Carbohydrate changes in kiwifruit buds during the onset and release from dormancy

Carbohydrates were measured in axillary bud meristems from kiwifruit (Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson cultivar Hayward) to determine whether concentrations changed during winter dormancy. Buds were collected from kiwifruit vines growing in four sites, which spanned the climatic range that kiwifruit are grown in New Zealand, and from vines where the time of budbreak had been manipulated using hydrogen cyanamide. During winter, sugars comprised 78% of measured carbohydrates in meristems, with sucrose accounting for more than 86% of sugars detected (up to 200 mg g DW⁻¹). Starch concentrations in bud meristems showed little change during winter. Meristem sucrose and hexose concentrations increased rapidly from autumn until mid-winter, and this was correlated with leaf abscission. Sugar accumulation ceased in mid-winter and concentrations remained stable until spring, suggesting that bud meristem activity was low. Four weeks before visible bud movement, a marked decline in sucrose and increase in hexose concentrations, indicated activity in the meristems had increased prior to budbreak. The patterns of seasonal change and peak sucrose concentrations in meristems were similar at all sites. The only difference was in the timing of events, with changes in meristem sugars occurring earliest in vines growing at the coolest site, coinciding with their earlier cessation of and resumption of vine growth. Advancing budbreak, by applying hydrogen cyanamide to vines in late winter, also advanced changes in sugar concentrations within meristems. This work suggests that the concentration of sucrose in kiwifruit bud meristems has utility as an indicator of whether they are being induced into, maintained or released from winter dormancy.     

Changes on carbohydrates and nitrogen content in the bark tissues induced by artificial chilling and its relationship with dormancy bud break in Prunus sp.

Stem cuttings of peach, nectarine, plum and apricot, obtained from 1-year-old shoots at leaf drop in autumn, were exposed at a constant 3.0 ± 0.1 °C to simulate different chilling accumulation treatments (0, 500, and 1000 chilling hours). A set of 10 excised shoots was forced to budbreak after chilling accumulation; a second set of 10 excised shoots was used to analyse sugars, starch, and ammonium-, nitric- and proteinaceous-nitrogen content in the bark tissues. Sorbitol, fructose and glucose were the main sugars in the bark tissues, whereas sucrose and rafinose showed the lowest quantities in all Prunus sp. studied. Sorbitol and starch concentration decreased whereas glucose and fructose concentration increased with chilling. Ammonium-nitrogen showed the more dramatic increase with medium chilling treatment, decreasing again at high chilling exposure. No modifications in proteinaceous- and nitric-nitrogen levels were observed due to chilling. Chilling treatments increasing flowering intensity showed high ammonium- and proteinaceous-nitrogen content in the bark tissues of the stem cuttings, whereas those reducing flowering intensity showed high starch and nitric-nitrogen content, in three of the four Prunus sp. studied. Ammonium-nitrogen content gives the highest correlation with flowering intensity.     

Effects of duration of exposure to ethylene on dormancy release in freesia corms

The exposure of freesia corms to ethylene (C₂H₄) at ca. 10 μl/l air for only 5 h was sufficient to promote sprouting, either under a closed system in which corms were treated in a sealed space of 3–10 1 or under a flow system in which corms were exposed to a continuous flow of air containing C₂H₄. Under the closed system, little change in corm response to C₂H₄ was found with increasing duration of exposure from 5 to 48 h, and the C0₂ concentration reached nearly 4% after 48 h. On the other hand, under the flow system, in which CO₂ did not accumulate above 0.1%, the promotive effect of C₂H₄ was diminished by extended exposure from 5 to 48 h.Repeated treatment with C₂H₄ for 23 h daily on 4 successive days resulted in the lowering of the promotive effect as compared with a single treatment, but repeated application of C₂H₄ for 5 h daily showed the same effect as a single application and gave a high sprouting rate similar to smoke treatment, independent of ambient temperature ranging from 25 to 35° C.Corms exposed to C₂H₄ for 5 h daily, or to smoke for 4 days, exhibited a better chilling response and advanced flowering.     

Involvement of proline in response of chickpea (Cicer arietinum L.) to chilling stress at reproductive stage

Chickpea is sensitive to chilling stress, especially at its reproductive stage and experiences abortion of flowers and poor pod set at temperatures below 10 °C. The metabolic controls governing chilling-sensitivity in chickpea, particularly involving proline are not known. Hence, in the present study we explored the role of proline in this regard. A set of chickpea plants (cv. GPF2) growing under warm conditions of the glass house (temperature – 28/14 °C as average maximum and minimum till early flowering stage) was exposed to low temperature conditions of the field (8.3–9.6/2.8–5.3 °C; average maximum and minimum temperature, respectively) during the onset of reproductive phase while another set of plants continued to grow under warm conditions. In case of chilling-stressed plants, one set of the plants was treated with 10 μM proline while the other set not treated with proline served as control under low temperature conditions. In untreated chilling-stressed plants, the endogenous proline increased to 230 μmol g⁻¹ dry weight (DW) on 4th day of stress and decreased thereafter to reach 28 μmol on 7th day. In plants treated with 10 μM proline, its endogenous content reached 310 μmol g⁻¹ DW on 4th day and stayed significantly higher than untreated chilling-stressed plants. The proline-treated plants showed significant improvement in retention of flowers and pods leading to better seed yield compared to the untreated ones. The proline-applied plants also had greater pollen viability, pollen germination, pollen tube growth and ovule viability. The stress injury measured as oxidative stress, electrolyte leakage, loss of chlorophyll and decrease in leaf water content was mitigated significantly in proline-treated plants. Additionally, proline application increased the level of sucrose and trehalose (cryoprotectants) in chilling-stressed plants. The studies revealed that proline application was significantly effective in reducing the impact of chilling injury on reproductive growth in chickpea.     

Growth, stomata aperture, biochemical changes and branch anatomy in mango (Mangifera indica) cv. Chokanan in response to root restriction and water stress

Mango production is often subject to space and tree size management pressures among growers. This study found that root restriction contributed to reduced leaf expansion, thus inhibiting the growth of mango trees. There was even less leaf expansion under water stress conditions. Under well-watered conditions, restricted roots considerably reduced stomatal conductance and leaf water potential compared to control root growth. More rapid reductions in stomatal conductance and leaf water potential occurred under restricted root and water stress conditions compared to control trees. Leaf proline concentrations and abscisic acid (ABA) levels increased as a result of root restriction and water stress but decreased with re-watering. Re-watering also increased stomatal conductance, leaf water potential and peroxidase accumulation in plants with both restricted and non-restricted root growth. Anatomical studies of cross sections of secondary branches showed that root restriction and water stress brought about various changes: compacted cells, as estimated by epidermis thickness and area, as well as by cortex thickness, but with increases in schelerenchyma thickness, phloem and xylem thickness, schelerenchyma area, and pith area and diameter. These results suggest that reduction of soil volume and water stress could effectively control tree size through physiological and morphological changes; thereby bringing higher sustainable returns per hectare and greater effectiveness in orchard management.     

Movement behavior in response to landscape structure: the role of functional grain

Landscape structure can influence the fine-scale movement behavior of dispersing animals, which ultimately may influence ecological patterns and processes at broader scales. Functional grain refers to the finest scale at which an organism responds to spatial heterogeneity among patches and extends to the limits of its perceptual range. To determine the functional grain of a model insect, red flour beetle (Tribolium castaneum), we examined its movement behavior in response to experimental flour landscapes. Landscape structure was varied by manipulating habitat abundance (0%, 10%, 30%, and 100%) and grain size of patches (fine-2 × 2 cm, intermediate-5 × 5 cm, and coarse-10 × 10 cm) in 50 × 50 cm landscapes. Pathway metrics indicated that beetles used a similar proportion of all landscape types. Several pathway metrics indicated a graded response from the fine to the coarse grain landscape. Lacunarity analysis of beetle pathways indicated a non-linear change in space use between the fine and intermediate landscapes and the coarse-grained landscape. Beetles moved more slowly and tortuously (with many turns), and remained longer in both the overall landscape and individual patches, in fine-grained compared to coarse-grained landscapes. Our research demonstrates how detailed examination of movement pathways and measures of lacunarity can be useful in determining functional grain. Spatially explicit, organism-centered studies focusing on behavioral responses to different habitat configurations can serve as an important first step to identify behavioral rules of movement that may ultimately lead to more accurate predictions of space use in landscapes.     

Land-use and land-cover dynamics in response to changes in climatic,biological and socio-political forces: the case of southwestern Ethiopia

Few studies of land-use/land-cover change provide an integrated assessment of the driving forces and consequences of that change, particularly in Africa. Our objectives were to determine how driving forces at different scales change over time, how these forces affect the dynamics and patterns of land use/land cover, and how land-use/land-cover change affects ecological properties at the landscape scale. To accomplish these objectives, we first developed a way to identify the causes and consequences of change at a landscape scale by integrating tools from ecology and the social sciences and then applied these methods to a case study in Ghibe Valley, southwestern Ethiopia. Maps of land-use/land-cover change were created from aerial photography and Landsat TM imagery for the period, 1957–1993. A method called `ecological time lines' was developed to elicit landscape-scale explanations for changes from long-term residents. Cropland expanded at twice the speed recently (1987–1993) than two decades ago (1957–1973), but also contracted rapidly between 1973–1987. Rapid land-use/land cover change was caused by the combined effects of drought and migration, changes in settlement and land tenure policy, and changes in the severity of the livestock disease, trypanosomosis, which is transmitted by the tsetse fly. The scale of the causes and consequences of land-use/land-cover change varied from local to sub-national (regional) to international and the links between causes and consequences crossed scales. At the landscape scale, each cause affected the location and pattern of land use/land cover differently. The contraction of cropland increased grass biomass and cover, woody plant cover, the frequency and extent of savanna burning, and the abundance of wildlife. With recent control of the tsetse fly, these ecological changes are being reversed. These complex patterns are discussed in the context of scaling issues and current conceptual models of land-use/land-cover change.