Water Deficit and Inflorescence Development in Zea mays L.--The Role of the Developing Tassel

In the normal pattern of development of Zea mays (cv. Iochief)a single mature female inflorescence is produced at node 7.A brief episode of water deficit at the time of terminal maleinflorescence initiation induced the subsequent developmentof two to three mature female inflorescences at nodes 5–7.This growth of the inflorescences at lower nodes was accompaniedby a marked inhibition of the growth of the terminal male inflorescence.Removal of either the developing terminal inflorescence or ofthe axillary inflorescence at node 7 at this time also promotedthe growth of the lower axillary inflorescences. The growthof these inflorescences was further stimulated by a period ofwater deficit when only the inflorescence at node 7 was removed,but removal of the male inflorescence abolished the capacityof these inflorescences to respond to the water deficit Excisionof the male inflorescence immediately before or immediatelyafter the period of water deficit produced the same response.It is concluded that this response of the lower axillary inflorescencesto water deficit is mediated through an effect on the developingterminal male inflorescence. Zea mays, water deficit, inflorescence development, tassel, correlative inhibition     

Apical Dominance, Water Deficit and Axillary Inflorescence Growth in Zea mays: The Role of Abscisic Acid

In the sweet corn cultivar, Iochief, an episode of water deficitduring early tassel development results in a subsequent promotionof the growth of the lower axillary inflorescences. This responseis also produced by the application of abscisic acid (ABA) atthis period of growth to well-watered plants, and the hypothesisthat the response to water deficit was due to an increase inendogenous ABA concentration was examined. The ABA contentsof the tassel, leaf and axillary inflorescences were found toincrease during water stress, the increase in the tassel andaxillary buds being most rapid in the first 2 days of waterdeficit. This increase in free ABA content was followed after4 days of water deficit by a progressive increase in the concentrationof ‘bound’ ABA in the tissues. There was littleincrease in free ABA concentration after 4 days water deficit;this paralleled the subsequent growth response of the axillaryinflonscences which also was unaffected by prolonging the epidoseof water deficit beyond 4 days. In order to establish whether the response of the axillary inflorescencesto ABA was dependent upon the presence of the tassel, ABA wasapplied to watered plants with or without the developing tassel.As had been previously found with water stress, removing thetassel inhibited the response of the plant to applied ABA. Zea mays, apical dominance, water stress, inflorescence growth, abscisic acid     

Propagation of Zea mays L. by Shoot Tip Culture: A Feasibility Study

A procedure for the stimulation of axillary bud developmentfrom young shoots of maize, their subculture to root-inducingmedia and transfer as rooted plants to soil is described. Axillarybud development was enhanced by the addition of kinetin andauxin to the culture medium. Root initiation on explanted axillarybuds, while successful with some cultivars, was variable. Anumber of mature plants with normal tassels and ears were producedfrom the lowermost buds of an original stem explant. Buds fromhigher positions on the explant exhibited different potentialitieswith some, those normally from cob producing nodes, producingshort-stalked plants with terminal female influorescences. Agradient of bud potentiality along the stem appears to be establishedextremely early after each is initiated. Zea mays., corn, maize, shoot tip culture, clone, vegetative propagation     

Ammonium Tolerance and Carbohydrate Status in Maize Cultivars

Four maize (Zea mays L.) hybrids were grown hydroponically for4 weeks with 20 mM ammonium or nitrate as the sole nitrogensource. Dry matter production was strongly depressed by ammoniumnutrition in the hybrid Helga relative to plants grown on nitrate,and moderately decreased in the hybrid Melina. Ammonium hadno inhibitory effect on total yield in the other two hybrids(Ramses and DK 261). The relative growth rate (RGR) of rootsand shoots of the sensitive hybrid Helga decreased significantlyunder ammonium nutrition during the first 2 weeks of the experiment,while at the end of the experiment nitrogen form had no effecton the RGR in any of the four hybrids. The strong reductionin RGR of Helga in the early seedling stage was correlated withthe accumulation of twice the concentration of free ammoniumin the shoot tissue relative to the other hybrids. Helga wastherefore unable to sufficiently detoxify ammonia in the roots.Root concentrations of water soluble carbohydrates (WSC) inHelga and Melina in the early seedling stage did not differunder ammonium and nitrate nutrition. In contrast, Ramses andDK 261 both had elevated WSC concentrations in ammonium-fedroots. It is hypothesized that a sufficient supply of carbonskeletons for ammonium assimilation in the roots is requiredfor maximum growth under high ammonium concentrations, and thatthere is genotypic variability in this physiological trait. Ammonium; carbohydrates; growth rate; maize; nitrate; roots; Zea mays L     

Carbohydrate, Nitrogen and Dry Matter Accumulation and Partitioning of Maize Hybrids Under Drought Stress

Maize (Zea mays L.) productivity under drought stress dependsto some extent upon a hybrid's capacity to produce and translocateassimilate to its developing kernels during the stress periodand/or after the stress is relieved. The objective of this studywas to evaluate differences in carbon and nitrogen accumulationand partitioning under drought stress among maize hybrids thatdiffer in yield potential and/or physiological metabolism duringreproductive development. The hybrids B73 x LH38, FS854, B73xMol7and US13 were subjected to drought stress from the 7th leafstage until pollination was completed, at which time the soilof the stressed plots was replenished with water. For d. wtand chemical constituent determinations, plants of each hybridwere harvested from the irrigated and drought stressed plotsat silking, mid-grain fill, and physiological maturity. Averagedover hybrids, vegetative biomass at silking was reduced 25%as a result of the drought stress treatment, with B73 x LH38and FS854 accumulating more total biomass during the later portionof grain fill than the other two hybrids under both soil moisturetreatments. At silking, the total non-structural carbohydratecontent of the hybrids' vegetative tissue was not changed asa result of drought stress, whereas their reduced nitrogen (N)contents were decreased by an average of 33%. B73 x LH38 andFS854 had greater grain carbohydrate and reduced N contentsunder irrigation and smaller decreases in those variables asa result of soil moisture deficit than did the other two hybrids.These results indicate that the greater drought tolerance ofB73 x LH38 and FS854 to stress imposed during vegetative andearly reproductive development resulted from their more activeN uptake and assimilation and sugar production during the laterportion of grain fill and from their more efficient partitioningof assimilate to the developing kernels. Zea mays L., maize, drought stress, nitrogen, carbohydrates, hybrids, partitioning     

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.     

Root and Shoot Growth of Plants Treated with Abscisic Acid

Young seedlings of Capsicum annum L., Commelina communis L.and maize (Zea mays L.) were subjected to a mild water-stressingtreatment and/or treated with abscisic acid (ABA). Plants rootedin soil received a soil-drying treatment and their leaves weresprayed with a 10–⁴ M solution of ABA. Plants grown insolution culture were stressed by the addition of polyethyleneglycol (PEG) to the rooting medium and ABA was also added tothe rooting medium, either with or without PEG. The effectsof both treatments on the growth of roots and shoots and theultimate root: shoot dry weight ratio were very similar. Shootgrowth was limited both by water stress and by ABA application;while there was some evidence that mild water stress and/orABA application may have resulted in a stimulation of root growth.More severe water stress reduced the growth of roots but theoverall effect of stress was to increase the ratio of rootsto shoots. Capsicum annum L., Commelina communis L., Zea mays L., water stress, abscisic acid     

A Simple Instrument for Measuring Leaf Extension in Grasses, and its Application in the Study of the Effects of Water Stress on Maize and Sorghum

The design of a simple instrument to monitor leaf expansionin grasses is described. The instrument was used to comparethe effects of water stress on leaf extension of two cultivarsof maize and sorghum. The effect of withholding water for 3days was an appreciable reduction in the rate of leaf expansionin both plants, particularly during the light period. In well-wateredplants of both species, leaf extension continued at a steadyrate even when leaf turgor fell to around 0.1 MPa. In water-stressedmaize plants, leaf turgor during the light period fell to zeroand leaf growth ceased. When turgor was restored, followingstomatal closure, leaf extension resumed at a slow rate. Inunwatered sorghum plants, leaf turgor remained at a value greaterthan 0.1 MPa but the rate of leaf extension was significantlyreduced. The reduction in leaf turgor in the unwanted plantsresulted partly from an increase in solute potential. Zea mays L, maize, Sorghum bicolor L, leaf expansion, leaf turgor, water stress     

Root Growth and Water Uptake by Maize Plants in Drying Soil

Sharp, R. E and Da vies, W. J. 1985. Root growth and water uptakeby maize plants in drying soil.— J. exp. Bot. 36: 1441–1456. The influence of soil drying on maize (Zea mays L.) root distributionand use of soil water was examined using plants growing in thegreenhouse in soil columns. The roots of plants which were wateredwell throughout the 18 d experimental period penetrated thesoil profile to a depth of 60 cm while the greatest percentageof total root length was between 20–40 cm. High soil waterdepletion rates corresponded with these high root densities.Withholding water greatly restricted root proliferation in theupper part of the profile, but resulted in deeper penetrationand higher soil water depletion rates at depth, compared withthe well watered columns. The deep roots of the unwatered plantsexhibited very high soil water depletion rates per unit rootlength. Key words: Maize, roots, water deficit, soil water depletion     

Germination and Early Growth of Plants Studied Using Neutron Radiography

Seed swelling, germination, root extension, lateral root initiationand shoot growth were studied in soils of different water contents,using non-destructive, serial neutron radiography. Seeds fromthree varieties of soya beans (Glycine max L.) and one varietyeach of maize (Zea mays L.) and vetch (Vicia sativa L.) wereused. The seeds germinated when they had increased in size bya certain amount, if germination is taken as the time when theradicle first appears. The rate at which roots and shoots extendalso depend on soil water content. Glycine max L., Vicia sativa L., Zea mays L., Soya bean vetch, maize, seed germination, root extension, lateral root initiation, neutron radiography     

Cell Membrane Stability and Leaf Water Relations as Affected by Potassium Nutrition of Water-Stressed Maize

A field experiment was conducted to investigate the effect ofK nutrition under water stress conditions on cell membrane stabilitymeasured by the polyethylene glycol test, plant growth, internalplant water relations and solute and mineral concentrationsin maize (Zea mays L.). Water-stressed plants showed greateradaptation to water deficits at higher K levels. Cell membranestability increased, leaf water potential and osmotic potentialdecreased, turgor potential increased and stomatal resistancedecreased with increasing K nutrition. Osmotic adjustment wasevident and it may have been influenced by increased K⁺ concentrationsin leaf tissues with increasing K nutrition. Higher leaf thicknessand higher leaf water content were observed at higher K levels.Results suggested that higher supplies of K nutrition may increaseplant production during periods of water stress. Key words: Zea mays L., cell membrane stability, leaf water potential, osmotic adjustment, osmotic potential, potassium nutrition, water stress     

Development of maize plants from cultured shoot apices

Excised shoot apices of maize (Zea mays L.), comprising the apical meristem and one or two leaf primordia, have been cultured and can form rooted plantlets. The plantlets, derived from meristems that had previously formed 7–10 nodes, develop into mature, morphologically normal plants with as many nodes as seed-grown plants. These culture-derived plants exhibited the normal pattern of development, with regard to the progression of leaf lengths along the plant and position of axillary buds and aar shoots. Isolation of the meristem from previously formed nodes reinitiates the pattern and number of nodes formed in the new plant. Thus, cells of the meristem of a maize plant at the seedling stage are not determined to form a limited number of nodes.     

The Growth and Development of Maize (Zea mays L.) at Five Temperatures

The objectives of this work were to measure growth and developmentrates over a range of temperatures and to identify processeswhich may limit vegetative yield of maize (Zea mays L.). Twosingle cross Corn Belt Dent maize hybrids were grown from sowingin a diurnal temperature regime of 16/6 °C day/night andin constant temperature environments of 16, 20, 24 and 28 °C.The 16/6 °C environment was close to the minimum for sustainedgrowth and 28 °C was near the optimum. Entire plants wereharvested at stages with 4, 6, 7 and 8 mature leaves in alltemperature treatments except 20 °C in which the final twoharvests were carried out at 9 and 10 mature leaves. Mean totalleaf number varied between 19.5 and 16.0 with the maximum occurringat 16/6 °C. Although harvests were carried out at comparableleaf numbers, and hence at similar developmental stages, thetime interval between sowing and harvest decreased considerablyas temperatures increased. The relative rates of dry weight and leaf area accumulationwith time increased with a Q₁₀ of 2.4 between 16 and 28 °C,while leaf appearance rate increased with a Q₁₀ of 2.9 overthe same range; both rates were highest at 28 °C. Althoughdry matter partitioning to the shoots increased with temperature,the area of individual leaves varied in a systematic patternwhich resulted in maximum leaf area, leaf area duration andconsequently dry weight being realized at 20 °C for anygiven stage of development. Zea mays, corn, low temperature stress, temperature response, growth, development     

The Effect of Water Stress on the Vegetative Growth of White Clover (Trifolium repens L): Comparison of Long-term Water Deficit and a Short-term Developing Water Stress

White clover plants were subjected to either a short-term developingwater stress or long-term stable levels of water deficit on‘water stress columns’. The short-term stress reducedplant water status to –2?0 MPa over 15 d. The water stresscolumns imposed only mild levels of water stress (a reductionof 0?35 MPa in leaf water potential for the more severe treatment)but these were maintained for several weeks. The absolute growthof plants on the control columns was maintained throughout theexperimental period. Vegetative growth was measured. Stolon, petiole, and laminagrowth were all reduced to some extent when plants were grownsymbiotically. The two regimes gave comparable results. Whennitrate was supplied there was no effect of water stress. Aconsiderably reduced absolute growth rate did not result ina similar decrease in final organ size. Stolon growth was mostreduced by water stress. Leaf death during water stress wasas important as changes in growth in determining final dry matteryield. Consequently, the yield of petiole and lamina from plantsgrown without supplied nitrate on the water stress columns waslower than that of stolon at the end of the treatment period. The merits of the water stress column system for imposing long-termwater deficit are discussed. Key words: Trifolium repens, white clover, water stress, vegetative growth     

Flooding responses inZea mays L.

Summary This study was undertaken to determine the specific mechanisms of flooding injury inZea mays L., especially the role of water deficit. Maize plants in soil were artificially flooded in greenhouse and field, both with and without exchanging the soil solution with new water and nutrients. Plants in solution culture were rapidly stressed by replacing aeration gas with nitrogen. In all cases of measurable short term response, root and leaf growth rates decreased within 1 to 12 hours, and stomatal resistance increased 2 to 3 days later. Both growth rates and stomatal resistance recovered spontaneously during the flooding period. Over the long term (more than a week), growth rates were inhibited only when the soil solution was not periodically changed and Kjeldahl measured nitrogen deficiency was evident in the leaves. None of the above effects was associated with high root resistance to water uptake, plant water deficit, or a change in the osmotic balance of the leaves. The only water stress associated with the experiments was found immediately after draining plants that had been flooded for 2 weeks. In this instance, the preflooding root systems appeared damaged.     

Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?

Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plantswere grown in large volumes of soil and leaf growth rate wasmonitored on a daily basis. Half the plants were given a soildrying treatment and when they showed a significant restrictionof growth rate (compared to both their daily growth rate beforedrying and the average growth rate of well-watered plants onthe same day), leaf water relations were measured and xylemsap was extracted using several techniques. There was a significant negative log-linear relationship betweenthe rate of leaf growth and the concentration of ABA in thexylem for both species. There was no clear relationship betweenleaf growth rate and leaf water potential or turgor for eitherspecies. Assessment of different methods for sampling xylemsap suggests that exudates collected from stem stumps or samplescollected by pressurizing the whole root system are suitablefor estimating ABA concentration in xylem, at least with largeplants of maize or sunflower, provided the first few hundredcubic millimetres of collected sap are used for the assay. Centrifugationof sections of stems resulted in dilution of ABA in the xylemsap with sap squeezed from parenchyma tissue. This is because,at least in plants subjected to mild soil drying, the concentrationof the ABA in the xylem is far higher than that in the cellsap of stem tissue. Results support the proposal that ABA plays a major role asa chemical signal involved in the root-to-shoot communicationof the effects of soil drying. The non-hydraulic restrictionof leaf growth by a chemical signal can be explained by theextra root-sourced ABA in the xylem and may be an importantcomponent of the modification of growth and development whichresults from prolonged soil drought. Key words: Soil drying, ABA, leaf growth, Zea mays L., Helianthus annuus L.     

AXR1 acts after lateral bud formation to inhibit lateral bud growth in Arabidopsis

The AXR1 gene of Arabidopsis is required for many auxin responses. The highly branched shoot phenotype of mature axr1 mutant plants has been taken as genetic evidence for a role of auxin in the control of shoot branching. We compared the development of lateral shoots in wild-type Columbia and axr1-12 plants. In the wild type, the pattern of lateral shoot development depends on the developmental stage of the plant. During prolonged vegetative growth, axillary shoots arise and develop in a basal-apical sequence. After floral transition, axillary shoots arise rapidly along the primary shoot axis and grow out to form lateral inflorescences in an apical-basal sequence. For both patterns, the axr1 mutation does not affect the timing of axillary meristem formation; however, subsequent lateral shoot development proceeds more rapidly in axr1 plants. The outgrowth of lateral inflorescences from excised cauline nodes of wild-type plants is inhibited by apical auxin. axr1-12 nodes are resistant to this inhibition. These results provide evidence for common control of axillary growth in both patterns, and suggest a role for auxin during the late stages of axillary shoot development following the formation of the axillary bud and several axillary leaf primordia.     

Warm spring temperatures induce persistent season-long changes in shoot development in grapevines

Background and Aims

The influence of temperature on the timing of budbreak in woody perennials is well known, but its effect on subsequent shoot growth and architecture has received little attention because it is understood that growth is determined by current temperature. Seasonal shoot development of grapevines (Vitis vinifera) was evaluated following differences in temperature near budbreak while minimizing the effects of other microclimatic variables.

Methods

Dormant buds and emerging shoots of field-grown grapevines were heated above or cooled below the temperature of ambient buds from before budbreak until individual flowers were visible on inflorescences, at which stage the shoots had four to eight unfolded leaves. Multiple treatments were imposed randomly on individual plants and replicated across plants. Shoot growth and development were monitored during two growing seasons.

Key Results

Higher bud temperatures advanced the date of budbreak and accelerated shoot growth and leaf area development. Differences were due to higher rates of shoot elongation, leaf appearance, leaf-area expansion and axillary-bud outgrowth. Although shoots arising from heated buds grew most vigorously, apical dominance in these shoots was reduced, as their axillary buds broke earlier and gave rise to more vigorous lateral shoots. In contrast, axillary-bud outgrowth was minimal on the slow-growing shoots emerging from buds cooled below ambient. Variation in shoot development persisted or increased during the growing season, well after temperature treatments were terminated and despite an imposed soil water deficit.

Conclusions

The data indicate that bud-level differences in budbreak temperature may lead to marked differences in shoot growth, shoot architecture and leaf-area development that are maintained or amplified during the growing season. Although growth rates commonly are understood to reflect current temperatures, these results demonstrate a persistent effect of early-season temperatures, which should be considered in future growth models.     

Effect of Assimilate Supply on Development and Growth Potential of Axillary Buds in Roses

The effect of assimilate supply on axillary bud developmentand subsequent shoot growth was investigated in roses. Differencesin assimilate supply were imposed by differential defoliation.Fresh and dry mass of axillary buds increased with increasedassimilate supply. The growth potential of buds was studiedeither by pruning the parent shoot above the bud, by graftingthe bud or by culturing the bud in vitro. Time until bud breakwas not clearly affected by assimilate supply during bud development,Increase in assimilate supply slightly increased the numberof leaves and leaf primordia in the bud; the number of leavespreceding the flower on the shoot grown from the axillary budsubstantially increased. No difference was found in the numberof leaves preceding the flower on shoots grown from buds attachedto the parent shoot and those from buds grafted on a cutting,indicating that at the moment of release from inhibition thebud meristem became determined to produce a specific numberof leaves and to develop into a flower. Assimilate supply duringaxillary bud development increased the number of pith cells,but the final size of the pith in the subsequent shoot was largelydetermined by cell enlargement, which was dependent on assimilatesupply during shoot growth. Shoot growth after release frominhibition was affected by assimilate supply during axillarybud development only when buds sprouted attached to the parentshoot, indicating that shoot growth is, to a major extent, dependenton the assimilate supply available while growth is taking place.Copyright1994, 1999 Academic Press Assimilate supply, axillary bud, cell number, cell size, defoliation, development, growth potential, meristem programming, pith, Rosa hybrida, rose, shoot growth