三唑酮浸种后黄瓜幼苗的生理生化变化

黄瓜以一定浓度的三唑酮浸种后,幼苗的根长,株高受到明显抑制,但增大了根重、根冠比、子叶游离氨基酸含量及子叶呼吸速率,同时降低了子叶可溶性糖含量,30d苗龄第1、2片真叶中叶绿素、蛋白质含量、POD、CAT活力增有不同程度的提高,因此表现出一定的壮苗作用。其中50μmol/L对壮苗是最佳的,但高浓度对幼苗生长不利。     

The Relationship Between the Phosphorus Status of Subterranean Clover Plants and Losses in Chlorophyll from Detached Leaves: A Basis for the Visual Diagnosis of Phosphorus Deficiency

Leaves detached from subterranean clover plants (Trifolium subterraneumL.), grown in solution cultures at different phosphorus levels,were placed in water and in phosphate solutions. Losses in totalchlorophyll (a+b) of leaves in water were greater the lowerthe previous phosphorus supply to the plants from which theywere detached. In comparable leaves placed in phosphate solutionschlorophyll was maintained at levels at least as high as inleaves from non-deficient plants. For the latter there wereno differences between treated and untreated leaves. The differencesin colour change between treated and untreated leaves, therefore,increased with the deficiency in the phosphorus supply to theplants from which the leaves were detached, thus visibly reflectingtheir phosphorus status. A light intensity of 300 ft c (27 lx) or higher was necessaryfor maximum differences in leaf colour between treated and untreatedleaves, mainly because lower light levels reduced chlorophylllosses from leaves in water. Differences in colour between treated and untreated deficientleaves decreased with their age. However, valid comparisonsbetween treated and untreated leaf tissue could be ensured bythe use of treated and untreated leaflets. It is suggested that the results provide the basis for a simple,direct and visual diagnostic method, requiring no laboratoryequipment. Trifolium subterraneum L., subterranean clover, phosphorus deficiency, chlorophyll     

The Role of Roots in Control of Bean Shoot Growth

Restriction of root growth by growing bean plants (Phaseolusvulgaris L.) in very small pots led to the development of dwarfplants. The leaves of those plants were smaller and their internodesshorter than those of control plants which were grown in largerpots and had developed a more extensive root system. A largequantity of starch—much more than in control plants —accumulated in the leaves and shoots of the dwarf plants. Increasingthe amount of minerals which was supplied to the roots, enhancedleaf growth of the control plants but failed to affect the dwarfones, in spite of the fact that in both cases the treatmentincreased the content of N, P and K in all the plant organs.The leaf water content was similar in both treatments, but theleaf water potential was higher in the dwarf plants. Exogenousapplication of gibberellic acid (GA₃) to the dwarf plants overcamethe reduction of stem growth completely, and that of the leavespartially. Application of the cytokinin, benzyladenine (BA)did not affect stem growth, but increased that of the primaryleaves. A combined supply of GA₂ + BA restored completely thegrowth of the stem and the primary leaves, and partially thatof the trifoliate leaves. It is concluded that a limited rootsystem restricts shoot growth through an hormonal system inwhich at least gibberellins and cytokinins are involved, andthat the dwarfing is not a consequence of mineral or assimilatedeficiency, or due to water stress. Phaseolus vulgaris L., leaf growth, stem growth, root restriction, gibberellic acid, benzyladenine, cytokinin     

Studies in the Nutrition of Apple Rootstocks: 1. Effects of Deficiencies of Iron and Magnesium on Growth

Plants of the apple rootstock M.VII were grown for a singleseason by spraying their roots continuously with nutrient solutions:(a) complete, (b) low iron, (c) low magnesium, and (d) low ironand low magnesium. Detailed records were taken throughout theseason of fresh weight, shoot length, diameter, and leaf area,while the fresh and dry weights of component parts were determinedon harvested samples. The leaves of the iron-deficient plants were chlorotic and hada lower dry weight and higher water content per unit area thanthose of the control plants. Growth and net assimilation ratewere both reduced but the distribution of assimilates was similarto that in the controls. Total growth was also markedly reduced by the low-magnesiumtreatment, but the leaf symptoms were different and the plantswere morphologically distinct from the control plants. Verylittle chlorosis occurred, but necrosis and severe defoliation,progressing up the shoot, reduced the leaf area ratio and probablylargely accounted for the low net assimilation rate and relativegrowth rate. The diameter of the shoot was affected much morethan its length and the shoot/root ratio was greatly increased. Plants deficient in both iron and magnesium showed less defoliationthan when magnesium alone was low. More dry matter accumulatedin the old stem and less in the new shoot than would have occurredwith a simple combination of the single deficiencies.     

Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Flooding the soil for 5–7 d caused partial desiccationin leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’).The injury was associated with anaerobiosis in the soil, a largeincrease in the permeability of leaf tissue to electrolytesand other substances, a low leaf water content and an increasedwater saturation deficit (WSD). Desiccating leaves also lackedthe capacity to rehydrate in humid atmospheres, a disabilityexpressed as a water resaturation deficit (WRSD). This irreversibleinjury was preceded during the first 4–5 d of floodingby closure of stomata within 24 h, decreased transpiration,an unusually large leaf water content and small WSD. Leaf waterpotentials were higher than those in well-drained controls.Also, there was no appreciable WRSD. Leaflets detached fromflooded plants during this early phase retained their watermore effectively than those from controls when left exposedto the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydrationcould be simulated by excising leaves and incubating them withtheir petioles in open vials of water. Thus, such changes inflooded plants possibly represented a response to a deficiencyin the supply of substances that would usually be transportedfrom roots to leaves in healthy plants (negative message). Ionleakage and the associated loss of leaf hydration that occurswhen flooding is extended for more than 5 d could not be simulatedby isolating the leaves from the roots. Appearance of this symptomdepended on leaves remaining attached to flooded root systems,implying that the damage is caused by injurious substances passingupwards (positive message). Both ethylene and ethanol have beeneliminated as likely causes, but flooding increased phosphorusin the leaves to concentrations that may be toxic. Key words: Pisum sativum, Flooding, Foliar desiccation, Stomata, Ethylene     

Effects of Temperature Variation at Different Times on Growth and Yield of Sugar Beet and Barley

Sugar-beet and barley were grown in pots outdoors (environmentN) and, for five successive 4-week periods starting at sowing,batches of plants were transferred to three growth rooms whosetemperatures were either similar to the outdoor mean (environment^M), or 3° C hotter (environment H) or 3° C colder (environmentC). Some plants were harvested immediately after treatment;others were returned to environment N and harvested when mature. At the end of period 1, sugar-beet plants from environment Mhad more dry weight and leaf area than those outdoors. Immediatelyafter spending later periods in environment M, plants had smallerleaves and similar dry weight to those continuously outdoors.These differences disappeared by maturity. Warmth in the growthrooms (i.e. the difference H—C) during periods 1, 2, and3, while leaf area was increasing, increased the number andsize of leaves and usually also dry weight; in later periodsit had no effect. The effects induced during periods 2 and 3,but not period 1, persisted to maturity to give greater totaland root dry weight and yield of sugar. The final effects ondry weight were much larger than those immediately after treatment,and were the result of differences in growth outdoors aftertreatment which depended on differences in leaf area; the efficiencyof the leaves was not affected by previous treatment. Transferring barley to environment M from N had inconsistentimmediate effects on leaf area and dry weight which disappearedby the final harvest. Transfer during periods 2 and 3, beforethe ears had started emerging, increased shoot number and delayeddevelopment. The proportion of the ears that ripened and theyield of grain were usually less for plants that had spent aperiod in environment M than for plants permanently outdoors,which also had some green ears. Warmth in the growth rooms duringperiods 1 and 2 increased dry weight and leaf area immediately,but had negligible effects at maturity because the increasesin leaf area did not persist after ear emergence. Warmth laterhastened death of leaves, decreased total dry weight immediatelyand also at maturity, but increased the proportion of ears thatripened and hence usually grain weight. Variation in leaf areaduration after ear emergence (D), determined by effects on thetime the ears emerged and the rate the leaves died, accountedfor most of the variation in grain yield, but warmth after theears emerged decreased grain yield less than proportionallyto the decrease in D. Net assimilation rate (E) of sugar-beet was greater than ofbarley, and decreased less with age. E of both species was usuallygreater in environment M than outdoors in spite of less radiation.It was only slightly affected by temperature. Nitrogen and potassium uptake were increased by treatments thatincreased dry weight. The percentage contents suggest that extrauptake was a consequence and not a cause of the increase indry weight.     

Growth of Zea mays L. plants with their seminal roots only. Effects on plant development, xylem transport, mineral nutrition and the flow and distribution of abscisic acid (ABA) as a possible shoot to root signal

Maize (Zea mays L.) was grown in quartz sand culture eitherwith a normal root system (controls) or with seminal roots only(‘single-rooted’). Development of adventitious rootswas prevented by using plants with an etiolated mesocotyl andthe stem base was positioned 5–8 cm above the sand. Eventhough the roots of the single-rooted plants were sufficientlysupplied with water and nutrients, the leaves experienced waterdeficits and showed decreased transpiration as trans plrationalwater flow was restricted by the constant number of xylem vesselspresent in the mesocotyl. As a consequence of this restriction,transpirational water flow velocities in the metaxylem vesselsreached mean values of 270 m h^–1 and phloem transportvelocities of 5.2 m h^–1. Despite limited xylem transportmineral nutrient concentrations in leaf tissues were not decreasedin single-rooted plants, but shoot and particularly stem developmentwas somewhat inhibited. Due to the lack of adventitious rootsthe shoot:root ratio was strongly increased in the single-rootedplants, but the seminal roots showed compensatory growth comparedto those in control plants. Consistent with decreased leaf conductance,ABA concentrations in leaves of single-rooted plants were elevatedup to 10-fold, but xylem sap ABA concentrations in these plantswere lower than in controls, in good agreement with the well-wateredconditions experienced by the seminal roots. Surprisingly, however,ABA concentrations in tissues of the seminal roots of the single-rooted plants were clearly increased compared to the controls,presumably due to increased ABA import via phloem from the water-stressedleaves. The results are discussed in relation to the role ofABA as a shoot to root signal. Key words: Zea mays, seminal roots, plant development, xylem transport, mineral nutrition, ABA, shoot-to-root signal     

Meristem aging is not responsible for age-related changes in growth and abscisic acid levels in the Mediterranean shrub, Cistus clusii

To obtain new insights into the mechanisms underlying aging in perennials, we measured abscisic acid levels, growth and other stress indicators in leaves of Cistus clusii Dunal plants of different ages grown under Mediterranean field conditions. Recently emerged leaves from 9-year-old plants were compared to those of 1-year-old plants (obtained from cuttings from 9-year-old plants) to evaluate the effects of meristem aging on plant aging. Rooting and successful establishment of the cuttings allowed us to compare the physiology of plants with old meristems, but of different size. Plants obtained from cuttings were rejuvenated, with new leaves displaying a higher leaf area and chlorophyll content, but smaller leaf mass per unit area ratios and endogenous abscisic acid levels than those of 9-year-old plants. A comparative study in 1-, 4- and 9-year-old plants revealed that abscisic acid levels increase during the early stages of plant life (with increases of 90% between 1- and 4-year-old plants), but then remain constant at advanced developmental stages (between 4- and 9-year-old plants). Although leaf biomass was 53% smaller in 9-year-old compared to 4-year-old plants, the dry matter produced per shoot apical meristem was equivalent in both plant groups due to an increased number of leaves per shoot in the former. It is concluded that (i) C. clusii plants maintain the capacity to rejuvenate for several years; (ii) newly emerged leaves accumulate higher amounts of abscisic acid during early stages of plant life, but the levels of this phytohormone later remain constant; and (iii) although plant aging leads to the production of smaller leaves, the amount of biomass produced per shoot apical meristem remains constant at advanced developmental stages.     

Distribution and Redistribution of Molybdenum in Black Gram (Vigna mungo L. Hepper) in Relation to Molybdenum Supply

The effect of seven rates of molybdenum (Mo) supply on the distributionand redistribution of Mo in Vigna mungo (black gram) cv. Reguron a Mo-deficient sandy loam was examined from flower bud appearanceto pod set in one experiment and during pod filling to maturityin another. At the three lowest Mo supply rates, N deficiency symptoms typicalof Mo deficiency appeared, and shoot dry matter and shoot nitrogencontent were depressed. Increasing Mo supply increased Mo concentrationsin all plant parts but the response varied with Mo supply andwith plant part. In leaf blades and petioles, Mo concentrationsincreased slightly when the Mo supply increased from severelydeficient to deficient levels but further increases in Mo supplymarkedly increased the Mo concentrations, particularly in immatureand recently matured leaves. In petioles, Mo concentrationsgenerally exceeded those in the blades which they supportedat all levels of Mo supply. At Mo rates greater than that requiredfor maximum growth, Mo concentrations in basal stem segmentsexceeded those in petioles. Molybdenum concentrations in nodulesexceeded those in above ground plant parts except at the highestlevel of Mo supply where the concentrations in basal stem segmentsexceeded those in nodules. In Mo-adequate plants, Mo contents in the trifoliolate leavesdecreased with time suggesting that Mo was readily remobilized.By contrast, in stem segments at all levels of Mo supply, andin trifoliolate leaves in Mo-deficient plants, Mo contents remainedconstant or increased with time suggesting that Mo was not remobilizedin all plant parts or at all levels of Mo supply. Thus, theresults suggest that in black gram Mo was variably mobile, beingphloem immobile at low Mo supply, but phloem-mobile in all plantparts with the possible exception of stem segments at adequateMo supply. The relevance of these results for the developmentof plant tests for Mo deficiency diagnosis is discussed.Copyright1994, 1999 Academic Press Molybdenum, phloem-mobility, redistribution, black gram, Vigna mungo L. Hepper     

Relationships Between Nitrogen and Water Concentration in Shoot Tissue ofMolinia caeruleaDuring Shoot Development

Plants ofMolinia caeruleawere supplied with either a low (0.2mol m^-3) or high (10 mol m^-3) supply of nitrogen over two growingseasons. A total of 14 destructive plant harvests were made:when plants were in an over-wintering state prior to the secondseason; immediately following bud burst; and on 12 further occasionsthroughout the second season. The relationships between shootnitrogen concentration on a dry mass basis, shoot water contentand plant developmental stage were investigated. Shoot nitrogenconcentration on a dry mass basis fell as the growing seasonprogressed. In contrast, the concentration of nitrogen in tissuewater after bud burst showed only a slight reduction. The concentrationof nitrogen both on a dry mass basis and in tissue water wasgreater for plants receiving the higher supply of nitrogen.Shoot water content was highest immediately following bud burstthen declined as the season progressed, with plants receivingthe low nitrogen supply having slightly greater shoot watercontents. It was concluded that the decline in shoot nitrogenconcentration ofM. caeruleaon a dry mass basis as the mass increasedwas mainly explained by changes in shoot water content. Theobserved increase in the rate of decline of both shoot nitrogenconcentration and water content with increased shoot mass coincidedwith the cessation of leaf tissue production and was thereforedue to a switch from the production of leaves to other tissues.Copyright1999 Annals of Botany Company Molinia caerulea(L.), purple moor grass, nitrogen, water content, shoot development.     

Leaf Extension in Zea mays: I. LEAF EXTENSION AND WATER POTENTIAL IN RELATION TO ROOT-ZONE AND AIR TEMPERATURES

The temperature of the roots and shoots of Zea mays plants werevaried independently of each other and the rates of leaf extensionand leaf water potentials were measured. Restrictions of leafextension occurred when root temperatures were lowered from35 to 0 °C, but leaf water potentials were lowered onlyat root temperatures below 5 °C. Similar changes in ratesof leaf extension were measured at air temperatures from 30to 5 °. Between 30 and 35 °C air temperature, in anunsaturated atmosphere, restrictions of leaf extension wereassociated with low leaf water potentials. It was concluded that, at root temperatures 5 to 35 °C,and shoot temperatures 5 to 30 °C, water stress was notthe main factor restricting the extension of Zea mays leaves.     

Effects of Drought on CAM and Water Relations in Plants of Peperomia carnevalii

The mechanisms underlying the drought tolerance of Peperomiacarnevalii Steyermark (Piperaceae), a succulent herb growingin the understorey of seasonally dry forests, were examined.Crassulacean acid metabolism (CAM) was studied in the fieldand laboratory, and measurements of water status were made inplants subjected to drought in the greenhouse. Nocturnal acidaccumulation and day and night-time CO₂assimilation rates weregreatest in watered plants and decreased in drought. The proportionof CO₂recycled through CAM in droughted plants, with nocturnalCO₂uptake close to zero, was higher than in watered plants.Maximum quantum yield of chlorophyll fluorescence remained unchangedduring drought, but the PSII quantum yield at the photosyntheticphoton flux density at which the plants were grown was significantlydecreased. Leaf anatomy consists of a chlorophyll-less hydrenchymalocated beneath the upper epidermis, and a two-layered mesophyll.Leaves nearer to the apex are thinner than those nearer to thebase of the shoot. Drought caused a reduction in leaf thicknessdue to shrinkage of the hydrenchyma, but not of the mesophyll.This was associated with the occurrence of a gradient of osmoticpotential between these tissues. Comparison of water loss fromthin leaves of watered and droughted plants, either partly defoliatedat the lower nodes or intact, suggested that water moved fromthe thick to the thin leaves. This process was related to theoccurrence of a gradient of water potential between the thickand the thin leaves. Drought tolerance in P. carnevalii is achievedby the operation of CAM and the occurrence of water movementwithin and between leaves. Copyright 2000 Annals of Botany Company Crassulacean acid metabolism, fluorescence, hydrenchyma, mesophyll, Peperomia carnevalii, water relations     

Are Roots a Source of Abscisic Acid for the Shoots of Flooded Pea Plants?

Flooding the soil for 2–5 d decreased stomatal conductancesof pea plants (Pisum sativum L., cv. Sprite) with six or sevenleaves. This coincided with slower transpiration, increasedleaf water potentials and increased concentrations of abscisicacid (ABA) in the leaves. No increase in ABA was found in theterminal 20 mm of roots of flooded plants over the same timeperiod. Small stomatal conductances associated with increases in foliarABA were also found in plants grown in nutrient solution whenaeration was halted, causing the equilibrium partial pressuresof dissolved oxygen to fall below 05 It Pa. No increase in ABAconcentration in young secondary roots of the non-aerated plantswas detected after 24, 48 or 72 h, even when the shoot, thepresumed site of deposition for any ABA from the roots, wasremoved 5–6 h before analysis. Similarly, ABA concentrations in roots were not increased whenthe nutrient solution was de-oxygenated by continuous purgingwith nitrogen gas. The abscisic acid concentration in leaf epidermis,the tissue most likely to be the recipient of any ABA movingin the transpiration stream from oxygen-deficient roots, waslower than in the remaining parts of the leaf when examinedin the mutant Argenteum which possesses easily removable epidermallayers. It is concluded that the leaves of plants subjectedto flooding of the soil or oxygen shortage in the root environmentare not enriched substantially with ABA from the roots. A moreprobable source of this growth regulator is the leaf itself. Key words: Pisum sativum, flooding, roots, hormones, aeration stress, abscisic acid, Argenteum mutant     

Physiology of the parasitic association between maize and witchweed (Striga hermonthica): is ABA involved?

Striga hermonthica (Del.) Benth. is an obligate hemiparasiticangiosperm which can cause severe losses of yield in cerealcrops in the semi-arid tropics. The effects of this parasiteon the growth and stomatal conductance of three varieties ofmaize (Zea mays L.) during the first 6 weeks of the associationhave been studied. From 24 d after planting (DAP), infectedplants were significantly shorter than uninfected controls.When the plants were harvested 45 DAP, infected plants had fewerfully expanded leaves, less leaf biomass and less pseudo-stembiomass than uninfected controls. However, the parasitized plantshad more root biomass and hence a higher root:shoot ratio thanuninfected controls. The stomatal conductance of infected hostswas severely inhibited by comparison with that in uninfectedplants. The possibility that abscisic acid (ABA) may be involved inthe regulation of the parasitic association was investigated.ABA concentrations in leaf tissue of maize (cv. Cargimontana)and S. hermonthica were determined by radioimmunoassay. Whilethere was a difference between cultivars in the extent of theresponse, the concentrations of ABA were significantly higherin infected maize plants than in the uninfected controls. InS. hermonthica, leaf tissue ABA concentration was found to bean order of magnitude higher than in the host leaf tissue. Detachedleaves of S. hermonthica which were dehydrated at room temperatureuntil they had lost 10–20% of their fresh weight containedthree times the ABA concentration of control leaves. This suggeststhat leaves of S. hermonthica can synthesize or re-mobilizeABA in response to water deficit. It is not yet known whetherthis contributes to the higher concentration in infected hosts,but the results suggest that ABA has a role in this parasiticassociation. Key words: Striga hermonthica, abscisic acid, growth, parasitic angiosperm, stomatal conductance     

Temperature and Water Relations for Sun and Shade Leaves of a Desert Broadleaf, Hyptis emoryi

The temperature and water relations of sun versus shade leavesof Hyptis emoryi Torr. were evaluated from field measurementsmade in late summer. Throughout most of the day sun leaves hadhigher temperatures and higher resistances to water vapour diffusion,but lower transpiration rates and lower stem water potentials,than did shade leaves. Leaf absorptivity to solar irradiationwas less for 1.5-cm-long sun leaves (0.44) than for 4.0-cm shadeleaves (0.56). For both leaf types the stomatal resistance increasedas the water vapour concentration drop from the leaf to theair increased. Energy balance equations were used together with the measuredtemperature dependence of photosynthesis to predict the effectof variations in leaf absorptivity, length, and resistance onnet photosynthesis. The influence of leaf dimorphism on wholeplants was determined by calculating daily photosynthesis andtranspiration for plants with various percentages of sun andshade leaves. A hypothetical plant with all sun leaves in thesun had about twice the photosynthesis and half the transpirationratio as did plants with sun leaves in the shade or shade leavesin the sun or shade. Plants with both sun and shade leaves hadthe highest predicted photosynthesis per unit ground area. Thepossible adaptive significance of the seasonal variation insun and shade leaf percentages observed for individual H. emoryibushes is discussed in terms of water economy and photosynthesi     

Uptake of 32P by Young Plants of Banksia hookeriana Meissner When Healthy and Infected with Phytophthora cinnamomi Rands

Young plants of Banksia hookeriana were grown in acid-washedsand with adequate phosphate and water supply, and a proportionwere inoculated with Phytophthora cinnamomi. There were no majordifferences in growth between uninoculated and infected plants,but there was a large increase in uptake of ³²P with increasingroot disease. In healthy plants ³²P uptake was greatest in youngleaf tissue, but in diseased plants labelled phosphate was directedmore towards older leaves where the activity was almost twicethat of young leaves. Enhanced uptake with disease was ascribed to possible blockageof the ‘message’ or ‘signal’ of phosphatetranslocation from shoot to root, such that the diseased rootincorrectly treated the shoot as P deficient and increased Puptake. Key words: Banksia hookeriana, Proteaceae, ³²P uptake, Phytophthora cinnamomi     

Control of Flower Number in the First Inflorescence of Tomato (Lycopersicon esculentum Mill.): The Role of Gibberellins

The number of flowers in the first inflorescence of tomato plantswas increased by low temperatures and reduced by the applicationof GA³. The effect of GA³, was greater in a low temperatureregime (12 °C minimum) than at normal temperatures (16 °Cminimum). Increases in flower number could be produced by theremoval of young developing leaves but the treatment was nolonger effective if plants wen grown at low temperatures orwere treated with GA³. Young developing leaves were shown to be sources of diffusiblegibberellin-like substances. Leaves from plants grown in a normaltemperature regime yielded greater amounts of gibberellin-likesubstances than leaves from plants grown in the low temperatureregime. It is suggested that high levels of endogenous gibberellinsact to reduce the number of flowers formed in the first inflorescence,and that leaf removal and low temperatures influence flowernumbers by lowering levels of diffusible gibberellins in theplants. Lycopersicon esculentum, tomato, flower number, gibberellins, temperature     

Photosynthetic Determinants of Growth in Maize Plants: Effects of Nitrogen Nutrition on Growth, Carbon Fixation and Photochemical Features

Maize(Zea mays L.) plants were grown in a greenhouse with differentlevels of nitrate-N (2 to 20 millimolar). Nitrogen nutritionhad dramatic effects on plant growth and photosynthetic characteristicsof mature leaves. Increasing nitrogen resulted in greater biomassproduction, shoot/root ratios, and rates of leaf expansion duringthe day. The elongating zone of high-N plants had higher activities(per gram fresh weight) of sucrose synthase and neutral invertasethan low-N plants, suggesting that increased leaf growth wasrelated to a greater biochemical capacity for sucrose metabolism. Mature leaves of high-N plants had higher rates of photosynthesisand assimilate export (sucrose formation), and partitioned morecarbon into sucrose relative to starch. Increased photosyntheticrates (leaf area basis) were associated with higher levels ofribulose-l,5-bisphosphate carboxylase, phosphoenolpyruvate carboxylaseand pyruvate, phosphate dikinase (determined immunochemically).In addition, N-nutrition affected the functional organizationof chlorophyll in the leaves. Large increases in the numberof PS I reaction centers were observed which fully accountedfor increases in leaf chlorophyll content with increasing nitratesupply. Collectively, the results suggest that increased growth of maizeplants at high light and optimal nitrogen nutrition is relatedto greater capacity for photosynthesis and translocation inmature leaves, and possibly increased capacity for sucrose metabolismin expanding leaves. (Received May 22, 1989; Accepted August 28, 1989)     

Shoot Resistance to Water Flow in Cotton

Studies using excised cotton (Gossypium hirsutum L.) plants,attached to a free water source and undergoing transpirationcycles, were conducted at intervals over a 2 year period inorder to quantify shoot resistance components of cotton canopies.Leaf water potential was found to be a linear function of transpirationrate at rates above 0.1 mm h^–1, so shoot resistance wasevaluated as the slope of this function. The value of 4.8 104h (0.48 MPa h mm^–1) total shoot resistance was consistentfor 1.10 m tall, well irrigated, fruit-bearing cotton plants.Further tests, with pre-wrapped and exposed leaves, revealedthat total shoot resistance was comprised of an axial component(40%) and a leaf component (60%). The total shoot resistanceof 0.48 MPa h mm^–1 is likely to be relevant for modellingcotton water relations when LWP is evaluated on exposed, topof the canopy leaves, such as in the ‘big leaf’type models. Key words: Leaf water potential, axial resistance, leaf resistance     

The Effects of Infection by Rust (Puccinia lagenophorae Cooke) on the Growth of Groundsel (Senecio vulgaris L.) Cultivated under a Range of Nutrient Concentrations

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae Cooke, was grown at a rangeof nutrient concentrations in sand culture. There were statisticallysignificant interactions between the effects of infection andnutrient supply upon the dry weights of stems, leaves, rootsand reproductive tissues, leaf area and cumulative capitulumproduction. This interaction occurred since infection causedsignificant inhibitions of growth only at moderate or high nutrientconcentrations. At low concentrations rusted plants were similarto or slightly larger than controls. Both in controls and rustedplants root: shoot ratios increased as nutrient supply declined.The ratio of root: shoot dry weight was consistently reducedby infection whilst root length: leaf area ratio was relativelyunchanged. More detailed investigations confirmed that infection had littleeffect on plant growth under nutrient deficient conditions despitesuppression of the host's ability to increase root: shoot ratiosin response to nutrient stress. This reflected the inhibitionof relative growth rates in rusted plants at high but not lownutrient concentrations, which in turn reflected reduced netassimilation rates (NAR). Increases in leaf-area ratio (LAR)often ameliorated the decline in NAR in rusted plants. Senecio vulgaris L., Puccinia lagenophorae Cooke, nutrient deficiency, growth, root: shoot ratio