Stomatal behaviour and leaf water potential of chilled and water-stressed Solanum melongena, as influenced by growth history

Abstract Leaf diffusion resistance and leaf water potential of intact Solanum melongena plants were measured during a period of chilling at 6 °C. Two pretreatments, consisting of a period of water stress or a foliar spraying of abscisic acid (ABA), were imposed upon the plants prior to chilling. The control plants did not receive a pretreatment. In addition to intact plant studies, stomatal responses to water loss and exogenous abscisic acid were investigated using excised leaves, and the influence of the pretreatment observed. Chilled, control plants wilted slowly and maintained open stomata despite a decline in leaf water potential to –2.2 MPa after 2 d of chilling. In contrast plants that had been water stressed or had been sprayed with abscisic acid, prior to chilling, did not wilt and maintained a higher leaf water potential and a greater leaf diffusion resistance. In plants that had not received a pretreatment, abscisic acid caused stomatal closure at 35 °C, but at 6°C it did not influence stomatal aperture. The two pretreatments greatly increased stomatal sensitivity to both exogenous ABA and water stress, at both temperatures. Stomatal response to water loss from excised leaves was greatly reduced at 6°C. These results are discussed in relation to low temperature effects on stomata and the influence of preconditioning upon plant water relations.     

Ion Transport and the Effects of Acetic Acid in White Clover: I. PHOSPHATE ABSORPTION

Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. I. Phosphateabsorption.—J. exp. Bot. 39: 79–88. The effect of acetic acid on phosphate absorption by white clovertissue has been examined. At 1·0 mol m³ acetic acid phosphateabsorption by roots of intact plants was stimulated by 36% (P< 0.001). At 5.0 and 10 mol m^–3 acetic acid there wasmarked inhibition of absorption by both suspension culturesof cells and the roots of intact plants. The inhibition waspH dependent with decreasing pH causing increased inhibition.Acetic acid caused changes in the membrane electropotential(E) with concentrations of 2·0 mol m^–3 or lesscausing persistent polarization whereas at 5·0 mol m^–3and higher concentrations the polarization was followed by agreater depolarization. Intracellular pH as measured by thefluorescence of fluorescein was lowered by acetic acid. Calculationsindicate that for white clover roots the proton motive force(pmf) appears to provide sufficient energy for phosphate absorption.It is proposed that acetic acid influences phosphate absorptionthrough its dependence on proton cotransport and that changesin J E affect the rate of phosphate absorption because of thedependence of the pmf on E. Key words: Phosphate absorption, intracellular pH, acetic acid, proton motive force, Trifolium repens, membrane electropotential     

Ion Transport and the Effects of Acetic Acid in White Clover: II. POTASSIUM ABSORPTION

Dunlop, J., Knighton, M. V. and White, D. W. R. 1988. Ion transportand the effects of acetic acid in white clover. II. Potassiumabsorption.—J. exp. Bot. 39: 89–96. Acetic acid stimulated K⁺ influx into cells of white cloverin suspension culture and net K⁺ influx by roots of intact whiteclover plants. At concentrations of acetic acid up to 2·0mol m^–3 the stimulation continued unabated for at least2 h. However, at higher concentrations the rate of absorptiondeclined to near zero values after 2 h. When acetic acid wasremoved from the solution there was a net efflux of K⁺. Thestimulation was pH dependent with a maximum at pH 5·0.There was maximum stimulation at an acetic acid concentrationof 2·0 mol m^–3 Net H⁺ efflux was reduced by 1·0 mol m^–3 aceticacid. When Rb⁺ uptake and H⁺ efflux were measured at a rangeof RbCl concentrations Rb⁺ uptake increased with concentrationwhereas H⁺ efflux was maximum in the absence of Rb⁺ (and K⁺)and decreased as RbCl concentration was increased Acetic acid caused a hyperpolarization of the membrane electricalpotential difference (E) of about 25 mV. In 1·0 mol m^–3acetic acid the hyperpolarization persisted for at least 2 hwhereas at 10 mol m^–3 d E subsequently depolarized tovalues around –80 mV. With a slight lag, the time courseof the stimulation of the rate of K⁺ absorption followed thepolarization and depolarization of E. These results imply thatthe linkage between K⁺ and H⁺ movements is probably throughE. Key words: Proton efflux, membrane electrical potential difference, Trifolium repens     

The Role of Maturation Drying in the Transition from Seed Development to Germination: IV. PROTEIN SYNTHESIS AND ENZYME ACTIVITY CHANGES WITHIN THE COTYLEDONS OF RICINUS COMMUNIS L. SEEDS

Drying of immature seeds of Ricinus communis L. cv. Hale (castorbean) during the desiccation-tolerant phase of development causesthem to germinate upon subsequent rehydration. This desiccation-inducedswitch from development to germination is also mirrored by achange in the pattern of soluble and insoluble protein synthesiswithin the cotyledons of the castor bean. Following rehydrationof seeds prematurely dried at 40 d after pollination (DAP),cotyledonary proteins characteristic of development (e.g. storageproteins) are no longer synthesized; hydrolytic processes resultingin their degradation commence (after 12 h) in a manner similarto that observed following imbibition of the mature seed. Apattern of protein synthesis recognizable as germination/growth-associatedoccurs; premature drying has elicited a redirection in metabolismfrom a developmental to a germinative mode. Desiccation is alsorequired for the induction (within cotyledons of 35 DAP seeds)of enzymes involved in protein reserve breakdown (leucyl ß-naphthylamidase;LeuNAase) and lipid utilization (isocitrate lyase; ICL), anevent intimately associated with the post-germinative (growth)phase of seedling development. Thus, at a desiccation-tolerantstage of development, premature drying results in the suppressionof the developmental metabolic programme and a permanent switching-onof the germination/growth metabolic programme. Key words: Desiccation, metabolism, seed development, seed germination, castor bean, cotyledons     

Internal Structure and Hydraulic Conductivity of Basidiomycete Translocating Organs

Eamus, D., Thompson, W., Cairney, J. W. G. and Jennings, D.H. 1985. Internal structure and hydraulic conductivity of basidiomycetetranslocating organs.–J. exp. Bot. 36: 1110–1116. The presence in rhizomorphs of Armillaria mellea and cords ofPhallus impudicus of wide diameter hyphae (5–20 {diaeresis}m),which run for considerable distances along these linear organs,has been demonstrated. The longitudinal hydraulic conductivityof these organs has been determined experimentally and similarvalues were obtained when the hydraulic conductivity was calculatedtheoretically on the basis that the vessel hyphae were the solechannel for water movement along these organs. The experimentaldata have been discussed in relation to other data for long-distancetranslocation in basidiomycete linear organs. It is concludedthat the vessel hyphae are the main channels for turgor-driventranslocation. Key words: -Basidiomycete fungi, translocation, hydraulic conductivity     

ABA Levels and Effects in Chilled and Hardened Phaseolus vulgaris

Leaf abscisic acid (ABA) levels of chilled P. vulgaris weremeasured after 18 h chilling at 5°C, at a saturation deficitof 1.24 g m^–3 (SD), and after chilling in a water-saturatedatmosphere. Changes were also followed during a chill hardeningperiod of 4 d at 12°C, 2.1 g m^–3 SD. It was foundthat hardening resulted in an almost 5. fold increase in ABAlevels after 3 d at 12°C, and this decreased to approximatelycontrol levels on the fourth day. Subsequent chilling of hardenedplants produced no change in ABA levels from that of controlplants (22° C). In contrast, non-hardened plants chilledat 1.24 g m^–3 SD had ABA levels almost 3 times the levelof control plants. However, chilling in a water-saturated atmosphereresulted in a decrease in ABA levels. In addition, the response of leaf diffusion resistance (LDR)to exogenous ABA fed via the transpiration stream was measuredat 5 ° C and 22° C in hardened and non-hardened plants.Use of tritium-labelled ABA was made to calculate the stomatalsensitivity to ABA. It was found that exogenous ABA caused anincreased in LDR at 22°C in both hardened and non-hardenedplants. However, the sensitivity of the hardened plants to ABAwas greater in terms of rate of closure and amount of ABA requiredto close the stomata. At 5°C, however, ABA caused stomatalopening and the maintainance of open stomata in non-hardenedplants. In hardened plants, ABA caused stomatal closure at 5°C.These results are discussed in relation to the locking-openresponse of chilled P. vulgaris stomata. Key words: Chilling, Stomata, ABA, Phaseolus vulgaris     

The Influence of Prior Water Stress and Abscisic Acid Foliar Spraying on Stomatal Responses to CO2, IAA, ABA, and Calcium in Leaves of Solanum melongena

The influence of a water stress or foliar ABA spraying pretreatmenton stomatal responses to water loss, exogenous ABA, IAA, Ca²⁺,and CO₂ were studied using excised leaves of Solanum melongena.Both pretreatments increased stomatal sensitivity of water loss,in the presence and absence of CO₂, but decreased stomatal sensitivityto exogenous ABA. CO₂ greatly reduced the effect of exogenouslyapplied ABA. IAA decreased leaf diffusion resistance for controland ABA sprayed leaves, but did not influence the LDR of previouslywater-stressed leaves. CA²⁺ did not influence LDR of any leavesof any treatments. Key words: Water stress, stomatal response, pretreatments     

Why fly? The possible benefits for lower mortality

In adult endotherms—birds and mammals—mortality rates are lower in flying than non-flying species. Rates vary with size, but allowing for this they are higher in penguins than flying birds, and in rodents than bats. These observations are most simply explained in terms of predation since flight, allowing movement in three dimensions, increases the chances of escape.
There are various problems in obtaining and comparing data on rates of mortality and this partly explains a wide scattering of points. Nevertheless the main results are statistically significant, mostly at P<0.001. Amongst birds, there are several other significant differences. Mortality rates are lower at lower latitudes, and in aquatic compared to terrestrial species, with cliff-nesters having lower rates than other aquatic birds and co-operative breeders than other terrestrial ones. No latitudinal effect was detected in mammals. The exceptionally low rates of mortality in bats and swifts are attributed to their being particularly hard to catch.     

The Presence of Tyrosinase and Related Proteins in Human Epidermis and Their Relationship to Melanin Type

The present study was carried out to investigate the abundance of tyrosinase and related proteins (TRP-1 and TRP-2) in human epidermis and their relationship to melanin type. Positive immunocytochemical staining was seen for all three proteins in epidermal melanocytes. For each protein the numbers of positively stained melanocytes were similar in all subjects studied irrespective of skin type. Following 5 daily suberythemal doses of UVB the melanocytes were larger, more dendritic, and increased in number. With TRP-1 and TRP-2 the increase in number in response to UVB was unrelated to skin type and, hence, with melanin type but with tyrosinase there was a much greater increase in skin types III and IV than in skin type I and II. The enhanced numbers of tyrosinase-positive melanocytes were accompanied by increased staining intensity, suggesting a greater expression of tyrosinase in the melanocytes from skin types III and IV compared with skin types I and II. This increase in tyrosinase could be related to the greater levels of eumelanin found in skin types III and IV, and this is in keeping with the view that higher levels of tyrosinase are associated with the production of eumelanin than phaeomelanin.