Nitrogen Deficiency in Small Closed Communities of S24 Ryegrass. I. Photosynthesis, Respiration, Dry Matter Production and Partition

Small communities of S24 ryegrass were grown under supplementarylights in a glasshouse at 20°C, and abundantly suppliedwith a complete nutrient solution containing 300 p.p.m. of nitrogen,until they had a leaf area index of 5 and fully interceptedthe light. Half were then given a solution containing only 3p.p.m. of nitrogen (LN) while the rest were kept at 300 p.p.m.(HN). The LN plants had a rate of single leaf photosynthesis lowerthan that of the HN plants at all but the lowest light intensities(33 per cent lower at the saturating irradiance of 170 W m^–2).Similarly, the LN communities had rates of canopy gross photosynthesis(P_sc) markedly lower than those of the HN communities. A comparisonof the observed rates of P_sc with those predicted by a mathematicalmodel of canopy photosynthesis indicated that it was the effectof nitrogen on single leaf photosynthesis, rather than differencesbetween the communities in leaf area, which led to the observeddifferences in P_sc. The superiority of the HN communities in terms of P_sc was partlyoffset by a higher rate of respiration so that they only exceededthe LN communities in terms of canopy net photosynthesis atirradiances in excess of 180 W m_–2, and produced only15 per cent more total dry matter. Nevertheless, the HN plantsdirected less of that dry matter into root and more into topsso that they came to possess twice the weight of live laminae,and the HN communities twice the leaf area, of their nitrogendeficient counterparts. Lolium perenne, S24 ryegrass, photosynthesis, respiration, dry matter production and partition, nitrogen dekieacy     

The Volatilization of Ammonia from Perennial Ryegrass During Decomposition, Drying and Induced Senescence

The volatilization of gaseous ammonia was measured from cutherbage (leaf lamina + sheath) of perennial ryegrass (Loliumperenne L.), during a 70 d period of either decomposition ordrying, and also from intact plants of perennial ryegrass subjectedto induced senescence by shading. Volatilization during decompositionamounted to 20–47% of the herbage nitrogen, but volatilizationduring drying, and from intact plants during induced senescence,amounted to less than 1% of the herbage nitrogen. During decomposition, volatilization of ammonia was proportionallygreater from herbage containing 3.52% nitrogen than from herbagecontaining 2.32% nitrogen. Volatilization occurred more rapidlyat 20 °C than at 10 °C but, with both samples of herbageand at both temperatures, at least 4 d elapsed before appreciablevolatilization occurred. Ammonia, atmosphere, decomposition, leaves, Lolium perenne L, nitrogen, perennial ryegrass     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: II. METHOD FOR MONITORING GENERATIVE GROWTH AND DEVELOPMENT IN SOLUTION CULTURE

Growth of barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)under N-limitation was investigated in solution culture, withspecial emphasis on the generative growth stage. Three differentregimes for limiting nitrate-N availability while keeping otherelements in surplus were employed. In the ‘high, decreasingnitrogen’ (HN) treatment, the relative nitrogen additionrate (RA) was maintained at 0.08 d^–1 until the ears startedto develop and was then decreased stepwise to, finally, RA 0·005d^–1. In the ‘low, decreasing nitrogen’ (LN)treatment, plants received 45% of the nitrogen added in HN.In the ‘constant nitrogen’ (CN) treatment, RA washeld constant at 0·0375 d^–1. Cumulative nitrogenadditions at termination of the experiment (day 147 after sowing)were 192, 179 and 87 mg plant^–1 for HN, CN, and LN cultures,respectively. Nitrogen availability limited nitrogen acquisitionin all treatments except in the CN culture at plant ages above110 d. Stepwise decrease of RA largely synchronized transitionsin developmental stages in the different cultivars and nitrogenregimes (HN and LN), and eventually yielded plants that wereclose to completing their life cycle. Normal maturation wasnot obtained in the CN treatment. The HN and LN treatments wereused for formal analysis of post-anthesis growth. A sigmoidfunction was fitted to growth data and from this, organ weightsand nitrogen concentrations at maturity (defined as cessationof growth) were derived. The two modern cultivars, Golf andMette, clearly outperformed the more primitive cv. Laevigatumin terms of allocation of nitrogen to ears, particularly inthe LN culture. The stepwise decrease of RA appears suitablefor studies of post-anthesis growth and nitrogen relations inbarley, with regard to both genotypic variation and variationcaused by differences in cumulative amounts of nitrogen added. Key words: Barley, development, growth, nitrogen concentration, post-anthesis     

Combined Effects of Partial Defoliation and Nutrient Availability on Cloned Betula pendula Saplings: II. CHANGES IN NET PHOTOSYNTHESIS AND RELATED BIOCHEMICAL PROPERTIES

The combined effects of partial defoliation and nutrient availabilityon net photosynthesis and related biochemical variables werestudied in cloned Betula pendula Roth saplings. The saplingswere randomly assigned to different nutrient levels (5, 1·5and 0·5 mol N m^–3) in aerated nutrient cultureand to the following defoliation treatments: (1) control (nodamage), (2) damage of the developing main stem leaves (halfof the leaf lamina removed), and (3)removal of the developingmain stem leaves (entire leaf lamina removed). The leaf immediatelybelow the damaged area in the treated plants, and the correspondingleaf in the control plants, were selected for study. Net photosynthesismeasurements and biochemical determinations were made 2, 8 and14 d after assigning the treatments. At intermediate and lownutrient levels the final net photosynthetic capacity was significantlyhigher in the saplings with the topmost leaves removed thanin the undamaged control saplings, indicating that the expressionof compensatory photosynthesis after partial defoliation isnot inhibited by nutrient deficiency. The photosynthetic enhancementwas closely associated with the increased initial activity ofribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). However,the increased activity of Rubisco was not exclusively the resultof a higher amount of Rubisco. The expression of compensatoryphotosynthesis after partial defoliation in our study cannotunequivocally be attributed to an increased flow of nitrogento the remaining leaves. Key words: Partial defoliation, nutrient availability, net photosynthesis, nitrogen, Rubisco     

Influence of S-ethyl Dipropylthiocarbamate on Atrazine Absorption by Wheat

Wheat (Triticum sativum L. cv. Nisu) grown in 0·5 Hoaglandssolution containing sub-toxic concentrations of S-ethyl dipropylthiocarbamate(EPTQ (0,0·0625,0·125,0·25, and 0·5p.p.m.w.) were exposed to ¹⁴C-ring labelled-2-chloro-4-ethylamino-6-isopropylamino-s-triazine(atrazine). Total ¹⁴C-atrazine absorption was increased to 182per cent in wheat treated with 0•5 p.p.m.w. EPTC when comparedto the EPTC untreated wheat. Detoxification and metabolism ofEPTC were not appreciably altered by EPTC pretreatment. Thisresulted in an increased atrazine content in the wheat leavespretreated with 0·5 p.p.m.w. EPTC that amounted to 370per cent of the unchanged atrazine present in the leaves ofEPTC untreated wheat.     

Relationship between Leaf Structure and Gas Exchange in Wheat Leaves at Different Insertion Levels

Net photosynthesis rate (P_n), stomatal conductance to CO₂ andresidual conductance to CO₂ were measured in the last six leaves(the sixth or flag leaf and the preceding five leaves) of Triticumaestivum L. cv. Kolibri plants grown in Mediterranean conditions.Recently fully expanded leaves of well-watered plants were alwaysused. Measurements were made at saturating photosynthetic photonflux density, and at ambient CO₂ and O₂ levels. The specificleaf area, total organic nitrogen content, some anatomical characteristics,and other parameters, were measured on the same leaves usedfor gas exchange experiments. A progressive xeromorphic adaptation in the leaf structure wasobserved with increasing leaf insertion levels. Furthermore,mesophyll cell volume per unit leaf area (V_mes/A) decreasedby 52·6% from the first leaf to the flag leaf. Mesophyllcell area per unit leaf area also decreased, but only by 24·5%.However, nitrogen content per unit mesophyll cell volume increasedby 50·6% from the first leaf to the flag leaf. This increasecould be associated to an observed higher number of chloroplastcross-sections per mm² of mesophyll cell cross-sectional areain the flag leaf: values of 23000 in the first leaf and 48000in the flag leaf were obtained. P_n per unit leaf area remainedfairly constant at the different insertion levels: values of33·83±0·93 mg dm^–2 h^–1 and32·32±1·61 mg dm^–2 h^–1 wereobtained for the first leaf and the flag leaf, respectively.Residual conductance, however, decreased by 18·2% fromthe first leaf to the flag leaf. Stomatal conductance increasedby 41·7%. The steadiness in P_n per unit leaf area across the leaf insertionlevels could be mainly accounted for by an opposing effect betweena decrease in V_mes/A and a more closely packed arrangement ofphotosynthetic apparatus. Adaptative significance of structuralchanges with increasing leaf insertion levels and the steadinessin P_n per unit leaf area was studied. Key words: Photosynthesis, structure, wheat     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: III. POST-ANTHESIS KINETICS OF NET NITRATE UPTAKE AND THE ROLE OF THE RELATIVE ROOT SIZE IN DETERMINING THE CAPACITY FOR NITRATE ACQUISITION

Barley (Hordeum vulgare L., cvs Golf, Mette, and Laevigatum)was grown under nitrogen limitation in solution culture untilnear maturity. Three different nitrogen addition regimes wereused: in the ‘HN’ culture the relative rate of nitrate-Naddition (RA) was 0·08 d^–1 until day 48 and thendecreased stepwise to, finally, 0·005 d^–1 duringgrain-filling; the ‘LN’ culture received 45% ofthe nitrogen added in HN; the ‘CN’ culture was maintainedat RA 0·0375 d^–1 throughout. Kinetics of net nitrateuptake were measured during ontogeny at 30 to 150 mmol m^–3external nitrate. V_max (which is argued to reflect the maximuminflux rate in these plants) declined with age in both HN andLN cultures. A pronounced transient drop was observed just beforeanthesis, which correlated in time with a peak in root nitrateconcentration. Similar, but less pronounced, trends were observedin CN. The relative V_max (unit nitrogen taken up per unit nitrogenin plants and day) in all three cultures declined from 1·3–2·3d^–1 during vegetative growth to 0·1–0·7d^–1 during generative growth. These values are in HN andLN cultures 15- to more than 100-fold in excess of the demandset by growth rates throughout ontogeny. Predicted balancingnitrate concentrations (defined as the nitrate concentrationrequired to support the observed rate of growth) were below6·0 mmol m^–3 in HN and LN cultures before anthesisand then decreased during ontogeny. In CN cultures the balancingnitrate concentration increased during grain-filling. Apartfrom the transient decline during anthesis, most of the effectof ageing on relative V_max can be explained in terms of reducedcontribution of roots to total biomass (R:T). The loss in uptakeper unit root weight is largely compensated for by the declinewith time in average tissue nitrogen concentrations. The quantitativerelationships between relative V_max and R:T in ageing plantsare similar to those observed for vegetative plants culturedat different RAs. The data support the contention that the capacity for nitrateacquisition in N-limited plants is under general growth control,rather than controlled by specific regulation of the biochemicalpathway of nitrate assimilation. Key words: Barley, nitrogen concentration, root: total plant biomass ratio, V_max     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

Chloroplast ultrastructure of sugar beet (Beta vulgaris L.) cultivated in normal and elevated CO2 concentrations with two contrasted nitrogen supplies

Sugar beet (Beta vulgaris L., cultivar Celt) plants were grownunder simulated field conditions in pots and supplied with adequateor deficient nitrogen (HN and LN, respectively) combined withtwo CO₂ concentrations, ambient (c. 350µmol mol^–1C0₂—AC), or elevated CO₂ (c. 600 µmol mol^–1CO₂—HC). Chloroplast structure in mesophyll palisade cellsof mature leaves (leaf number 19 in HN and 9 in LN), sampledat midday on 16 August 1993 was studied by transmission electronmicroscopy and quantified stereologically. The ultrastructureof palisade parenchyma chloroplasts was affected by the elevatedCO₂ concentration and strikingly affected by nitrogen supply.Chloroplast diameter (cross-sectional length) was slightly,but not significantly, greater in HC than AC treatments withinan N treatment, but was smaller in LN than HN; chloroplast cross-sectionalarea also increased with HC in both N treatments, but only significantlyso in LN. Elevated CO₂ reduced the proportion of total thylakoids(significant at 5% and 0.1% in HN and LN, respectively) dueto decreased granal thylakoids, but the proportion of inter-granal(stromal) thylakoid membranes was not affected compared to chloroplastsfrom plants grown with ambient CO₂. Chloroplast stroma increasedas a proportion of chloroplast volume with elevated comparedto ambient CO₂ with HN but not LN. Starch inclusions were notsignificantly different with elevated compared to ambient CO₂at HN, but the proportion of starch increased considerably atelevated compared to ambient C0₂ at LN, indicating an over-productionof assimilates. Plastoglobuli in chloroplasts increased withdeficient N, but decreased with elevated CO₂. Larger chloroplastswith a greater proportion of stroma, but a smaller proportionof granal thylakoids, suggest increased CO² assimilating capacityand decreased light harvesting/PSII capacity with elevated CO₂. Key words: Chloroplast, ultrastructure, elevated CO₂ concentration, nitrogen deficiency, sugar beet, Beta vulgaris     

Effects of Nitrogen on the Development and Growth of the Potato Plant. 1. Leaf Appearance, Expansion Growth, Life Spans of Leaves and Stem Branching

Potatoes (Solanum tuberosum L) were planted in pots in a temperature-controlledglasshouse to collect data on the rate of leaf apearance, leafexpansion, apical lateral branching and active life spans ofleaves The treatments consisted of three rates of nitrogen supply,i e the NI treatment with 2 5 g N per pot and the N2 and N3treatments with 8 and 16 g N per pot, respectively The rate of leaf appearance was 0·53 leaves d^–1(one leaf per 28 °C d) and was negligibly affected by nitrogensupply The rate of leaf expansion was related to leaf numberand nitrogen supply The areas of mature leaves increased withleaf number on the main stem to reach a maximum for leaf numbers12–14, and declined for higher leaf numbers Leaves onapical lateral branches declined in mature area with increasein leaf number The expansion rate of leaves was the dominantfactor that determined the mature leaf area, irrespective ofleaf number and nitrogen treatment The smallest leaves wereobserved at the lowest rate of nitrogen supply Nitrogen promotedapical branching and hence the total number of leaves that appearedon a plant The proportion of total leaf area contributed byleaves on apical branches increased with time and nitrogen supply Active life span, i e the period of time between leaf appearanceand yellowing of the leaf, showed a similar relation to leafnumber as mature leaf area, at least in qualitative terms Leavesof the N3 treatment showed systematically longer life spansthan leaves of the NI and N2 treatment in the order of 3 weeksThe number of main stem leaves was not affected by nitrogensupply Potato, Solanum tuberosum L, leaf development, leaf extension, plant structure, nitrogen nutrition     

Combined Effects of Partial Defoliation and Nutrient Availability on Cloned Betula pendula Saplings: I CHANGES IN GROWTH, PARTITIONING AND NITROGEN UPTAKE

The combined effects of partial defoliation and nutrient availabilityon dry matter accumulation and partitioning, and on nitrogenuptake and partitioning, were studied in cloned Betula pendulaRoth saplings. The saplings were randomly assigned to differentnutrient levels (5, 1·5 and 0·5 mol Nm^–3)in aerated nutrient culture and to the following defoliationtreatments: (1) control (no damage), (2)damage of the developingmain stem leaves (half of the leaf lamina removed), and (3)removalof the developing main stem leaves (entire leaf lamina removed).Measured in terms of cumulative whole-plant dry weight (includingremoved leaf tissue), the birch saplings were unable to compensatefor the loss of the developing leaves (treatment 3) during the14 d study period. In response to leaf removal (treatment 3)the mean final percentage reduction in whole-plant dry weightwas actually greater than the initial mean percentage reductioncaused by the removal itself; the magnitude of the final reductionwas independent of nutrient availability. After removal of thedeveloping leaves, branch growth was favoured at the expenseof the growth of the rest of the shoot; the relative branchgrowth was most pronounced at the highest nutrient level. Atthe two highest nutrient levels the nitrogen uptake of the saplingswith the developing leaves removed was less than that of undamagedsaplings. We suggest, however, that the incapacity of the saplingsfor compensatory growth after removal of the developing leaveswas primarily due to the decreased total carbon gain of thesaplings rather than to the decreased nitrogen uptake rate. Key words: Partial defoliation, nutrient availability, birch sapling, dry matter, nitrogen     

Salinity-induced tissue-specific diurnal changes in nitrogen assimilatory enzymes in tomato seedlings grown under high or low nitrate medium.

We studied the salt stress (100 mM NaCl) effects on the diurnal changes in N metabolism enzymes in tomato seedlings (Lycopersicon esculentum Mill. cv. Chibli F1) that were grown under high nitrogen (HN, 5 mM NO(3)(-)) or low nitrogen (LN, 0.1 mM NO(3)(-)). NaCl stress led to a decrease in plant DW production and leaf surface to higher extent in HN than in LN plants. Total leaf chlorophyll (Chl) content was decreased by salinity in HN plants, but unchanged in LN plants. Soluble protein content was decreased by salt in the leaves from HN and LN plants, but increased in the stems-petioles from LN plants. Nitrate reductase (NR, EC 1.6.1.6) showed an activity peak during first part of the light period, but no diurnal changes were observed for the nitrite reductase (NiR, EC 1.7.7.1) activity. Glutamine synthetase (GS, EC 6.3.1.2) and glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities increased in HN plant leaves during the second part of the light period, probably when enough ammonium is produced by nitrate reduction. NR and NiR activities in the leaves were more decreased by NaCl in LN than in HN plants, whereas the opposite response was obtained for the GS activity. Fd-GOGAT activity was inhibited by NaCl in HN plant leaves, while salinity did not shift the peak of the NR and Fd-GOGAT activities during a diurnal cycle. The induction by NaCl stress occurred for the NR and GS activities in the roots of both HN and LN plants. Glutamate dehydrogenase (GDH, EC 1.4.1.2) activity shifted from the deaminating activity to the aminating activity in all tissues of HN plants. In LN plants, both aminating and deaminating activities were increased by salinity in the leaves and roots. The differences in the sensitivity to NaCl between HN and LN plants are discussed in relation to the N metabolism status brought on by salt stress.     

Studies in the Growth of Young of Pinus sylvestris L.: I. The Annual Cycle of Assimilation and Growth

The annual cycle of growth in plants of P. sylvestris L. varyingin age from 2 to 5 years was studied mainly by following theirweight changes through periodic sampling. Immediately followingbud-break there was a period of about 1 month in which, althoughmeristematic and extension growth were rapid in both shoot androot, there was no gain in weight by the plant. There was evidencethat the needles remaining from previous years contained a considerableamount of storage material which was utilized at this time.During May and June the main increase in weight was in the newshoots, but in August and September assimilates were more evenlydivided between the new shoots on the one hand, and the oldstem and the root on the other. The average relative growth-ratesfor the months May to September were between 1·0 and0·4 per cent, per day in plants growing in favourableconditions, the lower rates being found in older plants. Duringthe months October to March slow increase in weight occurredin needles, stem, and root, and the R.G.R.s in two experimentswere 0·21 and 0·15 per cent, per day. The netassimilation rate fell with increasing age and in the summerof the fifth year was 0·06g./g./week or 0·10g./dm.²/week.This low value of N.A.R. is discussed in relation to the knownhigh rate of production of P. sylvestris stands and their evergreenhabit.     

Uptake and Distribution of Copper in Chrysanthemum morifolium

The effects of various levels of copper on the uptake and distributionof copper in Chrysanthemum morifolium grown in solution cultureand peat-sand have been examined. Whole plants growing in shortdays were sampled at regular intervals, divided into roots,stem, leaves and lateral shoots, and analysed for copper. Thepartitioning of copper between these tissues showed that a relativelylarge proportion (30–40 per cent) of the total plant copperwas accumulated in the roots of normal plants during the harvestingperiod, compared with approximately 10 per cent in the rootsof copper deficient plants. Whilst the copper content (ug g^–1) of leaves and stemfrom normal plants was negatively correlated with the amountof dry matter produced (P < 0·001), the correspondingcopper deficient tissues showed little variation in copper contentwith increases in tissue dry weight. A more detailed investigationof the copper content of leaves from normal plants showed thatgradients existed within the plant with respect to both leafposition and time of harvest which could be described by a singlecubic surface equation (P < 0·001).     

Determination of Nitrate Reductase Activity in Barley Leaves and Roots

The inactivation of nitrate reductase in the leaves and rootsof barley (Hordeum vulgare L. cv. Mazurka) during and afterextracting was investigated. At 0 °C in the absence of casein,25 per cent of ‘total’. i.e. maximal in vitro, nitratereductase activity was lost during the 2 min extraction process,followed by a slower loss of activity while the extract wasstored in ice. Activity was maintained by adding a minimum of1 per cent casein to the extraction medium containing 0·1M phosphate (pH 7·5), 1 mM EDTA and 1 mM dithiothreitol.Nitrate reductase was stable for several hours in these extracts,but declined in a first order manner in the absence of dithiothreitol.Casein also prevented the initial loss while making root extracts,but had less effect during storage. Using casein and thiols, nitrate reductase activity in light,(as product of maximal in vitro rates and wt g^–1) in leaveswas 98 per cent of the total activity in 31-day-old plants grownwith full nutrient in water culture and 60-day-old field-grownplants receiving no fertilizer. Field-grown plants, however,exhibited only 17 per cent of the activity of culture-grownplants. Nitrate reductase in leaves of barley plants grown in waterculture had a diurnal rhythm. During the first 3 h of the lightperiod, activity increased to 1·3 x the ‘dark’value. This was followed by a temporary decrease and then byanother increase to a maximum of 1·7 x the ‘dark’value, occurring about 8 h after illumination. Activity thendecreased during the rest of the light period and in darkness. Hordeum vulgare L., barley, nitrate reductase     

Nitrate Reduction in Solanum tuberosum L.: Development of Nitrate Reductase Activity in Field-grown Plants

Nitrate reductase activity (in vivo method, substrate non-limiting)in unshaded leaves from the top of the canopy has been determinedfor field-grown potato plants over the course of the growingseason. The pattern of change was almost identical for plantsreceiving no added fertilizer and those receiving 24 g N m^–2.Activity increased to a peak at about 90 days after plantingand declined thereafter. On a fresh weight basis activity wasalways higher in fertilized plants. Nitrate reductase activitywas positively and significantly correlated with leaf proteincontent in high N plants (r² = 0.71; P = 0.05), but poorly correlatedwith both the nitrate content of the leaf lamina and the nitrateconcentration in petiole sap. Up until 90 days after planting(mid-July) there appeared to be a positive relationship betweenincreased activity of nitrate reductase and solar radiation.However, results obtained over two seasons showed that the declinein activity after this time was not consistently linked witha fall in the level of solar radiation. Remobilization of reduced-Nand stored nitrate from leaves and stems accompanied this declinein nitrate reductase activity and in the latter part of theseason appeared to account for all of the N gained by growingtubers. In unfertilized plants nitrate-N accounted for 5 per cent orless of total plant N. Fertilized plants contained up to 25per cent nitrate-N. While nitrate availability limited growthin unfertilized plants, sub-optimal rates of nitrate assimilationin fertilized plants, particularly during the early stages ofpost-emergence growth, may contribute to inefficient use ofacquired nitrate. The carbohydrate status of leaf lamina and petiole sap weremodified by N supply. The soluble sugar and starch contentsof low N leaves were higher than in their high N counterparts.By contrast, the concentration of soluble sugars in petiolesap increased to a higher value in high N samples. Althoughsap sugar levels declined in both treatments towards the endof the season, N application delayed this decline for severalweeks. Solanum tuberosum, nitrate reductase, nitrate assimilation, senescence     

Studies in the Nutrition of Apple Rootstocks: II. Effects of Concentration of Iron in the Nutrient Solution on Growth and Chlorophyll Content

Rooted one-year shoots were grown for one season by sprayingtheir roots with nutrient solution. Iron supplied as Fe-EDTAat four concentrations resulted in plants which were respectively(a) severely chlorotic, (b) mildly chlorotic, (c) dark greenand healthy (controls), and (d) dark green but with slight reductionin growth. Severely deficient plants showed 40–70 per cent reductionsin growth as measured by fresh weight, shoot length, diameterincrease, leaf area, net assimilation and relative growth-rates.Dry weights were reduced 70–80 per cent and of the totaldry-weight increment a greater proportion remained in the leaves,which had a lower dry weight and higher water content per unitarea. However, because the initial old stem formed a greaterproportion of the total dry weight, the leaf area ratio remainedabout 11 per cent lower than in the controls. Severely deficientplants had, per unit of chlorophyll, a higher dry-weight increaseand net assimilation rate than the controls. Mild deficiency caused 10–20 per cent reductions in growthand net assimilation rate; the leaf area ratio was normal. Possible mechanisms of the effects of low iron supply are discussed,while the small growth reduction at the highest Fe-EDTA concentrationis attributed to chelate toxicity     

The Influence of Donor Plant Genotype and Environment on Production of Multicellular Microspores in Cultured Anthers of Brassica napus ssp. oleifera

Studies of the effects of genotype and pre-flowering environmentalconditions on the production of multicellular microspores wereundertaken th four highly inbred lines of Brassica napus sap.oleifera. These lines were first grown in shaded and unshadedenvironments at 20/15°C arid unshaded at 30/25°C ina daylight phytotron. Buds were harvested from half the plantswhen first visible in the rosette and later from the remainingplants at the time when the first flower opened. The frequencyof microspores at a specific stage of development varied widelywithin a relatively narrow range of bud lengths. Uninucleatemicrospores were not detected in anthers from buds less than1·5 m or greater than 3·0mm long, but were generallypresent in frequencies of greater than 50 per cent in anthersfrom buds which were between 2·0 and 2·5 mm inlength. However, the bud length at which the highest frequencyof uninucleate microspores was detected varied significantlybetween genotypes and between the environments in which theywere grown. Examination of the remaining anthers from each budafter a period in culture revealed that the proportion of microsporesdeveloping into multicellular units varied greatly with budlength, an increase in frequency of multicellular microsporesbeing associated with an increase in the frequency of uninucleatemicrospores in the uncultured anther. Genotypes differed, however,in respect of the relationship between uninucleate microsporefrequency and production of multicellular units. Although thefrequency of multicellular units was as high as 57 percent,further development was limited and the number of embryoldsformed was low in all cases (<10 per cent). The frequency of multicellular units in pollen samples frombuds of a length in which uninucleate microspore frequency washigh varied significantly with genotype, temperature and lightconditions under which donor plants were grown, and the stageof inflorescence development at which buds were removed. Underconditions most conducive to multicellular unit formation (20/15°C,unshaded), the maximum frequency of multicellular units foreach genotype in buds from young inflorescences ranged from11·5 to 56·5 per cent. Shading or exposure tothe higher temperature was associated with a marked reductionin production of multicellular units. Higher frequencies ofmulticellular units were generally detected in microspore samplesfrom younger inflorescences irrespective of genotype or environment. Two of the four inbred lines were selected for a second experimentin which responses to vernalization and photoperiod durationwere monitored. There was a significant reduction in the numberof leaf nodes formed prior to floral initiation in both genotypesfollowing exposure to vernalization and/or a longer photoperiod,the response to photoperiod being more pronounced. Exposureto 4 weeks vernalization was accompanied by a significant increasein the frequency of multicellular units in both genotypes, thefrequency being double that in unvernalized plants under thelonger photoperiod. By contrast, genotypes differed sharplyin their response to photoperiod. In TB 20, the frequency ofmulticellular units was unaffected by an increase in day lengthirrespective of whether seed had been vernalized or not. Onthe other hand, in TB 42 the frequency of multicellular unitswas substantially greater in the 24 h day than in the 12 h day,being 27·3 per cent vs 13·0 per cent in the caseof unvernalized plants and 66·7 per cent vs 18·2per cent in the case of vernalized plants. Brassica napus, anther culture, pollen embryogenesis, genotype-environment interaction     

Photosynthesis by White Clover Leaves in Mixed Clover/Ryegrass Swards

Measurements of rates of net photosynthesis were made on singleBlanca white clover leaves on plants taken from a field-grown,mixed clover/perennial ryegrass sward during two regrowth periods. Net photosynthesis fell by 20 per cent in the first measurementperiod as leaf area index increased and the grass componentof the crop flowered, but did not change significantly in thesecond measurement period during which the grass remained vegetative. Leaves which had been artificially protected from shading inthe sward did not have significantly different photosyntheticcapacities from leaves in the undisturbed sward, even in thefirst measurement period. As leaf area index and sward height increased, successive cloverpetioles were longer, keeping the newly expanded leaves nearthe top of the sward where they received full light. It is suggestedthat it is this which allows successive clover leaves, unlikethose of vegetative grasses, to attain a high photosyntheticcapacity throughout a growth period. Trifolium repens, Lolium perenne, Photosynthetic capacity, shading, growth     

Identification of a Water-soluble Fungal Inhibitor in the Leaves of Acer platanoides L.

It was confirmed that the leaves of Acer platanoides containan antifungal inhibitory substance. Low concentrations of sterilecold water extracts inhibited the germination of the sporesof Cladosporium herbarum (three isolates), Cladosporium sphaerospermumand Cylindrocarbon radiclcola. In the concentration range 0·06–0·125per cent (w/v) of leaf material the inhibitory response wasdemonstrated to increase linearly as the concentration of leafmaterial increased logarithmically. Inhibitory activity wasfound in leaf samples collected during a period from July toOctober but activity had disappeared from leaves collected inthe following January. The inhibitory activity was located intwo components of the water extract by bioassay tests followingether extraction and separation by chromatography. One of theactive components has been identified as gallic acid by gaschromatography. Gallic acid has also been detected in dew collectedfrom leaf surfaces where it is suggested that it may play animportant part in the colonization of the leaves by fungi.