Some Physiological Characteristics of Two Tomato Cultivars, One Tolerant and One Susceptible to Tobacco Mosaic Virus

A comparison was made of physiological activity in the tomatocv. Potentate, susceptible to tobacco mosaic virus (TMV) withthat in cv. Virocross which is tolerant. Growth analysis overa 5-week period showed Potentate to have a higher relative growthrate and a higher net assimilation rate than Virocross. In reciprocalgrafts scion growth, including dry weight, was greater on Potentaterootstocks than on Virocross. Growth responses were studiedin these grafts following foliar sprays of N-6 benzyladenine(BA) and gibberellic acid (GA). The response of the scion toGA was similar in both cultivars and there was no interactionbetween GA and rootstock for scion growth. An interaction betweenstock and BA was found for leaf growth. Bleeding sap from Virocross contained more gibberellins, morecytokinins, and a lower concentration of amino compounds, especiallynon-protein acids, than Potentate. There were more gibberellinsin the roots of Potentate but no difference between shoots ofthe two cultivars. In reciprocal grafts TMV multiplied more rapidly in Virocrossscions on Potentate rootstock than on their own, but Virocrossstocks did not affect virus multiplication in Potentate scions.Spraying Potentate plants with BA reduced the rate of virusmultiplication. It is suggested that virus multiplication in the shoot may becontrolled by two distinct root factors, viz, the supply ofnative cytokinins and the amount and nature of the nitrogenouscompounds which directly influence the rate of shoot growth.     

The Effect of Number of Shoots on the Quantity and Distribution of Increment in Young Apple-trees: With three Figures in the Text

It is shown that the shoots of a young tree act additively ratherthan competitively, that is, each extra shoot produces a definiteextra increment in total weight, not that a constant incrementis divided among the shoots of the young tree. One-year apple-trees of 3 varieties were rigorously selectedfor size and weight, and in the spring disbudded to 1, 2, 3,or n, the natural number of shoots per plant. The treatmentswere applied in the 1st or 2nd year after planting and the incrementduring the treatment year was determined. Provided not morethan a few secondary shoots were produced on the current shoots,each additional primary shoot produced an increase in weight.In one variety plants with 1 primary shoot produced many secondariesand these plants were heavier than those with 2 primaries. The largest shoot was not greatly affected in size by the presenceof other shoots except in the variety which produced secondaryshoots readily. These were most abundant on plants with 1 primaryshoot, fewer on plants with 2, and almost negligible on plantswith 3 and n shoots. Treatment and varietal effects on the percentage distributionof increment as leaves, new stem, old-stem increment, and root,were small. The percentage of leaves in the 2nd year was abouthalf what it was in the 1st year; the percentage of root wasnearly the same in both years.     

Growth Dynamics and Morphology of Annual Shoots, According to their Architectural Position, in Young Cedrus atlantica (Endl.) Manetti ex Carriere (Pinaceae)

The influence of shoot architectural position on growth andbranching pattern of young Cedrus atlantica (Endl.) Manettiex Carrière trees were studied. Extension growth andtype of axillary products (lateral bud, sylleptic short or longshoots) of annual shoots of increasing branching order (mainstem, branches and branchlets) were recorded weekly during the1993 growing season. Annual final shoot length, duration ofextension, and maximum extension rate decreased with increasingbranching order. Sylleptic axillary shoots occurred only onannual shoots of the main stem and branches and were producedwhen extension rate was at its highest. Differences in growthrate and final length of annual shoots, according to their architecturalposition, were related to differences in the total number anddiversity of types of sylleptic axillary shoots produced. Itis suggested that types and numbers of sylleptic axillary shootsproduced are linked with threshold values for both final lengthand extension rate of the parent shoot. Copyright 1999 Annalsof Botany Company Atlas cedar, extension growth, sylleptic branching, tree architecture, morphology.     

The Acquisition and Utilization of Carbon in Early Spring by Kiwifruit Shoots

Measurements of net photosynthetic rate (at 1450µ molm^-2s^-1photosynthetically active radiation) of leaves, of leafand stem respiration, and of shoot growth of potentially-fruitinglaterals on kiwifruit (Actinidia deliciosa ) were used to estimateweekly shoot carbon balances over the first 10 weeks of shootgrowth (budburst to anthesis). Consistent differences in therate of shoot elongation, of internode expansion and of increasein basal diameter were found among shoots. Faster-growing (long)shoots acquired carbon by photosynthesis at a faster rate evenin the first few weeks after budburst, but the amount of carbonrequired to sustain this growth resulted in shoot carbon deficitswhich were approx. seven times greater than those of the slower-growing(short) shoots. It was estimated that the transition from shootcarbon deficit to carbon surplus occurred 3–4 weeks afterbudburst, irrespective of shoot growth rate. As a result ofsubsequent rapid increases in shoot photosynthetic rate, longshoots had a shoot carbon surplus of 4.4 g C week^-1in the weekbefore anthesis, approx. three times that of the short shoots.Defoliation (66%) of shoots 1 week after budburst, and subsequentremoval of later-emerging leaves to maintain the level of defoliation,had the effect of slowing shoot growth in the carbon deficitperiod, particularly for the long shoots. However, the durationof shoot expansion in the defoliated shoots was longer, resultingultimately in shoots which were longer than the control shoots.Linkages among early carbon balance dynamics of shoots, shootlength at anthesis, and fruit growth are discussed. Actinidia deliciosa ; kiwifruit; shoot growth; carbon acquisition; respiration; photosynthesis     

The Role of Different Daily Irradiations on Shoot Growth and Root/Shoot Ratio in Lucerne (Medicago sativa L.)

The effect of two levels of daily irradiation on shoot growthand root/shoot partitioning was investigated on two lucernevarieties (Medicago sativa L.). Individual plants were studiedunder constant temperature and optimal water and mineral nutritionconditions. For both lucerne varieties, daily irradiation did not changebiomass partitioning between shoots and roots. It can be shownthat leaf area expansion occurs independently of daily irradiationand that the process of shoot dry matter production is strictlyproportional to daily irradiation, since the ratio leaf area/shootdry matter is inversely proportional to it. From a model of shoot production of the isolated plant, we showthat the relative shoot specific activity is not affected bydaily irradiation. A simple model of partitioning leads us todetermine why partitioning remains the same for the two at thelevels of daily irradiation. Finally, the allocation between shoot and root turns out tobe independent of the main stem extension rate, which is fasterat the higher daily irradiation. Medicago sativa L., lucerne, daily irradiation, shoot production, root/shoot ratio, leaf area expansion, partitioning model     

Effects of soil mechanical impedance on root and shoot growth of Lolium perenne L., Agrostis capillaris and Trifolium repens L.

A method was used for applying a uniform mechanical impedanceto plant roots using sand packed at different bulk densitieswith depth within each growth cylinder. In a growth experiment,replicate cylinders were packed with sand to give the followingmechanical impedances: 0.25 MPa penetration resistance (negligibleimpedance), 1.40 MPa (moderate impedance) and 2.30 MPa (severeimpedance). Seedlings of Lolium perenne L., Trifolium repensL. and Agrostis capillaris were grown for 23 d in each impedancetreatment and effects on both roots and shoots were studied.Severe mechanical impedance affected both root and shoot growthrates for all three species resulting in smaller leaves andshorter roots. For the grasses, the root-to-shoot ratio at harvestwas the same for all the treatments, but a delay in the initiationof both shoots and roots was observed in the severe mechanicalimpedance treatment. The results are discussed in relation tothe possibility that roots penetrating the impeding treatmentsmay have caused signalling that kept shoot and root growth insynchrony. Differences observed in the response to mechanicalimpedance of T. repens compared to the other two species maybe a function of differences in the physiology between mono-and dicotyledonous species. Key words: Mechanical impedance, Lolium perenne, Trifolium repens, roots, shoots     

The Dormancy of Buds of Citrus sinensis (L.) Osbeck Inserted into Rootstock Stems: Factors Intrinsic to the Inserted Bud

Buds of sweet orange, harvested from shoots of different timeof flushing and from different positions along the shoot, wereused to examine whether lack of burst of inserted buds was acharacteristic of the bud. Bursting of inserted buds was significantlyslower in buds taken from (a) older branches (b) shoots producedunder winter conditions, and (c) basal rather than apical budson the same shoot. The slowness to burst when transferred matched a tendency todormancy in buds on shoot segments grown in vitro, suggestingthat the variation in budburst was intrinsic to the bud. Budburstwas correlated with the extent of secondary bud development;the majority of buds from apical regions of the shoot had developeda secondary bud by the time of implantation, but basal budshad not. Adequate vascular connections with the host tissueswere found in both burst and unburst buds. Citrus sinensis (L.) Osbeck, sweet orange, buds, endodormancy, budding     

Pattern of Shoot Growth in Zizyphus mauritiana and Z. oenoplia

Shoot polymorphism and patterns of sylleptic branching and shoottip abscission in two Zizyphus species are reported. Z. mauritiana(ber) produced three types of proleptic shoots: vigorous, normaland spur-type, by reiteration or following pruning;Z. oenopliahad only one type of shoot. Both species revealed up to thirdorder sylleptic branching on the vigorous proleptic shoots witha characteristic pattern and rhythm. Bud dormancy breaking chemicalsgiven as pre-pruning foliar sprays in ber, did not alter thepattern of sylleptic branching. Zizyphus oenoplia produced morefirst and second order sylleptic branches compared to Z. mauritiana.All main axes and 97% of first order sylleptic branches ofZ.mauritiana abscised their apical buds during summer, but inZ. oenoplia all main axes and 54% of first order sylleptic branchesremained active. Shoot tip abscission was almost complete onthe higher order sylleptic branches of both species. Activefirst order branches in Z. oenoplia were confined to the tophalf of the shoot. Both species had a few dormant apical budsduring the summer on their sylleptic branches, emerging mostlyfrom the middle portion of the shoot. Some of the most vigorousfirst order branches of Z. oenoplia, which had dormant apicalbuds during summer, showed a change in the frequency of syllepticbranching when they resumed growth following monsoon showers.These characteristic growth and branching patterns may haveadaptive value for canopy development under arid and semi-aridconditions. Copyright 1999 Annals of Botany Company Ber, branching pattern, shoot polymorphism, shoot tip abscission, sylleptic branching, Zizyphus mauritiana, Zizyphus oenoplia.     

Analysis of Growth and Yield of Winter and Spring Wheats

In a field experiment to investigate the physiological causesof variation in yield between autumn- and spring-sown wheatand between old and new varieties, the grain yields of the winterwheats were 3-15 per cent, greater than of the spring ones andthe new varieties Cappelle-Desprez and Jufy I yielded 40-70per cent, more than Squarehead's Master and Atle. Nitrogen fertilizerincreased the yields of Cappelle-Desprez and Jufy I more thanof Atle, and decreased the yield of Squarehead's Master by makingit lodge. Until ear emergence the winter varieties had greater leaf-areaindices (L) and dry weights, but smaller net assimilation rates(E), than the spring varieties. Square-head's Master had greaterL but smaller E, and similar dry weight to Cappelle-Desprez.Jufy I had similar E to Atlc, but greater L and dry weight.Nitrogen increased L and dry weight, but decreased E. All thedifferences in E between varieties and nitrogen treatments couldbe explained by the opposite effects on L, that is to say, thedifferences in E were caused by variation in mutual shadingarising from the differences in L and not by changes in leafphysiology. L of winter wheat reached its maximum at the end of May, butL of spring wheat continued to increase until ear emergence.Afterwards Ldecreased more rapidly for winter than for springwheat, so that eventually spring wheat had the greater L. Thesedifferences in the time changes of L partially compensated forthe shorter growth period of spring wheat, and tended to equalizethe grain yield from winter and spring sowings. After ear emergence total dry weight of winter varieties continuedto be greater than of spring ones, but the difference in dryweight of ears was much smaller because ear: shoot dry-weightratio was greater for the spring varieties. Total dry weight,ear dry weight and ear: shoot ratio were all greater in thenew than in the old varieties. Leaf area duration (D) afterear emergence was slightly greater for the winter than for thespring varieties and similar for old and new. The apparent efficiencyof this leaf area in grain production, measured by the grainleaf ratio (ratio of grain dry weight to D), was similar forwinter and spring varieties but greater for new than for old.This suggests that Cappelle-Desprez and Jufy I have higher grainyields because their ears photosynthesize more than do the earsof Squarehead's Master and Atle. Before ear emergence winter varieties had more shoots than springones, and old varieties more than new. After ear emergence therewere only small differences in numbers of ears; percentage survivalwas greater for spring than for winter and for new than forold varieties. Differences in dry weight between varieties were not causedby differences in nitrogen uptake.     

A critical re-examination of pressure-volume analysis of conifer shoots: comparison of three procedures for generating PV curves on shoots of Pinus resinosa Ait. seedlings

Prediction of water relations attributes for red pine (Pinusresinosa Ait.) derived from pressure-volume (PV) curves varieddepending on which of three methods was used. The sap expressionmethod entailed the enclosure of a shoot in a pressure chamberand expression of xylem sap by applying a constant selectedpressure until sap flow ceased, at which point xylem water potentialand shoot weight were measured. A sap expression PV curve wasformed by aggregating pairs of water potential-weight measurements,each pair supplied by one of 25 shoots. The repeat pressurizationmethod involved repeatedly measuring xylem water potential andshoot weight on a single shoot drying on a laboratory bench.Repeat pressurization PV curves were constructed from data providedby a single shoot. The composite method utilized single measurementsof xylem water potential and shoot weight on 25-30 differentshoots ranging in relative water content from about 1.0 to 0.5achieved by bench drying. Composite PV curves were constructedfrom aggregate data supplied by a population of shoots. Therewas close agreement in all PV attributes generated using repeatpressurization and sap expression methods. In contrast, withthe composite PV method, there was a fundamental differencein the slope of the linear region of the PV curves, causingosmotic potentials at full turgor and turgor loss to be morenegative, and relative water content at turgor loss to be lowerand symplast fraction to be higher. Comparison of compositeand repeat pressurization PV curves over the same ranges inwater content did not eliminate differences in derived waterrelations attributes. Differences in water potential isothermsrelated to the PV procedures used suggest that prolongedor repeatedexposure to gas at high pressure may introduce errors in theestimation of water relations attributes. Key words: Pinus resinosa, pressure chamber, pressure volume, tissue water relations     

Differences in Architecture and Shoot Growth during Stagnant and Extension Growth Phases of Acanthopanax sciadophylloides(Araliaceae)

The shoot growth of a deciduous tree, Acanthopanax sciadophylloidesFranch. et Savat. shows inter-annual intermittent repetitionof two distinctive phases, a stagnant growth phase (S-phase)and vigorous extension-growth (E-phase). To help understandthe differentiation mechanism, shoot development was studiedover time in both shoot phases. S-phase and E-phase shoots weredistinguished from each other by morphological traits: S-phaseshoots are characterized by higher allocation to leaves anda shorter period of stem growth, while E-phase shoots show continuousstem extension over the growing season. Specific leaf area didnot differ between the two phases. This shoot differentiationwas similar to the morphological differentiation of shoots betweenlong vs. short shoots found in some temperate trees. Leavesof both phases were well-dispersed through adjustment of petiolelength and leaf-blade size to reduce mutual shading within ashoot. Stem-wood density of current-year shoots was lower inE-phase compared with S-phase shoots. Leaves produced earlyin the season affected the growth phase of the following year.These results suggest that annual shoot differentiation of A.sciadophylloides was determined during the previous season andreflects leaf productivity in a given habitat during that growingseason. Copyright 2001 Annals of Botany Company Acanthopanax sciadophylloides, Araliaceae, biomass allocation, intermittent shoot growth, leaf display, shoot architecture, shoot differentiation     

Axillary Bud Formation in Two Isogenic Lines of Tomato Showing Different Degrees of Apical Dominance

Grafting experiments have been carried out in which rootstocksof the cultivar Craigella were paired with scions of an isogenicline Craigella Lateral Suppressor (ls ls) and vice versa, andthe levels of hormones in the roots and shoots of the graftedplants examined. The roots of Craigella plants differed from those of LateralSuppressor in that they contained a higher proportion of a cytokininthat co-chromatographed with N⁶ - (²—isopentenyl) adenosine.Reciprocal grafts did not lead to any qualitative or quantitativechanges in the cytokinins in the roots of either line. GraftingLateral Suppressor scions on Craigella rootstocks led to anincrease in the IAA content of the apical region and the ABAcontent of the stem tissue immediately below it, but when Craigellascions were grafted on Lateral Suppressor rootstocks there wereno changes in the level of either hormone. Cytokinins applied to the leaf axils of Lateral Suppressor plantsresulted in lateral bud initiation in the axils above the pointof treatment but not if the plants were also given a short periodof far-red light at the end of the photoperiod. Cytokinins wereineffective in initiating lateral buds in grafted Lateral Suppressorscions. It is suggested that root-produced cytokinins influence lateralbud outgrowth indirectly by way of their effect on the levelsof IAA and ABA in the shoot. Lycopersicon esculentum Mill., tomato, apical dominance, growth regulation, indol-3yl acetic acid, abscisic acid, cytokinins     

Shoot Growth and Mortality Patterns of Urtica dioica, a Clonal Forb

The growth and mortality patterns of the clonal forb Urticadioica were investigated at the level of the individual shootin two growing seasons, 1991 and 1992, in a natural stand. Shootheight and diameter at ground level of each shoot tagged inspring were measured repeatedly five times during the growingseason. Dry weights of these repeatedly measured shoots wereestimated using an allometric relationship between dry weight,height and diameter of harvested shoots. A large decrease inshoot density occurred with stand development from the beginningof the growing season in both the years: (1) shoot survivalrate was about 30% at the end of the growing season; (2) shootmortality rate per 10 x 10 cm subplot between censuses was positivelydependent on shoot density per subplot; (3) the mortality rateof individual shoots was negatively dependent on shoot size(height, diameter and weight) at each growing stage, suggestingone-sided competition between living and dying shoots; (4) shootsize (height, diameter and weight) variability in terms of thecoefficient of variation and skewness decreased in accordancewith shoot mortality. Symmetric competition between living shootswas detected by regression analysis based on a model for individualshoot growth considering the degree of competitive asymmetry.However, the competitive effect on individual shoot growth wasvery small (nearly absent). The mortality pattern of Urticadioica indicates that shoot self-thinning occurred from theearly growing stage as in non-clonal crowded monospecific stands,and contrasts with many clonal plants where shoot self-thinningrarely occurs or, if any, is confined only to a short periodof the later growing stage. The pattern of growth and competitionbetween living shoots of Urtica dioica contrasts with non-clonalcrowded plants undergoing intense competition (usually asymmetric)between individuals, but is a common feature of many clonalplants where shoot competition is supposed to be reduced by'physiological integration' between shoots. These form a newpattern not reported yet for clonal plants. It is pointed outthat clonal plants show a wider spectrum of the growth, competitionand mortality patterns of shoots than non-clonals. Some possiblemechanisms for the pattern of Urtica dioica are discussed.Copyright1995, 1999 Academic Press Shoot competition, diffusion model, individual shoot growth, shoot self-thinning, shoot size variability, Urtica dioica L     

Bud Content and its Relation to Shoot Size and Structure in Nothofagus pumilio(Poepp. et Endl.) Krasser (Nothofagaceae)

Buds of shoots from the trunk, main branches, secondary branchesand short branches of 10–21 year-old Nothofagus pumiliotrees were dissected and their contents recorded. The numberof differentiated nodes in buds was compared with the numberof nodes of sibling shoots developed at equivalent positionsduring the following growing season. Axillary buds generallyhad four cataphylls, irrespective of bud position in the tree,whereas terminal buds had up to two cataphylls. There were morenodes in terminal buds, and the most distal axillary buds, oftrunk shoots than in more proximal buds of trunk shoots, andin all buds of shoots at all other positions. The highest numberof nodes in the embryonic shoot of a bud varied between 15 and20. All shoots had proximal lateral buds containing an embryonicshoot with seven nodes, four with cataphylls and three withgreen leaf primordia. The largest trunk, and main branch, shootswere made up of a preformed portion and a neoformed portion;all other shoots were entirely preformed. In N. pumilio, theacropetally-increasing size of the sibling shoots derived froma particular parent shoot resulted from differences in: (1)the number of differentiated organs in the buds; (2) the probabilityof differentiation of additional organs during sibling shootextension; (3) sibling shoot length; (4) sibling shoot diameter;and (5) the death of the apex and the most distal leaves ofeach sibling shoot. Copyright 2000 Annals of Botany Company Axis differentiation, branching, bud structure, leaf primordia, neoformation, Nothofagus pumilio, preformation, size gradient     

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

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

Genetic Analysis of Growth in Tomato: the F1 generation

Some aspects of the genetic control of plant development wereinvestigated by combining the methods of growth analysis withthose of quantitative genetics. Four varieties of Lycopersiconesculentum and one of L. pimpinellifolium were included in adiallel cross and the growth of parents and hybrids were followedover a IO-week period. Whole plants and plants with side-shootsremoved were studied. Significant differences in growth-ratewere found between varieties and between the reciprocal inter-specifichybrids; the latter difference followed from the maternal variationin seed size. The growth-rate was reduced by removing the side-shoots.A diallel analysis showed that the control of log fruit weightand number was largely additive but similar analysis of dryweight and leaf-area data showed considerable variation withtime. Extreme caution is, therefore, necessary in generalizingfrom a genetic analysis made at only one point of time. Thisdifficulty was largely overcome and much more information concerningthe inheritance of factors influencing plant development providedby carrying out a genetic analysis of the measured growth-rates.     

Leaf Abscission in Varieties of Phaseolus vulgaris (L. ) and Glycine max (L. ) Merrill/emdash a--Correlation with Propensity to Produce Adventitious Roots

In field trials of Phaseolus vulgaris large differences wereobserved between varieties in the rate at which the leaves abscised.Similar differences were found in the rate of decline of thechlorophyll content of excised leaf discs. A grafting experimentshowed that the differences in leaf abscission depended on thegenotype of the scion and on that of the rootstock. Scion andstock effects of each genotype were similar, and additive. Rootstock/scioncombinations which conferred enhanced leaf retention producedgreater yields of seed and of seed nitrogen. When shoots ofdelayed-senescence genotypes of P. vulgaris were held in waterthey produced more adventitious roots than did shoots of rapid-senescencegenotypes. This relationship between senescence pattern andadventitious rooting was also observed among varieties of Glycinemax, and between isogenic lines of G. max differing in the leafabscission alleles Ab/ab. These results are discussed in relationto current theories of leaf senescence, abscission, and theproduction of yield.     

A Quantitative Analysis of the Uptake of Carbon and of the Supply of 14C-labelled Assimilates to Areas of Meristematic Growth in Lolium temulentum

A quantitative analysis of the ¹⁴C-labelled assimilate suppliedby leaves on the main shoot to terminal meristem, stem, tillers,and roots was conducted during parallel periods of reproductiveand vegetative development in Lolium temulentum. The initial rate of entry of carbon into the shoot varied withthe area and photosynthetic efficiency of the assimilating leaf.Subsequently, respiratory losses of carbon during translocationand incorporation of assimilate at the site of utilization alsovaried. The combined effect of these differences resulted inthe supply of recently assimilated carbon being twofold greaterin reproductive shoots than in vegetative shoots, while withinshoots the carbon supply of the youngest fully expanded leafranged from four-or five-fold greater than the oldest leaf inyoung shoots, to two-or three-fold greater in older shoots.In both reproductive and vegetative shoots, the two or threeyoungest leaves thus dominated the supply of carbon for meristematicgrowth. Meristematic tissue in expanding leaves and leaf primordia atthe terminal meristem of the vegetative shoot received 18–27per cent of the total shoot carbon. This meristem utilized aboutthe same proportion of shoot carbon when it developed into aninflorescence, indicating no major change in the level of meristematicactivity. The proportion of shoot carbon utilized in stem growthincreased as both reproductive and vegetative shoots aged; thisincreased meristematic activity in stem internodes was accompaniedby reduced export of carbon to roots, which received less than10 per cent of the shoot carbon when the experiments ended.The main shoot translocated 20–30 per cent of its recentlyassimilated carbon to developing and rooted tillers, which assinks for carbon were thus as important as the terminal meristemand stem. This outward flow of carbon continued relatively uncheckedwhen donor and receptor shoots developed inflorescences.     

Assessing Costs of Reproduction in Mountain Birch: The Importance of Considering the Modular Level

We studied the effects of production of male catkins on growthand the subsequent year's male catkin production in mountainbirch, Betula pubescens subsp. czerepanovii at both the shootand branch level. (Shoot is defined here as the product of asingle growing season while branch refers to a structure consistingof several shoots.) Like heterophyllous trees in general, mountainbirch canopy expansion takes place via the production of longshoots. We found phenotypic trade-offs between long shoot growthand male reproduction at the shoot level in the year of catkinproduction. Generative parental long shoots (long shoots withmale catkins) were significantly shorter than the vegetativeones (long shoots without a male catkin). In contrast, we foundno effects of male reproduction on the subsequent year's malecatkin production at the shoot level. Although the mean lengthof secondary long shoots (long shoots growing from the lateralbuds of parental long shoots) did not differ between vegetativeand generative parental long shoots, there was considerablebetween-individual variation in the response of individual trees.In addition, production of male catkins diminishes canopy expansionin mountain birch because the number of secondary long shootsproduced by generative parental long shoots was smaller thanthat of vegetative parental long shoots. At the branch level,the association between total long shoot growth and male catkinproduction was positive, i.e. no trade-off was found. This maybe because the strong sink strength (the ability of a branchto import assimilates from elsewhere in the tree) of branchesbearing reproductive long shoots masks possible trade-offs.We emphasize the importance of considering several levels ofthe modular hierarchy when analysing costs of reproduction inmodular organisms. Copyright 2000 Annals of Botany Company Hierarchical structure, modularity, mountain birch, short and long shoots, trade-off, Betula pubescens subsp.czerepanovii (Orlova) Hämet-Ahti     

Carbohydrate and osmotic requirements for high-frequency plant regeneration from protoplast-derived colonies of indica and japonica rice varieties

The effects were studied of various carbohydrates and osmoticstress, created by high agarose or carbohydrate concentrations,on the regeneration of fertile plants from protoplast-denvedcolonies of several indica (IR43, Jaya, Pusa Basmati 1) andjaponica (Taipei 309) rice varieties. Observations of the culturesdeveloped on media containing one of these carbohydrates (cellobiose,fructose, glucose, lactose, maltose, mannitol, sorbitol or sucrose),each at 88 mM, indicated that maltose was the preferential carbonsource for the proliferation of embryogenic callus and shootregeneration. Maltose-containing medium induced shoot formationin 24–66% of the protoplast-derived tissues, dependingupon the rice variety, compared to shoot regeneration from 4–32%of the tissues in sucrose-supplemented medium. Media containing288 mM maltose or an equimolar combination of 88 mM maltoseand 200 mM mannitol, caused water loss from calli and promotedthe growth of embryogenic calli. These calli formed shoots withgreater frequencies when subsequently transferred to shoot regenerationmedium with 88 mM maltose. A medium containing 88 mM maltoseand semi-solidified with 1.0% (w/v) instead of 0.5% (w/v) agarosehad a similar beneficial effect on the growth of embryogeniccalli and simultaneously supported high-frequency (48–55%)shoot formation. The optimum shoot regeneration frequencies(60–78%) were obtained when protoplast-derived colonieswere serially cultured on to shoot regeneration medium containing1.0% (w/v) agarose for 4 weeks, followed by a 2-week cultureperiod on the same medium with 0.5% (w/v) agarose. Plants regeneratedon medium containing maltose and/or 1.0% (w/v) agarose werephenotypically normal and fertile. Key words: Carbohydrates, Oryza sativa L, indica and japonica rice, osmotic stress, plant regeneration, protoplast-derived colonies