Rhizome Apices Research Articles

Dryopteris mengshanensis (dryopteridaceae) from china: a new species

Dryopteris mengshanensis J. X. Li & X. J. Li, sp. nov. of Dryopteris Adans. belonging to Dryopteridaceae from Tashan mountain of Fei County, Linyi City, China is described and illustrated. It is closer to D. laoshanensis J. X. Li et S. T. Ma but differs for its height (60~78 cm), rhizome apex and stipe base densely covered with dark brown, margin brown, entire narrowly lanceolate scales, the upper middle of the stipe and the rachis densely covered with two types of small scales: 1) dark brown, entire narrowly lanceolate scales and 2) margin toothed, ovate-lanceolate scales. Leaves are ovate, bipinnate, pinnules oblong or rectangular circular, apex obtuse or flat, subentire margin. The lower middle of the rachis and stipe are castaneous, costae and rachiole have two kinds of small scales: 1) margin toothed lanceolate scales and 2) cystiform, apex caudate scales. Sori orbicular, larger, dorsal on both sides of the main vein below the middle of the pinnule, each in a line 4 to 5 pairs, located between the margin and midvein, less near the midvein. Spores perispore with massive ornamentation are very distinct. Bangladesh J. Bot. 53(3): 711-716, 2024 (September) Special

Plant growth regulators improve the growth and physiology of transplanted Thalassia Hemprichii fragments

IntroductionThe transplantation of seagrass fragments with shoots and rhizomes is the most common method for the ecological restoration of damaged seagrass meadows.MethodsThe aim of this study was to explore the effects of exogenous addition (10 mg per month for 3 months) of three commonly used plant growth regulators (PGRs), including indoleacetic acid (IAA), gibberellin (GA3), and paclobutrazol (PP333) on the growth and physiology of transplanted Thalassia hemprichii fragments (TTFs), with and without the rhizome apex (RA), using a simulation test. [Results] IAA and GA3 elevated the photosynthetic capacity and growth rate of TTF leaves but did not significantly alter leaf length and width. In contrast, PP333 reduced the leaf photosynthetic capacity and growth rate, while greatly increasing the leaf width and root viability. Additionally, PP333 treatment led to an increase in antioxidant enzyme activities (peroxidase [POD], superoxide dismutase [SOD], and catalase [CAT]), as well as malondialdehyde (MDA) and total phenol contents in TTFs, indicating some stress effects on the seagrass. Furthermore, IAA and GA3 decreased soluble sugar and protein contents and increased starch content in TTF tissues, whereas PP333 treatment elevated both nonstructural carbohydrate and soluble protein contents. The presence of RA positively affected the growth and physiology of T. hemprichii compared with TTFs without RA. There was a significant interaction between the PGRs and RA on leaf growth rate, chlorophyll fluorescence variables, and photosynthetic pigment content of the TTFs (p < 0.05).DiscussionThis study provides guidelines for the application of PGRs during the transplantation of T. hemprichii fragments for the restoration of seagrass meadows.

Metabolome and transcriptome analyses identify the underground rhizome growth through the regulation of rhizome apices in Panax ginseng

Panax ginseng C. A. Mey. is a well-known oriental medicine as a stimulant and dietary supplement. The ginseng rhizome, as one of the principal medicinal organs, plays an important role in aboveground organ growth and root development, although no studies on ginseng rhizome growth have been recorded. In this study, we identified that shoot apical meristem (SAM) was included in the rhizome bud, which could regulate the underground rhizome growth of ginseng. In microscopic examination, ginseng SAM included the central zone, peripheral zone, rib zone, and organizing center; secondary root structures were observed in ginseng main roots and lateral roots; primary root structures were observed in ginseng fibrous roots; rhizome had a stem structure with pith and discontinuous cambium. The metabolites in different underground ginseng organs were identified using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS), with oleanane (OA)-type ginsenosides accumulating primarily in the rhizome buds. In addition, ginseng rhizome buds contained a low level of 3-indoleacetonitrile (IAN, one type of auxin), a high amount of abscisic acid (ABA), and a high level of jasmonoyl-isoleucine (JA-Ile, active form of jasmonic acid). ABA and JA-Ile could drastically limit the shooting rate of ginseng embryonic calli, however IAN boosted the rooting rate. Furthermore, the expression of genes involved in ginsenoside biosynthesis, phytohormone production, and shoot stem cell regulatory pathways were studied. This is the first study of SAM in medicinal herbs, and we believe that the results may offer new information about the development of ginseng underground rhizomes.

Discovery of a new species of Adder\u2019s tongue fern from India with comparative analysis of morphological and molecular attributes

Eusporangiate fern genus Ophioglossum L. is commonly known as Adder’s tongue fern as its fertile frond gives the appearance of snake tongue. A new species in this fern genus, O. trilokinathii belonging to Ophioglossaceae family has been discovered from the plateau region of Rajasthan State of northwestern India. The new species can be distinguished from other taxa of this genus by its smaller habit, subglobose-tuberous rhizome, basipetal emergence of young roots, aggregation of old decaying roots on rhizome apex, fertile stalk as well as spike short and thick, trophophylls in rosette, ovate or orbicular and a unique sporoderm sculpture pattern under SEM having broad reticulations with thick and raised muri enclosing large hexagonal or irregular areas on the distal and proximal faces of the spores hitherto unreported in any of the presently known taxa of Ophioglossum. In addition, comparative study of stomatal structure, foliar anatomy and nucleotide sequence data of its three chloroplast DNA markers (trnL-F, rbcL and psbA-trnH) was carried out. In view of all the attributes including habitat, ecology, morphology, foliar anatomy, stomatal features, palynology and molecular phylogenetic data, the present study suggests that the Ophioglossum specimen collected from plateau region of Rajasthan represents a hitherto undescribed species thereby warranting its establishment as O. trilokinathii sp. nov. A detailed comparative account of the new taxon with its allied species has also been provided.

Ultrastructure of Hirschmanniella diversa early-stage infection in browning rhizomes of Indian lotus.

Browning rhizome (also known as “browning tuber disease”) in Indian lotus (Nelumbo nucifera) caused by the nematode Hirschmanniella diversa is an emerging agronomic problem. In this study, the authors documented the early infection processes of H. diversa in the apices of young rhizomes of Indian lotus by electron microscopy analysis using an artificial inoculation method. Nematodes were attracted to young rhizome apices, invading them via narrow indentations by 4.5 hr after inoculation. Host cells adjacent to the cavity around the invading nematodes were absent and appeared to have disintegrated during infestation. Following contact with the nematodes, host cell walls and cellular contents became electron-dense and less defined, likely due to digestive enzymes secreted by the invading nematodes. Nematodes invaded to a depth of about 1 mm by 24 hr after inoculation, but did not penetrate the plant any further vertically, similar to the observation of browning in mature rhizomes in the field. The authors propose that the invasion sites of young rhizome apices become blackish-brown blotches as rhizomes mature in the field due to oxidation.

Phylogenetic relationships of Neotropical lady ferns (Athyriaceae), with a description of Ephemeropteris, gen. nov.

We carried out a molecular phylogenetic analysis of Neotropical lady ferns (Athyrium s.str. and Anisocampium) using five plastid markers. We found two major results. First, three Neotropical species (Anisocampium skinneri, Athyrium palmense, A. tejeroi) formed a clade, and this clade was sister to the rest of Athyrium. The three members of this clade differ from Athyrium s.l. by creeping rhizomes with internodes 1–2 mm long, and rhizome apices that protrude beyond the current season's cluster of leaves. Also, the leaves are distichously arranged, lack trophopods, have petiole bases broadly U‐shaped in transverse section, and bear thin, membranous laminae. We recognize this clade as a new genus, Ephemeropteris, and provide three new combinations: E. palmensis, E. skinneri, and E. tejeroi. The name of the new genus is derived from the seasonal production of its leaves, which are produced during the wet season and die back (i.e., are ephemeral) at the beginning of the dry season. Ephemeropteris is largely restricted to the Pacific side of Central America, a region that exhibits a marked dry season from November to May. We provide a key to the seven genera (including Ephemeropteris) we now recognize in the Athyriaceae, and a taxonomic treatment of the three species of Ephemeropteris. The treatment includes descriptions, illustrations, nomenclatural data, specimens cited, and a dot‐distribution map. Our second major result from the phylogenetic analysis is that the remaining three Neotropical species of Athyrium s.str. are polyphyletic. One of our seven samples was resolved in the A. filix‐femina clade (sect. Athyrium), to which all species of Neotropical Athyrium were previously assumed to belong to. Our six other samples of Neotropical Athyrium were resolved in A. sect. Mackinnoniana, previously construed as entirely Asian.

Seagrass response to burial and breakage of expanding horizontal rhizomes: implications for clone spread

In seagrasses, elongation of horizontal rhizomes, and hence clone expansion, is supported by physiological integration. However, horizontal rhizomes are subjected to breakage by physical disturbances and to burial, often simultaneously. Little is known about the combined impact of such factors on the growth of apical rhizome regions. We factorially manipulated connections on runners of Cymodocea nodosa and sediment height for 1 mo at 2 sites within a meadow to test the hypothesis that breakage of interconnections close (10 cm) to the rhizome apex causing premature loss of physiological integration would negatively affect the performance of runners and reduce their ability to tolerate burial (60% of shoot height). Shoot survival, length of vertical internodes and horizontal rhizome network, biomass production, partitioning, and costs were unaffected by the investigated factors. Rhizome breakage interacted with burial for some characteristics. Breakage reduced branch length and rhizome diameter only in unburied runners, while burial reduced branch length only in intact runners. Moreover, burial stimulated leaf sheath elongation and greater branching, irrespective of the status of connections. These findings indicate that breakage only delays lateral spread and increases the risk of fragmentation by subsequent disturbances, and, contrary to our hypothesis, has no substantial influence on the capacity of runners to withstand transitory and moderate burial. The findings also reveal that runners may escape from burial not only vertically, but also horizontally, changing growth pattern and direction from predominantly unidirectional to multidirectional. This additional strategy could allow buried runners to accelerate space occupation even if disconnected from clones.

Rhizome phyllosphere oxygenation in Phragmites and other species in relation to redox potential, convective gas flow, submergence and aeration pathways

Underground rhizomes of emergent aquatic macrophytes are important for perennation, vegetative spread, competition and anchorage. In four species we examined the potential for the development of oxidized phyllospheres around rhizome apical buds, similar to the protective oxygenated rhizospheres around roots. Redox potentials and polarographic measurements of radial oxygen loss were recorded using platinum cathodes around the apical buds. The aeration pathway from atmosphere to phyllosphere was investigated anatomically and by applied pressurized gas flow. Redox potentials increased by +400, +45, +200 and +340 mV around rhizome apices of Phragmites australis, Oryza rhizomatis, Carex rostrata and Glyceria maxima, respectively. Radial oxygen loss from rhizome apices of Phragmites was increased by convective gas flow through the rhizome and by shoot de-submergence, and decreased by resistances applied within the aeration pathway and by shoot submergence. We conclude that oxygen passes via internal gas-space connections between aerial shoot, rhizome and underground buds and into the phyllosphere regions via scale-leaf stomata and surfaces on the buds. We suggest that oxidized phyllospheres may protect rhizome apices against phytotoxins in waterlogged soils, just as oxidized rhizospheres protect roots.

Produção da araruta 'Comum' proveniente de três tipos de propágulos

O trabalho foi desenvolvido em Dourados-MS, no período de 2/10/2003 a 21/8/2004, em Latossolo Vermelho distroférrico, textura argilosa. O objetivo foi avaliar a capacidade produtiva da araruta 'Comum', utilizando-se três tipos de propágulos. Os propágulos eram formados por pedaços de rizomas, com seis gemas, tomados da base (3,7 g a 9,0 g; média de 6,0 g), da parte média (7,1 g a 17,7 g; média de 11,9 g) ou da ponta do rizoma (10,2 g a 23,5 g; média de 16,7 g). Os tratamentos foram arranjados no delineamento experimental de blocos casualizados, com oito repetições. A colheita foi efetuada aos 324 dias após o plantio. A massa fresca das folhas, na época da colheita, não diferiu estatisticamente entre os tipos de propágulos. Houve aumentos significativos de 1,40 t ha-1; 8,88 t ha-1; 6,52 t ha-1; 1,13 t ha-1 e 1,23 t ha-1, respectivamente, nas massas frescas de raiz, de rizomas totais, dos rizomas grandes, médios e pequenos, das plantas originadas de propágulos da parte média dos rizomas, em relação às das bases. O número de rizomas por hectare e a massa unitária dos rizomas foram influenciados significativamente pelos tipos de propágulos, com diferenças variáveis dentro de cada tamanho de rizoma produzido. Os rizomas de tamanho médio e pequeno foram influenciados significativamente pelo tipo de propágulo, sendo maiores nas plantas originadas a partir da parte média dos rizomas, em relação às das plantas originadas a partir das pontas ou das bases. Nas condições em que foi conduzido o experimento, concluiu-se que, para o plantio da araruta 'Comum', deve-se recomendar o uso de propágulos formados por pedaços da parte média ou das pontas dos rizomas, com seis gemas.

Effect of El Nĩno on demographic, morphological, and chemical parameters in turtle-grass (Thalassia testudinum): an unexpected test of indicators.

We examined the response of demographic, morphological, and chemical parameters of turtle grass (Thalassia testudinum), to much-higher-than-normal rainfall associated with an El Niño event in the winter of 1997-1998. Up to 20 inches of added rain fell between December 1997 and March 1998. triggering widespread and persistent phytoplankton blooms along the west coast of Florida. Water-column chlorophyll concentrations estimated from serial Sea WiFS imagery were much higher during the El Niño event than in the previous or following years, although the timing and magnitude of phytoplankton blooms varied among sites. Seagrass samples collected in 1997, 1998, and 1999 provided an excellent opportunity to test the responsiveness of Thalassia to decline and subsequent improvement of water quality and clarity in four estuaries. Using a scoring technique based on temporal responsiveness, spatial consistency, and statistical strength of indicators, we found that several morphological parameters (Thalassia shoot density, blade width, blade number, and shoot-specific leaf area) were responsive and consistent measures of light stress. Some morphological parameters, such as rhizome apex density, responded to declines and subsequent improvement in water clarity, but lacked the statistical discriminating power necessary to be useful indicators. However, rhizome sugar, starch, and total carbohydrate concentrations also exhibited spatially and temporally consistent variation as well as statistical strength. Because changes in shoot density, as well as water clarity, affect rhizome carbohydrate levels, a composite metric based on Thalassia shoot density and rhizome carbohydrate levels together is probably more useful than either parameter alone as an indicator of seagrass health.

Carbon and nitrogen translocation between seagrass ramets

The spatial scale and the magnitude of carbon and nitrogen translocation was examined in 5 tropical (Cymodocea serrulata, Halophila stipulacea, Halodule uninervis, Thalassodendron cilia- tum, Thalassia hemprichii) and 3 temperate (Cymodocea nodosa, Posidonia oceanica, Zostera noltii) seagrass species using 13 Carbon ( 13 C) and 15 Nitrogen ( 15 N) as tracers in experiments conducted in situ. Seagrass leaf and rhizome production during the study period varied from <0.001 to 0.015 g DW shoot -1 d -1 and 0.002 to 0.017 g DW rhizome apex -1 d -1 , respectively. Based on measured leaf and rhi- zome growth rates, the demand of resources for leaf production varied from 0.19 to 4.99 mgC shoot -1 d -1 , and from 0.01 to 0.24 mgN shoot -1 d -1 , while the demand for rhizome production varied from 0.62 to 5.57 mgC rhizome apex -1 d -1 and from 0.02 to 0.12 mgN rhizome apex -1 d -1 . Seagrass leaves incor- porated the isotopes at rates ranging from 0.04 to 0.63 µg 13 C g DW -1 h -1 , and <0.01 to 0.35 µg 15 N g DW -1 h -1 . After 4 d, all incubated shoots had shared part of the incorporated 13 C and 15 N with ram- ets placed at maximum distances ranging from 2.7 (H. stipulacea) to 81 cm (C. nodosa), indicating that seagrass clonal integration may be maintained between 1.6 d (H. stipulacea) and 5.4 yr (P. ocean- ica). Resource translocation within seagrass clones was stimulated towards horizontal rhizome apices. Seagrass ramets, in 4 d, shared with their neighbours between 0.37 and 390 µg 13 C and between 0.02 and 178 µg 15 N. During the study period, resource translocation would supply <5% and up to 40% of the leaf carbon and nitrogen required by a neighbouring developing ramet, respec- tively, and <5% and up to 36% of the carbon and nitrogen required for rhizome growth; provided that the incorporated resources over 1 d were mobilised at similar rates over 4 d. These results con- clusively demonstrate physiological integration between seagrass ramets, and that resource translo- cation may be an important mechanism for young seagrass ramets to acquire resources and for sea- grass clones to expand and persist.

Vegetative dynamics and sexual reproduction of monospecific Thalassia hemprichii meadows in the Kalayaan Island Group

We surveyed eight offshore islands and shoals in the Philippine Kalayaan Island Group. The aims were to (1) map the distribution, (2) evaluate the demographic status, (3) elucidate the vegetative growth dynamics, and (4) quantify the sexual reproductive capacity of Thalassia hemprichii meadows in the region. We combined age reconstruction techniques and in situ estimations to attain such goals. We found T. hemprichii meadows only in Pag-asa Island. These meadows were generally young (mean age <1 year) and rapidly expanding (net recruitment ∼0.8 ln units per year). This was consistent with the horizontal rhizome apices being dense (162–334 apex m −2) and fast-spreading (36–56 cm per apex per year). The results for in situ measurements of plastochron interval (9.2 days), and relative leaf (3.7 cm 2 cm −2 per shoot per day) and areal growth rates (2.3–2.7 cm 2 per shoot per day) were similar to those of previous studies. The variation in the vertical internodal lengths showed a unimodal annual trend more distinctly in the south than in the north station, suggesting local, small-scale differences in environmental conditions between stations. Flower production was clearly seasonal, peaking around January 1999. Fruiting (128–134 m −2) and seedling recruitment (22–32 m −2) values were high, indicating a substantial contribution of sexual reproduction to the rapid expansion or meadow maintenance. The apparent disjunct occurrence of such young and highly reproductive meadows in the region merits further investigation.

Association of "Candidatus Phytoplasma australiense" with Sudden Decline of Cabbage Tree in New Zealand.

Sudden decline of the New Zealand cabbage tree (Cordyline australis) results in the rapid death of affected plants within months of first external symptoms becoming apparent. Symptoms, which have been observed in saplings and mature trees, include vascular discoloration and leaf yellowing followed by leaf desiccation and eventual plant collapse. Previous work failed to link the disease with any causal agent. A phytoplasma has now been detected in all symptomatic saplings and some symptomatic trees tested, using one-step and nested polymerase chain reaction (PCR) to amplify portions of the 16S rRNA gene. This phytoplasma was not detected in nonsymptomatic plants. Phytoplasma DNA was found in shoot and rhizome apices, leaves and wood tissue of saplings, and in the rhizome apex and trunk tissues of adult trees. Sequencing of the PCR products from selected samples indicated that the phytoplasma is "Candidatus Phytoplasma australiense." Phytoplasma cells were detected by transmission electron microscopy in phloem sieve tubes of the rhizomes of affected saplings. One sapling with early symptoms recovered after injection with tetracycline antibiotic, but two saplings with advanced symptoms did not recover. It is concluded that "Candidatus Phytoplasma australiense" is present in symptomatic plants and is the cause of sudden decline.

Studies on the growth and development of the rhizome and lateral rhizome buds in Elytrigia repens: some effects of parent shoot excision

In experiments conducted under controlled conditions, excision of the shoot of Elytrigia repens (L.) Nevski increased the rate of rhizome elongation and promoted the growth of the lateral rhizome buds. Measurements with a transducer showed that the long-term growth response of the rhizome to shoot excision (4-6 days) was preceded by an immediate but transient (10 min) increase in growth rate. These various responses were associated with the occurrence of guttation from the rhizome apex, increases in the water content of the rhizome apex and lateral buds, and a 62% increase in rhizome water (pressure) potential. Parent shoot excision also induced a transition from rhizome to shoot development at the rhizome apex and caused lateral buds to develop as shoots instead of rhizomes when released from apical dominance. These developmental responses were associated with reductions in the dry weight of the rhizome apex and lateral buds and increases in the total N, amino-N, and nitrate content of the rhizome apex when expressed on a dry weight basis. These results provide evidence that, in E. repens, competition for water by the parent shoot may limit rhizome growth and contribute to the correlative inhibition of the lateral buds. They are also consistent with previous evidence that the C:N ratio may be an important morphogenetic factor in the mechanism controlling the path of bud and rhizome development.Key words: Elytrigia repens, water, nitrogen, rhizome, apical dominance.

Vegetative propagation and sexual reproduction in the woodland understorey pseudo-annual Circaea lutetiana L.

On the forest floor of deciduous woodlands, relative light intensity gradually declines during the early growing season. The woodland understorey pseudo-annual Circaea lutetiana L. completes its life-cycle at the end of summer. These pseudo-annuals are clonal plants which survive the winter only as seeds and as hibernacles produced by the rhizome apices. In this paper, we asked several questions related to the life-history of C. lutetiana. It was found that shoot formation in early spring did not exhaust the old hibernacle. A trade-off between rhizome + hibernacle number and weight might be expected when plants grow under resource limitation. It was hypothesised that both number and weight of rhizomes and hibernacles will be affected by light availability. Since the effect of resource supply on the size number trade-off will depend on the developmental pattern of the rhizome system, rhizome development was studied as well. Soon after the shoots emerged, 1st order rhizomes were formed in May on the nodes of the old hibernacle. First-order rhizomes branched in June and 2nd order rhizomes (side-branches) were continuously produced throughout the growing season. The phenology and developmental rate of plants growing in different light treatments were plastic. On average 30% of rhizome biomass was formed during the vegetative phase, and rhizome and fruit production were only partly separated in time. The ratio of total rhizome biomass to total fruit biomass was not affected by light. Also flower bud removal did not lead to an increase in rhizome production, which suggests that division of biomass to both reproductive modes is rather rigid. The number of 1st order rhizomes was not affected by the light treatments. Under light limitation, both rhizome number and weight of single rhizomes were reduced. In contrast, fruit number, but not weight of single fruits, was limited.

Growth and population dynamics of Thalassodendron ciliatum in a Kenyan back-reef lagoon

The size, rhizome growth, and demography of a Thalassodendron ciliatum (Forssk.) den Hartog population in a back-reef lagoon (Chale lagoon, Kenya), was examined using techniques based on age determinations. The results obtained reveal that vertical growth of the T. ciliatum shoots is very fast, involving the production of, on average, 42 internodes (i.e. 42 leaves) per year. Annual length increments declined from young shoots (17 cm year −1) to older shoots (6 cm year −1). Vertical growth is not constant over the year with internodal length sequences suggesting the presence of two adverse periods for vertical growth in a year. As a result, the T. ciliatum population allocated a significant fraction of their biomass production (31%) to upright stems, which can grow for up to 5 years (the maximum life span of vertical shoots). The vertical growth of this species is the fastest reported to date for an undisturbed seagrass population, whereas the horizontal growth rates (16 cm year −1) rank amongst the slowest. The turnover time of the shoots was about 1 year (i.e. the median shoot life span), with shoot mortality and recruitment maintaining a close balance (0.71 ± 0.04 natural log units year −1 and 0.65 natural log units year −1, respectively), indicating that the population is in a steady state condition. Because horizontal rhizome growth was slow (producing six shoots per rhizome apex year −1), shoot recruitment through branching of vertical shoots (20% of the vertical shoots bearing branches) is an important component of clonal growth of this population. These results demonstrate that vertical growth is an essential component of the production of T. ciliatum, to which it allocates considerable resources. This allocation is used to raise the photosynthetic tissues well above the sediments, thereby preventing competition with other benthic phototrophs. It also guarantees sufficient shoot recruitment for maintenance of the population.

The effect of plant size on vegetative reproduction in a pseudo-annual

The relationship between plant size and vegetative reproduction in clonal plants appears complex because vegetative expansion, growth, and reproduction are not clearly separable in such plants. In ‘pseudo-annuals’, which are clonal plants surviving the winter only as seeds and hibernacles produced by the rhizome apices, vegetative growth and reproduction are clearly separate processes so that the relationship between vegetative reproduction and plant size can be studied. We used the pseudo-annual Helianthus x laetiflorus Pers. to study the relationship between plant size and total rhizome biomass, rhizome (hibernacle) biomass, and number of hibernacles. We manipulated resource acquisition of the plants by reducing leaf area (leaf-clipping) and by fertilization, thus affecting plant size. Furthermore, we studied the success of thin and thick hibernacles in terms of future growth and reproduction in a separate experiment. The results showed that vegetative reproduction was positively related to plant size. The ratio between the number of hibernacles and mean hibernacle weight was affected by plant size in such a way that in small plants both number of hibernacles and mean hibernacle weight were reduced to the same extent as compared to those in large plants. However, the size distributions of plants of the next generation growing from thin and thick hibernacles did not differ. It remains unclear therefore why this pseudo-annual species produces thick hibernacles at all.

Nutrient constraints on establishment from seed and on vegetative expansion of the Mediterranean seagrass Cymodocea nodosa

Nutritional constraints were examined on establishment from seed and vegetative development of patches of the seagrass Cymodocea nodosa Ucria (Aschers.) growing in phosphorus-deficient sandy sediments in the shallow Alfacs Bay of the Spanish Mediterranean coast. Seedlings were extremely P-deficient, this P-deficiency increasing with seedling age, which may be a major reason for the failure of most seedlings (90%) to initiate patches, and the arrest of their vegetative proliferation for up to 3 years. Shoots located at the colonising apices of horizontal rhizomes had, in contrast, three-fold higher P and two-fold higher N concentrations, which could facilitate the rapid horizontal expansion of existing patches. Apical shoots may receive nutrients from older shoots connected along the rhizome chains, as suggested by exponentially increasing gradients of N and P concentrations towards the rhizome apex. These results indicate that resource limitation probably plays a more important role in constraining the initiation of patches from seedlings in nutrient-poor areas than the expansion of existing patches.

Changes in abscisic acid and indole‐3‐acetic acid in axillary buds of Elytrigia repens released from apical dominance

Growth of axillary buds on the rhizomes of Elytrigia repens (L) Nevski is strongly dominated by the rhizome apex, by mechanisms which may involve endogenous hormones. We determined the distribution of indole‐3‐acetic acid (IAA) and abscisic acid (ABA) in rhizomes and measured (by gas‐chromatography‐mass spectrometry) their content in axillary buds after rhizomes were decapitated. The same measurements were also made in buds induced to sprout by removing their subtending scale leaves. The ABA content tended to be higher in the apical bud and in the axillary buds than in the adjacent internodes, and tended to decline basipetally in the internodes and scale leaves. IAA was similary distributed, except that there was less difference between the buds and other rhizome parts. After rhizomes were decapitated, the ABA content of the first axillary bud declined to 20% of that of control values within 24 h, while the IAA content showed no marked tendency to change. The ABA content also declined within 12 h in the first axillary bud after rhizomes were denuded, while the content of IAA tended to increase after 6 h. These changes occurred before the length of the first axillary bud increased 24–48 h after rhizomes were decapitated or denuded. We conclude that the release of axillary buds from apical dominance in E. repens does not require IAA content to be reduced, but is associated with reduced ABA content.

Plant regeneration of Iris pallida Lam. and Iris germanica L. via somatic embryogenesis from leaves, apices and young flowers

Irones are violet-scented ketonic compounds contained in the rhizome of certain species of iris. As cultivation of the iris tends to decrease, a selection program has been initiated to find the best performing clones in terms of growth and yield. Parallel to this selection, in vitro regeneration studies have been carried out in order to multiply interesting clones. A method of rapid multiplication by somatic embryogenesis associated with multibudding was developed. Callus was obtained from leaf bases, flower pieces or rhizome apices; the best explants were flower pieces. The induction media used to obtain embryogenic callus were Murashige & Skoog (1962) media. Assays with adding of proline in these media have showed that it could double the yield of embryogenic callus. The embryogenic expression medium was the Knudson's orchid agar (Knudson 1946) medium. Conformity of the plants obtained was checked by comparing their chemotypes with those of the mother plants.