Early stomatal closure in waterlogged pea plants is mediated by abscisic acid in the absence of foliar water deficits

Abstract Soil waterlogging decreased leaf conductance (interpreted as stomatal closure) of vegetative pea plants (Pisuin sativum L. cv. ‘Sprite’) approximately 24 h after the start of flooding, i.e. from the beginning of the second 16 h-long photo-period. Both adaxial and abaxial surfaces of leaves of various ages and the stipules were affected. Stomatal closure was sustained for at least 3 d with no decrease in foliar hydration measured as water content per unit area, leaf water potential or leaf water saturation deficit. Instead, leaves became increasingly hydrated in association with slower transpiration. These changes in the waterlogged plants over 3 d were accompanied by up to 10-fold increases in the concentration of endogenous abscisic acid (ABA). Waterlogging also increased foliar hydration and ABA concentrations in the dark. Leaves detached from non-waterlogged plants and maintained in vials of water for up to 3 d behaved in a similar way to leaves on flooded plants, i.e. stomata closed in the absence of a water deficit but in association with increased ABA content. Applying ABA through the transpiration stream to freshly detached leaflets partially closed stomata within 15 min. The extractable concentrations of ABA associated with this closure were similar to those found in flooded plants. When an ABA-deficient ‘wilty’ mutant of pea was waterlogged, the extent of stomatal closure was less pronounced than that in ordinary non-mutant plants, and the associated increase in foliar ABA was correspondingly smaller. Similarly, waterlogging closed stomata of tomato plants within 24 h, but no such closure was seen in ‘flacca’, a corresponding ABA-deficient mutant. The results provide an example of stomatal closure brought about by stress in the root environment in the absence of water deficiency. The correlative factor operating between the roots and shoots appeared to be an inhibition of ABA transport out of the shoots of flooded plants, causing the hormone to accumulate in the leaves.     

cDNA and protein sequence of a major pea seed albumin (PA 2 : Mr≈26 000)

Summary Pea albumin 2 (PA2:M_r26000) is a major component of the albumin fraction derived from aqueous salt extracts of pea seed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and chromatography on DEAE-Sephacel resolve PA2 into two closely related components (PA2a and PA2b). A cDNA clone coding for one of these components has been sequenced and the deduced amino acid sequence compared with partial, chemically-determined sequences for cyanogen bromide peptides from both PA2 components. Complete amino acid sequences were obtained for the C-terminal peptides. The PA2 molecule of 230 amino acids contains four imperfect repeat sequences each of approximately 57 amino acids in length.The combined sequence data, together with a comparison of PA2-related polypeptides produced in vitro and in vivo, indicate that PA2 is synthesized without a signal sequence and does not undergo significant post-translational modification. Although both forms of PA2 contain Asn-X-Thr consensus sequences, neither form is glycosylated. Accumulation of PA2 contributes approximately 11% of the sulfur-amino acids in pea seeds (cysteine plus methionine equals 2.6 residues percent). Suppression of levels of PA2 polypeptides and their mRNAs in developing seeds of sulfur-deficient plants is less marked than that for legumin, in spite of the lower content of sulfur-amino acids in legumin.     

Photoinactivation of δ-aminolevulinic acid dehydratase from maize by flavin mononuclotide

The -aminolevulinic acid dehydratase activity was irreversibly inactivated by irradiation of the enzyme in presence of flavin mononucleotide. The loss of enzyme activity was dependent on time of irradiation, concentration of FMN and intensity of irradiance. It required oxygen and was markedly enhanced in heavy water. The presence of levulinic acid (a competitive inhibitor of -ALAD) during irradiation prevented the inactivation considerably indicating photooxidative damage at or near the active site. Superoxide dismutase, sodium benzoate and sodium formate offered no protection, but singlet oxygen quenchers like azide and tryptophan were effective. NADH, electron donor to excited flavins, also prevented the loss of enzyme activity. These results indicate that singlet oxygen produced by light absorption of FMN was responsible for the photooxidative inhibition of the enzyme.Abbreviations ALAD -aminolevulinic acid dehydratase - FMN flavin mononucleotide - O₂ ^- superoxide - H₂O₂ hydrogen peroxide - 10₂ singlet oxygen - LA levulinic acid - PBG porphobilinogen - BSA bovine serum albumin - BME 2-mercaptoethanol - SOD superoxide dismutase - pHMB para-hydroxymercuribenzoate - DTT dithiothreitol - FAD flavin adenine dinucleotide - NADH nicotinamide adenine dinucleotide     

C-NMR analysis of Aspergillus mutants disturbed in pyruvate metabolism

The metabolic consequences of two defects in pyruvate metabolism of the hyphal fungus Aspergillus nidulans have been investigated by natural abundance ¹³C-NMR spectroscopy. A pyruvate dehydrogenase complex (pdh) mutant, grown on acetate, accumulates alanine upon starvation which is derived from mannitol reserves. The -alanine level increases further upon incubation with the non-permissive substrate -glucose. -Glutamate is absent from these spectra as it is required both for the transamination of pyruvate and as a reaction on an impaired energy metabolism in such a pdh-deficient strain. A pyruvate carboxylase (pyc) mutant, grown upon acetate, only starts to accumulate alanine after a long incubation period with -glucose, due to the long-lasting presence of phosphoenolpyruvate carboxykinase and malic enzyme, which are both induced by growth on acetate. When this strain is grown on -fructose and -glutamate, alanine also accumulates within 3 h upon transfer to -glucose.     

The effects of mechanically-induced stress and plant growth regulators on the growth of lettuce,cauliflower and bean (Phaseolus vulgaris L.) plants

The plant growth regulators, gibberellic acid (GA₃), ethephon and chlormequat chloride (CCC) were sprayed on young lettuce, cauliflower and bean (Phaseolus vulgaris) plants, which had either been given or not been given a mechanically-induced stress (MIS) treatment. MIS was applied by brushing the plants with paper for 1.5 minutes each day. GA₃ increased extension growth of bean and leaf length of lettuce in unbrushed plants as much as in brushed ones. CCC and ethephon were less effective at reducing the height of brushed bean plants compared to unbrushed ones. The effects of CCC on the growth of cauliflower and lettuce plants was not influenced by brushing, whereas unbrushed plants responded more readily to ethephon than did brushed ones. The effects of CCC on growth were generally similar to those of MIS whereas the effects of ethephon were in many ways different to MIS.The results are discussed in relation to the use of PGR and MIS treatments for modifying plant growth.     

Physiological effects of temperature and growth regulators on foliar chlorophyll,soluble protein,and cold hardiness in citrus

Leaf chlorophyll (Chl, A, B) and total soluble protein were assayed in greenhouse-grown 1.5-year-old trees of 2 citrus types, trifoliate orange (Poncirus trifoliata (L.) Raf.) and sour orange (Citrus aurantium L.) exposed to 12 h (day/night) photoperiods in growth chambers under high (30°/21°C, day/night; noncold-hardening) and low (16°/5°C; cold-hardening) temperature regimes. Trees were sprayed 2 × per week for 5 weeks with one of the following solutions at 100 M: napthaleneacetic acid (NAA), paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol) (PPP333), benzyl-adenine (BA), abscisic acid (ABA), gibberellic acid (GA₃), minerals only (N, P, K, S, Ca, Mg) and BA (+) minerals. NAA, PP333, ABA and GA₃ decreased Chl A, B and soluble protein in both citrus types under cold-hardening conditions in contrast to increases with the use of BA and BA (+) minerals especially in trifoliate orange. Both BA and GA₃ increased Chl A, B and protein synthesis under high temperature in both citrus types. Under noncold-hardening temperatures, GA₃ enhanced Chl A, B but sharply reduced foliar protein concentration. Dieback of both cultivars following exposure to temperatures down to –6.7°C was decreased 7% by NAA sprays during noncold-hardening temperatures. Cold tolerance of noncoldhardened trifoliate orange trees was also improved with ABA and PP333. Foliar sprays of NAA (sour orange) and PP333 and BA (+) minerals (trifoliate) increased cold tolerance of cold-hardened trees by 8%. Results indicate that spray applications of growth regulators influence physiological factors associated with foliar functioning and cold tolerance in citrus during different temperature regimes.Summary Growth promoters (BA) and inhibitors (NAA) have the potential to promote cold hardines through either a strong stimulatory effect on foliar physiology or a marked inhibition of growth in general. This suggests that each growth regulator may possess an independent role in the cold-hardiness phenomenon and may also interact with physiological processes other than soluble protein and chlorophyll metabolism. The relationship between soluble protein levels in citrus foliage and the degree of cold hardiness remains uncertain and is essentially unresolved pending more specific qualitative research.University of Florida Agricultural Experiment Station Series No. 7446.This paper reports the results of research only. Mention of a trademark of a proprietary product does not constitute a recommendation for use by the U.S. Department of Agriculture to the exclusion of other products that may also be suitable.     

Cytokinin metabolism in tomato plants. II. Metabolites of kinetin and benzyladenine in decapitated roots

Decapitated tomato plants were supplied via the roots with [8-¹⁴C]-kinetin or [8-¹⁴C]-benzyladenine in a nutrient solution for a period of 24 h. After this time the root material, the root sap produced during the 24 h period and the nutrient solution remaining at the end of the experiments were analysed for cytokinins. HPLC techniques and chemical treatments were used to tentatively identify radioactive metabolites formed. Uptake of kinetin and benzyladenine by the roots was found to be limited but once within the root tissues metabolism was both rapid and extensive.At least 14 metabolites of kinetin were recovered from root tissue and root sap. Many of these appeared to be degradation products. There was, however, some evidence of formation of zeatin-like derivatives. Side-chain cleavage of the original kinetin which occurs rapidly is suggested as a possible route for the eventual production of these endogenous cytokinin forms.The benzyladenine taken up by the roots was apparently both ribosylated and glucosylated. No unmetabolized benzyladenine was detected in the root tissues after 24 h. Only very low levels of radioactivity were associated with the retention time of adenine, suggesting that in the case of benzyladenine side-chain cleavage is of limited importance.The significance of these reactions in relation to the potential use of cytokinins in the regulation of plant growth is discussed.     

Paleolimnological evidence for recent acidification of Big Moose Lake,Adirondack Mountains,N.Y. (USA)

Big Moose L. has become significantly more acidic since the 1950s, based on paleolimnological analyses of sediment cores. Reconstruction of past lakewater pH using diatom assemblage data indicates that from prior to 1800 to ca. 1950, lakewater pH was about 5.8. After the mid-1950s, the inferred pH decreased steadily and relatively quickly to about 4.6. Alkalinity reconstructions indicate a decrease of about 30 eq · l^-1 during the same period. There was a major shift in diatom assemblage composition, including a nearly total loss of euplanktonic taxa. Chrysophyte scale assemblages and chironomid (midge larvae remains also changed in a pattern indicating decreasing lakewater pH starting in the 1950s. Accumulation rates of total Ca, exchangeable and oxide Al, and other metals suggest recent lake-watershed acidification. Cores were dated using²¹⁰Pb, pollen, and charcoal. Indicators of watershed change (deposition rates of Ti, Si, Al) do not suggest any major erosional events resulting from fires or logging. Accumulation rates of materials associated with combustion of fossil fuels (polycyclic aromatic hydrocarbons, coal and oil soot particles, some trace metals, and sulfur) are low until the late 1800s-early 1900s and increase relatively rapidly until the 1920s–1930s. Peak rates occurred between the late 1940s and about 1970, when rates declined.The recent decrease in pH of Big Moose L. cannot be accounted for by natural acidification or processes associated with watershed disturbance. The magnitude, rate and timing of the recent pH and alkalinity decreases, and their relationship to indicators of coal and oil combustion, indicate that the most reasonable explanation for the recent acidification is increased atmospheric deposition of strong acids derived from combustion of fossil fuels.     

Normalizing the thermal effects of radiofrequency radiation: body mass versus total body surface area

The current guideline for exposure to radiofrequency radiation (RFR) was developed through assessment of the biological effects data collected primarily from the rat. The consensus that a lack of hazardous biological effects occurred below a whole-body-averaged specific absorption rate (SAR) of 4.0 W/kg led to the proposition of a 0.4 W/kg guideline with a built-in safety factor of 10. This paper demonstrates that if the RFR absorption rate in the rat had been normalized with respect to total body surface area rather than body mass, the exposure guideline would be 2.3 W/m2, which translates to an SAR of approximately 0.06 W/kg for an adult human. It is further shown that a given RFR absorption rate, normalized as a fraction of a species' heat loss per unit of surface area, is independent of body mass over a range of 0.03-100 kg; however, a normalization of the RFR absorption rate to heat loss per unit of body mass is highly dependent on the species' mass. Normalizing the rate of RFR absorption to the surface area of the rat indicates that the current RFR exposure guideline of 0.4 W/kg may be too high.     

Sodium-Dependent Proline Uptake in the Rat Hippocampal Formation: Association with Ipsilateral-Commissural Projections of CA3 Pyramidal

Na+-dependent uptake of L-[3H]proline was measured in a crude synaptosomal preparation from the entire rat hippocampal formation or from isolated hippocampal regions. Among hippocampal regions, Na+-dependent proline uptake was significantly greater in areas CA1 and CA2-CA3-CA4 than in the fascia dentata, whereas there was no marked regional difference in the distribution of Na+-dependent gamma-[14C]aminobutyric acid ([14C]GABA) uptake. A bilateral kainic acid lesion, which destroyed most of the CA3 hippocampal pyramidal cells, reduced Na+-dependent proline uptake by an average of 41% in area CA1 and 52% in area CA2-CA3-CA4, without affecting the Na+-dependent uptake of GABA. In the fascia dentata, neither proline nor GABA uptake was significantly altered. Kinetic studies suggested that hippocampal synaptosomes take up proline by both a high-affinity (KT = 6.7 microM) and a low-affinity (KT = 290 microM) Na+-dependent process, whereas L-[14C]glutamate is taken up predominantly by a high-affinity (KT = 6.1 microM) process. A bilateral kainic acid lesion reduced the Vmax of high-affinity proline uptake by an average of 72%, the Vmax of low-affinity proline uptake by 44%, and the Vmax of high affinity glutamate uptake by 43%, without significantly changing the affinity of the transport carriers for substrate. Ipsilateral-commissural projections of CA3 hippocampal pyramidal cells appear to possess nearly as great a capacity for taking up proline as for taking up glutamate, a probable transmitter of these pathways. Therefore proline may play an important role in transmission at synapses made by the CA3-derived Schaffer collateral, commissural, and ipsilateral associational fibers.