Translocation of Calcium in Relation to Tomato Fruit Growth

Regulation of the uptake and distribution of calcium in thetomato plant was investigated in plants grown in recirculatingnutrient solutions at electrical conductivities of 2,7,12 and17 millisiemens (mS). Despite an increased calcium content inthe nutrient solution at high conductivity (7–17 mS),the accumulation of calcium by fruit was progressively reducedby increasing salinity, particularly in the distal half. Theincidence of blossom-end rot in fruit (BER) also increased withsalinity. The uptake of water and ⁴⁵Ca by plants was substantially reducedin the high salinity treatment (17 mS) and, to a lesser extent,by high relative humidity (90 per cent r.h. at 20 °C). Further,the translocation of ⁴⁵Ca from roots to shoots was reduced byhigh salinity, while the percentage distribution of ⁴⁵Ca tothe apex was reduced by high humidity. Only approx. 2 per centof the ⁴⁵Ca taken up by a plant was imported by the truss. The uptake of ⁴⁵Ca and its distribution among pedicel, calyxand berry by detached fruit in 24 h showed that fruit from highsalinity plants had a reduced uptake and a lower accumulationof ⁴⁵ Ca in the berry than in the calyx. In addition, plants grown at high conductivity had a lower rateof xylem sap exudation from decapitated plants. The fruit ofthese plants had a smaller xylem cross-sectional area in thefruit pedicel and a smaller calyx than those of the low conductivitytreatment. Calcium, translocation, tomato, fruit, blossom-end rot     

Regulation of the Partitioning of Dry Matter and Calcium in Cucumber in Relation to Fruit Growth and Salinity

The regulation of the partitioning of dry matter and calciumin relation to fruit growth was investigated in cucumber plantsgrown in the salinity range of 3-8 mS cm^-1 in NFT (NutrientFilm Culture), with or without a fruit pruning treatment. Thedry weight gain of the plants was proportional to the outdoorintegral irradiance, with a common daily rate of 1 g MJ^-1 m^-2in two crops grown under summer (18 MJ m^-2 d^-1) and autumn (7MJ m^-2 d^-1) conditions. Within the salinity range studied, thereduction of plant dry weight was 9% mS^-1 cm^-1. However, fruitdry weight was only reduced at salinities above 5·5 mScm^-1, although the daily dry matter accumulation by fruit, asa percentage of total dry matter accumulation, was increased.Salinity reduced the dry matter accumulation in the young shootproportionally more than in the fruit. Although the total plantCa content was reduced by 13% mS^-1 cm^-1, the Ca content of theyoung shoot was reduced by 16·6%, compared to 11% inthe fruit. Pruning fruit reduced neither plant dry weight norCa uptake. The growth of the remaining fruit, and to a lesserdegree of the young shoot, accounted for all surplus assimilates.Thus, fruit were the dominant sinks for assimilates whilst themature leaves were the strongest sinks for Ca. Nevertheless,the fruit sustained the capacity to import Ca better than theyoung shoot, when supplies of both assimilates and Ca were reducedby high salinity.Copyright 1994, 1999 Academic Press Cucumber, Cucumis sativus L., salinity, fruit pruning, dry matter and calcium     

Uptake and Transport of Calcium and the Possible Causes of Blossom-end Rot in Tomato

The possible causes of blossom-end rot (BER) in tomato fruitwere investigated by comparing the uptake of calcium by theroots, the distribution of ⁴⁵Ca within the fruit and the vascularbundle network in the fruit of susceptible cultivars (Calypsoand Spectra) with those of a less susceptible cultivar (Counter)grown in a range of salinities (electrical conductivity of 5,10 and 15 mS cm^–1). The daily calcium uptake rates at5 mS cm^–1 as estimated from the xylem exudation of thedecapitated stem stump in young plants of Calypso and old plantsof Spectra, were lower than that of Counter. The uptake of ⁴⁵Caby, and the transport to, the distal part of the detached fruitof susceptible cultivars, especially Calypso, were less thanin Counter at 10 mS cm^–1. The number of vascular bundlesin both proximal and distal fruit tissues was similar in allcultivars and was only slightly reduced by salinity. However,the number of bundles containing lignified xylem vessels, asdetected by safranin staining, was reduced substantially bysalinity, particularly in Calypso. The estimated area of thefruit tissue served by individual xylem bundles in the BER susceptiblefruit grown at high salinity was greater than in Counter. Theincidence of BER in all trusses was linearly related to theproduct of average daily irradiance and daily temperature throughoutthe year. Temperature appears to be the major environmentalfactor which induces BER, regardless of cultivars and salinitytreatment. The most likely causes of BER in susceptible cultivarsare the interactions of (a) light and temperature on fruit enlargement,(b) inadequate xylem tissue development in the fruit and (c)competition between leaves and fruit for the available Ca. Key words: Lycopersicon esculentum, calcium transport, susceptibility to blossom-end rot, root exudation, xylem     

Diurnal regulation of NO3-uptake in soybean plants II. Relationship with accumulation of NO and asparagine in the roots

Experiments were performed with soybean plants to test the hypothesisthat the inhibition of NO₃^– uptake in darkness is dueto feedback control by NO₃^– and/or Asn accumulating inthe roots. Xylem export of N compounds was shown to depend onwater flux in both excised root systems and ¹⁵N-labelled intactplants, suggesting that the shortage of transpiration in darknessmay be responsible for the retention of NO₃^– and Asn inthe roots. This was verified in experiments where the light/darkpattern of transpiration was modulated in intact plants by changingthe relative humidity of the atmosphere. Any decrease of transpirationat night was associated with a concurrent stimulation of NO₃^–and Asn accumulations in the roots. However, the light/darkrhythmicity of NO₃^– uptake was only marginally affectedby these treatments, and thusappeared quite independent fromtranspiration and root NO₃^– or Asn levels. Typically,the maintainance of a constant transpiration during the day/nightcycle did not suppress the inhibition of NO₃^– uptake indarkness, whereas it almost prevented the dark increase in rootNO₃^– and Asn contents. These data strongly support theconclusion that the effect of light on NO₃^– uptake isnot mediated by changes in translocation and accumulation ofN compounds. Key words: Glycine max, light/dark, cycles, nitrate uptake, transpiration, transport of N compounds, accumulation of N compounds     

Effects of Diurnal Changes in the Salinity of the Nutrient Solution on the Accumulation of Calcium by Tomato Fruit

Tomato fruit grown in diurnally fluctuating salinities (8 mScm^–1 during the day and 3 mS cm^–1 at night; 8/3mS cm^–1), accumulated the same amount of dry matter andmagnesium (Mg) as those in constant 3 or 8 mS cm^–1, butan intermediate amount of calcium (Ca). Raising the salinityof the nutrient solution by enriching with macronutrients orby adding NaCl had similar effects. The uptake of ⁴⁵Ca by tomato plants during the day was greaterthan at night and was reduced by salinity in both periods. Whilethe uptake of ⁴⁵Ca by 8/3 mS plants at night was similar tothat of 3 mS plants, the daily uptake was less than that in3 and 5.5 mS plants. The Ca content of tomato fruit increased with truss number at3 and 5.5 mS cm^–1 but not at 8/3 and 8 mS cm^–1.Within the same truss, the distal fruit had a lower Ca contentbut higher Mg content than the proximal fruit. The reductionin Ca content of the distal fruit at 8/3 mS cm^–1 was similarto that at 5.5 mS cm^–1. The Ca content of the tissue atthe distal end of the 8/3 mS fruit was lower than that of the5.5 mS fruit. Similarly, the distribution of ⁴⁵Ca to the distalhalf of the detached 8/3 mS fruit was less than that of 5.5mS fruit. A reduced uptake and inadequate distribution of Cato the truss and to the distal end of the 8/3 mS fruit werethe main causes of these differences. Lycopersicon esculentum(Mill.), tomato, fruit, calcium, magnesium, diurnal salinity     

Distribution of 14C Assimilates in the Cowpea (Vigna unguiculata L.) in Relation to Fruit Abscission and Treatment with Benzyladenine

The distribution of ¹⁴C assimilates from ¹⁴C-sucrose was studiedin relation to premature fruit abscission in two cowpea cultivars,Adzuki and Mala. In both cultivars most of the radioactivitywas recovered in the fruits, constituting 63–85 per centof the total ¹⁴C imported from the fed leaflet. This was followedby the root, leaves and stem in descending order, except thatin Mala, import by the stem was greater than that by the leaves.Adzuki imported 56 per cent more ¹⁴C than Mala, from the fedleaflet. In Adzuki, which exhibits a relatively low degree ofabscission of young fruits, the ratio of ¹⁴C accumulated bypeduncle 1 (oldest) fruits to that of peduncle 3 (youngest)fruits was 0·31; while in Mala it was 0·61. Ratiosof the combined accumulation by peduncles 1 and 2 fruits topeduncle 3 fruits were 0·81 for Adzuki, and 1·88for Mala. The more mature fruits of Mala thus constituted amore potent sink for ¹⁴C assimilates than those of Adzuki. In Adzuki, benzyladenine treatment of young fruits at each pedunclewas not significantly effective in reversing or modifying thenormal gradient of assimilates in fruits of different ontogeny.However, in Mala, BA treatment of the youngest fruits caused43 per cent increase in ¹⁴C import, when compared with correspondingfruits of control plants. In Adzuki, BA had no significant effecton total fruit weight, whereas in Mala the weight was increasedby about 36 per cent.     

Effect of Day Length and Night Temperature on Starch Accumulation and Degradation in Soybean

The effect of the day length on the accumulation and the degradationof the starch in leaf, stem and root tissues of prefloweringsoybean plants was determined by growing plants under a 7 or14 h light regime. As has been reported previously, the rateof starch accumulation by leaves was inversely related to daylength. High sucrose content was associated with a high rateof starch accumulation. Stem tissue showed diurnal fluctuationsin starch content and the rate of accumulation was also inverselyrelated to day length. This starch resulted from photosynthesiswithin the stem itself. A negligible amount of starch was foundin root tissue of both sets of plants. The rate of starch breakdown in leaves of 7 h plants was significantlyless than that in 14 h plants. Nevertheless, leaf starch inshort day length plants was depleted at least 4 h prior to theend of the dark period. In both sets of plants, degradationof stem starch started simultaneously with that in the leavesand continued throughout the dark period, although at a muchlower rate than that of leaves. Thus, stem starch acted as abuffer once leaf starch was depleted, providing carbohydratesto the plant, although in small quantities. To determine if soybean leaves adjust their rate of starch accumulationduring the light period to different dark period temperatures,plants were grown under temperature regimes of 30/20 ^°Cand 30/30 ^°C. Plants did not differ in rate of starch accumulationor CO₂ exchange rate, but did show large differences in growthcharacteristics. High temperature plants had significantly greaterleaf area and tended to have greater leaf area ratio. Thus,despite similar rates of starch accumulation on a leaf areabasis, high temperature plants accumulated greater amounts ofstarch on a per plant basis. Glycine max(L.)Merr., soybean reserve carbohydrates, remobilization, source-sink realtionships     

Nitrate Accumulation and its Relation to Leaf Elongation in Spinach Leaves

The leaf elongation rate (LER) of spinach leaves during theday was twice that during the night when grown at a photon fluxdensity of 145 µmol m^–2 s^–1. All leaves showedthe same LER-pattern over 24 h. Due to low turgor, LER was lowin the afternoon and in the first hours of the night until wateruptake restored full turgor. Osmotic potential remained constantdue to increased nitrate uptake and starch degradation in thisperiod. LER increased to high rates in the second part of thenight and in the morning. The lower rate in the dark comparedto the light was not caused by the lower night temperatures,as increased photon flux density during growth resulted in equalrates in the light and the dark. Increased relative humiditydecreased LER and afternoon rates were most sensitive to waterstress. A ‘low light’ night period did not changeLER-pattern during the night or on the following day. We concludethat nitrate is not an obligatory osmoticum during the nightand can be exchanged for organic osmotica without decreasingLER. During the night the turgor is first restored by increasingwater uptake, nitrate uptake and starch degradation. This resultedin increased leaf fresh weight in this period. Thereafter, elongationincreased by simultaneous uptake of nitrate and water. Nitrateconcentration was, therefore, constant in the older leaves.In the younger leaves nitrate concentration increased to replacesoluble carbohydrates. The vacuoles of the old leaves were filledwith nitrate before those of the young leaves. Key words: Spinacia oleracea L., nitrate accumulation, osmotic potential, organic acids     

Induction of Light Dependent Pyruvate Transport into Chloroplasts of Mesembryanthemum crystallinum by Salt Stress

Mode of photosynthesis in Mesembryanthemum crystallinum changesfrom C₃ to Crassulacean acid metabolism (CAM) when the plantswere stressed with high salinity. [¹⁴C]Pyruvate uptake for 30s into intact chloroplasts isolated from leaves of the CAM modeof M. crystallinum was enhanced more than 5-fold in the lightcompared with that in the dark. The stromal concentration ofpyruvate in the light reached to more than 2.5 times of themedium. In contrast, little or no pyruvate uptake occurred inchloroplasts from C₃ leaves in either light or dark condition.The initial uptake rate (10 s incubation at 4°C) into theCAM chloroplasts in the light was about 3-fold higher than therate in the dark. K_m and V_max of the initial uptake in the lightwere 0.54 mM and 8.5 µmol (mg Chl)^–1 h^–1 respectively.These suggest that pyruvate was actively incorporated into theCAM chloroplasts against its concentration gradient across theenvelope in the light. When hydroponically grown M. crystallinumwere stressed by 350 mM NaCl, the capacity of chloroplasts forpyruvate uptake was induced in 6 d corresponding to the inductionof the activities of PEP-carboxylase and NAD(P)⁺-malic enzymesin response to salt stress. (Received October 12, 1995; Accepted January 19, 1996)     

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     

The Diurnal Pattern of Nitrate Uptake and Reduction by Spinach (Spinacia oleracea L.)

Spinach plants were grown in bowls of aerated nutrient solutionin a controlled environment chamber for 24 h, and harvestedevery 3·5-5 h to record their growth, nitrate and wateruptake, and plant nitrate concentration. Twelve such experimentsare described, either with a 14/10 h dark/light regime, or continuouslight or darkness. The irradiance was either 110, 320, or 510µmol m^-2 s^-1 (PPFD). All these regimes began at the endof the light period of a 14/10 h dark/light regime (510 µmolm^-2 s^-1) lasting approximately 2 weeks. Nitrate uptake rate per g of dry weight of plant continued almostunabated at about 17 µmol h^-1 through the initial 14-hdark period, and then fell away sharply if the light was notrestored, but increased slightly when it was. With continuouslight at 510 µmol m^-2 s^-1, uptake rate rose steadily forthe first 24 h of light, and then fell sharply for about 6 h.Shoot nitrate concentration increased about three-fold in thedark phase, and declined in the light at a rate which was positivelyrelated to the irradiance. Root nitrate concentration was severaltimes higher than that of the shoot: its diurnal change wassmaller (relative to the mean) than that of the shoot. Nitratereduction occurred to a small extent in the dark, and increasedrapidly as soon as the lights came on, to remain at a roughlyconstant rate (related to the irradiance) throughout the lightphase. Dry matter increase in the light was related to irradiance,but with little increase above 320 µmol m^-2 s^-1. Respiratoryweight loss in the dark was not detectable. Rate of fresh weightincrease was approximately constant throughout light and darkperiods. The results compare quite well with the predictions of a simplesimulation model, based on the pump/leak principle.Copyright1994, 1999 Academic Press Spinacia oleracea, nitrate, uptake, reduction, influx, efflux, diurnal, regulation, model, simulation     

Effects of Cycloheximide and Light on Leaf Senescence in Maize and Hydrangea

The senescence of maize and hydrangea leaves after detachmentand darkening was studied in terms of the loss of chlorophylland protein. Chlorophyll contents of the detached leaves decreasedin the dark in both plants. Cycloheximide at 0.1 mM effectivelyinhibited the loss of chlorophyll in maize, but did not do soin hydrangea. Continuous irradiation with white light of 4.6Wm^–2 prevented the loss of chlorophyll in hydrangea leaves,while it caused bleaching of maize leaves. Reducing agents suchas ascorbic acid and glutathione did not prevent the bleachingby light. In maize leaves, the amount of protein decreased inthe dark more slowly than that of chlorophyll, and cycloheximideslightly prevented the protein decrease. Continuous light irradiationof 4.6 Wm^–2 delayed the loss of protein more effectivelythan cycloheximide did. (Received January 31, 1981; Accepted May 21, 1981)     

Some Effects of Light Intensity, Daylength and Temperature on Growth of Fruiting and Non-fruiting Watermelon (Citrullus lanatus)

Plants of watermelon [Citrullus lanatus(Thunb.) Matsum. &Nakai, cv. Early Yates] were grown for up to 3 months aftergermination in controlled environment cabinets, and variousaspects of vegetative growth and fruit development were measured.Effects of light intensity were studied by comparing growthat 8, 16 and 32 klx at constant temperature and daylength (25^°C, 14 h). Effects of daylength were studied by comparing8, 14 and 24 h at constant light intensity and temperature (32klx, 25 ^°C), and effects of tem perature were studied bycomparing 20^°, 25^°, 30^°, 35^° and 40 ^°C atconstant light intensity and day- length (32 klx, 14 h). Withincreasing light intensity and daylength lateral growth waspromoted whereas main shoots were less affected. Increase intemperature above 25 ^°C resulted in longer main shoots andprolific lateral growth, due both to more and to longer laterals.Environmental differences had little effect on internode lengthbut did affect the size of basal leaves. However, an increasein total leaf area at higher temperatures or with Continuouslight was mainly due to more leaves rather than larger leaves.The presence of developing fruit greatly reduced vegetativegrowth of plants. Main shoot length, lateral growth, numberof leaves, and even size of individual leaves, were all reduced.This reduction did not apply to d. wt of whole plants. Fruitingplants were very efficient, on a leaf area basis, in accumulatingd. wt. At 25 ^°C at the two higher light intensities with14 h days the presence of one developing fruit was inhibitoryto the setting of any subsequent fruit. With short days or lowlight, more fruits were set but they were small. With continuouslight or high temperature more than one fruit could developand they were large.     

Carbon Dioxide Exchange of Developing Apple (Malus pumila Mill.) Fruits

The carbon dioxide exchange of developing apple fruits was monitoredduring development. The results of measurements on detachedfruits in the laboratory were consistent with those made onattached fruit in the field. Respiration rate at 20 °C inthe dark declined from 120 ng CO₂ g^–1 fr. wt. s_–1on 5 June (4 weeks after full bloom) to less than 3 ng g^–1fr. wt. s^–1 by late September. In the light, net CO₂ evolutionwas much decreased, but on no occasion did photosynthesis exceedrespiration and no net CO₂ uptake was detected. The Q₁₀ fordark respiration over the interval from 15 to 25 °C changedfrom 2.8 in early June to 1.6 in early August     

The Effects of {delta}-Aminolevulinic Acid and Inhibitors of RNA and Protein Synthesis on Phytochrome Mediated Chlorophyll Accumulation in Sorghum bicolor

In 5-d-old etiolated seedlings of Sorghum bicolor, 12 h of darknessafter 5 min in red light eliminated a lag before the accumulationof chlorophylls in subsequent continuous white light. Increasingthe dark period to 24 h and 36 h, increased the rate of chlorophyllaccumulation in the later stages of greening. Exogenous -aminolevulinicacid neither completely removed the lag, nor increased the rateof chlorophyll accumulation. Cycloheximide (25 µg ml^–1)and 6-methyl purine (5.0 µg ml^–1), given continuouslyor only until the 12 h dark period following the red light irradiation,restored the lag and decreased the rate of chlorophyll accumulation.D-threo-chloramphenicol (400µg ml^–1) also decreasedthe rate of chlorophyll accumulation but did not restore thelag. Addition of these inhibitors even 12 h after red lightirradiation decreased the rate of chlorophyll accumulation.Rifampicin (Rifamycin SV, 400 µg ml^–1) did not havesuch effects. Key words: Chlorophylls, Phytochrome, -Aminolevulinic acid, Sorghum bicolor     

佛手山药组织培养的研究

以佛手山药块茎、叶片、茎段为外植体, 探讨了其组织培养技术。结果表明：块茎培养以暗培养MS+6-BA1.0 mg·L^-1+NAA0 1 mg·L^-1效果较好;叶片诱导的适宜培养基为MS+ 6-BA0.5～1.0 mg·L^-1+NAA2.0 mg·L^-1, 暗培养;茎段培养都是光培养,无节茎段以MS+6-BA1.0 mg·L^-1+NAA0.5 mg·L^-1较好;带节茎段的初代培养则以MS+6-BA0.5～1.0 mg·L^-1+NAA0.1 mg·L^-1效果较好,继代增殖培养基为MS+6-BA0.5 mg·L^-1+NAA0.1 mg·L^-1,生根培养基为1/2MS +NAA0.5 mg·L^-1。     

Alteration of the Pattern of Distribution of Photosynthetic Products in the Tomato by Manipulation of the Plant

To increase the proportion of photosynthates exported from tomatoleaves and to examine how far the subsequent distribution islinked with the activity of physiological sinks two types ofprocedures were used. In the first experiment the number ofsources of photosynthates was reduced by removing leaves orexcluding light from them and the growth of the fruit increasedby applying growth regulators. By this means a 30–50 percent increase in the export of radio-active photosynthates inthe first 24 h from a test leaf exposed to ¹⁴CO₂ was recorded.The enhanced activity of the sinks induced by growth regulatorsalthough increasing the amount of ¹⁴C material leaving a leafdid not increase the proportion of the exported fraction whichentered the fruit. In contrast a reduction in the number ofphotosynthetic sources increased both the absolute and relativeamounts entering the fruit from the treated leaf. In the second experiment grafts were made between potato andtomato in both directions. When the potato was the rootstockboth tomato and potato leaves exposed to ¹⁴CO₂ exported a higherproportion of the radioactive assimilates than when the tomatowas the rootstock. Movement was greater from scion to root-stockthan vice versa. The results are discussed in the context of fruit productionby the tomato and the extent to which yield of fruit is determinedby internal factors.     

Anatomy and Transpiration of the Avocado Inflorescence

Structure and function of the inflorescence of cv. 'Hass' and'Fuerte' avocado (Persea americana Mill.) were examined by scanningelectron microcopy (SEM) and by porometry. Sepals and petalscould not be distinguished by their position in the flower,by visual gross morphology or by microscopic surface structureand were hence designated as tepals. These tepals were arrangedin two whorls of three, followed by two whorls of three outerand three inner stamens, each opposite a tepal. The most conspicuousfeature of tepals, developing leaves and peduncles was the densecover of hair which were most frequent on the adaxial tepalsurface (925-1200 trichomes mm^-2), followed by their abaxialsurface (625-1000 mm^-2) and peduncles (375-655 mm^-2). Stomatawere absent from the adaxial surfaces of both tepal and leaves,as well as peduncles. On the tepals, abaxial stomata appearedfunctional, small (8-9 x 11-13 µm) and scarce with 2·8-3·4stomata mm^-2, i.e. very low relative to avocado leaves (350-510stomata mm^-2) or young fruit (50-75 stomata mm^-2. However, flowersincluding tepals transpired 1·2-1·3 mmol underfield conditions in Southern California (1·6-2 kPa),i.e. in excess of leaves (0·7-1·1 mmol) and peduncles(0·6-0·8 mmolH₂O m^-2 s^-1). This situation wasattributed to the few small but functional abaxial stomata onthe tepal, in contrast to 80% closed stomata and dense epicuticularwax cover in form of rodlets on young and dendritic crystalson old leaves including the guard cells, and absence of stomatafrom the peduncle.Copyright 1993, 1999 Academic Press Persea americana Mill., avocado, bioenergetics, flower, fruit, leaf, peduncle, scanning electron microscopy, stomata, transpiration, petals, sepals, tepals     

Diurnal Changes in Asparaginase Activity in Pea Leaves: I. THE REQUIREMENT FOR LIGHT FOR INCREASED ACTIVITY

During the growth of leaves of Pisum sativum L., levels of asparaginase(E.C. 3.5.1.1 [EC] ) showed a diurnal variation during a 3 d periodof leaf expansion, increasing in the light and decreasing inthe dark period; the greatest diurnal variation being foundin half-expanded leaves. Asparaginase activity in half-expandedleaves reached a maximum after 4 h exposure to light and thisactivity was maintained over the rest of the light period. Changesin asparaginase activity were not influenced by diurnal temperaturechanges. The increase in asparaginase activity during the lightperiod was directly proportional to the photon flux densityover the range 0–285 µmol m^-2 s^-1 PAR. The increaseof asparaginase activity during illumination of detached leaveswas inhibited by the photosynthetic electron transport inhibitors3-(3', 4'-dichlorophenyl)-1, 1-dimethylurea (DCMU) and atrazine.These observations indicate that the increase in asparaginaseactivity in half-expanded leaves is dependent upon non-cyclicelectron transport. Key words: Pisum sativum, asparaginase, photosynthetic electron transport     

The Use of 14C-Ethane Diol as a Quantitative Tracer for the Transpirational Volume Flow of Water and an Investigation of the Effects of Salinity upon Transpiration, Net Sodium Accumulation and Endogenous ABA in Individual Leaves of Oryza sativa L.

Yeo, A. R., Yeo, M. E., Caporn, S. J. M., Lachno, D. R. andFlowers, T. J. 1985. The use of ¹⁴C-ethane diol as a quantitativetracer for the transpirational volume flow of water and an investigationof the effects of salinity upon transpiration, net sodium accumulationand endogenous ABA in individual leaves of Oryza sativa L.—J.exp. Bot. 36: 1099–1109. Oryza sativa L. (rice) seedlings growing in saline conditionsexhibit pronounced gradients in leaf sodium concentration whichis always higher in the older leaves than the younger ones.Individual leaf transpiration rates have been investigated todiscover whether movement of sodium in the transpiration streamis able to explain these profiles from leaf to leaf. The useof ¹⁴C labelled ethane diol to estimate transpiration was evaluatedby direct comparison with values obtained by gas exchange measurements.Ethane diol uptake was linearly related to the transpirationalvolume flow and accurately predicted leaf to leaf gradientsin transpiration rate in saline and non-saline conditions. ¹⁴C-ethanediol and ²²NaCl were used to compare the fluxes of water andsodium into different leaves. The youngest leaf showed the highesttranspiration rate but the lowest Na accumulation in salineconditions; conversely, the older leaves showed the lower transpirationrates but the greater accumulation of Na. The apparent concentrationof Na in the xylem stream was 44 times lower into the youngerleaf 4 than into the older leaf 1. Exposure to NaCl (50 molm^–3) for 24 h elicited an increase in endogenous ABA inthe oldest leaf only, but no significant changes occurred inthe younger leaves. Key words: —Salinity, rice, Oryza sativa L., transpiration, volume flow, abscisic acid