The Effect of Copper Supply on the Senescence and the Retranslocation of Nutrients of the Oldest Leaf of Wheat

The contents of Cu, N, P, K, Zn, Mn and Ca were followed duringthe life of the oldest leaf of wheat plants (Triticum aestivumL. cv. Gamenya) grown at deficient and sufficient supplies ofCu. At both levels of Cu, the Cu content of the oldest leafbehaved in a similar way to the contents of N and Zn, whichdeclined markedly during leaf senescence. By contrast to Cu the P and K contents declined markedly, priorto leaf senescence, whereas the Ca and Mn contents increasedthroughout the life of the leaf and did not decline during leafsenescence. Interactions among Cu supply, the supply of other nutrients(e.g. N), and leaf senescence account for the variable mobilityof Cu in wheat. Similar interactions between nutrient supplyand senescence may explain contradictory reports on the redistributionof other nutrients which are variably mobile in plants.     

Copper as essential to wheat reproduction

Summary The role of Cu in promoting the reproductive phase of growth was examined using Thatcher spring wheat (Triticum aestivum L.). Plants were grown in limed Bladen soil (pH 5.3) in a controlled growth room. The plants were first harvested when five leaves had developed (day 23) and some top leaves of Cu-deficient (-Cu) plants had rolled (withertip) indicating a Cu deficiency. The leaves were shorter on Cu than Cu-sufficient (+Cu) plants, and fewer leaves developed. As they entered the reproductive growth phase, +Cu plants accumulated reducing sugars and reduced 2, 3, 5- triphenyltetrazolium chloride (TTC) in their stems, while Cu plants had lower concentration of the reducing sugars and very little TTC was reduced indicating a reduction in energy and in reducing capacity. Thin-layer-chromatography showed that top leaves of Cu plants contained higher concentrations of aspartic acid, alanine, and serine; and less aminobutyric acid than +Cu plants. Nitrate, P, and K concentrations were higher, and Ca and Cu were lower in Cu than in +Cu plants.Contribution of U.S. Department of Agriculture, Agricultural Research Service, Plant Stress Laboratory, Northeast Region, Beltsville, MD 20705 and North Central Region, Department of Agronomy, University of Nebraska, Lincoln, NE 68583 as Paper No.5187, Journal Series, Nebraska Agricultural Experiment Station.Contribution of U.S. Department of Agriculture, Agricultural Research Service, Plant Stress Laboratory, Northeast Region, Beltsville, MD 20705 and North Central Region, Department of Agronomy, University of Nebraska, Lincoln, NE 68583 as Paper No.5187, Journal Series, Nebraska Agricultural Experiment Station.     

Absorption and Distribution of Copper in Plants with Sufficient or Deficient Supplies

Wheat, red clover and ryegrass were grown in flowing solutionculture with sufficient (+ Cu) and deficient (–Cu) suppliesof copper. The rates of Cu absorption (µg g^–1 dryroot day^–1) did not differ greatly between species ineither treatment. Wheat plants, when transferred from the –Cu to the +Cu treatment, absorbed Cu at a much slower rate thanthose which had remained throughout in the + Cu treatment. Inall plants considerable proportions of the absorbed Cu wereretained in the roots, even when the plants were Cu-deficient,and the concentration in roots usually exceeded that in anypart of the shoots in both treatments. Transferring wheat plantsfrom the +Cu to the –Cu treatment decreased the concentrationin all plant parts except old leaves; similarly, transferringfrom the –Cu to +Cu treatment increased the concentrationin all parts of the shoots, execept old leaves, and in the roots. Lolium perenne, Trifolium pratense, Triticum aestivum, ryegrass, red clover, wheat, absorption, copper, flowing solution culture     

Development of an ELISA for estimation of the copper nutritional status of wheat and cotton

Studies were carried out with hydroponically grown wheat and cotton to develop the Cu-requiring protein phenolase as a biomarker of Cu nutrient status. Isozymes of phenolase whose levels were reduced by Cu deficiency were identified by Western blots. A competitive enzyme-linked, immunosorbent assay (ELISA) was developed that could detect as little as 25 ng of phenolase. The ELISA revealed that Cu-sufficient cotton leaves had about 4-fold more phenolase antigen than did Cu-sufficient wheat leaves. In both species, the level of phenolase was reduced by 2- to 5-fold in leaves of Cu-deficient plants. Because the immunoassay for phenolase protein is rapid, inexpensive, and can be carried out with small amounts of leaf material, it has potential as a tool for assessment of the Cu status of crop plants.Abbreviations ELISA enzyme-linked immunosorbent assay - HRP horseradish peroxidase - TBS Trisbuffered saline (20 mM Tris-HCl, pH 9.5, 150 mM NaCl) - TBST Tris-buffered saline containing 0.05% Tween-20     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

Male Sterility and Anther Wall Structure in Copper-deficient Plants

Anther development and pollen sterility were followed in plantsof wheat, oat, barley, sweetcorn, sunflower, petunia and subterraneumclover grown at a range of copper supplies. Copper-deficientplants had increased pollen sterility. Lignified wall thickenings were reduced or absent in the endotheciaof anthers from Cu-deficient plants. Reduced seed set may resultboth from reduced pollen fertility or failure of the stomiato rupture due to decreased lignification of anther walls. Triticum aestivum L., wheat, Hordeum vulgare L., barley, Avena sativa L., oat, Zea mays L., corn, sweetcorn, maize, Helianthus annuus L., sunflower, Petunia hybrida L., Trifolium subterraneum L., subterranean clover, male sterility, anther development, copper deficiency     

Effects of Abscisic Acid on Growth of Wheat (Triticum aestivum L)

Daily application of abscisic acid (ABA) to growing wheat plants,although initially inhibiting growth, resulted, after a shortlag, in an increase in the number of leaves and tillers. Thismay have been due to reduced apical dominance. At 84 days thetotal dry weight and area of all leaves produced up to thistime was less for the plants treated with ABA than for the controlplants. However, the area of green, living leaves and the dryweight were not significantly affected by the ABA treatment.Further effects of the daily ABA treatment were the inhibitionof transpiration, especially on the abaxial surface, the reductionof leaf size, the promotion of flowering and the stimulationof trichome formation on the leaf surfaces. ABA did not promoteleaf senescence in whole plants and actually increased leaflongevity. Triticum aestivum L., wheat, leaf senescence, transpiration, growth, flowering, abscisic acid     

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     

Leaf Emergence of Spring Wheat Receiving Varying Nitrogen Supply at Different Stages of Development

We examined effects of nitrogen (N) supply on leaf emergenceof spring wheat (Triticum aestivum L.) grown in sand with nutrientsolution containing different N concentrations (9NO₃: 1NH₄).In expt 1, the cultivar 'Gamenya' received nutrient solutiontwice weekly containing a constant N supply ranging from 50to 2400 µM N. In expts 2 and 3, cultivars 'Aroona' and'Gamenya' were irrigated hourly with nutrient solution containingeither low (L = 50 µM N) or high (H = 2000 µM N)N supply. In expt 2, the N supply to half of the plants receivingL and H was changed at the double ridge stage of apical development,producing plants receiving LL, LH, HL and HH. In expt 3, N supplywas changed firstly when the main stem apex was vegetative (oneto two leaves) and secondly when the main stem apex was at doubleridge stage (four to five leaves), producing plants receivingLLL, LHL, HLH and HHH. Leaves on the main stem and primary tillerswere counted. Rate of leaf emergence was estimated from regressionof number of leaves against thermal time; the phyllochron wascalculated as 1/ rate of emergence. Severely N-deficient plants (which had at least a 60% reductionin shoot dry weight) had slower rates of leaf emergence (expt1). Fluctuating N supply sometimes, but not always, changedthe rate of leaf emergence (expts 2 and 3). The N supply beforedouble ridge stage had bigger effects on the phyllochron thanthat afterwards (expt 3). The phyllocrons of the main stemswere generally lower than those of tillers, with a greater differencebetween stems in N-deficient plants. Low N supply at the vegetativeapex stage decreased the total number of leaves on the mainstem, while low N supply after double ridge did not.Copyright1994, 1999 Academic Press Nitrogen, stress, spring wheat, Triticum aestivum, leaf emergence, phyllochron, apical development     

Influence of Xylem Water Potential on Leaf Elongation and Osmotic Adjustment of Wheat and Lupin

The leaf elongation rate and osmotic pressure at full turgorof wheat (Triticum aestivum L.) and lupin (Lupinus cosentiniiGuss.) were measured in well watered plants, in plants thatwere allowed to dry the soil slowly over 7 d, and in plantsin which the water potential of the leaf xylem was maintainedhigh by applying pressure to the roots during the drying cycle.Maintenance of high xylem water potentials failed to preventa reduction in the rate of leaf elongation as the soil dried,while the osmotic pressure at full turgor and the degree ofosmotic adjustment increased as the soil water content decreased.The rate of leaf elongation was reduced more and the degreeof osmotic adjustment was higher in leaves with high xylem waterpotentials than in those in which leaf xylem potentials wereallowed to decrease as soil water content decreased. Osmoticadjustment was linearly correlated with the reduction in leafelongation rate in both wheat and lupin. Key words: Osmotic adjustment, leaf elongation, turgor regulation     

Copper Supply in Relation to Content and Redistribution of Copper Among Organs of the Wheat Plant

The relationship of copper supply to the content and movementof copper among organs of wheat plants was examined at sevenstages in their growth from seedlings to maturity on a copperdeficient sand. In the absence of copper (Cu₀), plants becameseverely copper deficient and produced no grain; developmentof tillers, leaves, stems, and inflorescences was delayed andgrowth of roots strongly depressed; leaf senescence was retardedand tiller growth was prolonged. Application of a marginal supplyof copper (Cu₁) overcame all symptoms and promoted growth andgrain production. Increasing copper supply eightfold (Cu₂) didnot change vegetative or grain production. Copper concentrations in stems, individual leaves, and wholetops were highest and responded most strongly to copper supplywhen they were young. As they aged, Cu₁ and Cu₂ leaves lostcopper rapidly; the first Cu₀ leaves retained their copper andremained healthy for more than 7 weeks even though younger leavesdeveloped severe copper deficiency. In all treatments, lossof copper from the oldest leaf paralleled senescence and theloss of nitrogen. It is suggested that copper does not move out of plant leavesuntil they lose organic nitrogen compounds. As a result, copperbehaves in non-senescent leaves as if it is not mobile in plantphloem. But under conditions favouring senescence, copper ishighly mobile: in the present experiment, 67 per cent of thecopper present in vegetative organs of the Cu₂ primary shootat flowering moved from them during grain development and thiscould account for all of the copper found in the grain at maturity. The retention of copper by leaves before senescence, its rapidloss during senescence, and the effect of copper deficiencyin delaying senescence resulted in the oldest leaf of severelydeficient Cu₀ plants in the present experiment having a highercopper concentration than that of copper adequate Cu₁ and Cu₂plants. This behaviour could account for the many reports ofanomalous C-shaped ‘Piper-Steenbjerg’ curves inthe relationship of yield to copper concentrations in planttops. The coupling of copper movement from leaves to nitrogenmovement can also account for the unusually high values reportedfor critical concentrations of copper in tops of plants givenhigh levels of nitrogen fertilizers. Old organs should not be included in samples for diagnosis ofcopper deficiency. Only young organs should be used. In thepresent experiment, the copper concentration of young leavesgave a good indication of the copper status of wheat: a valueof 1 µg g^–1 in young leaves indicated copper deficiency. copper, nitrogen, phloem transport, mineral transport, deficiency diagnosis, wheat, Triticum aestivum L.     

Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the translocation and partitioningof nitrogen on the seventh day after anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. A 9-d drought treatment was imposed just after anthesisand this coincided with the period of endosperm cell divisionin the grains. Warigal, which had a higher grain yield thanCondor under drought, absorbed up to 15-times more nitrogenand translocated 1.5-fold more nitrogen to the shoot via thexylem. In both varieties, nitrogen redistributed from vegetativeorgans accounted for more than 60 per cent in control and 70per cent in droughted plants of the nitrogen needed for eargrowth. The net loss of nitrogen increased by 4-3 per cent inthe leaves, but decreased by 60 per cent in the stem under drought.Stem and roots appeared to play an important role in the nitrogeneconomy of droughted plants: less nitrogen was translocateddirectly to the grains from the senescing leaves and 40–60per cent more nitrogen was translocated to the roots. Nearlyall the nitrogen reaching the roots in the phloem was reloadedinto the xylem stream and translocated back to the shoot. Thetransfer of nitrogen through the stem was reduced under droughtand this resulted in a constant C:N ratio of the grains whichmay be important in the regulation of endosperm cell division. Triticum aestivum L., wheat, drought, nitrogen, senescence, translocation     

The Relationship between Sugar and Amino Acid Export to the Phloem in Young Wheat Plants

The relationship between amino acid and sugar export to thephloem was studied in young wheat plants (Triticum aestivumL. ‘Pro-INTA, Isla Verde’) using the EDTA-phloemcollection technique. Plants grown with a 16 h photoperiod showeda rapid decrease in the concentration of sugars and amino acidsin the phloem exudate from the beginning of the dark period.When plants grown with a 16 h photoperiod were kept in the darkfor longer than 8 h the free amino acid content in leaves andexudate (on a dry weight basis) increased continually throughoutthe 72 h of darkness. During the first 24 h of darkness thesugars in the phloem exudate decreased to 30% of the initialvalue, and returned to the control level when plants were returnedto light. When plants grown under low light intensity for 10d were transferred to high light intensity, they showed an increasein leaf sugar content (dry weight basis) after 3 d but therewere no differences in leaf free amino acid content (dry weightbasis) compared to low-light plants. The sugar concentrationin the phloem exudate was increased by higher light intensities,but there was no difference in the amino acid concentrationof the phloem exudate, and thus the amino acid:sugar ratio inthe phloem decreased in the high-light plants. The present resultssuggest that amino acids can be exported to the phloem independentlyof the export of sugars. Copyright 1999 Annals of Botany Company Sugar exudation, amino acid transport, nitrogen, phloem, transport, wheat, Triticum aestivum L.     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

Growth of Near-isogenic Wheat Lines Differing in Development--Plants in a Simulated Canopy

An understanding of the principal factors regulating the growthof temperate cereals will identify opportunities to manipulatecrop growth. In an accompanying paper (Gomez-Macpherson, Richardsand Masle,Annals of Botany82: 315–322, 1998), growth aroundthe start of floral initiation was studied in isogenic wheat(Triticum aestivumL.) lines grown as spaced plants. In thispaper, two of the same near-isogenic wheat lines were grownas mini-canopies in a growth chamber. The objective was to determinewhether results obtained using spaced plants also apply to plantsgrown in a simulated canopy as a first step to emulate fieldconditions. Biomass of plant organs, leaf area and leaf andtiller appearance were determined from sowing to ear emergenceof the early developing line. Contrary to results obtained usingspaced plants, lines differed in their above-ground biomassaccumulation, although total plant biomass accumulation wassimilar. After the early line reached terminal spikelet stage(TS), biomass partitioning to the roots and leaves decreased,whereas partitioning to the stem and ear increased. This resultedin a lower root:shoot ratio in the early flowering line thanin the late line which remained vegetative. Tiller senescencealso began after TS in the early line whereas no tiller senescencewas observed in the late line during the experiment. Furthermore,after TS, net assimilation rate was greater and leaf area ratiowas lower in the early line. It is suggested that, after reachingTS, plants grown in a canopy become source limited comparedto widely spaced plants, or compared to plants that have notreached TS, and this results in less root growth.Copyright 1998Annals of Botany Company Development, growth, partitioning,Triticum aestivumL., wheat.     

Effect of Drought on Metabolism and Partitioning of Carbon in Two Wheat Varieties Differing in Drought-tolerance

A model was constructed to describe the partitioning of carbonon the third and seventh day from anthesis for well-wateredand droughted plants of two wheat varieties (Triticum aestivumL. cv. Warigal and Condor). The glasshouse-grown plants weredetillered so that a simplified model could be derived for themain stem. The 9-d drought treatment, imposed just after anthesisduring the period of cell division in the grains, reduced grainyield by 18 per cent in Warigal and 30 per cent in Condor. Netcarbon fixation was up to 60 per cent higher in Warigal thanCondor towards the end of the drought period and this correlatedwith better osmotic adjustment in the flag leaf. Carbon partitioningbetween plant organs responded to water deficit more rapidlythan net carbon fixation. On day 3, carbon allocation to theroots of droughted plants was maintained in Condor and increasedby 14 per cent in Warigal, whereas carbon allocation to theear decreased in both varieties. However the roots did not competewell with the ear when the water deficit became more severe.Warigal accumulated 3 times more stem reserves than Condor underdrought. In the roots, the pattern of carbon allocation betweenrespiration and carbon accumulation changed soon after impositionof drought. Although total root respiration decreased underdrought it became more energy efficient, particularly for Warigal,as less respiration took place via the alternative pathway.On day 3, the larger carbon allocation to the roots and thelower root respiration accounted for the 4-times larger sugaraccumulation in droughted roots of Warigal compared with thoseof Condor. Osmotic adjustment in mature leaves and roots maybe of importance for the maintenance of vital processes andfor recovery after drought. Triticum aestivum L., wheat, drought, carbon, partitioning     

Observations on the Distribution of Mineral Elements in the Leaf of Wheat (Triticum aestivum L.), with Particular Reference to Silicon

Wheat (Triticum aestivum L. cv. Wheaton) plants were grown inwater culture or in soil. Basal leaves (B) were harvested after3 weeks from the water culture plants, while flag leaves werecollected from soil-grown material at the time of inflorescenceemergence (E0) and 7 d after emergence (E + 7). Mineral distributionin bulk frozen leaves was investigated using SEM and X-ray microanalysis.The elements detected were silicon, phosphorus, chlorine, sulphur,potassium and calcium. Potassium was present in all cell typesat all harvests, chlorine was almost entirely confined to theadaxial and abaxial epidermi, while sulphur was only rarelydetected in the E0 and E + 7 leaves. Phosphorus was presentat higher levels in the E + 7 leaves than in the B or E0 leaves.At the B harvest calcium was confined to the adaxial epidermalcells, but in the E0 and E + 7 leaves it was present in bothepidermi. Silicon was, initially, mainly detected in the abaxialepidermal cells, but in older (E + 7) leaves it was presentin both epidermi and in some internal tissues. Mineral transportwithin the leaf and ionic environment at silica deposition sitesare discussed. Wheat, Triticum aestivum L., leaf, mineral distribution, X-ray microanalysis, silicon, calcium     

Errors in Leaf Area Measurement with an Automatic Area Meter due to Leaf Chlorophyll in Crop Plants

This study revealed that an area meter with a semi-automaticfeeding mechanism underestimated the area of yellowish leavesand wavy leaves in crop plants. It is recommended that areameasurements should be made using photocopied leaves and leafsegments. The degree of underestimation should be checked whenchlorophyll meter (SPAD) values are less than 30.Copyright 1999Annals of Botany Company Glycine max Merr., Hordeum vulgare L., leaf area meter, leaf colour, Oryza sativa L.,Solanum tuberosum L., SPAD, Triticum aestivum L., Zea mays L.     

Cultivars of Hexaploid Wheat of Contrasting Stature and Chlorophyll Retention Differ in Cytokinin Content and Responsiveness

The work reported here compared cytokinin content and sensitivityin a selection of hexaploid wheat (Triticum aestivum L.) cultivarsusing the following measurements: leaf cytokinins at three timepoints during light-growth and at four 24 h intervals afterlight-grown plants were transferred to darkness; sensitivityof root growth to direct applications of isopentenyl adenosine([9R]iP); and, sensitivity of germination and subsequent rootand shoot growth to 18 h imbibition of seeds in benzyladenine(BA). Accumulation of zeatin riboside-type cultivars was greatestduring light-growth in Tibet Dwarf, a wheat with an extremedwarf phenotype, intermediate in Omar standard and dwarf cultivars,and lowest in the standard and dwarf versions of Itana. Cytokininlevels were otherwise not directly correlated to plant staturein these wheats. There were no cultivar-associated qualitativedifferences in the types of cytokinins detected in this study.During the 16 h light period, the content of zeatin riboside-typecytokinins increased up to tenfold and then declined to basallevels during dark growth. Chlorophyll retention during dark-growthwas correlated with leaf cytokinin content. Data collected ata restricted number of sampling points during dark-growth suggesteda cyclic accumulation of [9R]iP-type cytokinins and the apparentcycle in Tibet Dwarf was offset by 24 h. Tibet Dwarf showedthe greatest root growth inhibition after exposure of seedlingroots to [9R]iP or imbibition of seeds in BA. Neither of thesetreatments affected shoot growth in any of the cultivars. Wheat; Triticum aestivum ; cytokinin; zeatin riboside; benzyladenine; root inhibition     

Influence of reproductive organs on plant senescence in rice and wheat

The chlorophyll and protein contents of the flag, second and third leaves gradually decreased during the reproductive development of rice (Oryza sativa L. cv. Rasi) and wheat (Triticum aestivum L. cv. Sonalika) plants, whereas proline accumulation increased up to the grain maturation stage and slightly decreased thereafter. In rice plant, the rate of decrease in chlorophyll and protein and increase in proline level were higher in the flag leaf than in the second leaf. It was opposite in wheat plant. The export of [³²P]-phosphate from leaves to grains gradually increased reaching a maximal stage at the grain development stage, and then declined. The export of this radioisotope was greater in rice than in wheat. Removal of panicle at the anthesis and grainfilling stages delayed leaf senescence of rice plant, while in wheat the ponicle removal at any stage did not have a marked effect on delaying leaf senescence. The contents of chlorophyll and protein of glumes were higher in wheat than in rice. The variation of such source-sink relationship might be one of the possible reasons for the above effect on leaf senescence.