Sorbitol metabolism by apple seedlings

The aims of this work were to compare the roles of sorbitol and sucrose in seedlings of Malus domestica, to discover which tissues synthesize sorbitol and which break it down, and to examine these tissues for enzymes of sorbitol metabolism. The detailed distribution of label was determined after supplying intact seedlings with ¹⁴CO₂, and excised parts of seedlings with [U-¹⁴C]fructose and [U-¹⁴C]sorbitol. The results showed that appreciable synthesis of sorbitol occurred only in the leaves but did not depend directly on photosynthesis. All tissues examined metabolized sorbitol but metabolism was extensive only in root apices, and in leaves which had been kept in the dark. The above experiments suggest that sorbitol supplements but does not replace sucrose. Extracts of apple leaves showed no trace of either a polyol or a polyol phosphate dehydrogenase but did exhibit sorbitol-6-phosphate phosphatase activity. A limited number of experiments with extracts of the blades of Laminaria digitata indicated that they contained mannitol-1-phosphate phosphatase and mannitol dehydrogenase.     

Nonstructural carbohydrates in dormant and afterripened wild oat caryopses

Nonstructural carbohydrates were determined in both embryo and endosperm of dormant (nongerminating) and afterripened (germinating) intact caryopses of wild oat ( Avena fatua L.). No changes in endosperm starch or soluble sugar were observed at the onset of germination (18 h). No changes in glucose, fructose, sucrose or starch within dormant or afterripened embryos correlated with onset of visual germination. In afterripened embryos, depletion of raffinose (18 h), stachyose (18 h) and galactose (24 h) was correlated with germination. In contrast, raffinose-family oligosaccharide levels in dormant embryos remained constant for 7 days following imbibition. Germination of isolated dormant embryos on 88 m M galactose-containing media was accompanied by decreased endogenous levels of raffinose and stachyose. Isolated embryos from dormant caryopses incorporated ¹⁴C from ¹⁴C-fructose into both raffinose and stachyose during 24 h of imbibition. In contrast, no ¹⁴C incorporation into stachyose was observed in embryos from afterripened caryopses. No ¹⁴C incorporation into raffinose was observed at 18 and 24 h. When in vitro activities of α galactosidase were measured, no temporal differences between dormant or afterripened caryopses were detected in either embryo or endosperm tissue. Although the mechanism associated with differences in utilization of raffinose and stachyose is yet unidentified, alterations in raffinose-family oligosaccharide metabolism in the embryo appear to be a unique prerequisite for afterripening-induced germination.     

Indolylacetic acid oxidase in dormant apple embryos

The IAA oxidase activity was studied during the culture of dormant apple embryos. The effect of different factors on this enzyme activity was investigated either by adding them to the reaction mixture or to the culture medium. Phloridzin was found to be the best phenolic cofactor. The development of IAA oxidase activity was stimulated by phloridzin and GA₃. The properties of apple embryos IAA oxidase allow to postulate the presence of two enzyme systems able to oxidize IAA in the material studied. The involvement of peroxidase activity in IAA oxidation was also investigated. The differences in the changes of peroxidase and IAA oxidase activities during the culture of dormant apple embryos do not permit to consider the activity of peroxidases to be identical with that of IAA oxidase.     

Sorbitol metabolism and sink-source interconversions in developing apple leaves

In apple (Malus domestica Borkh.) sorbitol is the primary product of photosynthesis, the major translocated form of carbon, and a common fruit constituent and storage compound. Previous work on sorbitol metabolism has revealed a NADPH-dependent aldose 6-phosphate reductase (A6PR) in green tissues, and a NAD-dependent sorbitol dehydrogenase in nongreen tissues. Results here show a decrease in sorbitol dehydrogenase activity and an increase in A6PR activity as leaves developing in the spring undergo the transition from sink to source. Sorbitol dehydrogenase activity reached a minimum as A6PR peaked. These changes were related to increases in leaf carbohydrate levels, especially sorbitol, and to increases in rates of net photosynthesis. Studies conducted in the autumn on senescing leaves also showed changes in enzyme activites, leaf carbohydrate levels, and photosynthesis. At this time, however, sorbitol dehydrogenase increased in specific activity, whereas A6PR activity, leaf carbohydrates, and photosynthetic rates all decreased substantially. Other experiments showed differences in the ability of young and mature leaves to metabolize sorbitol and in the distribution of sorbitol enzymes in leaves at transitional developmental stages. The results suggest that sorbitol metabolism in apple is tightly controlled and may be related to mechanisms regulating partitioning or source and sink activity.     

Viability of heat-stressed cells of micro-organisms as influenced by pre-incubation and post-incubation temperatures

The viability of heat-stressed cells of Escherichia coli was influenced by the temperature of incubation prior and subsequent to heat treatment. The effect of pre-incubation temperature on the viability of heated cells was almost constant regardless of heating temperature in the range 48–54°C. The involvement of the change in fluidity of the membrane was suggested as a cause of the effects of pre-incubation and post-incubation. These phenomena were observed with other Gram negative and positive bacteria, and yeasts.     

In vitro growth response of Prunus cerasifera shoots as influenced by different light-dark cycles and sucrose concentrations

Trials were carried out to test if the higher growth response shown by shoot clusters of Mr. S. 2/5, a clonal selection of Prunus cerasifera, submitted to short and frequent light-dark regimes could be related to the amount of sucrose added to growth medium.The reduction of sucrose from 30 gl^-1 (control) to 22.5 gl^-1, 15 gl^-1 and 7.5 gl^-1 caused a progressive and remarkable inhibition of shoot tip growth. With 15 gl^-1 the value of some growth parameters was reduced by more than half. Under 16-h daylength, the best sucrose concentration was 30 gl^-1, while with 4-h light-2-h dark no statistical differences appeared between 30 gl^-1 and 22.5 gl^-1 sucrose. Compared to 16-h light-8-h dark, the 4-h light-2-h dark cycle at the three highest sucrose concentrations gave rise to higher values of fresh and dry weight as well as increasing the number of axillary shoots produced.The increment in growth response induced by the shorter light-dark regime decreased with diminishing growth capacity in the cultures when sucrose concentration was lowered, but it was still appreciable even with 7.5 gl^-1. Since the 4-h light-2-h dark cycle induced a favourable effect in culture growth with all sucrose concentrations, we conclude that the greater growth response observed with this light regime was not triggered by carbohydrate availability but by some other unknown factors.     

Flowering of Watsonia laccata as influenced by corm storage and forcing temperatures

The genus Watsonia, belonging to the family Iridaceae, is comprised of about 50 species including W. laccata (Jacquin) Ker Gawler that flowers from September to November following low temperature and winter rainfall. Therefore, we hypothesized that flowering would be favored by forcing at low greenhouse temperatures. Using clonal W. laccata corms, four experiments were designed to investigate the effect of temperatures during corm storage, forcing, and their interaction on growth and flowering. Corm formation is favored by growing plants at 18°–20°/15°–17 °C and 21°–23°/18°–20 °C, day/night temperatures. Flowering was earliest with corms produced at 24°–26°/18°–20 °C and forced at 18°–20/15°–17 °C, and was significantly delayed when forced at 27°–29°/24°–26 °C. Flowering was, however, favored by 2 or 4 weeks of high temperatures (27°–29°/24°–26 °C) prior to forcing at low temperatures (18°–20°/15°–17 °C). The number of florets was not significantly affected by corm storage, forcing temperatures, or their interaction, although forcing at high temperatures tends to reduce the floret number. Burn symptom at the tips of leaves was frequently observed, and further studies are required to understand the cause of the tip burn and how to correct the symptom.     

Winter peridermal conductance of apple trees: lammas shoots and spring shoots compared

Lammas shoots are flushes formed by some woody species later in the growing season. Having less time to develop, tissue formation is suggested to be incomplete leading to a higher peridermal water loss during consecutive months. In this study, we analysed morphological and anatomical parameters, peridermal conductance to water vapour and the level of native embolism in mid-winter and late-winter of lammas shoots and normal spring shoots of the apple varieties Malus domestica ‘Gala’ and ‘Nicoter’. Lammas shoots showed a significantly higher shoot cross-sectional area due to larger pith and corticular parenchyma areas. In contrast, phloem was significantly thicker in spring shoots. No pronounced differences were observed in xylem and collenchyma thickness or mean hydraulic conduit diameter. The phellem of spring shoots was composed of more suberinised cells compared to lammas shoots, which led to a significantly higher peridermal conductance in the latter. The amount of native embolism in mid-winter did not differ between shoot types, but in late-winter lammas shoots were more embolised than spring shoots. Data show that the restricted vegetation period of lammas shoots affects their development and, in consequence, their transpiration shield. This may also pose a risk for winter desiccation.     

Light interception in apple trees influenced by canopy architecture manipulation

Improvement of light penetration within tree canopies has been a constant objective of fruit tree architecture manipulation through the setting up of training systems. Recently, centrifugal training, i.e. the removal of fruiting shoots in the tree centre and on the underside of branches, has been proposed to improve fruit size and colour as well as return-bloom as compared to conventional solaxe-trained trees with equivalent crop loads. The present study was conducted to quantify the benefits of centrifugal training on light interception by the fruiting shoots via computer-assisted three-dimensional representations of foliage geometry. Data were collected on six 5-year-old apple trees cv.Galaxy, trained either with solaxe or centrifugal training systems, using an electromagnetic 3D digitiser. The 3D distribution of the foliage in the tree canopy was recreated by combining both the spatial locations of shoots (as measured from 3D digitising) and foliage reconstruction. Light interception efficiency properties of the trees were characterised by silhouette to total area ratio (STAR) values computed from images of the 3D mock-ups. Compared to the solaxe system, centrifugal training significantly improved the STAR of the whole tree by 20%. It also increased both leaf area and STAR of the fruiting shoots by approximately 15%, regardless of their position in the canopy. In this paper, we discuss the role of this enhanced light interception by the canopy in increasing the autonomy of the fruiting shoot, i.e. improved fruit size and colour, and return-bloom.     

Diheteroarylurea derivatives as adventitious rooting adjuvants in mung bean shoots and M26 apple rootstock

The present research investigates the biological profile of eight symmetrical diheteroarylureas and phenylheteroarylureas, testing their hypothetical cytokinin-like activity and rooting activity. Cytokinin-like activity was assayed by the betacyanin (so-called amaranthin) accumulation test and by the tomato regeneration test. The rooting activity was assessed using the mung bean rooting test, the apple stem slice test and the rooting of apple microcuttings. Three compounds, 1,3-di(pyrazin-2-yl)urea (3a), 1,3-di(benzo[d]oxazol-5-yl)urea (3b) and 1,3-di(benzo[d]oxazol-6-yl)urea (3c), enhanced adventitious root formation in apple stem slice test, but only 3b and 3c were active in the mung bean rooting test. Compound 3b, that showed the best rooting activity, was also able to enhance the adventitious root formation in apple microcuttings. None of the compounds showed cytokinin-like activity.     

Alkaloid yields ofVeratrum fimbriatum as influenced by site,season and other factors

Alkaloid content ofVeratrum fimbriatum is much greater during rapid growth in early spring than the rest of the year. Top growth at the expense of stored food reserves did not deplete alkaloids. Individual plants were in two categories regarding high or low percentage alkaloid producers.     

Photosynthesis and distribution of photosynthates in apple shoots treated by pinching and bark ringing

Individual leaves on apple shoots treated by pinching and/or ringing were supplied with¹⁴CC₂ and the rate of photosynthesis and the pattern of photosynthate distribution was studied. The ringing of the shoots as well as the ringing and pinching done together reduces the rate of photosynthesis almost by half. Pinching itself had no effect on the rate of photosynthesis. Removing the main sink — the growing shoot apex — by pinching leads to the accumulation of photosynthates in the shoot, mainly in the first internode below the pinching point. Accumulated assimilates were soon used up by the axillary meristems which were stimulated to grow by pinching. Very small amounts of assimilates (about 1 %) were translocated to adjacent shoots which were supplied by their own leaves. When adjacent shoots were defoliated, more assimilates were translocated there (nearly 8%), however, a strong tendency to accumulate the assimilates in the internode below the pinching point was observed. Assimilates are not located in matured leaves. The presence of an active sink located near the donor stimulates the mobilization of assimilates present in the donor leaf.     

Diurnal changes in water content of the stems of apple trees, as influenced by irrigation

Abstract Groups of apple trees within an orchard were irrigated by either releasing a fine mist within the canopy or spraying water on the soil. Diurnal changes in the water content of the xylem were inferred from measurements of density made with a gamma probe. Transpiration rates were estimated from leaf temperatures, and water potentials and changes in radial dimension of the stem were recorded. Xylem water content and water potential declined each morning and recovered in the afternoon. Radial dimensions of the xylem followed a similar pattern, but the percentage change was very small in relation to the change in water content of the same tissue. The decline in water content is unlikely to have been caused by cavitation, as it was readily reversed in the afternoon. It is more likely to have been caused by changes in the volume of water occupying already-cavitated fibres or intercellular spaces. Water potential and xylem water content were highest in the mist-irrigated trees and least in the unirrigated controls.     

Calcium complexes in the xylem sap of apple shoots

Summary Concentrations of total calcium, ionic calcium, citric and malic acids have been measured in xylem sap extracted from apple shoots. Ionic calcium, as measured by an ion selective electrode, was about 50 per cent of the total calcium. The remainder of the soluble calcium was present as complexes with citric and malic acids. The implication of these findings on the mobility of calcium in the xylem is discussed.     

Uptake and translocation of paclobutrazol by shoots of M.26 apple rootstock

When ¹⁴C-paclobutrazol, a gibberellin synthesis inhibitor, was applied to different parts of actively-growing M.26 apple rootstock shoots it was translocated acropetally when applied to the young stem and, to a lesser extent, from the youngest unrolled leaf. Paclobutrazol was not translocated out of leaf laminae, shoot tips or from one-year-old wood but translocation occurred out of a treated petiole into the attached leaf. No basipetal translocation was detected. This translocation pattern suggested movement through the xylem.Localised application of paclobutrazol caused a reduction in shoot extension and leaf production when the young stem or shoot tip were treated; the effect decreased as older parts of the stem were treated. Treatment of laminae or petioles had only a slight effect on shoot extension and treatment of one-year-old wood was ineffective. Combined treatment of the shoot tip plus young stem was similar in effect to treatment of the complete shoot.It is suggested that paclobutrazol exerts its effects on shoot growth by inhibiting gibberellin biosynthesis in the shoot tip and the expanding leaves.The findings contribute to an understanding of the requirements for efficient orchard application of foliar sprays of paclobutrazol.