The Elongation Rate of Wheat Leaves: II. EFFECT OF SUDDEN LIGHT CHANGE ON THE ELONGATION RATE

Oscillations of the elongation rate of wheat leaves were observedafter sudden illumination and after extinguish the light. Thestimulus for these oscillations was perceived by the alreadymature leaves. The water potential of the plant influences theelongation rate immediaely, and a sudden change in the transpirationrate (opening or closing of stomata owing to light stimulus)changes the water potential. Artificial changes of the waterpotential, such as those caused by altering the osmotic potentialof the root medium to -5x10⁵ Pa or dipping the leaves into water,changed the elongation rate within a few minutes. Reducing thetranspiration rates by means of transpiration inhibitors (phenylmercuricacetate (PMA) and abscisic acid (ABA)) down to 60% of the normaltranspiration rates prevented the oscillations. Likewise, theoscillations were prevented if the transpiring plant surfacewas redused by cutting off the two mature leaves while the elongationrate of the 3rd leaf was being recorded.     

Growth and Development in the Young Tomato: III. THE EFFECT OF NIGHT AND DAY TEMPERATURES ON VEGETATIVE GROWTH

Tomato seedlings were grown in a 12-hour day at constant andalternating day and night temperatures ranging from 10°to 30° C. The pattern of results was similar at light intensitiesof 400 and 800 f.c. The maximum rate of dryweight accumulationoccurred at a constant temperature close to 25° C. The effectsof day and night temperatures on total dry weight showed a considerabledegree of independence. The optimum day temperature was 25°C irrespective of the night temperature; the optimum night temperatureincreased from 18° to 25° C over the whole range ofday temperature. On average, day temperature affected totaldry weight twice as much as night temperature. High night temperaturesto some extent compensated for low day temperatures. The optimumday and night temperatures for leaf growth were both 25°C. On average day temperature affected leaf growth one and ahalf times as much as night temperature. By 12-hourly sampling it was shown that the cotyledons and leavesgrow throughout both day and night and that high night temperatureaccelerates nocturnal growth (cotyledons by cell expansion,young leaves by cell multiplication). Plants having receivedonly one night at 25° C, as compared with 15° C, showa slightly greater assimilation during the following light period,apparently as a consequence of increased photosynthetic surface.The respiratory loss in dry weight during darkness was not significantlyaffected by temperature over the range 15–25° C.     

Control of Wheat Root Elongation Growth: I. EFFECTS OF IONS ON GROWTH RATE, WALL RHEOLOGY AND CELL WATER RELATIONS

Pritchard, J., Tomos, A. D. and Wyn Jones, R. G. 1987. Controlof wheat root elongation growth. I. Effects of ions on growthrate, wall rheology and cell water relations.—J. exp.Bot. 38: 948–959. The nature of the ions in the bathing medium of hydroponicallygrown wheat seedlings strongly influenced root growth rate.In 0·5 mol m^–3 CaSO₄ the growth rate was 32 mm24 h^–1 (used as 100% control rate). K⁺ and SO^– ions(10 mol m^–3) each inhibited extension growth (to about40% and 70% of the control value respectively). In the absenceof K⁺, Cl^– greatly reduced the inhibition due to SO₄^2–.Measurement of tissue plasticity and elasticity in the expandingzone with an Instron-type tensiometer indicated that both werea function of growth rate although relationship of plasticityto growth rate was the steeper and the more pronounced. Turgor pressure at the proximal end of the expanding zone wasnot correlated to growth, being approximately 0·65 MPain all treatments. In mature tissue turgor pressure varied withtreatment, but was also not related to growth rate. Cell membranehydraulic conductivity (5 x 10^–7 ± 1·3 (10)m s^–1 MPa^–2) was not influenced by the presenceof K⁺. We propose that K⁺ and SO₄^{2 –} influence root growthrates by modulating the rheological properties of the wallsof the expanding cell. The physiological significance of these properties is discussed. Key words: Growth, wall extensibility, turgor pressure, wheat roots     

The Effect of Rapid Temperature Increase on the Growth Rate of Wheat Leaves

The growth rate of the first leaf of eight-day-old wheat plants was measured using a DLT-2 highly sensitive linear displacement transducer. Leaf extensibility was evaluated from the growth rate under the increase in the pulling force by 2 g. An increase in the air temperature resulted in the doubling of the transpiration rate and immediate slowing of the leaf growth followed by the leaf shrinkage. However, growth was later resumed almost completely. Heat treatment did not induce any changes in the leaf extensibility, indicating that cell-wall mechanical properties were not changed. Growth retardation was supposed to result from a decrease in the water content in the leaf tissues because the balance between water influx from roots and its loss through transpiration was shifted toward the water loss. An initial drop in the relative water content (RWC) indicates such a misbalance. Subsequent growth resumption coincided with a decreased water deficiency. Since the rate of transpiration was not reduced, RWC and growth rate restoring evidently occurred due to the activated water uptake by roots, which can be explained by the increased hydraulic permeability detected in our experiments.     

Hemoglobin-digesting Acid Proteinases in Soybean Leaves: CHARACTERISTICS AND CHANGES DURING LEAF MATURATION AND SENESCENCE

Three proteinases which digest hemoglobin rapidly at acid pH (3.5 to 4.5) were identified in crude extracts of soybean (Merr.) leaves and separated by chromatography on DEAE-cellulose. All three enzymes were endopeptidases as judged by the ratio of α-amino-nitrogen plus peptide nitrogen over α-amino-nitrogen in the trichloroacetic acid-soluble portion of hemoglobin digests. Proteinase I did not bind to diethylaminoethyl cellulose and was not inhibited by any of the proteinase inhibitors tested. Proteinase II was partially inhibited by phenylmethylsulfonyl fluoride, N-ethylmaleimide, and p-chloromercuribenzoate. The inhibition by phenyl-methylsulfonyl fluoride can probably be accounted for by the presence of contaminating carboxypeptidase. Proteinase III was the most anionic of the three and required the presence of sulfhydryl reagents to prevent the irreversible loss of activity. All the proteinase preparations digested soy-bean ribulose bisphosphate carboxylase as shown by the disappearance of the large subunit of that protein, when partially digested preparations were subjected to electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. These experiments confirmed that the three proteinases were endopeptidases. All three proteinases were present throughout leaf development; proteinase I predominated in expanding leaves, whereas proteinase III became the predominant enzyme as the leaves matured. Senescence (yellowing) was associated with a decline in the activities of all three proteinases.     

Cytokinins in the Leaves of Ginkgo biloba: I. The Complex in Mature Leaves

Cytokinin conjugates of zeatin, ribosylzeatin, and their respective dihydro derivatives tentatively have been identified as the major cytokinins present in mature Ginkgo biloba L. leaves. Ribosylzeatin was present in higher levels than zeatin and dihydrozeatin. No evidence could be found that 6-(2,3,4-trihydroxy-3-methylbutylamino)purine occurs as a metabolite in the mature leaves. From the available evidence, it is concluded that cytokinin conjugates are probably the major metabolites formed in the leaves of this deciduous gymnosperm.     

Red Light-inhibited Mesocotyl Elongation in Maize Seedlings: I. The Auxin Hypothesis

Red light-inhibited mesocotyl elongation, which occurs in intact Zea mays L. seedlings, was studied in excised segments which included the coleoptile (or parts therefrom) and apical centimeter of the mesocotyl. Experiments took into account, first, the ability of the segments to regenerate auxin supply sites, and, second, that auxin uptake can be greatly reduced if there is no cut surface, apical to the elongating cells, to act as a port of entry. In all cases, auxin completely reversed the inhibition of elongation by light. The results support the hypothesis that light regulates mesocotyl elongation by controlling auxin supply from the coleoptile. Sucrose concentration had no effect on auxin reversal of light-inhibited elongation, but relatively high concentrations of gibberellic acid (10 μm) could substitute for auxin in this system.     

The Role of the Coleoptile Apex in Controlling Organ Elongation: I. THE EFFECTS OF DECAPITATION AND APICAL INCISIONS

It has been widely accepted for over 50 years that the elongationrate of a coleoptile is dependent on the supply of auxin fromthe apex. The original coleoptile decapitation experiments whichprovided support for this view have been repeated but the measurementsof coleoptile elongation were made with greater temporal andspatial precision. The experiments confirm that Avena and Zeacoleoptile elongation is retarded by decapitation but the locationand timing of the growth rate changes are not consistent withthe hypothesis that decapitation reduces growth rate solelyby removing the major supply of auxin. Evidence is presentedthat wounding is the prime cause of the effects of decapitation.Data are also presented showing that the recovery of growthrate of coleoptiles after decapitation or wounding is not dearlyassociated with any events near the cut surface and hence thetraditional explanation of this phenomenon (‘regenerationof the physiological tip’) is misleading. Key words: Coleoptile, decapitation, apex     

Rate of Leaf Appearance and Final Number of Leaves in Wheat: Effects of Duration and Rate of Change of Photoperiod

This study was conducted to test the hypothesis that photoperiodor its rate of change significantly affects the rate of leafappearance (RLA) and final number of leaves (FNL) in wheat,as suggested from several time-of-sowing experiments. Two wheatcultivars (Condor and Thatcher) were sown in the field on 2Sep. 1992 at Melbourne (38°S). Photoperiod was extendedartificially to give five treatments up to terminal spikeletinitiation (TS) viz.: natural photoperiod (rate of change ofphotoperiod = 2 min d^-1), two faster rates of change (8·5and 13·3 min d^-1) and two constant photoperiods of 14·0and 15·5 h. After TS, the two constant photoperiods wereextended to 15·0 and 16·5 h, respectively, andtreatments were re-randomised, i.e. some plots received differentphotoperiod regimes before and after TS. The rate of leaf appearance maintained strong linear relationshipswith thermal time. It was greater for Condor [0·012-0·013(°C d)^-1] than for Thatcher [0·011-0·012 (°Cd)^-1] and did not alter during plant development or in responseto the change in photoperiod at TS. Rate of leaf appearanceon the main culm was not influenced by the rate of change ofphotoperiod nor by the average photoperiod. Cultivar and photoperiod significantly affected FNL on the mainculm. Condor produced more leaves than Thatcher under long butnot under short photoperiods. The rate of change of photoperioddid not affect FNL independently of the effect of average photoperiod.Most of the variation in FNL due to photoperiod resulted fromdifferences in duration of leaf initiation. The lack of effects of the photoperiod treatments on RLA contrastwith previous reports of its effects on the rate of phasic developmentfrom seedling emergence to double ridge. Therefore, the numberof visible leaves on the main culm (NL) at double ridge andat TS were not constant. However, NL on the main culm at doubleridge was closely correlated with FNL.Copyright 1994, 1999 AcademicPress Triticum aestivum L., wheat, leaf appearance, phyllochron, photoperiod     

The Effects of Dwarfing Genes Rht1 and Rht2 on Cellular Dimensions and Rate of Leaf Elongation in Wheat

The gibberellin insensitivity genes, Rht1 and Rht2, reducedepidermal cell lengths in leaves of isogenic lines of field-and laboratory-grown wheat (Triticum aestivum L.). Rht dosagesof zero (wild type), two (semi-dwarf) and four alleles (doubledwarf) had a linear negative effect on cell length in flag leavesof field-grown plants, and in the sheaths and blades of leafnumber 1 in laboratory grown plants. Decrease in cell length,rather than reduced cell number, accounted for most to all ofthe reduction in blade and sheath length. In sheaths, cell widthincreased with Rht dosage, but not sufficiently to compensatefor decreased length in determining average projected surfacearea. Rates of extension of leaf number 1 in laboratory-grownplants were negatively and linearly correlated with Rht dosage.Maximal growth rate was maintained longer in wild type thanin double dwarf, but the total duration of measurable extensionin leaf number 1 was not affected by Rht dosage. Cell size, elongation, Rht, wheat, Triticum aestivum L     

Hormonal Regulation of Hypocotyl Elongation in Lactuca sativa L.: I. EVIDENCE AGAINST THE INVOLVEMENT OF GIBBERELLINS IN THE ELONGATION OF HYPOCOTYL IN SEEDLINGS GROWN IN THE DARK

The kinetics of extension induced by GA₃¹ in the hypocotyl ofintact seedlings of Lactuca sativa are similar in the dark andin the light, and differs fundamentally from the kinetics ofelongation in the dark without GA₃. Both in continuous lightand in the dark, GA₃-induced promotion starts 24 h after incubation.In the dark, even low concentrations of GA₃, which do not affectthe length measured after 6 d when the extension of hypocotylalmost ceases, remove the lag period of 48 h which precedesextension, and prolong the high rate of elongation. FollowingGA₃ supply the hypocotyl length in the dark and in the lightdoes not differ until 48 h; thereafter the rate of elongationin the light is less, so that the final length of the hypocotylis 40 per cent shorter than that of the dark-grown seedlingswithout GA₃. IAA supplied apically to light-grown seedlings induces a weakpromotion at a concentration of 1 mg l^–1 only. With anincreasing concentration of GA₃ supplied simultaneously, theconcentration of IAA inducing a significant promotion decreases.A combined supply of both these regulators, however, does notrestore the light-mediated inhibition of hypocotyl elongationcompletely. The maximum decrease in hypocotyl length induced by the growthretardants AMO-1618, CCC, and B-9 supplied from the beginningin the dark does not exceed 70 per cent. Saturating doses ofGA₃ supplied in combination with any one of the retardants compensateonly a fraction of the decrease. The results have been interpreted to show that native GAs arenot involved in extension growth in the dark.     

The Growth Rate of Wheat Leaves in Relation to the Extension Zone Sugar Concentration Manipulated by Shading

The main objective of this study was to determine the relationshipbetween the relative rate of growth of emerging wheat leavesand the hexose sugar concentration of the extension zone. Shortperiods of intense shading (to 20 or 5% of full sun for up to14 d) were used to decrease hexose concentrations. Shading decreased hexose concentrations to a fraction of thatof controls and also resulted in thin and narrow leaves thatwere less in dry weight than control leaves of the same length.Shading did however increase the length of the zone of extendingtissue at the leaf base by 30%. The effect of hexose concentrations on the relative rate ofleaf growth was evaluated by determining the ratio between growthrates of shaded and control leaves. This ratio declined as hexoseconcentrations declined and the relationship was described bya rectangular hyperbola (r > 0.95, P < 0.01). Combineddata from many leaves on the main shoot and its tillers fromtwo irrigated wheat crops all conformed to the same relationship.The hexose concentrations where the ratio of growth rates washalf the maximum rate were 0.42 mg g^–1 fr. wt. for extensiongrowth and 1.74 mg g^–1 fr. wt. for dry weight growth.These values were significantly (P < 0.01) different. These results were compared with data from emerging leaves offield crops and it was concluded that hexose concentrationshad not limited leaf growth rates, the lowest values recordedbeing 2.5–3.0 mg g^–1 fr. wt. It was further suggestedas unlikely that leaf growth rates of wheat crops in the fieldwould be limited by hexose concentrations.     

The Rate of Water-loss from Stripped Leaves

Stripping off the epidermis of Sedum leaves is found to increasethe rate of water-loss by amounts of the order of 700 per cent.A high resistance of the pores of the stomatal epidermis tothe diffusion of water-vapour from the mesophyll is thus indicated. Stripping one surface of a leaf considerably increases the rateof transpiration from the other (untouched) surface. The explanationof this is under investigation. In conclusion, the writer wishes to thank Dr. F. M. Haines forsuggestions, interest and criticism. Thanks are also due tothe staff of the Chelsea Physic Garden and to Mr. I. R. McGregorfor his valuable technical assistance.     

Osmotic Stress in Coleoptiles and Primary Leaves of Wheat: I. EFFECTS ON SIZE, WEIGHT, TOTAL PROTEIN, DNA, AND PHOSPHORUS

Seedlings of wheat (Triticum durum, cv. Balcarceño-INTA)were water-stressed in darkness with 20% polyethylene glycol(PEG) 6000 or 0.3 M mannitol added to the root medium. At differenttimes and up to a total of 36 h of treatment the coleoptileand primary leaves were cut and analysed. The height and freshweight of shoots were lower in treated plants than in controlplants. Dry weight was not significantly different between controland water-stressed plants. Total protein concentration decreasedsignificantly (P < 0.01) after 36 h of PEG 6000 treatment.Total DNA concentration decreased in controls but not significantly(P < 0.025) in treated seedlings. This result was interpretedas indicating that cell elongation prevailed over cell divisionin controls and that cell enlargement was affected in stressedplants. Total phosphorus concentration fell in control and treatedseedlings. However, phosphorus specific radioactivity increasedby 116% in control plants, 93% in mannitol-treated plants, and22% in PEG 6000-treated seedlings. These data suggest that anearly metabolic effect of water stress may be on phosphorusturnover in shoots.     

Regulation of Ethylene Biosynthesis in Virus-Infected Tobacco Leaves : II. TIME COURSE OF LEVELS OF INTERMEDIATES AND IN VIVO CONVERSION RATES

Ethylene production was stimulated severalfold during the hypersensitive reaction of Samsun NN tobacco to tobacco mosaic virus (TMV). Exogenous methionine or S-adenosylmethionine (SAM) did not increase ethylene evolution from healthy or TMV-infected leaf discs, although both precursors were directly available for ethylene production. This indicates that ethylene production is not controlled at the level of methionine concentration or availability, nor at the level of SAM production or concentration. In contrast, 1-aminocyclopropane-1-carboxylic acid (ACC) stimulated ethylene production considerably. Thus, ethylene production is primarily limited at the level of ACC production.     

Water Movement into and through Tradescantia virginiana (L.) Leaves: I. UPTAKE DURING CONDITIONS OF DYNAMIC EQUILIBRIUM

Water uptake into the ventral epidermis and the other tissuesof excised T. virginiana leaves was measured separately andsimultaneously when the uptake rates were steady. It was foundthat uptake into the ventral epidermis was proportionately greater,compared with uptake into the remainder of a leaf, than wouldbe expected from the ratio of conductances of the two pathways.This result led to the conclusion that not only is the epidermisa pathway for water transport in the transpiration stream butthat it is an important site of evaporation for stomatal transpiration.     

The Diffusive Conductivity of the Stomata of Wheat Leaves

A leaf chamber (described in detail) was used alternately witha resistance porometer to measure resistance to viscous flowof air through the leaf, and with a diffusion porometer to measurethe differential diffusive flow of hydrogen and air (V_H–V_A)through the leaf and the component of hydrogen flow (V'_H) movingstraight across the leaf. The resistance of the mesophyll isneeded for interpretation: estimates by three different methodsfor viscous flow did not agree very well, but two differentmethods for diffusive flow gave good agreement. For wheat leaves,only very large errors are important. Formal analysis is in three appendixes: I. Interpretation ofviscous and diffusive flow in small pores involves some problemsin molecular physics, complicated by the particular geometryof the wheat stoma. With some uncertainty, formal expressionsare derived for the viscous resistance of a single stoma, rv,and for the resistances to diffusion of hydrogen and air, andof water vapour and carbon dioxide, all expressed as r_s persquare centimetre of leaf surface. The analysis for hydrogen/airis the most uncertain; that for water vapour and carbon dioxideis more reliable. II. An indication is given of the flow characteristicsof the leaf-chamber system, from which rv can be derived, andof the basis for estimating mesophyll resistance. III. The methodof converting estimates of r_s into estimates of V_H–V_Aand V'_H is given. The results presented are expressed as nearly as possible interms of the quantities which were measured. For five leavesthe dependence of V_H–V_A on V'_H agrees well with theoreticalpredictions; the dependence of V_H–V_A (and V'_H) on rv,on average, agrees well with prediction, but involves the assumptionthat the stomata get shorter as they close. The agreement isgood enough to suggest that the formal expressions for r_s interms of stomatal dimensions and molecular gas constants arereliable enough to be carried forward into future transpirationand assimilation studies. The minimum value of ra for watervapour (c. 3 sec cm⁺¹) is close to values found elsewhere bydifferent techniques. At very small stomatal openings there was a large deviationfrom predicted behaviour, such as would occur if the imposedexcess air pressure further closed the stomata during viscousflow experiments.     

小麦叶内硝酸还原的代谢库

随营养液中No_3~-浓度升高,叶片内No_3~-总量、代谢库大小(NIPS)及硝酸还原酶(NR)活性均升高,其中MPS与NK活性呈同步变化;No_3~-浓度达2.0mmol/L时,两者趋于稳值;若再增加NO_3~-浓度,则被吸收的NO_3~-积累于液泡中,而代谢库中NO_3~-含量(MPS)与NO_3~-总量之比有一定程度降低。低氮(NO_3~-浓度为1.0 mmol/L)情况下,反应液中无NO_3~-时,叶片内NR活性品种间有差异,但在50 mmol/L NO_3~-反应液中则品种间无差异;NK活性高的品种鲁麦8号及品种321叶内有大的NO_3~-代谢库,反应液中NO_3~-对NR活性刺激程度低,代谢库NO_3~-含量与叶NO_3~-总量之比高,而叶组织长时间反应过程中其NR活性衰减速率低。