Physiological Changes in Phaseolus vulgaris in Response to Long-term Ozone Exposure

The effects of ozone on Phaseolus vulgaris cv. Lit were investigatedusing open-top chambers (OTCs) ventilated with charcoal andPurafil filtered air (CF treatments), ambient air (NF treatments)and ambient air to which low, medium or high concentrationsof ozone were added (NFL, NFM and NFH). Ozone additions of 8,16 and 23 nl l^–1 were made during phase 1 of the experiment(0–44 d after emergence, DAE), and additions of 15, 30and 47 nl l^–1 were made during phase 2 (45–99 DAE).Ozone was added to the chambers between 1100 and 1800 h GMT,for 3 or 4 consecutive days each week. The seasonal 7-h meanozone concentrations were 8, 21, 27, 33 and 38 nl l^–1in the CF, NF, NFL, NFM and NFH treatments, respectively. No visible symptoms of ozone injury or significant physiologicalchanges were detected in P. vulgaris during phase I of the experiment.In phase 2, the photosynthesis (Pn) and stomatal conductance(gs) of NFH-plants were inhibited by 73% and 86%, respectively,during ozone exposure, and recovered to pre-exposure valueson the following day. These observations were made prior tothe appearance, 60 DAE, of bronze lesions on the leaves of NFH-plants.The photosynthetic capacity and gs of NFH-leaves decreased asthe severity of ozone injury increased. Rates of weight lossfrom excised leaves also increased with increasing ozone injury.Microscopic investigations of the bronzed regions revealed extensivecellular breakdown, including tonoplast and chloroplast enveloperupture, and the aggregation of the cytoplasmic contents towardsone end of the cell. Severely damaged leaves abscised from the plants, resultingin premature canopy senescence in the NFM and NFH treatments.This, coupled with the lower photosynthetic capacity of existingleaves led to 25 % lower yield in the NFH than the NF treatment(P < 0.05). Phaseolus vulgaris, green bean, ozone, symptom development, photosynthesis, cell ultrastructure     

Effect of Rate of Photosynthesis on the Pattern of Assimilate Distribution in the Graminaceous Plant

Infrared gas analysis and a quantitative radiocarbon tracertechnique were used to measure photosynthesis and the distributionof ¹⁴C-labelled assimilate in Lolium temulentum and a uniculmbarley exposed continuously or intermittently to contrastinglight intensities. Plants grown for 10–20 d in low light(<50 W m^–2 of visible light) exported a greater proportionof their assimilate to growing leaves at the terminal meristemand a smaller proportion to their roots and tillers than equivalentplants in high light (150 W m^–2). A single day's exposure(8.4 h photoperiod) to a contrasting light regime elicited achange in the pattern of assimilate distribution in the samediurnal period, but 2–3 d exposure was required for asubstantial shift in the pattern of supply of assimilate tomeristems. The data indicated that in terms of assimilate distributioncomplete adaption to a new light regime is attained in about7 d.     

Effect of Photoperiod on Growth of Sugar Beet

Sugar beet grown in controlled environments were given similardaily amounts of visible radiation during three different photoperiodtreatments. Plants were given (a) 115 W m^–2 visible irradiancefrom fluorescent and tungsten lamps for 12 h; (b) 88 W m^–2of the same light for 16 h or (c) 115 W m^–2 from fluorescentand tungsten lamps for 12 h extended to 16 h with low intensity(3 W m^–2) incandescent light from the tungsten lamps only.Plant growth was increased similarly in both long day treatments[(b) and (c)] and dry weights were 25 per cent greater thanin the 12 h photoperiod (a) after 6 weeks. Leaf area was increasedby 18 per cent and net assimilation rate by 10 per cent in the16 h photoperiod at 88 W ^m–2 (b). By contrast, extendingthe photoperiod with 4 h of incandescent light (c) triggereda photomorphogenic increase in leaf expansion which increasedleaf area per plant by 47 per cent and leaf-area ratio by 12per cent.     

Differences between Spinach and Kidney Bean Plants in Terms of Sensitivity to Fumigation with NO2

Fumigation of plants of five species with NO₂ in darkness causedvisible injuries to leaves, with the most severe injuries inkidney bean plants and the least severe in spinach plants. Fumigationof these plants in the light caused virtually no visible injuries.NO₂-fumigated leaves accumulated nitrite in the darkness butnot in the light. The level of accumulated NO₂^– was decreasedby light much more rapidly in spinach leaves than in those ofkidney bean, with much less injury to spinach leaves than tothose of kidney bean. A larger amount of NO₂^– accumulatedin the trifoliate leaves of kidney bean plants cultivated withNO₃^– as a main source of nitrogen than in those of plantscultivated with NH₄⁺, and the former plants were more susceptibleto injury from NO₂ than the latter. Administration of NO₂^–to leaves of spinach and kidney bean plants induced the destructionof Chi in the light. The extent of the destruction of Chi wassmaller in spinach than in kidney bean, consistent with theirrespective responses to NO₂. The NO₂^–-induced destructionof Chi was inhibited to some extent by scavengers of free radicals.Activities of superoxide dismutase (SOD) were higher in leavesof spinach than in those of kidney bean. These results indicatethat NO₂^– is the toxic species generated by fumigationwith NO₂ and that spinach has a greater tolerance for NO₂ thankidney bean, probably as a result both of a higher capacityfor reduction of NO₂^– and a higher level of activity ofSOD. (Received June 5, 1991; Accepted January 27, 1992)     

Synchronization of Phosphorylation of a Chloroplast Protein with the Cell Division Cycle in Heterosigma akashiwo

Fumigation of plants of five species with NO₂ in darkness causedvisible injuries to leaves, with the most severe injuries inkidney bean plants and the least severe in spinach plants. Fumigationof these plants in the light caused virtually no visible injuries.NO₂-fumigated leaves accumulated nitrite in the darkness butnot in the light. The level of accumulated NO₂^– was decreasedby light much more rapidly in spinach leaves than in those ofkidney bean, with much less injury to spinach leaves than tothose of kidney bean. A larger amount of NO₂^– accumulatedin the trifoliate leaves of kidney bean plants cultivated withNO₃^– as a main source of nitrogen than in those of plantscultivated with NH₄⁺, and the former plants were more susceptibleto injury from NO₂ than the latter. Administration of NO₂^–to leaves of spinach and kidney bean plants induced the destructionof Chi in the light. The extent of the destruction of Chi wassmaller in spinach than in kidney bean, consistent with theirrespective responses to NO₂. The NO₂^–-induced destructionof Chi was inhibited to some extent by scavengers of free radicals.Activities of superoxide dismutase (SOD) were higher in leavesof spinach than in those of kidney bean. These results indicatethat NO₂^– is the toxic species generated by fumigationwith NO₂ and that spinach has a greater tolerance for NO₂ thankidney bean, probably as a result both of a higher capacityfor reduction of NO₂^– and a higher level of activity ofSOD. (Received October 4, 1991; Accepted January 31, 1992)     

Ineffectiveness of Abscisic Acid in Stomatal Closure of Yellow Lupin, Lupinus luteus var. Weiko III

Stomata of yellow lupin leaves are remarkably insensitive toabscisic acid (ABA). Stomatal resistance was monitored usingboth a viscous now porometer and a diffusion porometer. Resultswere confirmed with scanning electron microscopy. When exogenousABA solutions were supplied via petioles, 10^–6 M solutionshad no effect on stomatal resistance. Upper (adaxial) stomatawere not affected by 10^–5 M ABA but lower stomata showed3-fold more resistance after 2 h. Stomata of both surfaces closedafter 30 min in 10^–4 M ABA. Isolated epidermal peels of lupin leaves were floated on ABAsolutions yet upper surface peels showed no stomatal closingin 10^–4 M ABA, while lower surface stomata closed to abarely significant extent. Stomata of intact leaves were not very sensitive to darkness,showing at most a doubling in resistance after 6 h darkness.Complete stomatal closure, however, was readily produced bywilting leaves. Hence, lupin stomata are physically capableof closing. Endogenous ABA levels of water-stressed leaves increased approximately10-fold, which corresponds to concentrations below 10 µMABA. It is concluded that ABA is unlikely to play a role incontrolling short-term stomatal response of lupins.     

Reactions of birch leaves to changes in light during early ontogeny: comparison between in vivo and in vitro techniques to measure carbon uptake

Trends in several photosynthetic parameters and their responseto changed growth light were followed for 15 d in leaves ofyoung birch saplings using a rapid-response gas exchange measuringequipment. These in vivo measurements were compared to biochemicalassays that were made from the same leaves after the gas exchangestudies. The measurements were made on leaves that were selectedprior to the study and were at that time of similar age. Forthe first 7 d the photosynthetic parameters were followed fromthe growth conditions of moderate light (200 µmol m^–2s^–1; referred to as controls later in the text). On day7 some of the saplings were transferred to grow either underhigh (450 µmol m^–2 s^–1; referred to as highlight plants) or low (75 µmol m^–2 s^–1; referredto as low light plants) light and the capability of the preselectedleaves for acclimation was followed for 6 d. For comparison,at the end of the experiment the measurements were made on bothcontrols and on young leaves that had developed under high andlow light. Generally the in vivo measured rate of CO₂ uptake (gross photosynthesis)both at 310 ppm CO₂ and 2000 ppm CO₂ corresponded very wellto the biochemically determined CO₂ fixation capacity in vitroafter rapid extraction (measured as the initial and total activityof Rubisco, respectively). However, if the flux of CO₂ intothe chloroplasts was limited by the closure of the stomata,as was the case of the high light plants, then the in vitromeasured Rubisco activity was greater than the in vivo measuredCO₂ uptake. V_max, calculated from the mesophyll conductanceat 1% O₂, exceeded the initial activity of Rubisco (assayedat saturating RuBP and CO₂) constantly by 60%. The catalyticactivity of Rubisco in birch leaves was overall very low, evenwhen calculated from the total activity of Rubisco (K_cat 0.63–1.18 s^–1), when compared to herbaceous C₃ species. Signs of light acclimation were not observed in most of thephotosynthetic parameters and in chloroplast structure whenmature birch leaves were subjected to changes in growth lightfor 6 d. However, the change of the growth light either to highor low light caused day-to-day fluctuations in most of the measuredphotosynthetic parameters and in the case of the high lightplants signs of photoinhibition and photodestruction were alsoobserved (decrease in the amount of chlorophyll and increasein chlorophyll a/b ratio). As a result of these fluctuationsthese plants achieved a new and lower steady-state conditionbetween the light and dark reactions, as judged from the molarratio of RuBP to Rubisco binding site. Key words: Acclimation, photosynthesis, light, Rubisco, birch     

Carbon Partitioning in Mature Leaves of Pepper: Effects of Daylength

Grange, R. 1. 1985. Carbon partitioning in mature leaves ofpepper: effects of daylength.—J. exp. Bot. 36: 1749–1759. The partitioning of recently fixed carbon has been examinedin mature pepper leaves grown in 6, 10 or 14 h photoperiodsat different irradiances chosen to give similar radiation integralsand in a 6 h photoperiod at the lowest of these irradiances.The partitioning of carbon into export, starch, sugars and respirationwas followed over the photopenod and the subsequent night ina mature leaf. The maximum export rate during the day (approximately 18 µgC cm^–2 leaf h^–1) was not significantly differentamong the treatments. Net photosynthesis rate was directly relatedto irradiance; the proportion of net photosynthesis exportedduring the day was 33% in 6-h days and 57% in 14-h days. Leafstarch accumulation (as a proportion of net photosynthesis rate)increased slightly when plants were grown in 6-h days. The remobilization of starch and sugars at night allowed exportrates to remain similar over 24 h when plants were grown in10-h or 14-h photoperiods. Leaves grown in 6-h days showed nosignificant changes in export rate during the first few hoursof night but exhausted their starch reserves during the nightand export rates declined. Sucrose and hexose levels decreased at the onset of darkness,but did not fall below 40 µg cm^–2 in plants grownin 10-h or 14-h photoperiods; when this level was reached after3–4 h of darkness, starch breakdown began. In leaves grownin both 6-h treatments, sucrose levels fell below 40 µgcm^–2 when starch reserves were depleted during the nightand the export rate decreased concurrently. The results are discussed in relation to the control of exportand starch metabolism in the leaf. Key words: Pepper, partitioning, daylength     

A Comparative Study of Germination Responses to High Irradiance Light

Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (19–2 mol m^–2 d^–1), medium (9·6mol m^–1 d^–1) and low (2·3 mol m^–2 d^–2) These photon doses have been found by previous workers to inhibitgermination in several species. High and low photon doses wereapplied only as continuous light, but the medium dose was appliedas both continuous light and as a 12 h light/12 h dark photoperiod.All four treatments, plus a dark control, were carried out at15 °C; the high and low doses were also applied with a dailyalternation of 10/20 °C. The majority of species (15) fell into one of two groups. Inseven species germination was relatively high and consistentacross all treatments, including darkness; in the other eightspp germination was inhibited only in darkness. Mostly thesedata confirmed published results for the same species In contrast in Agrostis capillaris and A. stolonifera germinationwas high only at alternating temperatures, irrespective of photondose, but was also slightly promoted by a constant temperaturecombined with light/dark alternations. Only in Bromus sterilisand B. ereclus was germination inhibited by light, in B. erectusat all photon doses and in B. sterilis only at the highest photondose These results suggest that inhibition of germination by highirradiance light is not widespread among native British species Aira caryophyllea, Arrenatherum elatius, Festuca ovina, F. rubra, Hordeum murinum, Milhim effusum, Silene dioica, Achillea millefolium, Brachypodium syhaticum, Digitalis purpurea, Holcus lanatus, Leucanlhemum vulgare, Phleum pratense, Poa trivialis, Taraxacum officinale, Agrostis capillaris, A. stolonifera, Bromus erectus, B. sterilis, seed, dormancy, germination, light, High irradiance reaction, alternating temperatures, photoperiod     

The Relationship between Sucrose and Starch during 'Dark' Export from Leaves of Uniculm Barley

Uniculm barley plants were grown in 8 h photoperiods at a quantumflux density of 655 µE m^–2 s^–1. Groups ofplants were transferred to four different light environmentsfor one 8 h photoperiod (106, 270, 665, and 975 µE m^–2s^–1) and harvested at intervals throughout the succeedingdark period for subsequent carbohydrate analysis of the youngestmature leaf. Sucrose was the predominant carbohydrate in the leaves (attaininga level of c. 100 mg dm^–2 after 8 h at 975 µE m^–2s^–1) but starch was also of significance (20 mg dm^–2after 8 h at 975 µE m^–2 s^–1). During the dark period, following a photoperiod at the threehighest light levels (270, 665, and 975 µE m^–2 s^–1),sucrose was exported first while the starch level remained fairlyconstant. When the-sucrose level fell to 15–20 mg dm^–2starch degradation began. This critical sucrose level was reachedearlier in those plants subjected to lower quantum flux densitiesduring the preceding photoperiod. The delay in the remobilizationof starch suggests an important regulatory mechanism which maybe dependent upon the sucrose level. At 106 µE m^–2s^–1 the sucrose level rose to only 10 mg dm^–2. Herethere was no discernible delay in the depletion of sucrose orstarch.     

The Effects of Light Intensity at Different Stages in Flower Initiation and Development of Chrysanthemum morifolium

Rooted chrysanthemum cuttings were raised in growth cabinetsat a ‘standard’, constant light level of 125 J cm^–2day^–1 and were induced to flower by giving daily cyclesof 8 h light followed by 16 h of uninterrupted darkness. Sampleswere transferred at weekly intervals to either a higher lightlevel of 375 J cm^–2 day^–1 or a lower light levelof 31 J cm^–2 day^–1 where they remained for 2 weeksbefore they were returned. It was shown that receptacle formationnormally began in the second week of inductive short-days (short-days8–14) and floret initiation in the third week (short-days15–21) when plants were grown throughout in the standardenvironment Receptacle formation was delayed and significantlymore leaves were formed below the flower if short-days 8–14were spent in low light. Transfer to high light for this periodhad no apparent effect Transfer to low light at the onset offloret formation retarded their further development and reducedthe total number of florets formed Transfer to high light atthis stage slightly increased the number of florets formed butdid not appear to affect their development. The data for stageof flower development after 11 weeks of growth reflected theseeffects of light level on the early development of the apex The total and flower dry weights of plants transferred to lowlight for 2 weeks were generally smaller than those of plantswhich had remained throughout in the standard condition Highlight only produced lasting increases in weight when the transferswere made during the later stages of growth. Most of the additionaldry matter formed at this time was accounted for in increasedflower weight The correlation between flower development andflower weight ratio previously found under constant environmentsalso applied to transferred plants except when the light levelwas changed for the last 2 weeks of growth; relatively highvalues of flower weight ratio were then obtained by transferto high light and relatively low values by transfer to low light.     

The Effect of Current Photosynthesis on the Origin of Translocates in Old Tomato Leaves

The rate of carbon transport from an old tomato leaf (54 days),grown at 80 W m^–2, was measured under light flux densitiesbetween 7 and 90 W m^–2. Under low light, the rate of carbontransport over a 6 h period was about 1 mg C dm^–2 h^–1,well in excess of the concurrent photosynthetic rate. The lossfrom these leaves of ¹⁴C-leaf assimilate which was fixed beforethe experimental period amounted to 62 per cent of the totalinitial uptake and was higher than that from leaves with higherconcurrent photosynthetic rates. The higher loss of ¹⁴C fromleaves with low photosynthetic rates was due to a greater contributionof ¹⁴C from the starch and residue fractions. The rate of transportappeared to be determined by the concentration of the labilesucrose, not the total sucrose concentration. In comparisonwith young fully-expanded tomato leaves (Ho, 1976) the sizeof the labile sucrose pool appeared to decrease with age. Thephotosynthesistranslocation coefficient was low (k₁k₂=0•21)for an old tomato leaf. Based on these results a scheme of carbonpartitioning in relation to translocation is proposed. Criteriafor assessing the efficiency of translocation in leaves arediscussed.     

Effects of Cytokinin and Several Inorganic Cations on the Polyamine Content of Lettuce Cotyledons

Kinetin (4.7 x 10^–5 M) and 6-benzyladenine (2.22 x 10^–5M) were found to increase ca. 2-fold the putrescine contentin cotyledons of lettuce (Lactuca sativa L.) seedlings grownfor 3 days under fluorescent light. On the other hand, severalinorganic ions (K⁺, Na⁺, Ga⁺⁺, Mg⁺⁺) at a concentration of 3x 10^–2 M reduced the putrescine content. The combinationof kinetin with one of several inorganic ions at the same levelmarkedly increased the spermine content, but the putrescinecontent decreased; calcium and magnesium ions were less effective.The physiological significance of these findings is discussed. (Received July 4, 1982; Accepted November 6, 1982)     

Carbon Partitioning and Export in Mature Leaves of Pepper (Capsicum annuum)

The partitioning of recently fixed carbon by mature pepper leaveshas been examined over a 10 h photoperiod using a constant specificradioactivity ¹⁴CO₂ labelling technique. Changes in the ratesof carbon partitioning into export, starch, sucrose and hexoseswere examined following changes in irradiance during the photoperiod.Leaves grown under 80 W m^–2 PAR were exposed to this irradiancefor the first 4 h of the photoperiod then the iiradiance wasdecreased. Leaves accumulated sufficient reserves in the first4 h to maintain export at the initial rate (approximately 20µg carbon cm^–2 leaf h^–1) over the following6 h of the photoperiod when the net photosynthesis rate (Pn)was decreased to 10% of the initial rate by the decreased irradiance.Export was initially maintained by the depletion of sucroseand hexose and then by carbon from the degradation of starchin the light. If leaves were exposed to low irradiance at the beginning ofthe photoperiod, then the export rate was linearly related tothe Pn during that period. When Pn exceeded that required tomaintain an export rate of approximately 20 µg carboncm^–2 h^–1, then more carbon was partitioned intostarch. At low initial irradiance, a greater proportion of photosynthatewas partitioned into export rather than starch and at high initialirradiancc the reverse occurred. There was a linear relationship between starch accumulationrate and Pn for all leaves but the relationship between Pn andexport rate was only significant for leaves with low levelsof reserve carbon. The results show that mature pepper leaves subjected to differentirradiances maintain constant export rates through alterationsof carbon partitioning. Export at low Pn is maintained at theexpense of sugar and starch reserves, with partitioning in highirradiance being predominantly to starch. Key words: Carbon partitioning, Starch, Export, Pepper (Capsicum annuum L.)     

The Response of Bean Plants to UV-B Radiation Under Different Irradiances of Background Visible Light

Plants of Phaseolus vulgaris L. (cv. Stella) were grown in controlledconditions under three different irradiances of visible lightwith or without UV-B (280–320nm) radiation. The biologicallyeffective UV-B radiation (UV-B_BE) was 6.17 kJ m^–2 d^–1,and simulated a c. 5% decrease in stratospheric ozone at 55.7?N,13.4?E. The photon flux densities of the photosyntheticallyactive radiation (PAR, 400–700 nm) were either 700 µmolm^–2–1 (HL), 500, µmol m^–2 s^–1(ML) or 230 µmol m^–2 s^–1 PAR (LL). Under highlight (HL) conditions plus UV-B radiation, bean plants appearedmost resistant to the enhanced levels of UV-B radiation, andresponded only by increasing leaf thickness by c. 18%. A smallincrease in UV screening pigments was also observed. Both thelower irradiances (ML and LL) increased the sensitivity of theplants to UV-B radiation. Changes in leaf structure were alsoobserved. Photosystem II was inhibited under ML and LL togetherwith UV-B radiation, as determined by Chi fluorescence inductionand calculation of the fluorescence half-rise times. Leaf reflectivitymeasurements showed that the amount of PAR able to penetrateleaves of UV-B treated plants was reduced, and that a possiblecorrelation may exist between the reduced PAR levels, loss ofChi and lowered photosynthetic activity, especially for LL +UV-Bgrown plants, where surface reflection from leaves was highest.Changes in leaf chlorophyll content were mostly confined toplants grown under LL + UV-B, where a decrease of c. 20% wasfound. With regard to protective pigments (the carotenoids andUV screening pigments) plants subjected to different visiblelight conditions responded differently. Among the growth parametersmeasured, there was a substantial decrease in leaf area, particularlyunder LL + UV-B (c. 47% relative to controls), where leaf dryweight was also reduced by c. 25%. Key words: Chlorophyll fluorescence induction, bean, flavonoids, Phaseolus vulgaris, reflectance, UV-B radiation     

Promotion by gibberellin of lettuce seed germiation as a function of presoaking period

Germination of lettuce seeds (Lactuca sativa L. cv. Grand Rapids)was examined in the presence of various doses (10^–5.0–10^–3.0M) of gibberellic acid applied at various times (hour 0–8)of soaking. Germination promotion by gibberellic acid was greateras the dose of gibberellic acid was increased and attenuatedwith the length of the presoaking period. As an exception, ca.95% germination was always evoked by the largest dose (10^–3M) of gibberellic acid given at any time of soaking. The dose-responsecurve obtained for each presoaking period had a distinct sigmoidalprofile. Synergistic and photoreversible promotion by red light of thegibberellin-induced germination was also investigated. Far-redlight pulse given 6 hr after the red pulse was still effectivein removing the red light action. Application of enzyme kineticsto the gibberellin action and also to the synergism betweengibberellin and red light was suggested. ¹National Institute for Basic Biology, Myodaiji, Okazaki 444,Japan. (Received December 18, 1979; )     

DNA Levels in Dividing and Developing Plastids in Expanding Primary Leaves of Avena sativa

The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (40–45 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 10^–15 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 10^–15g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 10^–12g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA     

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)     

Light affects the flux of Ca2+ from excised tomato leaves within four seconds

The flux of Ca²⁺ from excised tomato leaves, conditioned in100 mM KCI for 60 min, was shown to be affected by turning anincandescent light (32 µmol m^–2 s^–1) on oroff. Calcium concentrations were measured with a single junctioncombination electrode connected to a high impedence electrometeramplifier interfaced with a microcomputer. Net Ca²⁺ fluxes fromexcised leaves 30 s prior to and 30 s after turning on the lightwere 68 and 122pmol g ^–1 dry weight s ^–1 respectively.The Ca²⁺ fluxes for the 30 s prior to and 30 s after turningoff the light were 113 and 51 pmol g^–1 dry weight s^–1respectively. Close examination of the first 10 s after thelight was turned off showed that there was a 4 s delay in theflux of Ca²⁺ . The heat given off by the incandescent bulb hadno effect on Ca²⁺ flux during these short time periods. Theeffect of light on the Ca²⁺ flux was evident for at least 2h after the initial treatment. Key words: Ca²⁺, signalling, light, tomato     

Somatic Embryogenesis and Analysis of Peroxidase in Cultured Lettuce (Lactuca sativa L.) Cotyledons

Somatic embryos were induced in lettuce cotyledons culturedon Murashige and Skoog's (MS) medium containing either 2 mgl^–1 6-benzylaminopurine (BA) and 0.2 mg l^–1 naphthaleneaceticacid (NAA) or 0.2 mg l^–1 BA and 2 mg l^–1 NAA. Bothcombinations induced a frequency of over 70%. The explants culturedonly in the presence of 2,4-dichlorphenoxyacetic acid (2,4-D)did not produce somatic embryos. The development of the embryoidswas studied histologically and by scanning electron microscopy.Peroxidase activity was assayed and the isoenzyme pattern ofcalluses was determined by polyacrylamide gel electrophoresis.Callus from an embryogenic line showed a much higher peroxidaseactivity than that from a non-embryogenic line, one extra peroxidaseisozyme band being present and typical of the embryogenic callus.No qualitative differences were detectable between the embryogeniccalluses. Lactuca sativa L, lettuce, somatic embryogenesis, peroxidases, isoenzymes