Shoot Axis Research Articles

Short-rotation plantations of balsam poplars, aspen and willows on former arable land in the Federal Republic of Germany. II. Nutritional status and bioelement export by harvested shoot axes

As part of a comprehensive interdisciplinary research program the nutritional status of a balsam poplar ( P. trichocarpa cv. Muhle Larsen), an aspen ( P. tremula × tremuloides cv. Astria) and a willow clone ( Salix viminalis) on former arable soils at three different locations in the FRG was monitored by means of foliar analysis. Bioelement concentrations in shoot axes at the end of the rotations and the nutrient export via harvested biomass are described. The methodological approach is a partly factorial fertilization trial with the nutrients N, P, K, Mg and Ca. The foliar nutrient levels in combination with the results of the fertilization trial, in terms of biomass yield, clearly show the balsam poplars and the aspen to be well supplied with all macronutrients on all sites, independently of the fertilization regimes. Both these species are obviously characterized by an excellent capacity to acquire nutrients which are presumably accumulated in these substrates as a consequence of earlier fertilization and liming. In contrast, the willows proved to be very N-demanding and need repeated fertilization with N at all sites under study to achieve optimum yield. Salix was able to increase growth considerably in the second rotation by about 44–300% as compared with the first rotation cycle. The increase of foliar N (only ca. 6% more with 100 kg N ha −1 year −1 than the unfertilized control), however, was rather low as compared to the growth effects caused by the same treatment in the second rotation, leading to low correlative values between foliar N, tree height, and growth. All foliar nutrient levels measured in the experiments are in good accord with values reported in literature for optimal production. In terms of five-year growth periods, total bioelement removals via shoot biomass for all clones are 90–270 kg N, 15–45 kg P, 30–180 kg K, 55–350 kg Ca, and 5–25 kg Mg ha −1. Nitrogen fertilization of Salix viminalis resulted in higher N concentrations in shoot axes, and N amounts removed via harvest increased as a consequence of N fertilization by ca. 26–47% (50 and 100 kg N applied annually). However, with values between 16% and 39%, only a low percentage of the applied N was incorporated into shoot biomass and, therefore, the efficiency of fertilized N was rather low.

Short-rotation plantations of balsam poplars, aspen and willows on former arable land in the Federal Republic of Germany. I. Site–growth relationships

As part of a comprehensive interdisciplinary research program the relationships between site conditions and growth of a balsam poplar ( P. trichocarpa cv. Muhle Larsen), an aspen ( P. tremula × tremuloides cv. Astria) and a willow ( Salix viminalis) are being tested since 1983 in three experimental short-rotation plantations on former arable soils distributed over the FRG. The site conditions, the experimental design and the growth behaviour after two (experimental sites Abbachhof in the Jurassic region of Upper Palatia and Canstein in the eastern Rhenanian Mountains) and after one rotation (site Wildeshausen in the lowlands of NW Lower Saxony) are described. Each rotation lasted for five years. The methodological approach is a partly factorial fertilization trial with the nutrients N, P, K, Mg and Ca. Shoot biomass of the tested clones after the first five-year rotation period showed cumulative dry-matter amounts between 10 and 37 t × ha −1. Highest production was measured from balsam poplars and aspen at Abbachhof, while shoot growth at Canstein and Wildeshausen as a rule was remarkably lower with no clear differences between the tested clones. Based on the first five-year rotation cycle, the average annual shoot axes production of the unfertilized aspen and balsam poplars were 5.1 and 5.9 t ha −1 at Abbachhof. Production was very low for all clones at Canstein and Wildeshausen and for Salix viminalis at Abbachhof with values around 2–4 t ha −1. After the second rotation period, a clear differentiation between the sites showed up, resulting in an 2.5–3-fold increase of cumulative shoot biomass of all three species at Canstein to values of ca. 50–70 t ha −1, resulting in annual shoot axes production of ca. 10 to 14 t ha −1. In contrast, at Abbachhof Muhle Larsen remained at a similar level of production as in the first rotation period (30–35 t ha −1), while Salix significantly increased, and the aspen reduced shoot biomass. Salix shoot yields responded significantly to nitrogen fertilization at Abbachhof (50 and 100 kg N ha −1 year −1) by ca. +33 and +73% (first rotation) and +29 and +47% (second rotation), and at Canstein by ca. 25% in the 100 kg N ha −1 year −1-treatment. At Abbachhof, the aspen reduced growth as compared to the first rotation, probably due to heavy attack by defoliating insects. The balsam poplar Muhle Larsen proved to be the most interesting species tested. In all respects, it seems to be well supplied with nutrients for optimal growth and does not need any fertilization or pesticide treatment for at least 10–15 years. So far, no effects of P, K, and Mg fertilization with/without combination with liming were detected.

Uptake of phloem-specific cardenolides by Cuscuta sp. growing on Digitalis lanata and Digitalis purpurea

Cuscuta europaea, C. platyloba and C. reflexa were cultivated on stems of Digitalis lanata und D. purpurea in the second year of vegetation as well as on petioles of rosettes of D. purpurea in the first year of vegetation. C. reflexa was most suitable as parasite because it formed relatively thick shoot axes and revealed the best rates of infection. Cardenolides were taken up by the parasitising Cuscuta sp. from the host plants. Within the parasite the cardenolide concentration decreased from the haustorial region to the shoot tip. The main cardenolides present in Cuscuta were identified as the monoglycosides strospeside (gitoxigenin digitaloside) and verodoxin (gitaloxigenin digitaloside). These cardenolides were found irrespective of growth of the parasite on D. lanata or D. purpurea though the bulk cardenolides of these species are tetraglycosides and the cardenolide profiles of D. lanata and D. purpurea differ from each other. However, strospeside and verodoxin are structurally related to digitalinum verum (gitoxigenin glucosyldigitaloside) and glucoverodoxin (gitaloxigenin glucosyldigitaloside) present in the phloem sap of D. lanata. They are obviously derived from these cardenolides by deglucosylation.

Anatomical study of the bud union in „Chip" and „T" budded 'Jonagold' apple trees on MM 106 rootstock

The traditional methods for vegetative propagation of apple and its varieties are the T-budding, and the winter grafting, but this latter way is a difficult and expensive procedure.
 In our experiment carried out in the Fruit Tree Nursery Soroksár, the healing process of chip- and T-budded apple trees 'Jonagold' on MM 106 rootstock was studied.
 The budding (T- and Chip-) was made in the first week of August, samples for microscope examination were taken monthly after this time until leaf fall.
 The investigated part of plants was made soft with 48 % HF (hydrogenfluoride), then cross and longitudinal section were made and examined by microscope.
 Based on analysis of microscope pictures in case of Chip-budding, it was established, that development had started quickly after budding on the rootstock and scion too. But the callus originated almost entirely from the rootstock tissue as new parenchyma cells fills the gap between the two components of graft (scion and stock), becoming interlocked and allowing for some passage of water and nutrients between the stock and the scion. This quantity of callus in case of T budding was under the scion buds larger, than the Chip-budded unions, where the thickness of callus mass is uniformly thick round the chip. The large mass of callus pushes the scion bud outwards from the shoot axis, which later results in a larger shoot-curvature above the bud union.
 Following this process on the Chip-budding it can be observed also, that a continuity of the cambium is established between bud and rootstock. Then the newly formed cambium started typical cambial activity, forming new xylem and phloem.
 Later the callus begins to lignify, and it is completed within about 3 months after budding.

Metabolism of exogenous auxin by Arabidopsis thaliana: Identification of the conjugate N‐(indol‐3‐ylacetyl)‐glutamine and initiation of a mutant screen

The accumulation of conjugates of indole‐3‐acetic acid (IAA) in Arabidopsis thaliana was studied by incubating tissues with high concentrations of exogenous IAA, followed by reverse phase HPLC analysis of the extracts. Using fluorescence detection, indole‐3‐acetyl‐aspartate, indole‐3‐acetyl‐glutamate, and indole‐3‐acetyl‐glucose were observed and quantitated in extracts of tissue after 24 h incubation with 500 μM IAA. In addition, a new metabolite was detected and positively identified as indole‐3‐acetyl‐glutamine by fast atom bombardment mass spectrometry, exact mass measurement, and tandem mass spectrometry in comparison with a synthetic standard. The amounts of individual conjugates formed differed between leaves, shoot axes and roots. In all three tissues, indole‐3‐acetyl‐aspartate was the most abundant conjugate, the highest level being observed in roots. Highest levels of indole‐3‐acetyl‐glutamine were observed in leaves, where it was the second most abundant conjugate and comprised approximately 12% of the fluorescent metabolites. Accumulation of the three amide conjugates was dramatically inhibited by cycloheximide, whereas accumulation of indole‐3‐acetyl‐glucose was little affected. Based on these data, a screen for Arabidopsis mutants altered in the IAA‐inducible system for auxin conjugate formation was initiated. The first mutant to be isolated and characterized produces more indole‐3‐acetyl‐glutamine and less indole‐3‐acetyl‐aspartate than wild‐type, and is allelic to an existing class of photorespiration mutants (gluS) deficient in chloroplastic glutamate synthase.

Browsing damage by roe deer on Norway spruce seedlings planted on clearcuts of different ages: 2. Effect of seedling vigour

The effects of browsing damage by roe deer ( Capreolus capreolus L.) on Norway spruce ( Picea abies (L.) Karst) seedlings planted on clearcuts of different ages were studied in a field experiment. The experiment was established in 1993 on 0- to 4-year-old clearcuts in four sites, and seedling observations were made until May 1995. Half of the seedlings were planted in May and the other half was planted in October. Planting in two different seasons allowed the separation of the different effects of surroundings on the risk for a seedling to be browsed. Seedling vigour was estimated, using a needle colour index ranging from yellow to dark green. In addition, concentrations of nitrogen in needles and shoot axes were analysed. The needle colour index was well correlated with nitrogen concentration in both needles and shoot axes. The frequency of browsing was higher for seedlings with a dark green colour (high nitrogen concentration) than for seedlings with a light green or yellow colour (low nitrogen content). The average needle colour index was also correlated with the average frequency of browsing damage over different sites and years. Browsing damage tended to decrease with the height of surrounding vegetation, mainly owing to reduced seedling vigour, as long as the vegetation was shorter than the seedling. In cases where the vegetation was higher than the seedling, the physical protective afforded by the vegetation seemed to dominate. The needle colour index of seedlings tended to increase with height of slash which was most likely explained by a fertilising effect from decaying plant tissues. Browsing damage tended however to be reduced with increasing slash height. The increasing risk for a seedling to be browsed because of higher vigour, as a result of higher slash, seems to be balanced by the physical protection afforded by slash.

Distribution of Cu2+-diamine oxidase during ontogeny of seedlings of Vigna radiata cultivars

Activity of Cu2+-diamine oxidase (DAO; E.C.1.4.3.6.) was measured in Vigna radiata (L.) Wilczek cultivars K851, MH8320 and Pusa Baisakhi in light and in dark during ontogeny of seedlings. DAO activity was always the highest in cv. K851. In both light and dark grown seedlings maximum DAO activity was detected on day 2 after germination. Thereafter, in light grown seedlings it declined consistently upto non-detectable levels. In dark, DAO activity was higher than in light and it had the second maximum on day 7 following a similar declining pattern as observed for the light grown seedlings. The DAO activity was higher in a shoot apex alongwith leaves than in roots and shoot axis.

The viviparous8 mutation delays vegetative phase change and accelerates the rate of seedling growth in maize

SummaryPost‐embryonic shoot development in plants can be divided into a juvenile vegetative, an adult vegetative, and a reproductive phase, which are expressed in different domains on the shoot axis. The number and position of the phytomers in each phase are determined by the time at which a plant begins and ceases making phytomers of a particular phase and the rate at which phytomers are made during that phase. The viviparous8 (vp8) mutation of maize increases the number of juvenile vegetative phytomers and decreases the number of adult vegetative phytomers by affecting both of these processes. vp8 increases the number of juvenile vegetative phytomers by increasing the rate of leaf initiation early in shoot development and delaying the juvenile‐to‐adult transition (vegetative maturation). It reduces the number of adult phytomers because the delay in vegetative maturation is not matched by a corresponding delay in flowering time; vp8 plants produce a tassel at the same time as wild‐type plants. Thus, Vp8 normally controls the production of a factor that functions both to repress the rate of growth early in shoot development and to promote vegetative maturation, but which has no major role in floral induction. vp8 dramatically enhances the phenotypes of the dwarf and Teopod mutants and requires a functional Glossy15 gene to prolong the expression of juvenile epidermal traits. Evidence suggesting that vp8 does not affect phase change by reducing the level of abscisic acid is discussed.

Energy requirement for foliage construction depends on tree size inyoung Picea abies trees

The relationship between stand biomass production, and tree age and size is generally a curve with a maximum. To understand why wood production decreases in the final stages of stand development, the influence of increasing tree size on foliage chemical composition and substrate requirement for foliage construction in terms of glucose [CC, g glucose (g dry mass) – 1] was investigated in the evergreen conifer Picea abies (L.) Karst. Because it was already known that irradiance affects both foliage morphology and chemistry in this species, and it was expected that the foliage in large overstory trees would intercept on average more light than that in saplings in understory, irradiance was measured in the sampling locations and included in the statistical models. CC of needles increased with increasing total tree height (TH) and was independent of relative irradiance. A major reason for increasing CC with increasing TH was a greater proportion of carbon-rich lignin in the needles in large trees. However, lignin did not fully account for the observed changes in CC, and it was necessary to assume that certain other carbon-rich secondary metabolites such as terpenes also accumulate in the foliage of large trees. Enhanced requirements for needle mechanical strength as evidenced by greater lignin concentrations in large trees were attributed to increased water limitations with increasing tree height. Because water relations may also control the sink capacities for assimilate usage, apart from the mechanical requirements, they may provide an explanation for the accumulation of other energetically expensive compounds in the needles as well. Biomass partitioning within the shoot was another foliar parameter modified in response to increasing tree size. The proportion of shoot axes, which serve to provide needles with mechanical support and to supply them with water, decreased with increasing TH. This may limit water availability in the needles, and/or manifest a lower water requirement of the needles containing proportionally more supporting and storage substances, and consequently, less physiologically active compounds such as proteins. Probably the same factors which caused CC of the needles to depend on TH, were also responsible for greater CC of the shoot axes in larger trees. These results collectively suggest that increasingly more adverse water relations with increasing tree size may provide a mechanistic explanation for the decline in foliar biomass and its functional activity during stand ageing.

The Concept of Morphological Polarity and its Implication on the Concept of the Essential Organs and on the Concept of the Organisation Type of the Dicotyledonous Plant

Dicotyledons are polarly organised in several ways. In plant morphology polarity, a principle, allowing comparison of different plant structures has until yet not been studied. A division**.of the plant in shoot and root as polar structures leads to the distinction of four instead of three basic organs: leaf, shoot axis, root axis and root cap together with the root hairs. The flower is a1so polarly organised, its poles are formed by the carpels and the stamens. The foliage leaves are also polarly organised which is reflected by the morphological relationship of foliage leaf, stamen and carpel. The stamen uses the hypophyll*** as base of construction and the carpel uses the epiphyll**** as base of construction. Hypophyll and epiphyll are the two poles of the foliage leaf. Root and shoot, the polar entities of the vegetative plant and stamen and carpel, the polar entities of the generative plant are, morphologically correlated. Stamen and carpel can be understood as a combination of the basic organs of vegetative and generative parts of the plant. The basic organs of the generative plant are pollen grain and embryo sack with their gametophytes. The quantitative comparison of variable proportions is supplemented by a qualitative comparison of polarities. The result is that the organisation type of the Dicotyledons can yet be understood as constituted of morphological related parts. * in german Grundorgane ** in german: Gliederung *** in german: Unterblatt **** in german: Oberblatt 1. INTRODUCTI0N

G2-and early-M-specific expression of the NTCYC1 cyclin gene in Nicotiana tabacum cells.

We have previously reported the isolation of a cDNA encoding a mitotic cyclin, NTCYC1, from a tobacco cell suspension library. Here we describe the expression patterns of NTCYC1 and of Ntsuc1, a suc 1 plant homologue, in synchronized tobacco cell suspensions. Furthermore, the expression pattern of this cyclin is compared to that of Ntcdc2-1, a Nicotiana tabacum homologue of cdc2. While no NTCYC1 transcript was detected in cells synchronized in the G1 and S phases, NTCYC1 expression was observed in late G2 and early M phases, disappearing in the G1' of a new cell cycle. On the other hand, Ntsuc1 and Ntcdc2-1 exhibited a constitutive expression during the cell cycle. A functional analysis performed by microinjecting NTCYC1 mRNA into immature Xenopus oocytes, indicates that NTCYC1 could participate in the control of the G2/M transition in plant cells. Subsequently NTCYC1 expression was used to assess the status of mesophyll cells in expanded leaves of N. tabacum. Depending on leaf position along the shoot axis, a large population of mesophyll cells appeared with a 4C DNA content, suggesting a G2 arrest. It was found that leaves with such a population also contained high levels of NTCYC1 transcripts. With respect to these results concerning a naturally occurring G2-arrested cell population, the regulation of NTCYC1 expression in planta is discussed.

Effects of Phase Transition on the Development of Lateral Buds in Maize

Different lateral bud structures are generated along the main shoot axis in maize (Zea mays L.). This study was conducted to show how the structural diversity of the lateral buds is generated. The growth and development of lateral buds of three hybrids were investigated under field conditions at Tokyo, Japan, on a silt loam (Andosols). Six plants per hybrid were harvested as each leaf emerged and the morphological features and the length of each lateral bud were determined. We observed in mature plants that the lateral buds consisted of two discrete populations acropetally along the main stem (i) lower lateral buds that remained in a vegetative state, and (ii) upper lateral buds, including grain‐bearing shoots, that terminated in reproductive organs. Lower lateral buds elongated sequentially up the stem and grew for a specific time interval. The phase transition of the apical meristem to tassel initiation evoked a change in the bud growth pattern. At tassel initiation, the upper lateral buds were still in an incipient state without establishing a complete bud structure. During the reproductive phase that followed, elongation of the upper lateral buds occurred simultaneously. These results suggest that lateral bud growth during the vegetative phase was regulated independently from the reproductive phase during plant development. Lateral buds that are at a certain development state could be responsive to the change in physiological signals during the transition between vegetative and reproductive phase.

Inheritance and Gibberellic Acid Sensitivity of a Dwarf Red Beet Mutant

Few genes have been identified in red beet. A spontaneously occurring dwarf mutant was identified in the late 1970s and again in 1994 in several breeding populations. Mutant plants are characterized by extreme dwarfing of both root and shoot. Young leaves are narrow, thin and strap-like while older leaves are thicker and deeply veined. The shoot axis forms a compressed rosette. Neither the shoot axis nor the root axis of field-grown plants exceeds 3 cm in height. Genetic analysis of F2 and backcross populations revealed the dwarf phenotype is conditioned by a single recessive gene. Several experiments were conducted to determine if the dwarf phenotype was due to a lack of gibberellic acid (GA) production. Exogenous application of GA3 at concentrations ranging from 1 to 1000 ppm on dwarf plants a) following seeding and b) during reproductive growth revealed a linear increase in plant height. Control dwarf plants receiving a water-only treatment were 18% as tall as plants receiving regular application of 1000 ppm GA3. A wild-type phenotype during reproductive growth was recoverable following regular GA3 application.

An altered body plan is conferred on Arabidopsis plants carrying dominant alleles of two genes

In this paper, we describe a late-flowering ecotype of Arabidopsis, Sy-0, in which the axillary meristems maintain a prolonged vegetative phase, even though the primary shoot apical meristem has already converted to reproductive development. This novel heterochronic shift in the development of axillary meristems results in the formation of aerial rosettes of leaves at the nodes of the primary shoot axis. We present evidence that the aerial-rosette phenotype arises due to the interaction between dominant alleles of two genes: ART, aerial rosette gene (on chromosome 5) and EAR, enhancer of aerial rosette (on chromosome 4): EAR has been tentatively identified as a new allele of the FRI locus. The possible role of these two genes in the conversion of shoot apical meristems to reproductive development is discussed.

Highly Branched Phenotype of the Petunia dad1-1 Mutant Is Reversed by Grafting.

The recessive dad1-1 allele conditions a highly branched growth habit resulting from a proliferation of first- and second-order branches. Unlike the wild-type parent, which has lateral branching delayed until the third or fourth leaf node distal to the cotyledons, dad1-1 initiates lateral branching from each cotyledon axil. In addition to initiating lateral branching sooner than the wild type, dad1-1 sustains branching through more nodes on the main shoot axis than the wild type. In keeping with a propensity for branching at basal nodes, dad1-1 produces second-order branches at the proximal-most nodes on first-order branches and small shoots from accessory buds at basal nodes on the main shoot axis. Additional traits associated with the mutation are late flowering, adventitious root formation, shortened internodes, and mild leaf chlorosis. Graft studies show that a dad1-1 scion, when grafted onto wild-type stock, is converted to a phenotype resembling the wild type. Furthermore, a small wild-type interstock fragment inserted between a mutant root stock and a mutant scion is sufficient to convert the dad1-1 scion from mutant to a near wild-type appearance. The recessive dad1-1 phenotype combines traits associated with cytokinin overexpression, auxin overexpression, and gibberellin limitation, which suggests a complex interaction of hormones in establishing the mutant phenotype.

δ13C-Variationen bei einjährigen Fichtensämlingen als Pflanzenphysiologische Reaktion auf S-, Al- und Ca-Gaben

Abstract In this study vessel cultures of spruce seedlings were grown with increased amounts of S, Al and Ca applied to soil. Growth development, mineral distribution and stable carbon isotope ratios were measured in plants after the first growing season. Increased sulphate additions to soil are characterized by reduced growth and lower δ13C-values, but take no effects on mineral composition of the seedlings. δ13C-values of plants rose for 0,4%‰ with higher additions of aluminium into soil. Injured roots suggest water deficits that can explain the shift towards higher δ13C-values. CaCO3 increases the pH of the soil and causes up to 0,6‰ higher δ13C-values of the plants. Furthermore the addition of CaCO3 effects the balance and relations of nutrient composition (Ca, Mg, K). All observed variations in δ13C occur in needles, shoot axis, and in extracted cellulose in common. Changed soil conditions correspond with reactions of the plants in growth, mineral distribution and δ13C.

Gene expression in leaves ofArabidopsis thalianainduced to senesce by nutrient deprivation

Senescence was induced in leaves of Arabidopsis thaliana by transferring rosettes from a nutrient-sufficient medium to water. A visible gradient of yellowing along the shoot axis became apparent within 5 d. Leaves were grouped into four age-classes, representing fully green (nodes 17-20) through about one-third (nodes 13-16) and one-half (9-12) to more than 80% yellow (5-8). The decrease in chlorophyll and carotenoid content with increasing tissue senescence was accompanied by a loss of total protein and of specific polypeptides identified by electrophoresis and Western blotting. Heterogeneity in the rates at which photosynthetic proteins decreased during senescence could be related to differences in susceptibility to proteolysis conferred by location (soluble proteins are more labile than membrane components) and association with stabilizing components such as pigments. The abundance of senescence-related mRNAs was determined by Northern analysis using heterologous DNA probes and also cDNAs isolated from Arabidopsis by differential library screening. Expression of the plastid gene psbA increased until the most extreme stage of senescence, in contrast to the pattern of the protein it encodes, D1, which was almost undetectable in all but mature green tissue. Transcripts corresponding to two senescence-enhanced cDNAs from Brassica napus, LSC54 and LSC94, were strongly up-regulated in senescing Arabidopsis leaves. Two Arabidopsis cDNAs, LdeVA8 and LdeVA32, detected mRNAs of increasing abundance up to mid-senescence and decreasing thereafter. Another homologous clone, LdeVA43, hybridized with a transcript showing some enhancement in early senescence. Partial base sequences of LdeVA8 and LdeVA32 revealed homologies with genes encoding a metallothienin-like protein and catalase, respectively. LSC54 also encodes a putative metallothionein. The possible significance of the patterns of gene expression in senescing rosette leaves of A. thaliana is discussed.

Direct somatic embryogenesis and plantlet regeneration from cotyledonary leaves of safflower

Somatic embryos were induced directly on adaxial surface of cotyledonary leaves within 8–10 days of culture on Murashige and Skoog medium containing 5.37 to 10.74 μM 1 — napthaleneacetic acid and 2.22 μM benzyl adenine. Germinated embryos with shoot axes developed into complete plants after transfer onto half stength Murashige and Skoog medium containing 1.07 μM 1 — napthaleneacetic acid. Histological studies suggested direct origin of somatic embryos with broad-base attachment.

Specification of chimeric flowering shoots in wild-type Arabidopsis.

Within wild-type Arabidopsis populations, a subset of the plants were found to have a single chimeric shoot on their primary shoot axes. The chimeric shoots were located below the lowest primary-axis flower; and they exhibited features of both flowers and paraclades (lateral flowering shoots). Morphological analyses of chimeric shoots indicated that they developed from single primordia. In each chimeric shoot, the side furthest from the apical meristem was specified as 'flower'--while the side closest to the meristem was specified as 'paraclade'--suggesting that a stimulus from outside the apical meristem can directly induce primordia to develop as flowers. It is concluded that the development of the teratological chimeric shoots resulted from the overlap of the vegetative and floral specification processes within single primordia.

Hypotheses for the Evolution of Apical Dominance in Plants: Implications for the Interpretation of Overcompensation

Apical is the preferential growth of a plant shoot (or root) from the or terminal meristem, and the corresponding suppression of lateral subtending meristems and branches. The most obvious consequence of is a linear directional growth pattern resulting in an extended shoot axis, e.g. tall rather than bushy growth forms. Although the physiology of has been the subject of a vast of body of literature (Cline 1991), the ecological and evolutionary implications of have been scarcely addressed (Salisbury and Marinos 1985). Under what circumstances is favoured by natural selection? Are there predictable patterns in the strength of across different habitat types or different life history strategies? Are there tradeoffs associated with strong that may define potential fitness costs? In this paper I present a framework for addressing these questions by considering several hypotheses for the adaptive significance of in plant shoots, and the interpretation of plant responses to the disruption of by ecological factors. I use the term apical dominance in a broad sense to also include apical which is sometimes used to distinguish the control exerted by an meristem on daughter branches (Cline 1991). Apical may be disrupted by damage resulting from a variety of factors, but the one that has received the most attention recently in the literature is herbivory. In several species, flower, seed and/or biomass production have been shown to increase following herbivory or simulated herbivory involving removal or destruction of the shoot apex (e.g. Inouye 1982, Argall and Stewart 1984, Sheldon 1986, Aarssen and Turkington 1987, Paige and Whitham 1987, Benner 1988, Maschinski and Whitham 1989, Michaud 1991, Mopper et al. 1991, Strauss 1991). Such examples of overcompensation following herbivore damage have been interpreted by some as an adaptive response that has evolved as a consequence of natural selection due to herbivory, although reports of effects on lifetime fitness are lacking (see Belsky (1986) and Belsky et al. (1993) for recent critiques). Aarssen and Irwin (1991) however, interpreted such overcompensation as a product of release from and hence an indirect consequence of whatever selection factors favour dominance. Under this interpretation, incurs an apparent cost in terms of reduced growth potential resulting from lateral meristem inhibition. The critical question however is, does this reduced growth potential translate into realized fitness costs, i.e. does overcompensation result in increased fitness when is disrupted? Below I address this question through several predictions associated with alternative hypotheses for the adaptive significance of (Table 1).