Phosphorus-31 NMR Studies of Wild-Type and NaCl-Tolerant Citrus Cultured Cells

Ben–Hayyim, G. and Navon, G. 1985. Phosphorus–31NMR studies of wild–type and NaCl–tolerant Citruscultured cells.—J. exp. Bot. 36: 1877–1888. Theinternal pH of the cytoplasm and vacuole and the relative distributionof internal P_i concentrations between those two cell compartmentshave been determined by ³¹P nuclear magnetic resonance spectroscopyin wild–type and NaCl–tolerant cell lines of Shamoutiorange (Citrus sinensis L. Osbeck). Wild–type cells accumulatehigher amounts of P_i than the NaCl–tolerant cells whenexposed to equal external P_i concentrations. This additionalP_i is located mainly in the vacuole. When both types of cellsare exposed to increasing external P_i concentrations, the internalP_i concentrations increase. The cytoplasmic P_i concentrationreaches saturation at a rather low external P_i concentrationwhile the vacuolar P_i can be increased by a large factor. Transferof cells from aerobic to anaerobic conditions causes an immediateincrease of P_i in the cytoplasm and a slow acidification. Exposureof cells to NaCl during the period of their growth results inan increase in total P_i concentration with a large increasein the ratio of vacuolar to cytoplasmic P_i levels. When thesecells are exposed to NaCl for a short time, total internal P_iconcentration docs not change significantly but its proportionschange in favour of the vacuole. pH values of the cytoplasmand the vacuole under all these conditions are rather constant,the value being 5.8–6.0 for the vacuole and 7.4–7.6for the cytoplasm. Moreover, subjecting these cells to a widerange of external pH values does not change their intracellularpH. These results indicate that a strong regulation of internalpH is operating in both types of cells. The presence of a phosphorylatedmetabolite with an unusual pH titration curve, located in thevacuole, is also reported. Key words: Citrus, callus, ³¹P-NMR, NaCI tolerance, intracellular pH     

Stem CO2 efflux in six co‐occurring tree species: underlying factors and ecological implications

Stem respiration plays a role in species coexistence and forest dynamics. Here we examined the intra‐ and inter‐specific variability of stem CO₂ efflux (E) in dominant and suppressed trees of six deciduous species in a mixed forest stand: Fagus sylvatica L., Quercus petraea [Matt.] Liebl, Quercus pyrenaica Willd., Prunus avium L., Sorbus aucuparia L. and Crataegus monogyna Jacq. We conducted measurements in late autumn. Within species, dominants had higher E per unit stem surface area (E_s) mainly because sapwood depth was higher than in suppressed trees. Across species, however, differences in E_s corresponded with differences in the proportion of living parenchyma in sapwood and concentration of non‐structural carbohydrates (NSC). Across species, E_s was strongly and NSC marginally positively related with an index of drought tolerance, suggesting that slow growth of drought‐tolerant trees is related to higher NSC concentration and E_s. We conclude that, during the leafless period, E is indicative of maintenance respiration and is related with some ecological characteristics of the species, such as drought resistance; that sapwood depth is the main factor explaining variability in E_s within species; and that the proportion of NSC in the sapwood is the main factor behind variability in E_s among species.     

Seed quality effects in bulb onions (Allium cepa L.)

The nature and persistence of seed quality effects produced by a range of seed production treatments was investigated in the autumn-sown onion crop. Genotypically equivalent seed lots raised in different glasshouses within the same year were found to germinate at significantly different rates. The seed lot which emerged earlier produced larger seedlings and this difference in size persisted throughout the growing period. In a comparison between the effects of hand crossing and self-pollination techniques the hand crossing method produced a much lower total seed yield but heavier seeds and larger plants. The induced effects persisted throughout the year but were not significant in the mature bulb characters. The implications of these results upon the control of seed production for plant breeding and genetical experiments is discussed.     

A new species of Oxalis section Corniculatae (Oxalidaceae) from the Balearic islands

A new species, Oxalis ferae Llorens, Gil & Cardona (Oxalidaceae) from the Balearic islands (Spain) is described and illustrated. It is considered to be endemic to Mallorca. The morphological differences between the more closely related taxa of Oxalis section Corniculatae are discussed. IUCN threatened category and observations on the ecology of the populations are noted.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 489–493.     

Cell Surface Saccharides in Three Phytomonas Species Differing in Host Specificity

ABSTRACT. Cell surface carbohydrates of three phytoflagellates, Phytomonas francai. Phytomonas serpens and Phytomonas sp. from different hosts including cassava, coreid insect Phthia picta and the milkweed plant Euphorbia hyssopifolia, respectively, were analysed by agglutination assays employing a battery of highly purified lectins with affinity for receptor molecules containing N-acetylglucosamine (d-GlcNAc), N-acetylgalactosamine (D-GalNAc), galactose, mannose-like (D-Man-like) residues and fucose, and by binding assay using radiolabeled [¹²⁵I]-wheat germ agglutinin (WGA) and fluorescent WGA lectin, as well as glycosidases of known sugar specificity, Escherichia coli K with mannose-affinity fimbrial lectin was also used as an agglutination probe. In general, the presence of D-GlcNAc. D-GalNAc and D-Man-like residues was detected in the phytomonads' plasma membrane. These sugar moieties were confirmed in whole cell hydrolysates as assessed by gas-liquid chromatography (GLC) which in addition, also showed the presence of galactose and xylose. However, marked differences in cell surface carbohydrate structures were observed. Wheat germ agglutinin, which binds to sialic acid and/or d-GlcNAc-containing residues, shows selective agglutinin activities for P. francai and Phytomonas sp., while Bandeiraea simplicifolia II agglutinin (which recognizes d-GlcNAc units) specifically bound to Phytomonas sp. Helix pomatia agglutinin which binds to D-GalNAc-containing residues reacted preferentially with Phytomonas sp. and P. serpens. Con A, which recognizes D-Man-like receptors, agglutinates all the phytomonads; however, the higher interaction was observed with Phytomonas sp. P. francai was selectively agglutinated in the presence of E. coli fimbrial lectin. Fluorescence WGA binding was significantly decreased by N-acetylglucosaminidase activities and the cell agglutination was not altered by neuraminidase treatment, suggesting the presence of an exposed D-GlcNAc moiety on the P. francai and Phytomonas sp. surfaces. Binding studies with [¹²⁵I]-WGA essentially confirmed the fluorescence WGA binding and agglutination assays.     

Marcescence and senescence in a submediterranean oak (Quercus subpyrenaica E.H. del Villar): photosynthetic characteristics and nutrient composition

We have studied some characteristics of marcescent leaves (withered retained leaves) and senescent leaves in Quercus subpyrenaica, a tree species that plays a major role in the climatic transition forests between temperate and mediterranean environments in north-eastern Spain. Leaves were taken from the upper and lower halves of the tree crown, both in the south- and north-exposed parts of the tree. Leaves receiving low photosynthetic photon flux density (PPFD) undergo autumnal senescence, which is associated with decreases in photosynthetic pigments and decreases in the chlorophyll a to chlorophyll b ratio. Leaves receiving higher PPFD underwent senescence at a later date. Leaves situated in the upper, south-exposed part of the tree, which receive the highest PPFD, showed no signs of senescence and remained photosynthetically active for a longer period of time, marcescence occurring suddenly at the end of the season. Marcescence is unlikely to cause an improvement in nutrient recycling, since the removal of nutrients proceeded similarly in marcescent and senescent leaves. Marcescence may increase the time-span of the assimilation capacity for a significant period of time during September and October, when high light intensities and mild temperatures occur. The phenomena triggering marcescence may be related to low temperatures.     

Protein and oil concentration of soybean seed cultured in vitro using nutrient solutions of differing glutamine concentration

Oil and protein are the most valuable components of soybean seed. Evidence indicates that growth and composition of soybean seed are controlled by supplies of carbon and nitrogen provided by the maternal plant to the seed, but it is difficult experimentally to control and quantify the precise amount of carbon and nitrogen provided to the seed by the whole plant. To examine whether oil and protein concentrations are affected by the supply of nitrogen to the seed, immature soybean seeds (Glycine max cv. Williams 82) were grown in vitro in nutrient solutions containing 20, 40, 60 or 80 mM of glutamine. The seeds were incubated in Erlenmeyer flasks for 8 days at 25°C. The rate of dry matter accumulation changed from 7.2 to 8.3 mg seed⁻¹ day⁻¹ as the glutamine concentration increased from 20 to 80 mM but the differences were not significant (P 0.05). Seed protein concentration increased as glutamine concentration increased from 294 mg g⁻¹ at 20 mM glutamine to as high as 445 mg g⁻¹ at 80 mM glutamine. Typical in vivo protein concentration of mature soybean seeds is about 400 mg g⁻¹. Oil and protein concentrations were negatively correlated (r²= 0.44), which indicates that oil and protein synthesis are interrelated. Protein synthesis was favoured over oil synthesis when nitrogen became more abundant. The seeds used in this study clearly demonstrated a capacity to respond to nitrogen availability with changes in seed protein concentration.     

Leaf anatomical properties in relation to differences in mesophyll conductance to CO2 and photosynthesis in two related Mediterranean Abies species

Abies alba and Abies pinsapo are closely related species with the same ribulose 1·5‐bisphosphate carboxylase/oxygenase (Rubisco) large subunit (rbcL) but contrasting hydraulic traits and mesophyll structure occurring in the Iberian Peninsula under contrasting conditions. As photosynthesis and hydraulic capacities often co‐scale, we hypothesize that these species differ in mesophyll conductance to CO₂ (g_m). g_m and key anatomical traits were measured in both species. Drought‐adapted population of A. pinsapo has higher photosynthesis than the more mesic population of A. alba, in agreement with its higher hydraulic capacity. However, A. alba exhibits the largest stomatal conductance (g_s), and so water use efficiency (WUE) is much higher in A. pinsapo. The differences in photosynthesis were explained by differences in g_m, indicating a correlation between hydraulic capacity and g_m. We report a case where g_m is the main factor limiting photosynthesis in one species (A. alba) when compared with the other one (A. pinsapo). The results also highlight the discrepancy between g_m estimates based on anatomical measurements and those based on gas exchange methods, probably due to the very large resistance exerted by cell walls and the stroma in both species. Thus, the cell wall and chloroplast properties in relation to CO₂ diffusion constitute a near‐future research priority.