Structural Adaptation of the Leaf Mesophyll to Shading

Structural characteristics of the mesophyll were studied in five boreal grass species experiencing a wide range of light and water supply conditions. Quantitative indices of the palisade and spongy mesophyll tissues (cell and chloroplast sizes, the number of chloroplasts per cell, the total cell and chloroplast surface area per unit leaf surface area) were determined in leaves of each of the species. The cell surface area and the cell volume in spongy mesophyll were determined with a novel method based on stereological analysis of cell projections. An important role of spongy parenchyma in the photosynthetic apparatus was demonstrated. In leaves of the species studied, the spongy parenchyma constituted about 50% of the total volume and 40% of the total surface area of mesophyll cells. The proportion of the palisade to spongy mesophyll tissues varied with plant species and growth conditions. In a xerophyte Genista tinctoria, the total cell volume, cell abundance, and the total surface area of cells and chloroplasts were 30–40% larger in the palisade than in the spongy mesophyll. In contrast, in a shade-loving species Veronica chamaedris, the spongy mesophyll was 1.5–2 times more developed than the palisade mesophyll. In mesophyte species grown under high light conditions, the cell abundance and the total cell surface area were 10–20% greater in the palisade mesophyll than in the spongy parenchyma. In shaded habitats, these indices were similar in the palisade and spongy mesophyll or were 10–20% lower in the palisade mesophyll. In mesophytes, CO₂ conductance of the spongy mesophyll accounted for about 50% of the total mesophyll conductance, as calculated from the structural characteristics, with the mesophyll CO₂ conductance increasing with leaf shading.     

Structure and CO2 Exchange in the Needles of Pinus sylvestris and Abies sibirica

The morphological and functional organization of the needles of Scotch pine (Pinus sylvestris L.) and Siberian fir (Abies sibirica Ledeb.), which differ in their light requirement were studied. The characteristic properties of the high-light-requiring pine included high rates of apparent photosynthesis and dark respiration, high assimilation number, numerous folds in mesophyll cell walls, and increased partial volume of intercellular spaces and hyaloplasm in the mesophyll. In the needles of shade-enduring fir, the higher efficiency of photosynthesis at low light intensities depended on the higher number of membranes and higher pigment content in the chloroplasts. The low assimilation number in fir indicated a shortage of photosynthetic reaction centers. The relative volume of the vascular cylinder and the vascular bundles in the needles and the partial volume of chloroplasts in the hyaloplasm, are considered as indices of the rate of assimilate export from mesophyll cells and their possible damping at different levels of structural organization.     

Cultivation of Gigartina skottsbergii (Gigartinales, Rhodophyta): Recent advances and challenges for the future

This study integrates landings statistics and biological studies of the red algaGigartina skottsbergii Setchell & Gardner. The analysis of the landings and carrageenan production in Chile suggeststhat this resource will suffer a strong harvesting pressure during the nextyears. Biological results on sporulation, germination, sporeling growth and survivorship in laboratory,indoor tanks and field conditions, indicated that cultivation of this species istechnically feasible, as spores can be seeded on ropes and other substrata. Vegetative propagation of this species through tissue fragmentationis also possible. Vegetative fragments of this carrageenophyte have 20 to30% higher growth rates than whole fronds in suspended culture systems. Protoplast production can be also explored for bypassing restrictions inspore availability. Major advantages that encourage the cultivation of G. skottsbergii include its gel quantity and quality, its pathogen-freecondition, a high reproduction potential and its regeneration capacity. Onthe other hand, the major constraints are related to its relatively slowgrowth as compared to other carrageenophytes, limited availability ofspores and high mortality during juvenile stages.     

Metabolite control of Sorghum C4 phosphoenolpyruvate carboxylase catalytic activity and phosphorylation state

Kinetic analyses were performed on the nonphosphorylated and in vitro phosphorylated forms of recombinant Sorghum C4 phospho enolpyruvate carboxylase (C4 PEPC). The native enzyme was purified by immunoaffinity chromatography and its integrity demonstrated by Western blot analyses using anti N- and C-terminus antibodies. At suboptimal pH (7.1 to 7.3) and PEP concentration (2.5 mM), phosphorylation, positive metabolite effectors e.g., glucose-6-phosphate, glycine and dihydroxyacetone-phosphate, or an increase in pH strongly activated the enzyme and lowered the inhibitory effect of L-malate. C4 PEPC phosphorylation strengthened the effect of the positive effectors thereby decreasing further the enzyme's sensitivity to this inhibitor. L-malate also decreased the phosphorylation rate of C4 PEPC, a process antagonized by positive metabolite effectors. This was shown both in vitro, in a reconstituted phosphorylation assay containing the catalytic subunit of a cAMP-dependent protein kinase or the Sorghum leaf PEPC-PK and in situ, during induction of C4 PEPC phosphorylation in mesophyll cell protoplasts.     

Studies on the effect of protoplast density and genotype mixing on cell regeneration

Genotypes of Solanum tuberosum, assessed for their differential response to a protoplast regeneration protocol, were identified. This enabled comparisons to be made in relation to their abilities to regenerate into dividing cells and colonies. Protoplasts from genotypes with contrasting regeneration responses were plated as single or mixed genotype cultures at various plating densities in replicated, randomised experiments, and the effect on the regeneration of particular cell types observed. Protoplasts from single genotype cultures showed intergenotypic variation in the extent of cell regeneration and there were significant effects of genotype mixing and density × genotype mixing interactions. Overall, the effect of mixing was beneficial to a regenerating culture but significant density genotype mixing interactions showed only a positive benefit at the lowest plating density. The protoplast mixing phenomenon was not correlated with the behaviour of the same genotypes at the plantlet level in experiments with in vitro meristem cultures.     

Subcellular compartmentation of pyrophosphate and dark/light kinetics in comparison to fructose 2,6-bisphosphate

Subcellular compartmentation of pyrophosphate (PP₁) was determined by rapid membrane filtration of evaeuolated oat mesophyll protoplasts. By improving both the extraction procedure and its assay via bioluminescence, PP₁ recovery from samples was quantitative and linear down to below 200 fmol. Based on the content of the different fractions obtained after membrane filtration and compared to the respective pools of marker metabolites [cytosol, fructose 2,6-bisphosphate (F26BP); chloroplast stroma, ribulose bisphosphate] rather than enzymes, we found ca 2/3 of the total cellular content to be chloroplast-assotiated. Referred to compartmental volumes, cytosolic and stromal concentrations of PP₁ were nearly equal (70–100 μ M ). PP₁ was higher in evacuolated compared to racuotated protoplasts which indicates a possible role of the tonoplast-located H⁺ pumping PP₁ase in regulating the cellular pool size of PP₁. During dark-light-transition the pool sizes of PP₁ changed only marginally in both vacuolated and evacuolated protoplasts, while there were pronounced changes in those of F26BP, starch and sucrose. Thus our findings support the notion that the cellular pool size of PP₁ is kept rather constant. They are, however, in contrast to the assumption that appreciable PP₁ levels only exist in the cytosol.     

Protoplasten aus Basidien und vegetativen Zellen von Coprinus radiatus

Aus dem dikaryotischen Mycel und dem Hymenium dreier verschiedener Entwicklungsstadien der Fruchtkörper von C. radiatus sind Protoplasten hergestellt worden. Dabei zeigte sich, daß auch aus differenzierten pilzlichen Zellen Protoplasten isoliert werden können. Zum enzymatischen Abbau der Zellwände wurden das chitinolytisch aktive Autolysat dieses Pilzes sowie im Handel erhältliche Enzyme verwendet. Die Protoplastenbildung setzt nach einer Inkubationszeit von 15 bis 30 Minuten in der Enzympräparation ein und ist nach 2 bis 4 Stunden abgeschlossen. Es wird nachgewiesen, daß Basidien die einzigen Zellen des bereits differenzierten Hymeniums sind, aus denen Protoplasten isoliert werden können. Die Protoplastenbildung erfolgt an Perforationen im Apikalbereich der Basidien, vermutlich den Loci der später einsetzenden Sterigmenbildung. Die Ausbeute an Basidialprotoplasten beträgt durchschnittlich 8,4 times 10⁵ je g Fruchtkörperfrischgewicht.