Short communication. A steep Ca2[IMAGE]-dependence of a K[IMAGE] channel in a unicellular green alga

An increase of cytosolic Ca² in the unicellular green alga Eremosphaera viridis activities Ca²-dependent K channels causing a hyperpolarization of the plasma membrane. Data from parallel calcium, and potential measurements were combined with I/V relationships. This yielded a steep Ca²-dependence of K channels with a co-operativity of 4 and an affinity of 300 nM.Key words: Eremosphaera viridis, plasma membrane, Ca²-dependent K channel, co-operative binding.      

Potassium Transport Across the Membranes of Chara: II.42K FLUXES AND THE ELECTRICAL CURRENT AS A FUNCTION OF MEMBRANE VOLTAGE

Smith, J. R. 1987. Potassium transport across the membranesof Chara. II. ⁴²K fluxes and the electrical current as a functionof membrane voltage.—J. exp. Bot. 38: 752–777. The current required to clamp the trans-membrane voltage ofinternodal cells of Chara australis at different levels wasmeasured simultaneously with either the ⁴²K influx or efflux.Examination of the voltage-dependence of the ratio of the electricalcurrent to the unidirectional tracer fluxes yielded no evidenceof any amplification of the electrical driving force on theK⁺ ions. There was thus no evidence for the interaction of K⁺ions with themselves or any other species during their passageacross the membrane. These measurements allow the determinationof , the fraction of the electrical current carried by K⁺ ions.When the external [K⁺] = 10 mol m^–3, the average valueof was 0?85 for V_m > –125 mV and 07?5 for V_m <–150 mV. When the external [K⁺] = 0?1 mol m^–3, was 0?6 for V_m < –80 mV and 0?1 for V_m > –250mV. It was also found that the conductance associated with K⁺transport was inhibited by hyperpolarization. Key words: Potassium, conductance, flux-ratio     

The Structure and Functions of Xyloglucan

Xyloglucan is a polysaccharide found in the primary cell wallsof all higher plants examined. Its cellulose-like backbone,which is about 0.15 to 1.5 µm long, consists of 300 to3 000 ß-(14)-linked D-glucopyranose residues. About60–75% (or, in grasses, about 30–40%) of the glucoseresidues have side-chains attached to position 6. The majorside-chains are: D-xylopyranosyl--1 -, D-galactopyranosyl-ß-(12)-D-xylopyranosyl--I , L-arabinofuranosyl-(1 -2)-D-xylopyranosyl--1-, and (except in grasses) L.-fucopyranosyl--(1 -2)-D-galactopyranosyl-ß-(1-2)-D-xylopyranosyl--1-. There is some regularity in the distribution of these side-chainsalong the backbone. Xyloglucan plays two very different r?les in the control ofcell growth: (a) as a major building material of the wall [concentrationof xyloglucan in the wall in vivo 10% (w/v)] it probably directlydictates wall extensibility and, therefore, the rate of cellexpansion and (b) it can be broken down to a fucose-containingoligosaccharide which [at a concentration of 0.0000001% (w/v)]exerts a hormone-like anti-auxin effect on growth. In addition,xyloglucan lacking fucose is used by certain dicotyledonousseeds as a food reserve which is mobilized after germination.Xyloglucan is, therefore, the subject of considerable currentinterest in several apparently disparate areas of botany. Key words: Xyloglucan, ‘oligosaccharin’, hemicellulose, auxin, anti-auxin, growth, cell walls, reserve carbohydrate     

An Assessment of Gibberellin Structure-activity Relationships

Information on the biological activities of gibberellins (GAs)in the barley aleurone, Tangin-bozu dwarf rice, dwarf pea, lettucehypocotyl and cucumber hypocotyl bioassays is reviewed and discussedin the context of GA structure-activity relationships. The barley aleurone bioassay exhibits a limited response toGAs and it is suggested that this may be because the aleuronecells are able to carry out few GA interconversions. Consequentlyactivity is determined by the degree of compatibility betweenthe GAs and a receptor site. In this assay high biological activityis associated with GAs having a 3ß-hydroxy--lactonestructure. This activity is substantially enhanced by the additionalpresence of a 13-hydroxyl group. The substitution of a -lactoneor a -lactol for a -lactone results in reduced activity while3ß,13-dihydroxy GAs with either 20-carboxyl or 20-methylfunctions are completely inactive. The Tanginbozu dwarf ricebioassay responds to many more GAs than the barley aleuronesystem possibly because the rice seedlings can carry out extensiveGA interconversions. Under these circumstances GAs that areinactive per se can be metabolically converted to active forms.There is no interaction between the 3ß- and 13-hydroxyfunctions of GA molecules in the rice assay. Activity appearsto be determined by the degree oxidation of the C-20 group.The order of activity is usually -lactone > -lactol >-lactone > methyl > carboxyl. It is suggested this mayindicate that in rice seedlings C₂₀-GAs are converted to C₁₉-GAsvia a Baeyer-Villiger type oxidation. Activity in the dwarfpea bioassay is dependent upon GAs possessing both 3ß-and 13-hydroxyl groups and is again related to the state ofoxidation at the C-20 locus. In the lettuce bioassay activityis restricted to GAs with a -lactone function. In some instancesa -lactone, but not a -lactol, can substitute effectively. Thismay imply that the applied C₂₀-GAs are not converted to C₁₉-GAsand that the response to the -lactone results from the six-memberedring mimicking the -lactone at the receptor site. Only GAs havinga 19,10 or a 19,20 lactonic bridge show substantial activityin the cucumber bioassay. The additional presence of eithera 12- or a 13-hydroxyl group severely reduces activity.     

Comparison of the Effects of Root Temperature on Nitrate and Ammonium Nutrition of Oilseed Rape (Brassica napusL.) in Flowing Solution Culture: II. CATION-ANION BALANCE

Macduff, J. H., Hopper, M. J., Wild, A. and Trim, F. E. 1987.Comparison of the effects of root temperature on nitrate andammonium nutrition of oilseed rape (Brassica napusL.) in flowingsolution culture. II. Cation-anion balance.—J. exp. Bot.38: 1589-1602. The effects of root temperature and form of N nutrition (NH4or NOJ) on the mineral composition of the plant, the balanceof inorganic cation-anion uptake and on the apparent net effluxof H ⁺/OH^–ions from the roots were studied with 49-d-oldoilseed rape (Brassica napusL. cv. Bien venu) in flowing solutionculture. Plants were pre-treated for 14 d at a root temperatureof 5 °C prior to constant root temperatures of 3, 7, 11or 17°C for 14 d, with a common shoot temperature of 20/15°Cday/night. Nitrogen was supplied as NH⁺₄4 or NO^–₃ at 10mmol m³. Values of Q₁₀ (7-17°C) for mean unit absorptionrates of all the major nutrient ions (K⁺ , Mg⁺⁺ , NH⁺₄, SO₄,H₂PO₄, NO₃), except Ca⁺⁺, were > 2.0 over the first 5 d oftreatment but thereafter were < 1.5; the apparent effectof temperature on uptake rates diminished with time. Under NH⁺₄nutrition, inorganic cation uptake (Mg^{+ +} + K⁺+Ca^{+ +} +NH⁺₄)exceeded inorganic anion uptake (SO4 ^–₄+ H₂PO₄) over 14d at all temperatures, with the proportion of cation uptakeas NH4 remaining constant (0.67-0-68) irrespective of root temperature.The net efflux of H ⁺ from the roots approximately balancedNH⁺₄ uptake (1:1) over 14 d at each temperature and also balancedthe difference between the total uptake of inorganic cationsand inorganic anions. Under NO₃ nutrition, the sum of the netefflux of OH and the change in the carboxylate contents of plantsover 14 d approximately balanced the sum of NO₃ and SO ^–₄reduced in the plant. The majority of the negative charge associatedwith the reduction of NO₃ and SO ^–₄ was apparently effluxedas OH, but this fraction was lower at low root temperatures.The results are discussed in terms of mechanisms that have beenproposed to regulate the internal pH of plants. Key words: Brassica napus, oilseed rape, root temperature, cation-anion balance, H⁺/OH efflux.     

Adaptation of the Euryhaline Charophyte Lamprothamnium papulosum to Brackish and Freshwater: Turgor Pressure and Vacuolar Solute Concentrations During Steady-State Culture and After Hypo-osmotic Treatment

The euryhaline charophyte Lamprothamnium papulosum (Wallr.)J. Gr. was adapted to media with decreasing salinities rangingfrom 550 to 0 mosmol kg^–1. Vegetative plants grown inmedia with osmotic pressures (⁰) in the range of 550 to 130mosmol kg^–1 maintained a constant turgor pressure () at309 + 7 mosmol kg^–1. The ions K+, Na+ and Cl–, werethe predominant solutes in the vacuole. Changes in their concentrationsaccount for the variation in internal osmotic pressure (¹) with,⁰. The divalent ions Mg²⁺, Ca²⁺ and were also present in significant amounts, but their concentrationsdid not alter with changes in, ⁰. In cells subjected to hypo-osmotic shock the regulation of was incomplete. The turgor pressure increased from 302 to 383mosmol kg^–1. The first rapid response to the sudden decreasein ⁰ was a loss of K⁺ and Cl^–. In contrast to the decreasein ionic concentrations an accumulation of sucrose occurredwhich could account for the increase of . The increase in sucroseconcentration started 24 to 48 h after the downshock and reachedits highest value after 3 to 4 weeks. The sucrose concentrationin the vacuole was up to 320 mol m^–3. During this timethe ionic content continued to decrease but did not counterbalancethe sucrose concentration sufficiently to regain the original. High sucrose levels accompanied by an enhanced were also observedduring the period of fructification (sexual reproduction: formationof antheridia and oogonia) in Lamprothamnium kept under conditionsof constant salinity. It is concluded that high sucrose content and elevated arecharacteristic of sexual reproduction in this charophyte. Lamprothamniumis able to tolerate different during various developmentalstages (e.g. vegetative and reproductive phases). Key words: Lamprothamnium papulosum, sucrose, turgor pressure     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: II. GERMINATION AT REDUCED WATER POTENTIAL

Seed germination rates (GR =inverse of time to germination)are sensitive to genetic, environmental, and physiological factors.We have compared the GR of tomato (Lycopersicon esculentum Mill.)seeds of cultivar T5 to those of rapidly germinating L. esculentumgenotypes PI 341988 and PI 120256 over a range of water potential(). The influence of seed priming treatments and removal ofthe endosperm/testa cap enclosing the radicle tip on germinationat reduced were also assessed. Germination time-courses atdifferent 's were analysed according to a model that identifieda base, or minimum, allowing germination of a specific percentage(g) of the seed population (_b(g)), and a ‘hydrotime constant’(_H) indicating the rate of progress toward germination per MPa.h.The distribution of _b(g) determined by probit analysis was characterizedby a mean base (_b) and the standard deviation in _b among seeds(_b). The three derived parameters, _b, _b) and _H, were sufficientto predict the time-courses of germination of intact seeds atany . A normalized time-scale for comparing germination responsesto reduced is introduced. The time to germination at any (t_g())can be normalized to be equivalent to that observed in water(t_g(0)) according to the equation t_g(0)=[l–(/_b(g))]t_g().PI 341988 seeds were more tolerant of reduced and had a morerapid GR than T5 seeds due to both a lower _b and a smaller _H.The rapid germination of PI 120256, on the other hand, couldbe attributed entirely to a smaller _H. Seed priming (6 d in–1.2 MPa polyethylene glycol 8000 solution at 20 ?C followedby drying) increased GR at all >_b(g), but did not lower theminimum allowing germination; i.e. priming reduced _H withoutlowering _b. Removing the endosperm/testa cap (cut seeds) markedlyincreased GR and lowered the mean required to inhibit germinationby 0.7 to 0.9 MPa. However, this resulted primarily from downwardadjustment in _b during the incubation of cut seeds at low inthe test solutions. The difference in _b between intact and cutseeds incubated at high was much less (0.l MPa), indicatingthat at the time of radicle protrusion, the endosperm had weakenedto the point where it constituted only a small mechanical barrier.In the intact seed, endosperm weakening and the downward adjustmentin embryo _b ceased at < –0.6 MPa, while the reductionin _H associated with priming proceeded down to at least –1.2MPa. Based on these data and on the pressure required to pushthe embryos from the seeds at various times after imbibition,it appears that the primary effect of priming was to shortenthe time required for final endosperm weakening to occur. However,as priming increased GR even in cut seeds, priming effects onthe embryo may control the rate of endosperm weakening. Key words: tomato, Lycopersicon esculentum Mill., water potential, germination rate, seed priming, genetic variation     

An Error in the Calibration of Xylem-water Potential against Leaf-water Potential

An error occurs in the calibration of xylem pressure potential() against leaf-water potential () when the calibration is madeusing plant material in which the water stress has been inducedartificially after excision. The impostion of water stress afterexcision affects the determination more than it affects , consequentlythe relationship between these two indices of water stress isaltered. Care should be exercised to ensure that identical proceduresare adopted during . calibrations and during susbsequent fieldmeasurements of with the pressure-chamber apparatus.     

The Meaning of Matric Potential

The commonly used equation, = P - + , which describes thepartitioning of plant water potential, , into components ofhydrostatic pressure, P, osmotic pressure, , and matric potential,, is misleading. The term , which is supposed to show the influenceof a solid phase on , is zero if a consistent definition ofpressure is used in the standard thermodynamic derivation. However,it can be usefully defined by = + _D, where _D is the osmoticpressure of the equilibrium dialysate of the system. The practicaland theoretical significance of this definition is discussed.     

Alterations in the Components of Peanut Leaf Water Potential during Desiccation

Changes in components of leaf water potential during soil waterdeficits influence many physiological processes. Research resultsfocusing on these changes during desiccation of peanut (Arachishypogeae L.) leaves are apparently not available. The presentstudy was conducted to examine the relationships of leaf water_l, solute _s and turgor _p potentials, and percent relative watercontent (RWC) of peanut leaves during desiccation of detachedleaves and also during naturally occurring soil moisture deficitsin the field. The relationship of _p to _l and RWC was evaluated by calculating_p from differences in _l and _s determined by thermocouple psychrometryand by constructing pressure-volume (P-V) curves from the _land RWC measurements. Turgor potentials of ‘Early Bunch’and ‘Florunner’ leaves decreased to zero at _l of–1.2 to –1.3 MPa and RWC of 87%. There were no cultivardifferences in the _l at which _p became zero. P-V curves indicatedthat the error of measuring _s after freezing due to dilutionof the cellular constituents was small but resulted in artefactualnegative _p values. Random measurements on two dates of _l, _s, and calculation of_p from well-watered and water-stressed field plots consistingof several genotypes indicated that zero _p occurred at _l of–1.6 MPa. It was concluded that the relationships of _p,_l, _s, and RWC of peanut leaves were similar to leaves of othercrops and that these relationships conferred no unique droughtresistance mechanism to peanut.     

Abscisic Acid Accumulation and Water Relations of Four Cultivars of Phaseolus vulgaris L. under Drought

Larqué-Saavedra, A., Rodriguez, M. T., Trejo, C. andNava, T. 1985. Abscisic acid accumulation and water relationsof four cultivars of Phaseolus vulgaris L. under drought.—J.exp. Bot 36: 1787–1792. Plants of four cultivars of Phaseolus vulgaris L. differingin drought resistance were grown in pots under greenhouse conditionsand prior to flowering water was withheld from the pots untilthe mid-day transpiration rate reached values below 1.0 µgH₂O cm^–2 s^–1 (designated the ‘drought’stage). At this point leaves were harvested on 3 or 4 occasionsover 24 h to determine the abscisic acid (ABA) concentration,total water potential (), solute potential (₁) and turgor potential(_p). Results showed that values of , ₁, and _p differed between cultivarswhen they reached the ‘drought’ stage. The stomatalsensitivity to changes in and _p, was as follows: Michoacán12A3 > Negro 150 Cacahuate 72 > Flor de Mayo. These datacorrelated well with the pattern of drought resistance reportedfor the cultivars. ABA accumulation at the ‘drought’ stage differedbetween cultivars at each sampling time, but overall differencesin ABA level between cultivars were not significant. ABA levelsdid not, therefore, correlate with the drought resistance propertiesreported for the cultivars. Results are discussed in relationto and hour of the day when bean samples were taken for ABAanalysis. Key words: Phaseolus vulgaris L., drought resistance, abscisic acid     

A comparison of the impacts of various nitrogen sources on acid-base balance in C3 Triticum aestivum L. and C4 Zea mays L. plants

This work aimed to study the impacts of acquisition and assimilationof various nitrogen sources, i.e. NO₃^–, NH₄⁺ or NH₄NO₃,in combination with gaseous NH₃ on plant growth and acid-basebalance in higher plants. Plants of C₃ Triticum aestivum L.and C₄ Zea mays L. grown with shoots in ambient air in hydroponicculture solutions with 2 mol m^–3 of nitrogen source asNO₃^–, NH₄⁺ or NH₄NO₃ for 21 d and 18 d, respectively,had their shoots exposed either to 320 µg m^–3 NH₃or to ambient air for 7 d. Variations in plant growth (leaves,stubble and roots), and OH^– and H⁺ extrusions as wellas the relative increases in nitrogen, carbon and carboxylatewere determined. These data were computed as H⁺/N, H⁺/C, (C-A)/N,and (C-A)/C to analyse influences of different nitrogen sourceson acid-base balance in C₃ Triticum aestivum and C₄ Zea maysplants. Root growth in dry weight gain was significantly reduced bytreatment with 320 µg m^–3 NH₃ in Triticum aestivumand Zea mays growing with different N-forms, whereas leaf growthwas not significantly affected by NH₃. In comparison with C₃Triticum aestivum, non-fumigated C₄ Zea mays had low ratiosof OH^–/N in NO₃^–3-grown plants and of H⁺/N in NH₄⁺- and NH ₄NO₃-grown plants. Utilization of NH₃ from the atmospherereduced both the OH^–N ratios in NO₃^– -grown plantsand the H⁺/N ratio in NH₄⁺ - and NH₄NO₃ -grown plants of bothspecies. Furthermore, Zea mays had higher ratios of (C-A)/Nin NH₄⁺ - and NH₄NO₃-grown plants than Triticum aestivum. Thismeans that C₄ Zea mays had synthesized more organic anion perunit increase in organic N than C₃ Triticum aestivum plants.Within both species, different nitrogen sources altered theratios of (C-A)/N in the order: NH₄NO₃>NH₄⁺>NO₃^–.Fumigation with NH₃ increased organic acid synthesis in NO₃^–- and NH₄⁺ - grown plants of Triticum aestivum, whereas it decreasedorganic acid synthesis in Zea mays plants under the same conditions.Furthermore, these differences in acid-base regulation betweenC₃ Triticum aestivum and C₄ Zea mays plants growing with differentnitrogen sources are discussed. Key words: Acid-base balance, ammonia, ammonium, nitrate, ammonium nitrate, C₃ Triticum aestivum L., C₄ Zea mays L.     

Optimization theory of stomatal behaviour II. Stomatal responses of several tree species of north Australia to changes in light, soil and atomospheric water content and temperature

In a companion paper several methods of calculating the marginal unit water cost of plant carbon gain (E/A) were tested to determine whether stomata were behaving optimally in relation to regulating leaf gas exchange. In this paper one method is applied to several tropical tree species when leaf-to-air vapour pressure difference (D), photosynthetic photon flux density, leaf temperature, and atmospheric soil water availability were manipulated. The response of leaves that had expanded during the dry season were also compared to that of leaves that had expanded in the wet season. Few differences in absolute value of E/A, or the form of the relationship, were observed between species or between seasons. In the majority of species, E/A increased significantly as either leaf-to-air vapour pressure difference increased, at a leaf temperature of either 33C or 38C, or as in photosynthetic photon flux density increased. In contrast, as leaf temperature increased at constant D, E/A was generally constant. As pre-dawn water potential declined, E/A declined. The relationship between E/A and D did not differ whether internal or ambient carbon dioxide concentration were kept constant. It is concluded that stomata are only behaving optimally over a very small range of D. If a larger range of D is used, to incorporate values that more closely reflect those experienced by tropical trees in a savanna environment optimization is incomplete.Key words: Stomatal optimization theory, marginal unit water cost.      

Anti-Auxin Activity of Xyloglucan Oligosaccharides: the R?le of Groups other than the Terminal {alpha}-L-Fucose Residue

The quantitatively major nonasaccharide (XG9) derived from xyloglucanby digestion with cellulase exhibits anti-auxin activity inthe pea stem segment straight-growth bioassay; the most effectiveconcentration of XG9 is c. 10^–9 M. Previous work had shownthat XG9 owes its biological activity to the presence of a terminal-L-fucopyranose residue. In order to investigate to what extentthe remainder of the XG9 molecule is essential for activity,several fucose-containing compounds were tested for their abilityto mimic the anti-auxin effect of XG9. A fucose-containing pentasaccharideof xyloglucan (XG5; probable structure FucGalXylGlcGlc) was,at 10^–8 M, about as effective an anti-auxin as 10^–9M XG9; unlike XG9, XG5 did not diminish in effectiveness at10^–7 M. The human milk trisaccharide, 2'-fucosyl-lactose[L-fucopyranosyl--(12)-D-galactopyranosyl-ß-(14)-D-glucose],whose FucGal unit is identical with that of XG9, inhibited auxin-inducedelongation over a wide range of concentrations centred on about10^–8 M. 2'-Fucosyl-lactose at 10^–8 M was about aseffective an anti-auxin as 10^–9 M XG9. Free L-fucose andmethyl--L-fucopyranoside were unable to inhibit auxin-inducedgrowth at any concentration tested (10^–10 M to 10^–6M) and neither compound interfered with the inhibition causedby 10^–9 M XG9 when co-incubated at concentrations up to10^–4 M. The results confirm the essential r?le of an -linkedterminal fucose residue in the anti-auxin activity of XG9 andshow that the sub-terminal galactose residue may also be required.Possible reasons why high concentrations of XG9 fail to antagonizeauxin-induced growth while high concentrations of XG5 and 2'-fucosyl-lactosecontinue to do so are discussed. Key words: Anti-auxin, oligosaccharin, fucose     

Quantitative effects of the genes Lf, Sn, E, and Hr on time to flowering in pea (Pisum sativum L.)

Flowering time in pea (Pisum sativum L.) is determined by genetically controlled responses to photoperiod and temperature. To investigate these responses, 11 lines homozygous for the flowering genes Lf, Sn, E, and Hr were grown under contrasting semi-controlled photothermal environments and the durations (d) from sowing to first flower (f) were recorded. The effects of the four genes were quantified using a two-plane photothermal model which linearly relates the rate of progress from sowing to flowering (1/f) with the mean pre-flowering values of temperature (T) and/or photo-period (P), based on 1/fa + bT (when P is longer than the critical photoperiod, Pc) and 1/fa + bT + cP (when P<Pc). The main effect of Lf alleles was on temperature sensitivity (b) when P>Pc, which increased in the sequence Lf^d<Lf< lf<lf^a. Gene Hr, when together with Sn, increased photoperiod sensitivity (c) and reduced the intercept (a) when P<Pc. Allele sn determined a single plane response to temperature alone (i.e. a day-neutral response). Gene E, when present with lf Sn, increased 1/f in both the thermal (P<Pc) and photothermal (PPc) domains, mainly by increasing a and b, respectively. Variations in the coefficients of the thermal and photothermal responses determined that the critical photoperiod varied with temperature in all photoperiod-sensitive genotypes. A common base temperature of 0.2C was determined amongst Day-Neutral Class genotypes (sn) and thermal time from sowing to flowering increased in the sequence lf^a<lf< <:f<Lf^d. Intra-Class variations attributed to the Lf alleles were also detected in the Late (Sn hr) and Late High Response (Sn Hr) Classes. The linear photothermal model provided a sound basis for studying the quantitative effects of flowering genes in pea.     

Correlation of decreased calcium contents with proline accumulation in the marine green macroalga Ulva fasciata exposed to elevated NaCl contents in seawater

The involvement of Na⁺, K⁺, Cl^- or Ca²⁺ in the regulation of salinity stress-induced proline accumulation via the inhibition of the activity of proline dehydrogenase (PDH; EC 1.4.3.1), a catabolic enzyme of proline, was investigated in the marine green macroalga Ulva fasciata Delile. After 6 h of exposure to elevated artificial seawater (ASW) salinity, adjusted either by increasing the NaCl content in 30 ASW (a change in ion ratio) or by concentrating ASW (a constant ion ratio), the contents of Na⁺, K⁺ and Cl^- linearly accumulated with increasing salinity from 30-90 (parts per thousand); the accumulation pattern of each ion was similar between the two treatments. An increase in NaCl content in ASW induced proline accumulation, but decreased both the PDH activity and the total water-soluble Ca²⁺ contents, while concentrated ASW had no effect. As compared to a constant value at 30, both the contents of total and water-soluble CA²⁺ and the activity of PDH decreased 1 h after exposure to 60 (adjusted by increasing NaCl content in 30 ASW) and concomitantly the content of seawater Ca²⁺ increased, while proline accumulated after 3 h. The addition of 15 mM ethylene glycol-bis-(2-aminoethyl ether) N,N,N-tetraacetic acid (EGTA) in 60 ASW (adjusted by increasing the NaCl content in 30 ASW) enhanced both the proline accumulation and the decrease in the content of total and water-soluble cellular Ca²⁺ and the activity of PDH; the effects of EGTA were reversed by 10 mM CaSO4. These results indicate that a loss of cellular Ca²⁺ is associated with the NaCl induction of proline accumulation via an inhibition of PDH activity in U. fasciata.     

Alternative Methods of Analysing Water Potential Isotherms: Some Cautions and Clarifications: I. THE IMPACT OF NON-IDEALITY AND OF SOME EXPERIMENTAL ERRORS

In recent years alternative ways have been proposed to transformmeasurements of leaf water potential, , and relative water content,R^*, in order to derive values of osmotic pressure at full turgidityin leaves and shoots, ^o(when 0). Two types of transformationsare usually considered: 1/ versus R^* and versus 1/R^*, and linearregression is used to fit the data in the region where turgoris thought to be zero. It appears that when ^o is estimated bylinear extrapolation of 1/Psi; versus R^* then apoplastic watermight not influence the accuracy of ^o but when the versus \/R^*transformation is used apoplastic water causes an underestimateof ^o. We examine the accuracy of the estimate of ^o obtainedfrom the two transformations when there are random errors in, systematic errors in , and when the osmotic solutions arenon-ideal. The 1/ versus R^* transformation generally producesthe best estimate of ⁰ by linear extrapolation.     

Reduced aleurone {alpha}-amylase production in aged wheat seeds is accompanied by lower levels of high-pI [IMAGE]-amylase transcripts and reduced response to gibberellic acid

With the aim of determining the level at which ageing exerts its effect on the expression of -amylase, GA3 regulation of -amylase production was studied in isolated aleurone layers from aged wheat seeds. GA3-induced -amylase activity was lower in the tissue from aged seeds than in controls. However, the proportion of ³⁵S-methionine incorporated into -amylase was higher in the aged than in control tissue. The pattern of -amylase isoforms was resolved by isoelectric focusing and showed that two isogroups were present with the activity of the high-pI isogroup being higher in the control than in the aged lot. These apparently contradictory results may be explained in terms of differences in isozyme expression. Studies on the expression of -amylase genes indicated a reduction in the level of high-pI mRNA in aged tissue. Dose-response curves showed lower GA3-responsiveness of aleurone layers from aged seeds as compared to the controls. From these results, it is proposed that the diminished capacity of -amylase production in aleurone from aged seeds is apparently due to a decrease in the expression of the high-pI -amylase genes, and this reduction is associated with a decrease in the response to GA3.Key words: Seed ageing, wheat aleurone, gibberellic acid, -amylase isozymes, gene expression.      

Hydrothermal time analysis of tomato seed germination responses to priming treatments

Controlled hydration of seeds followed by drying (seed priming) is used to break dormancy, speed germination, and improve uniformity of radicle emergence. To date, empirical trials are used to predict optimal priming conditions for a given seed lot. Since priming is based upon seed water relations, it was hypothesized that the sensitivity of germination to reduced water potential before priming might be mechanistically related to, and therefore predictive of, priming responsiveness. Analyses of germination of 13 tomato (Lycopersicon esculentum Mill.) seed lots at two temperatures (15C and 20C) and three water potentials (0, -0.28 and -0.43 MPa) showed that seed lot germination responses could be quantitatively characterized by parameters derived from thermal time, hydrotime, and hydrothermal time models (R²0.73-0.99). Six of the seed lots were primed at two temperatures (15°C and 20°C) and three water potentials (-1.0, -1.5 and -2.0 MPa) for various durations, dried, and their subsequent germination rates analysed according to hydropriming time and hydrothermal priming time models. The responses of germination rates to priming were characterized by hydropriming time (HP) and hydrothermal priming time (HTP) constants and the minimum water potential (min) and temperature (Tmin) for achieving a priming effect. The values of min and Tmin varied relatively little among tomato seed lots, and the generalized values of min=2.39 MPa and Tmin=9.10°C accounted for 74% (15°C), 57% (20°C), and 62% (across both temperatures) of the increase in germination rates following priming. Nonetheless, while the hydrothermal time models described germination patterns both before and after priming, there was relatively little predictive relationship between them.