulation of root respiration in a legume: Effects of the N source

A comparison was made of energy metabolism of nodulated N₂ fixing plants and non-nodulated NO₃-fed plants of Lupinus albus L. Growth, N-increment, root respiration (O₂ uptake and CO² production) and the contribution of a SHAM-sensitive oxidative pathway (the alternative pathway) in root respiration were measured. Both growth rate and the rate of N-increment were the same in both series of plants. The rate of root respiration, both O₂ uptake and CO₂ production, and the activity of the SHAM-sensitive pathway were higher in NO₃-fed plants than in N₂ fixing plants. The rate of ATP production in oxidative phosphorylation was computed also to be higher in NO₃-fed plants. It is concluded that both carbohydrate costings and ATP costings for synthesis + maintenance of root material were lower in N₂ fixing than in NO₃-fed plants. The respiratory quotient of root respiration was 1.6 in N₂-fixing plants and 1.4 in NO₃-fed plants. These values were slightly higher than the values calculated on the basis of CO₂ output due to N-assimilation and the experimental values of O₂ uptake, but showed the same trend: highest in N₂ fixing plants. Root respiration of NO₃-fed plants showed a diurnal pattern (both O₂ uptake, CO₂ production and the activity of the SHAM-sensitive pathway), whilst no diurnal variation in root respiration was found in N₂ fixing plants. However, C₂H₂ reduction did show a diurnal rhythm, which is suggested to be related to the diurnal variation in transpiration. Addition of NO₃ to N₂ fixing plants increased the rate of root respiration and the activity of the alternative pathway. This treatment did not decrease C₂H₂ reduction and H₂ evolution within 4 days. Withdrawal of NO₃-supply from NO₃-fed plants decreased the rate of root respiration but had no effect on the relative activity of the alternative pathway. It is suggested that the higher rate of root respiration and the higher activity of the SHAM-sensitive pathway in NO₃-fed plants is due to a larger supply of carbohydrates to the roots, partly due to a better photosynthetic performance of the shoots and partly due to a higher capacity of the roots to attract carbohydrates.     

The Ecological Strategies of Sea Turtles

By employing concepts such as "option" and "strategy" from gametheory, this study derives an ecologically-oriented dendrogramof the probable evolutionary history and the present relationshipsof sea turtles. An "armored tank" strategy is seen as differentiatingthe first ancestral testudines from the stem reptiles and providingenduring advantages while simultaneously imposing basic restrictionson all later forms. A "flipper" strategy is postulated as basicto development of the sea turtle line, again imposing limitationswhile conferring selective advantage. Modern sea turtle speciesare grouped into three lineages representing strategies of habitat-typeresource partitioning (a split-habitat, migratory pattern, aneritic residence pattern, and a pelagic residence pattern).Within the split-habitat, migratory group, further resource-partitioningby food-type separates the herbivorous Chelonia mydas populationsfrom omnivorous Eretmochelys imbricata and the (apparently)carnivorous Chelonia depressa. Herbivory is seen as integralto the split-habitat, migratory strategy and C. mydas is consideredthe most "traditional" species, with the migratory habit secondarilylost in the other two. At the same time, the enhanced philopatryselected for by the migration strategy is viewed as responsiblefor the fact that C. mydas seems to have the most active race-formationof the three species. Further habitat-type partitioning in theneritic group, together with food-type partitioning, separatesCaretta caretta from the two Lepidochelys species. L. kempiis represented as a consequence of Panamanian separation fromL. olivacea following the last establishment of the isthmusas a land barrier. The third, pelagic residence, strategy isrepresented by Dermochelys coriacea, with little further differentiationof the line. The paper attempts to show that the evolution ofsea turtles has been ecologically logical, that most conceivableniches for marine turtles are presently filled successfully,and that some predictions may be made with regard to gaps inour existing information.     

The Role of Extracellular Ca2+ in the Activation of Pectinaria Oocytes

Several events are associated with fertilization in oocytes. Two such events are an increase in cytoplasmic Ca²⁺ concentration and the resumption of meiosis. Oocytes of the marine annelid, Pectinaria gouldii , are in metaphase I arrest when they are spawned. In this report we investigate the relationship between Ca²⁺ and resumption of meiosis in this species. Meiosis in unfertilized oocytes could be re-initiated with the divalent cation ionophore, A23187. Oocytes in Ca²⁺ free sea water, however, did not resume meiosis in the presence of the ionophore. Furthermore, it was observed that Ca²⁺ must be present for at least 15 min following ionophore treatment for meiosis to resume. These results suggest that extracellular Ca²⁺ is required for the re-initiation of meiosis in this species.