The Survival of Germinating Orthodox Seeds after Desiccation and Hermetic Storage

Seeds of barley (Hordeum vulgare L.) and mung bean (Vigna radiata(L.) Wilczek), with orthodox seed storage behaviour, were imbibedfor between 8 h and 96 h at 15 °C and 25 °C, respectively,while barley seeds were also maintained in moist aerated storageat 15 °C for 14 d. These seeds and seedlings, together withcontrols, were then dried to various moisture contents between3% and 16% (wet basis) and hermetically stored for six monthsat —20°C, 0°C or 15°C. In both species, neitherdesiccation nor subsequent hermetic storage of the control lotsresulted in loss in viability. The results for barley seedsimbibed for 24 h were similar to the control, but desiccationsensitivity increased progressively with duration of imbibitionbeyond 24 h in barley or 8 h in mung bean; these treatmentsalso reduced the longevity of the surviving seeds in air-drystorage. Loss in viability in barley imbibed for 48 h was mostrapid at the two extreme seed storage moisture contents of 3·6%and 14·3%, and in both these cases was more rapid at15 °C than at cooler temperatures. Similarly, for mung beanimbibed for 8 h, loss in viability was most rapid at the lowest(4·3%) moisture content, but in this case it was morerapid at –20 °C than at warmer temperatures. Thus,these results for the storage of previously imbibed orthodoxseeds conform with the main features of intermediate seed storagebehaviour Key words: Barley, Hordeum vulgare L., mung bean, Vigna radiata (L.) Wilczek, desiccation sensitivity, seed longevity, seed storage behaviour     

Effects of some Cyclic 'Crown' Polyethers on Potassium Uptake, Efflux and Transport in Excised Root Segments and Whole Seedlings

The ionophores benzo-18-crown-6 (18-C-6), t-butylbenzo-18-crown-6(TBB) and di-t-butyldibenzo-30-crown-10 (30-C-10) were testedfor their effects on potassium ion absorption in onion rootsegments, and in wheat and mung bean seedlings. Potassium uptake,efflux and transport were progressively reduced in onion rootsegments and seedlings by 18-C-6 over the range 0.1–1.0mM. The effects of TBB (up to 0.3 mM) were more severe but otherwisegenerally similar to those of 18-C-6 in seedlings. Both ionophoresreduced growth, and at the highest concentrations, resultedin root potassium ion content falling below initial values after48 h treatment. The effects of 30-C-10 were evident at muchlower concentrations, inhibition of net potassium uptake occurringabove 10^–4 M. Between 10^–4 and 10^–4 M 30-C-10,however, a modest but significant stimulation of potassium uptakewas observed in onion roots and seedlings; growth of seedlingswas largely unaffected. The reductions in potassium absorptionwere attributed to the promotion, by the ionophores, of facilitateddiffusion down the electrochemical diffusion gradient, counteringthe efficiency of the potassium ion influx pump. Stimulationof uptake at certain concentrations of 30-C-10 was consideredmore likely to be due to an inhibition of passive potassiumefflux, rather than a stimulation of active influx. The importanceof stability constants, bonding and lipophilicity, in determiningthe relative effectiveness of the ionophores, is discussed. Allium cepa L, onion, Triticum aestivum L, wheat, Phaseolus aureus L, mung bean, cyclic ‘crown’ polyethers, potassium fluxes, ion transport     

O-Benzylhydroxylamine: An Inhibitor of Phenylpropanoid Metabolism in Plants

O-Benzylhydroxylamine (OBHA) is a potent inhibitor of phenylalanineammonialyase (PAL, EC 4.3.1.5 [EC] ) and phenylpropanoid metabolismas evidenced by its effects on three plant species [soybean(Glycine max (L.) Merr.), buckwheat (Fagopyrum esculentum Moench.),and mung bean (Vigna radiata L.)]. When supplied to roots, OBHA(10^–5 M) did not significantly inhibit light- or dark-growthof soybean seedlings, but reduced (25%) soluble hydroxyphenoliccompound accumulation in light-grown axes. Higher concentrations(510^–5 M) of OBHA caused reductions (25%) in axis freshweight of light-grown seedlings (72 h), but did not lower axisweight of dark-grown seedlings. Anthocyanin accumulation inhypocotyls of intact mung bean seedlings was reduced by 25%after 3 days light growth after treatment with OBHA (10^–5M) via root feeding. Anthocyanin content of excised, etiolatedbuckwheat hypocotyls floated on solutions of OBHA (10^–5M) and incubated in the light for 24 h was reduced by 40%. L-Phenylalanineand t-cinnamic acid, intermediates of phenylpropanoid metabolism,were able to partially reverse this inhibition in buckwheat.Extractable PAL activity (specific activity basis) in soybeanaxes was substantially reduced (20% in dark, 40% in light) asearly as 24 h after root feeding with OBHA (10^–5 M). Reductionof PAL activity (specific activity or per axis basis) by OBHAcompared to control levels, continued throughout a time courseof 96 h. Kinetic studies on soybean PAL revealed a K_m of 1.1mM for L-phenylalanine and an apparent K_i of 3.5 µM forOBHA. (Received May 31, 1985; Accepted August 6, 1985)     

Effects of Temperature on the In vivo Assay of Nitrate Reductase in some C3 and C4Species

Nitrate reductase (NR) activity was measuredin vivo in differentcrop species at 25–60 °C. Highest NR activity wasobserved at 40 °C in pigeon pea, cowpea, sunflower, sesameand sorghum, 45 °C in maize and 50 °C in bajra. At higherincubation temperatures NR activity declined in all species.In mung bean the optimum incubation temperature varied withthe season. In the summer crop of mung beans, NR activity wasmaximum at 50 °C while in the rainy season crop 30 °Cwas the optimum incubation temperature. NR in sesame was relativelyheat-tolerant. The results indicate that 30 °C is not theoptimum incubation temperature for all crop species. Nitrate reductase, temperature, in vivo assay     

Effect of {alpha}-Tomatine on the Integrity and Biochemical Activities of Isolated Plant Cell Organelles

Respiration in isolated mung bean shoot mitochondria was notaffected by either of the tomatine treatments (10^–3 M,pH 5, and 10^–5 M, pH 8) but was reduced in the excisedshoots by both treatments, although only at the higher of thetwo temperatures (5 °C and 25 °C). Inhibition was gradualand took at least 2 h. Tomatine treatment of excised shootsalso resulted in an increased leakage of K+. PS II activityin isolated spinach leaf chloroplasts was reduced only by thehigh pH tomatine treatment at 25 °C. Again, about 2 h treatmentwas required before significant effects were observed but thealkaloid did not cause disintegration of the chloroplast asmeasured by pigment release. Disruption of lysosomes isolatedfrom cauliflower inflorescence tissue and release of acid phosphatasewas enhanced by tomatine. Initially only 10^–5 M tomatineat pH 8 was effective but, later, effects could only be obtainedwith 10^–3 M alkaloid at pH 5. The differential susceptibilityof these organelles to tomatine is discussed in relation tomembrane structure and to the mode of toxicity of the alkaloid.     

Regulation of Tracheary Element Differentiation by Exogenous L-Methionine in Callus of Soya Bean Cultivars

The relationship between the induction of tracheary elementdifferentiation and exogenous L-methionine was examined in agar-growncultures of soya bean callus initiated from Glycine max L. ‘Wayne’and ‘Clark 63’. Although Wayne is a normal cultivarsoya bean, seedlings of Clark 63 exhibit abnormal growth at25 °C due to exessive ethylene biosynthesis at this temperature.Wayne callus showed increased xylogenesis in the presence ofexogenous L-methionine (3.7 µg 1^–1) in comparisonto IAA–KN controls at both 20 and 25 °C. Clark 63callus produced greater numbers of tracheary elements in responseto exogenous L-methionine only at 25 °C. The induction ofxylem differentiation was independent of the maintenance temperatureof the stock cultures of both cultivars. Xylogenesis initiatedbyan IAA–KN medium was inhibited by the addition of AgNO₃(20 mg 1^–1) to the extent of 76.5 per cent in cv. Wayneand 6 per cent in cv. Clark 63. The inhibitory effect was partiallyreversed by the addition of L-methionine (3.7 µg 1^–1)to the IAA–KN–AgNO₂ medium. These data support thehypothesis that xylogenesis in vitro involves auxin, cytokininand ethylene. differentiation, xylogenesis, L-methionine, ethylene, Glycine max L., soya bean, callus culture, auxin, kinetin     

Osmotic Adjustment and Osmotic Constituents in Roots of Mung Bean Seedlings

Osmotic adjustment in roots of mung bean seedlings (Vigna mungo(L.) Hepper) and the effect of cotyledon excision on the osmoticadjustment were investigated. The major osmotic constituentsin roots of intact seedlings were K⁺, Cl^–, free aminoacids and sugars (glucose, fructose and sucrose). All theseintracellular concentrations distinctly increased under osmoticstress and contributed to about 80% of the intracellular osmoticpressure of the root cell sap. Cotyledon excision remarkablysuppressed both the osmotic adjustment and the elongation inroots. However, the effect of cotyledon excision on intracellularK⁺ and Cl^– concentrations in roots was quite small. Twodifferent mechanisms are likely for the osmotic adjustment inroots. One is the K⁺ and Cl^–-dependent osmotic adjustmentwhich is cotyledon-independent, and the other is the osmoticadjustment dependent on the supply of free amino acids and sugarsfrom cotyledons. (Received September 20, 1986; Accepted January 14, 1987)     

Environmental Control of Flowering in Barley (Hordeum vulgare L.). II. Rate of Developement as a Function of Temperature and Photoperiod and its Modification by Low-temperature Vernalization

Plants of six contrasting genotypes of barley were raised fromvernalized (imbibed at 1 °C for 30 d) or non-vernalizedseeds and grown in 12 different controlled environments comprisingfactorial combinations of three photoperiods (10, 13 and 16h d^–1), two day temperatures (18 and 28 °C) and twonight temperatures (5 and 13 °C). Except at longer daysfor Athenais or Arabi Abiad, the 28 °C day temperature wasgenerally supra-optimal and delayed awn emergence. At lowertemperatures and in photoperiods shorter than the critical value,P_C, which delay awn emergence, the time from sowing to awn emergencefor five of the genotypes conformed to the equation 1/f=a +bT{macron}+cPwhere f is the time to awn emergence (d), T{macron} is meandiurnal temperature (°C), P is photoperiod (h d^–1)and a, b and c are genotype-specific constants. In Arabi Abiad,however, significant responses to temperature were not detected.The low temperature pre-treatment of the seeds reduced the subsequenttime to awn emergence in Athenais and the autumn-sown genotypesAger, Arabi Abiad and Gerbel B, especially in longer days, buteither had no effect or tended to delay awn emergence in thespring-sown types Emir and Mona. In the spring-sown types P_Cwas outside the range investigated (i.e. > 16 h d^–1),but in Ager it was approx. 13 h d^–1 and in Gerbel B justover 13 h d^–1. For plants of Arabi Abiad grown from vernalizedseeds P_c was almost 15 h, but     

The Effect of Ethylene and Temperature on ATP Accumulation from Various Substrates in Peanut (Arachis hypogaea L. ) Seeds

Peanut (Arachis hypogaea L. ) seed powder accumulated ATP fromAMP and phosphoenolpyruvate (PEP) at a rate of approx. 100 pmolmin^–1mg^– powder at 35° C. When peanut seed powderwas incubated with various substrates, which may result in PEPor AMP (ADP) synthesis, then ATP accumulated. The best substratecombinations examined so far were AMP + succinate, NADH₂, andAMP + malate + NAD, with activities of 33, 12 and 12 pmol min^–mg^–1powder,respectively; AMP + malate showed very low activity. Some combinationsexhibited linear activities with time, while others had an exponential-typeprofile. The temperature dependence of the ATP accumulationdemonstrated by the Ahrrenius plot had a double phase with atransition point at 25° C. The Ea values between 15°C and 25° C were 25 000–50 000 cal/mol, while above25° C the Ea values fluctuated between 6000 and 8000 cal/mol(depending on the substrate). The AMP + PEP combination exhibiteda single-phase profile between 15° C and 40° C, withan Ea value of 22 000 cal/mol. In the presence of some substrates,ethephon (ethylene) had a stimulatory effect and caused an increasein the Ea values at the high temperature phase. A comparisonof seed powder from dormant seeds with that from non-dormantseeds revealed that some substrate combinations accumulate ATPfaster in non-dormant seeds and others do so in dormant seeds. Key words: Arachis hypogaea, ATP, Ethylene, Dormancy, Peanut, Seed     

The Effect of Cooling on Photosynthesis, Amounts of Carbohydrate and Assimilate Export in Sunflower

Sunflower plants (Helianthus annuus L.) grown at 30°C werecooled to 13°C in the light in atmospheric CO² or low CO²,or in darkness. Photosynthetic rate at 30°C after coolingwhole plants in atmospheric CO² for 12 h during a photoperiodwas significantly lower than at the start of the photoperiodcompared to plants cooled at low CO², those cooled in the darkand those maintained at 30°C. Amounts of sucrose, hexosesand starch in leaves at 13°C increased throughout a 14 hphotoperiod to levels higher than in leaves at 30°C, whereamounts of sucrose and hexoses were stable or falling after4 h. Carbohydrate accumulation at 13°C during this photoperiodwas more than twice that at 30°C. After three photoperiodsand two dark periods at 13°C carbohydrate levels in leaveswere still as high as at the end of the first photoperiod, butless carbohydrate accumulated during the photoperiods than duringthe first photoperiod, and more was partitioned as starch. Amountsof soluble carbohydrate in roots were greater after 14 h at13°C than in roots of plants at 30°C. Loss of ¹⁴C fromleaves at 30°C as a proportion of ¹⁴CO2 fixed by them at30°C, decreased after exposure of plants to 13°C inthe light for 30 min prior to ¹⁴CO²feeding. Results indicatean effect of cold on the transport process that was light-dependent.It is inferred that the reduction in the proportion of ¹⁴C lostfrom leaves after 10 h cooling was due to reduced sink demand,whereas the rise in the proportion of ¹⁴C lost from leaves after24 h reflects reduced photosynthetic rate. The coincidence ofreduced photosynthetic rate with raised carbohydrate levelsin leaves maintained at 30°C throughout, whilst the restof the plant was cooled to 13°C in the light implies feedbackinhibition of photosynthesis. This may reduce the imbalancebetween source and sink in sunflower during the first days oflong-term cooling. Key words: Temperature, carbon export, carbohydrates, photosynthesis, sunflower     

Purification and Characterization of a Cytochrome P450 (trans-Cinnamic Acid 4-Hydroxylase) from Etiolated Mung Bean Seedlings

A Cyt P450 (P450_C4H) possessing trans-cinnamate 4-hydroxylase(C4H) activity was purified to apparent homogeneity from microsomesof etiolated mung bean seedlings. Upon SDS-polyacrylamide gelelectrophoresis, the purified preparation gave a single proteinband with a molecular mass of 58-kDa. Its specific P450 contentwas 12.6 nmol (mg protein)^–1. Using NADPH as electrondonor, purified P450_C4H aerobically converted trans-cinnamicacid to p-coumaric acid with a specific activity of 68 nmolmin^–1 nmol^–1 P450 in a reconstituted system containingNADPH-Cyt P450 reductase purified from the seedlings or rabbitliver microsomes, dilauroyl phosphatidylcholine, and cholate.This specific activity is by far the highest for reconstitutedC4H systems so far reported and provides direct evidence thatC4H activity is actually associated with a P450 protein. Inthe oxidized state P450_C4H showed a typical low-spin type absorptionspectrum with a Soret peak at 419 nm. A partial spectral shiftto the high spin state was observed when trans-cinnamic acidwas added to oxidized P450_C4H. By spectral titration, the dissociationconstant of the cinnamic acid-P450_C4H complex was determinedto be 2.8 µM. This value is similar to the K_m value (1.8µM) for trans-cinnamic acid determined in the reconstitutedsystem. (Received November 20, 1992; Accepted February 17, 1993)     

Protein Dysfunction and Inhibition of Amino Acid Incorporation in Root Segments from Wheat and Mung Bean Seedlings caused by some Amino Acid Analogues

The effects of para-fluorophenylalanine (p-FPA) and azetidine-2-carboxylicacid (AZ) on acid phosphatase and peroxidase activity, and onL-leucine incorporation, in root segments of Triticum aestivumL. cv. Fenman and Vigna radial a (L.) Wilczek, were studied.Incubation with 50 mmol^–3 AZ significantly reduced phosphataseand peroxidase activities in wheat roots, but with 20 mol m^–3p-FPA, only the peroxidase activity was reduced. In mung beanroots, phosphatase activity was inhibited by both AZ and p-FPA.Effects of the ortho- and meta- isomers of FPA on wheat rootphosphatase and peroxidase, and on mung bean phosphatase, werealso examined. Leucine uptake and incorporation were not inhibitedby 5 h pre-incubation with either p-FPA or AZ, but were inhibitedafter 24 h of pre-incubation. The results support the view that,in the shorter term, the analogues inhibit enzyme activity bybecoming incorporated to produce non-functional protein and,in the longer term, metabolism is further affected by inhibitionof protein synthesis. Key words: Fluorophenylalanin, Azetidine-2-carboxylic acid, Triticum aestivum, Vigna radiata     

Changes in the Cytoplasmic and Vacuolar pH in Intact Cells of Mung Bean Root-Tips under High-NaCl Stress at Different External Concentrations of Ca2+ Ions

The cytoplasmic pH and the vacuolar pH in root-tip cells ofintact mung bean seedlings under high-NaCl stress were measuredby in vivo ³¹P-nuclear magnetic resonance (³¹P-NMR) spectroscopy.When roots were incubated with high levels (100 mM) of NaClat the control external concentration (0.5 mM) of Ca²⁺ ions,the vacuolar pH increased rapidly from 5.6 to 6.2 within 3 h,while the cytoplasmic pH only decreased by a mere 0.1 pH uniteven after a 24-h incubation under high-NaCl conditions. Theincrease in vacuolar pH induced by the high-NaCl stress wasdiminished by an increase in the external concentration of Ca²⁺ions from 0.5 mM to 5 mM. The intracellular concentration ofNa⁺ ions in the root-tip cells increased dramatically upon perfusionof the root cells with 100 mM NaCl, and high external levelsof Ca²⁺ ions also suppressed the in flow of Na⁺ ions into thecells. The vacuolar alkalization observed in salt-stressed rootsmay be related to the inhibition of an H⁺-translocating pyrophosphatasein the tonoplast, caused by the increase in the cytoplasmicconcentration of Na⁺ ions. It is suggested that, although thevacuolar pH increased markedly under salt stress, the cytoplasmicpH was tightly regulated by some unidentified mechanisms, suchas stimulation of the H⁺-translocating ATPase of the plasmalemma,in roots of mung bean under salt stress. (Received April 18, 1992; Accepted July 6, 1992)     

Photothermal Time for Flowering in Faba Bean (Vicia faba) and the Analysis of Potential Vernalization Responses

One cultivar and one land-race of faba bean were subjected to18 potentially vernalizing pre-treatments (constant temperaturesof 1, 5 or 9 °C factorially combined with photoperiods of8 or 16 h d^–1 for 10, 30 or 60 d), and then transferredinto four different growing regimes (‘day’/‘night’temperatures of 18/5 °C or 24/13 °C factorially combinedwith photoperiods of 11 or 16 h d–1). Control plants weregrown entirely in the latter four regimes. The times from sowingto appearance of first open flowers were recorded for all plants.Control plants of the land-race Zeidab Local flowered soonerin long days and in the warmer regime. Pre-treatment reducedthe subsequent time to flower in the four growing-on regimesbut most of the variation in the total time to first flowerfor the pre-treated plants was accounted for by differencesin the combined photothermal time accumulated in the two successiveenvironments - which was predicted by a simple photothermalmodel. Thus, there was neither a specific low-temperature nora short-day vernalization response in this accession. Similarly,no true low-temperature or short-day vernalization responsewas detected in the cv. Maris Bead. However, this UK cultivarflowered later than predicted in the 24/13 °C regime, indicatingthat the 24 °C ‘day’ temperature was supraoptimal.Delays to flowering at 24/13 °C were, however, less evidentwhen plants were grown in long days or following prolonged (30–60d) pre-treatments at cool temperatures. Viciafaba faba, bean, flowering, photoperiodism, vernalization, photothermal time, screening germplasm.     

Comparison of Plasma Membrane and Tonoplast H+-Translocating ATPases in Phaseolus mungo L. Roots

Two membrane fractions were obtained from 16%/26% and 34%/40%interfaces following discontinuous sucrose density gradientcentrifugation of a 10,000–80,000xg pellet from mung bean(Phaseolus mungo L.) roots. The ATPases in the fractions differedfrom each other in their sensitivity toward various inhibitors,activation with salts, dependence of activity on pH, and K_mfor ATP.Mg²⁺. Judging from their sensitivity toward inhibitors,the ATPases in the low and high density membranes are consideredmainly of tonoplast and plasma membrane origin, respectively.Both ATPases were activated by gramicidin D and nigericin. ATP-inducedquenching of quinacrine fluorescence in both fractions requiredMg²⁺ and permeant anions such as Cl^– and quenching wascollapsed by carbonylcyanide p-trifluoromethoxyphenyl hydrazone.The sensitivities of quenching to the inhibitors were essentiallythe same as those of ATPase activity in the membranes. Thesefindings suggest the involvement of ATPases in H⁺-pumping acrossa plasma membrane and tonoplast. (Received April 12, 1985; Accepted October 11, 1985)     

High Temperature Sensitivity of Auxin-induced Ethylene Production in Mung Bean Hypocotyl Sections

High temperature sensitivities of IAA-induced and 1-aminocyclopropane-1-carboxylicacid (ACC)-dependent ethylene production in etiolated mung bean(Vigna radiata [L] Wilczek) hypocotyl sections were comparedat 30,40, 42.5°C. When ethylene production at 30°C wastaken as control, IAA-induced production at 40°C was firstenhanced and then suppressed after 3 h, whereas ACC-dependentproduction was enhanced two-fold throughout the 8 h experimentalperiod. However, when hypocotyl sections treated with 1 mM ACCat 30°C for several hours were transferred to 40°C,the ACC-dependent production rate fell below that at 30°C.An initial transient enhancement of IAA-induced ethylene productionat 40°C was supported by increased ACC synthase activityand thus by ACC content. At 42.5°C, both IAA-induced andACC-dependent production were almost completely suppressed.The results indicate that auxin-induced ethylene productionis affected by high temperatures in two different steps: a)at 40°C, the auxin action gradually deteriorates althoughconversion of ACC to ethylene is not affected at all, and at42.5°C, the conversion is nearly completely suppressed. (Received July 8, 1985; Accepted January 24, 1986)     

Effect of Root Zone Temperature on the Mineral Composition of Xylem Sap and Plasma Membrane K+-Mg++-ATPase Activity of Grafted-Cucumber and -Figleaf Gourd Root Systems

Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd- (FG, Cucurbita ficifolia Bouché)seedlings in order to determine the effect of solution temperature(12, 22, and 32°C) on the mineral composition of xylem sapand the plasma membrane K⁺-Mg⁺⁺-ATPase activities of the roots.Low solution temperature (12°C) lowered the concentrationof NO^–₃ and H₂PO^–₄ in xylem sap of CG plants butnot of FG plants. Concentrations of K⁺, Ca⁺⁺ and Mg⁺⁺ in xylemsap were less affected than anions by solution temperature.The plasma membrane of FG plants grown in 12°C solutiontemperature showed the highest K⁺- Mg⁺⁺-ATPase activity at allATP concentrations up to 3 mM and at low reaction temperatureup to 12°C, indicating resistance of figleaf gourd to lowroot temperature. (Received December 27, 1994; Accepted March 10, 1995)     

Light-induced H+ Efflux from Intact Cells of Cyanidium caldarium

Light-induced pH changes in suspensions of an acidophilic unicellularalga, Cyanidium caldarium Geitler, were studied as a functionof the pH of the medium. In the neutral pH region, alkalizationof the medium due to photosynthetic CO₂ uptake was observed.In the acidic pH region, illumination caused a significant decreasein the pH of the medium, indicating the efflux of H⁺ from thecells. Both the rate and extent of the pH decrease increasedas the pH of the medium was lowered to 3.0. The H⁺ efflux wasnot affected by 3-(3',4'-dichlorophenyl)-l,l-dimethylurea, butwas inhibited by phenylmercuric acetate. The fastest H⁺ effluxoccurred at 45°C, whereas its extent was almost constantfrom 25 to 50°C. The activity decreased at temperaturesabove 50°C and was inactivated completely at 60°C. Itsaction spectrum corresponded the spectrum for chlorophyll aabsorption. Results indicate that the light-induced H⁺ effluxis driven by photosystem I and is important in the maintenanceof the intracellular pH at the functional neutral region againsta steep pH gradient across the cell membrane. (Received May 6, 1981; Accepted August 8, 1981)     

Changes in the Soluble Protein and Free Amino Acid Content of Chill-Sensitive and Chill-Resistant Plants During Chilling and Hardening Treatments

The effects of low temperature (5 °C and 12°C) and droughttreatments on leaf soluble protein content and free amino acidcontent have been investigated in four species, which were rankedaccording to chilling-sensitivity: pea (chill-resistant), mungbean (highly chill-sensitive), and tomato and french bean (intermediatechilling-sensitivity). Drought treatment caused a 30–40% decrease in proteinlevels, and in all but the mung bean, a 100–200% increasein free amino acid concentration. Four days chilling at 5°C,85% r.h. caused leaf water content to decrease by almost 50%in the mung bean, but by only approximately 6–7% in theother three species. During this treatment the leaf solubleprotein content decreased in all four species although the decreasewas greatest and most rapid in the mung bean, commencing with8 h of chilling (coinciding closely with the onset of waterloss), and decreasing by over 80% after 4 d. In the chill-sensitivespecies (but not in the pea) the decrease in protein contentwas accompanied by an increase in free amino acid content. However,on a mgg^–1 dry wt. basis, this increase was insufficientto account for all the protein lost. When plants of each specieswere chilled at 5°C, 100% r.h., water loss was greatly reducedor prevented and there was no significant decrease in leaf solubleprotein. It is concluded that the protein decrease which occurredat 5°C, 85% r.h., was a response to water loss and not thedirect result of low temperature. However, chilling at 100%r.h. did cause an increase in free amino acid content of thechill-sensitive species, suggesting that this was a direct responseto low temperature. Although drought treatment caused a 6–20 fold increasein free proline content in the leaves of the four species examined,chilling (5°C) and chill-hardening (12°C) caused littlechange in free proline content, indicating that the accumulationof this ‘protective’ amino acid is unlikely to contributeto the effectiveness of the chill-hardening treatment. Key words: Low Temperature, Drought, Leaf soluble protein.content, Amino acids     

Use of the Plastochron Index to Evaluate Effects of Light, Temperature and Nitrogen on Growth of Soya Bean (Glycine max L. Merr.)

The plastochron index (PI) has been compared with leaf growthand biomass accumulation in young soya bean plants of severalcultivars that were grown in controlled environments with differentirradiance levels and durations, temperatures, and nitrogen(N) regimes. Increasing the photoperiod from 10 to 16 h day^–1 increasedthe plastochron rate (PR) and the proportion of axillary growth.Doubling the photosynthetic photon flux density (PPFD) to 1000µmol m^–2S^–1, increased PR and the proportionof roots to total plant weight, but decreased the proportionof stems plus petioles to total. In a series of experiments,the plants were grown in an 8 h photoperiod at constant temperaturesof 17, 20, 26 or 32 °C. As temperature increased, PR increased,but the duration of leaf expansion decreased. Leaves were largestat 20 and progressively smaller at 26, 32 and 17 °C. Biomasswas greatest for a given PI at 20 °C and decreased in theorder of 26, 32, and 17 °C. The proportion of axillary growthalso was greatest at 20 °C. When plants were grown in a15 h photoperiod at temperatures from 17.1 to 26.6 °C, leafsize continued to increase up to the highest temperature. At17 °C, the PR in the 15 h photoperiod (PPFD 390 µmol;m^–2S^–1) was about threefold greater than in 8 h(500 µmol m^–2 S^–1); biomass accumulation perday was about fivefold greater. Increasing N from 3 to 36 mMincreased PR about 10 per cent, altered biomass partitioningamong plant parts, and increased the biomass of the plants.The NO₂ form of N markedly stimulated axillary growth as comparedwith the NH₄⁺ form. Environment or cultivar had little influenceon the duration of leaf expansion in terms of PI. Cultivarsdid not differ consistently in biomass production and allocationin the different environments. Glycine max (L.) Merrill, soybean, soya bean, plastochron index, leaf development, growth analysis, partitioning, light, nitrogen, temperature