Growth analysis ofQuercus serrata seedlings withinMiscanthus sinensis grass canopies differing in light availability

The effects of different light regimes on the survival, growth and morphology ofQuercus serrata seedlings were studied in canopies ofMiscanthus sinensis. The seedlings of various ages (0–3 yr) were grown in three light regimes: under a denseM. sinensis canopy (TG plot) receiving 2.5%–8.7% of full sunlight, under a relatively sparse canopy (SG plot) receiving 3.8%–16.1% of light and in an adjacent open site (NG plot). There was a little difference in the survival ofQ. serrata seedlings among the three plots. Height and diameter of stem and total leaf area of the seedlings were significantly lower in the shadier plots. However, the first (bottom) flush of the stem was significantly longer in the TG plot than in the NG and SG plots. Total dry weights of individual 1- and 2-yr-oldQ. serrata seedlings in the TG plot were reduced to about one-twelfth of those in the NG plot. Although the relative proportion in dry weight of each organ did not differ significantly among the plots, leaf area ratio, specific leaf area and stem height per unit dry weight were significantly higher in shadier plots. The leaf area per unit stem height was increased considerably in the sunnier plots.     

Unequal distribution of osmiophilic particles in the epidermal periplasmic space of upper and lower flanks of gravi-responding rye coleoptiles

In various studies, auxin (IAA)-induced coleoptile growth has been reported to be closely correlated with an increased occurrence of osmiophilic particles (OPs) at the inner surface of the outer, growth-limiting epidermal cell wall, indicating a possible function related to the mechanism of IAA-induced wall loosening. In order to test whether changes in cell elongation rates of upper and lower flanks (UFs, LFs, respectively) during graviresponsive growth are reflected in appropriate changes in the occurrence of OPs, rye (Secale cereale L.) coleoptiles either as segments or as part of intact seedlings, were gravitropically stimulated by positioning them horizontally for 2 h. Ultrastructural analyses within the UFs and LFs of the upward-bending coleoptiles revealed a distinct imbalance in the occurrence of OPs. The number of OPs per transverse epidermal cell section of the elongation-inhibited UF on average amounted to twice the number of OPs counted in epidermal cell sections of the faster-growing LF. As a hypothesis, the results lead us to suggest that OPs are involved in the mechanism of wall loosening and that temporary growth inhibition of epidermal cells of the UF during upward bending is mediated by inhibition of OP entry into the cell walls. Thereby, more OPs accumulate near the inner surface of the outer wall of epidermal cells of the UF compared with the LF.     

High-irradiance responses induced by far-red light in grass seedlings of the wild type or overexpressing phytochrome A

The occurrence of phytochrome-mediated highirradiance responses (HIR), previously characterised largely in dicotyledonous plants, was investigated in Triticum aestivum L., Zea mays L., Lolium multiflorum Lam. and in both wild-type Oryza sativa L. and in transgenic plants overexpressing oat phytochrome A under the control of a 35S promoter. Coleoptile growth was promoted (maize, ryegrass) or inhibited (wild-type rice) by continuous far-red light (FRc). However, at equal fluences, hourly pulses of far-red light (FRp) were equally effective, indicating that the growth responses to FRc were not true HIR. In contrast, in maize and rice, FRc increased anthocyanin content in the coleoptile in a fluence-rate dependent manner. This response was a true HIR as FRp had reduced effects. In maize, anthocyanin levels were significantly higher under FRc than under continuous red light. In rice, overexpression of phytochrome A increased the inhibition of coleoptile growth and the levels of anthocyanin under FRc but not under FRp or under continuous red light. The effect of FRc was fluence-rate dependent. In light-grown rice, overexpression of phytochrome A reduced leaf-sheath length, impaired the response to supplementary far-red light, but did not affect the response to canopy shade-light. In grasses, typical HIR, i.e. fluence-rate dependent responses showing reciprocity failure, can be induced by FRc. Under FRc, overexpressed phytochrome A operates through this action mode in transgenic rice.Abbreviations FR far-red light - FRc continuous far-red light - FRp pulses of far-red light - HIR high-irradiance responses - LFR low-fluence responses - OPHYA transgenic rice overexpressing oat phytochrome A - Pfr far-red light-absorbing form of phytochrome - phyA phytochrome A - R red light - Rc continuous red light - VLFR very low-fluence responses - WT wildtype We thank Marcelo J. Yanovsky for his help with the photographs and Professor Rodolfo A. Sanchez for providing a reprint of the paper by P.J.A.L. de Lint. This work was supported by grants from UBA (AG041) and Fundacion Antorchas (A-13218/1-15) to J.J.C.     

Effect of thidiazuron in germinating tamarind seedlings

Summary Tamarind, a multipurpose tropical tree species, is economically important for sustainable development of wasteland due to its hardy nature and adaptability to various agroclimatic ocnditions. Reports on in vitro morphogenesis in this species are limited, due to its recalcitrant and callogenic nature. To overcome these limitations, an attempt was made to induce meristematic activity in seedling explants. Seedlings were germinated in medium with or without thidiazuron (4.54, 9.08, 13.12, 18.16 μM). This growth regulator restricted the differentiation of the apical meristem to form shoots. It triggered proliferation of the meristematic tissue at the cotyledonary node and a large number of meristematic buds appeared in a ridial pattern around the node. The meristematic activity extended to the junction of the epicotyl and hypocotyl, giving rise to buds in the form of protuberances in all sides of the junction. These buds differentiated to form shoot primordia and subsequently to shoots in medium devoid of growth regulators. Plants developed by micrografting of these shoots on seedling-derived rootstocks survived in soil.     

Integral association of phytochrome with a membranous fraction fromAvena shoots: in vivo characterization and physiological significance

Phytochrome in the far-red light absorbing form (Pfr) was observed to disappear in vivo more rapidly from the non-cation-requiring pelletable phytochrome population than from the supernantant phytochrome population of oat seedlings given an increasing dark incubation after red irradiation. The amount of pelletable phytochrome in the red light absorbing form (Pr) remained relatively stable while supernatant Pr was lost. These observations indicated that supernant Pfr was subject to loss during the incubation, while pelletable Pfr was subject to both dark reversion and loss.During the incubation, the ability of far-red irradiation to reverse the red-induced increase in phytochrome pelletability was lost, with kinetics similar to those of the loss of pelletable Pfr.Far-red reversibility of the red-induced increase in coleoptile elongation correlated with the change intotal Pfr in both supernatant and pelletable phytochrome populations, but with the change in the ratio of Pfr to total phytochrome only in the pelletable phytochrome population.The possible significance of these results is discussed with reference to the action of phytochrome in the photocontrol of physiological growth responses.Abbreviations Pfr phytochrome in the far-red light absorbing form - Pr phytochrome in the red absorbing form - Ptot total phytochrome     

Water potential of standing-dead shoots of an intertidal grass

Summary Dead stems and leaves of smooth cordgrass (Spartina alterniflora Loisel.) undergo substantial fungal decay in the standing position. We conducted a series of experiments to determine the probable range of water availabilities that cordgrass-fungal decomposers experience; we determined the effects of duration of wetting and drying, site on shoots, leaching of osmotica, and stage of decomposition on water potential () of cordgrass shoots. Dried pieces of cordgrass shoots took up water rapidly when submerged, rising from values which were probably less than –150 megapascals (MPa) water potential to about –3.5 (soaked in seawater) or –1.5 (soaked in tapwater) within 5 min. Air-drying resulted in a return to low (<–7.5 MPa) within an hour. Literature reports show that most litter and wood-decomposing fungi which have been tested cannot grow at more negative than –6 MPa. The more lignified stems showed a more negative matric than leaves at water contents greater than 25% fresh weight. As leaves decomposed in the marsh, their increased (from –1.7 to –0.5 MPa, under standard conditions of 30 min freshwater soaking and 30 min air-drying), similar to what other investigators have found for wheat and forest litter. The water content at which cordgrass leaves reached –6 MPa was about 23% fresh weight, within the range (15–32%) found for wheat straw and forest litter.     

Phytochrome-controlled extension growth of Avena sativa L. seedlings

The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat (Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of P_fr, the far-red light absorbing form of phytochrome (e.g., by [P_fr]0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by P_fr, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to P_fr. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by P_fr destruction. Following an irradiation, the growth responses are quantitatively determined by the level of P_fr established at the onset of darkness rather than by the actual P_fr level present during the growth period.Abbreviation P_fr far-red light absorbing form of phytochrome     

ABA-responsive RNA-binding proteins are involved in chloroplast and stromule function in Arabidopsis seedlings

The phytohormone abscisic acid (ABA) regulates essential growth and developmental processes in plants. Recently, RNA-binding proteins have been described as components of ABA signaling during germination. We have identified ten ABA-regulated RNA-binding proteins in Arabidopsis seedlings. Among those genes, AtCSP41B and cpRNP29 are highly expressed in seedlings. Using promoter:reporter gene analyses, we showed that both AtCSP41B and cpRNP29 were in particular expressed in photosynthetically active organs like green cotyledons, leaves, and petioles. The analysis of CFP-fusion proteins demonstrates that cpRNP29 localized to chloroplasts and AtCSP41B to chloroplasts and stromules. Whereas RNA-binding of cpRNP29 has previously been shown, we demonstrated through in vitro RNA-binding assays that recombinant AtCSP41B binds to RNA, and that chloroplast petD RNA can serve as a target of AtCSP41B. Developmental or environmental stimuli affected the expression of AtCSP41B and cpRNP29 in seedlings. Both genes were repressed during senescence, but only AtCSP41B was significantly repressed upon water stress. In addition, AtCSP41B and cpRNP29 exhibited low expression in etiolated seedlings compared to green seedlings, and cpRNP29 was regulated during the day photoperiod. Homozygous T-DNA insertion lines were isolated, characterized on the molecular level, and monitored for phenotypic changes. Taken together, the data show that both proteins are regulated during processes that are known to involve ABA signaling. Their localization in chloroplasts and RNA-binding activity suggest a role in chloroplast RNA metabolism in Arabidopsis seedlings.     

Chitinase activity in germinating cells ofMucor rouxii

Chitinase activity in germinating cells (4 h cultures) ofMucor rouxii was studied. The enzyme activity was recovered in a high speed supernatant of cell homogenates. No activity was detected in the mixed membrane fraction or in the cell walls. Maximum activity was observed at pH 7.6 and at 30–35°C using the chromogenic assay with chitin azure. The latter was digested by GS-chitinase in a manner dependent on substrate concentration and time of incubation. As with other chitinases, GS-chitinase was much more effective against nascent than against preformed chitin. The main product of nascent chitin digestion was diacetylchitobiose, although significant amounts of the trimer were also detected in the hydrolyzates. Allosamidin, an insect and fungal chitinase inhibitor, strongly inhibited hydrolysis of nascent chitin but not of chitin azure by GS-chitinase. The drug failed to inhibit the germination and the ensuing growth of the fungus. Results are discussed in terms of the possible role of GS-chitinase in germination.Abbreviations UDP-GlcNAc uridine 5-diphospho-N-acetylglucosamine - GlcNAc N-acetylglucosamine - GlcNAcP N-acetylglucosamine phosphate - PMB phosphate-magnesium buffer - C₂ N, N-diacetylchitobiose - C₃ N, N, N-triacetylchitotriose - RVB remazol brilliant blue - DPC descending paper chromatography - MU(Ch)₃ 4-methylumbelliferyl-N - N N-triacetylchitotriose     

Micropropagation of Cypripedium flavum through multiple shoots of seedlings derived from mature seeds

Cypripedium flavum, known as the rare lady’s slipper orchid, is one of the endemics with a yellow flower in China. Due to its conservation and commercial requirement, establishment of an efficient method for micropropogation is urgently needed. Multiple shoots were obtained by placing seedlings from seeds of C. flavum on Harvais media supplemented with two cytokinins (BAP or KIN) used alone or in addition to different concentration of potato homogenate. The effect of BAP was better than that of KIN on shoot multiplication. The Havais media supplemented with BAP (2.22 μM) and potato homogenate (20 g l⁻¹) was the most effective, providing high shoot multiplication frequencies (95%) associated with a high number of shoots per explant (2.55 shoots/plant). For root formation, high rooting and survival were achieved using 1/2 Harvais media supplemented with 0.6 g l⁻¹activated charcoals. High-level activated charcoal increased the number and the length of roots because the activated charcoal could absorb BAP in the media. This study demonstrated that C. flavum could be micropropagated by using multiple shoots of seedlings derived from mature seeds.     

Lectin synthesis in developing and germinating wheat and rye embryos

Wheat (Triticum aestivum L.) and rye (Secale cereale L.) lectins are specifically synthesized during seed formation. They accumulate exponentially in the primary axes in a period coinciding with the development of this complex organ. Since the specific lectin content also increases dramatically, there is apparently an outburst of lectin synthesis during the development of the primary axes. Germinating embryos also synthesize some lectin. The fortunate availability of a highly specific procedure for the isolation of cereal lectins enabled us to follow the kinetics of their synthesis during early germination. Stored mRNAs appear to be involved in this residual lectin synthesis.     

Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub

Shrub encroachment is a widely observed problem in Southern African savannas. Although the effects of herbivory and grass height on woody species recruitment have been studied individually, little information exists about how these factors interact. In this study seeds and seedlings of the encroaching shrub Dichrostachys cinerea were planted in clipped and unclipped grass plots, with and without large herbivores present. Seed germination, seedling survival and seedling predation were monitored for 8 months. Germination started earlier in plots where herbivores were excluded. Overall, the earlier the seeds germinated, the longer the seedlings survived. Clipping positively affected the number of germinated seeds, seedling growth and survival but effects varied among herbivore exclusion treatments and sites. Invertebrates caused the majority of the seedling damage. We conclude the recruitment of D. cinerea is influenced by the interplay of grass height and herbivory. In this study, the presence of large herbivores early in the wet season, and the absence of simulated grazing later on, affected the regeneration of D. cinerea negatively. However, differences in effects among sites suggest that the mechanisms found here may work differently in other habitats.      

Phytochrome-mediated phototropism in maize seedling shoots

Unilateral irradiation with red light (R) or blue light (BL) elicits positive curvature of the mesocotyl of maize (Zea mays L.) seedlings raised under R for 2 d from sowing and kept in the dark for 1 d prior to curvature induction. The fluenceresponse curve for R-induced mesocotyl curvature, obtained by measuring curvature 100 min after phototropic induction, shows peaks in two fluence ranges, designated first positive range (from the threshold to the trough), and second positive range (above the trough). The fluence-response curve for BL is similar to that for R but shifted two orders of magnitude to higher fluences. Blue light elicits the classical first positive curvature of the coleoptile, whereas this response is not found with R. Positive mesocotyl curvature induced by either R or BL is eliminated by R given from above just before the unilateral irradiation, whereas BL-induced coleoptile curvature is not eliminated. The above results collectively offer evidence that phototropic curvature of the mesocotyl is induced by R-sensitive photosystem(s). Mesocotyl curvature in the second positive range is reduced by vertical far-red light (FR) applied after phototropic induction with R, but is not affected by FR applied before R. Unilateral irradiation with FR following vertical irradiation with a high R fluence leads to negative curvature of the mesocotyl. It is concluded that mesocotyl curvature in the second positive range results from a gradient in the amount of the FR-absorbing form of phytochrome (Pfr) established across the plant axis. Mesocotyl curvature in the first positive range is inhibited by vertical FR given either before or after phototropic induction with R. Since the FR used here is likely to produce more Pfr than the very low fluences of R eliciting the mesocotyl curvature in the first positive range, it is assumed that FR reduces the response in this case by adding Pfr at both sides of the plant axis. By rotating seedlings on a clinostat with its axis horizontal, the kinetics of mesocotyl curvature can be studied in the absence of a counteracting gravitropic response. On the clinostat, the R-induced mesocotyl curvature develops after a lag, through two successive phases having different curvature rates, the late phase is slower than the early phase. Negative curvature of the coleoptile can be induced by either R or BL; the BL-induced negative curvature is found at fluences higher than those giving positive curvature. The clinostat experiments show that the negative coleoptile curvature induced by either R or BL is a gravitropic compensation for positive mesocotyl curvature.Abbreviations BL blue light - FR far-red light - Pfr phytochrome in the far-red-absorbing form - Pr phytochrome in the red-absorbing form - R red light C.I.W.-D.P.B. Publication No. 824     

Flooding induction of alcohol dehydrogenase in shoots and roots of barley seedlings

Barley (Hordeum vulgare) seedlings were exposed to flooding and activities of alcohol dehydrogenase (ADH) and their isoform profiles were determined. The flooding increased ADH activities in shoots and roots of the seedlings. By day 3, the activity increased to 4 and 3 times that of the initial level for the shoots and the roots, respectively. Only two bands of ADH isoform were found in the shoots and the roots of non-induced seedling, whereas five bands were identified in those of induced seedlings.     

Invasion of naturally senescing root cortices of cereal and grass seedlings byMicrodochium bolleyi

Summary In glasshouse experiments, invasion of wheat and grass (Dactylis glomerata) seedling roots byMicrodochium bolleyi was strongly correlated with the pattern and rate of natural senescence of the root cortex. The fungus did not enhance cortical senescence and did not damage roots except in a few instances when it invaded and killed their tips.M. bolleyi behaved as a weak parasite, largely restricted to invasion of naturally senescing cortices of cereal and grass roots.     

Temperature and seedling age affect susceptibility of perennial ryegrass seedlings to pathogenic fungi

Summary Effects of temperature and seedling age on survival of perennial ryegrass (Lolium perenne L.) seedlings grown on sand-wheat wholemeal cultures of different isolates ofFusarium spp. (9 isolates),Pythium spp. (9 isolates), andChaetomium spp. (1 isolate) are reported. Some isolates were virulent over the whole range of temperatures tested (7.5–27.5°C). The virulence of others depended on temperature. Most isolates were less virulent at intermediate temperatures (12.5–22.5°C) than at higher or lower temperatures. At 25°C ryegrass seedlings were susceptible to fungal attack for only a limited period after germination commenced. This period differed for different fungi, but for most isolates tested, seedlings were resistant after 2–3 days.     

Proteolysis in the axis of the germinating pea seed

Autoproteolytic, caseolytic and haemoglobin degrading activities, carboxypeptidase and aminopeptidase activities have all been measured in extracts prepared from the radicle of germinating pea seeds (Pisum sativum L.). With increasing time from the beginning of imbibition, the spectrum of protein degrading enzyme activities changed in a complex manner. As a proportion of total autoproteolytic activity, acid proteinases declined, while sulphydryl-and serine-active site endopeptidases accounted for increased proportions of the total activity. The distribution of protein degrading enzyme activities in the root tip compared with the balance of the root was determined after 4 days, at the onset of cell division in the root apex. On a fresh weight basis the tip was enriched ca. 2-fold in protein concentration and all of the exopeptidases. Autoproteolytic activity was concentrated in the tip to a lesser degree, and haemoglobin degrading activity not at all. In contrast, the root tip was depleted in caseolytic activity.Abbreviations AP aminopeptidase - BSA bovine serum albumin - CP carboxypeptidase - DAN diazoacetyl-D, L-norleucine - ME 2-mercaptoethanol - NEM N-ethyl maleimide - PMSF phenyl methyl sulphonyl fluoride - TCA trichloroacetic acid     

Cycling of amino-nitrogen between shoots and roots in wheat seedlings

Summary One part of a split root system of wheat seedlings received full nutrient solution with¹⁵N-nitrate, the other received an identical solution with unlabelled nitrate. Appearance of labelled amino compounds was measured in the xylem sap exuding from roots not supplied directly with¹⁵N-nitrate after removal of the¹⁵N-nitrate-fed roots. This material indicates cycling of nitrogen from the shoots and through the roots. About 60 per cent of the nitrogen in the xylem appears to be cycling in this way.     

Botanical aspects of cell-free protein synthesizing systems from cereal embryos

Some botanical aspects of cell-free protein synthesizing systems from cereal embryos have been investigated. The composition of the starting material determines both the stability and translation fidelity of the cell-free extracts. The active components of the extracts originate exclusively from the primary axes. Contamination with scutellum fragments does not affect the initial activity but results in a reduced stability. The presence of endosperm particles in the starting material leads to a strong decrease of the overall activity of the extracts and a loss of the capacity to synthesize large polypeptides.Abbreviations mRNA messenger RNA - AMV-RNA alfalfa mosaic virus RNA - TMV-RNA tobacco mosaic virus RNA - SDS sodium dodecyl sulphate - poly A⁺-RNA polyadenylic acid containing RNA - EDTA ethylenediaminetetraacetic acid - S.A. specific activity     

Effects of leaf litter on woody seedlings in xeric successional communities

We investigated the effect of leaf litter on the establishment of Eucalyptus incrassata, a mallee eucalypt. It has been suggested that litter accumulation may hinder seedling establishment, and that the removal of litter may be one of the mechanisms through which fire enhances recruitment. We conducted factorial experiments testing the effects of three kinds of leaf litter on E. incrassata seeds and seedlings at three contiguous sites with different land use histories. One site was an uncleared E. incrassata open mallee woodland (Mallee site), one a cleared area that had been ungrazed for about five years (Pasture site) and the third an area of mallee rolled some 40 years ago and permitted to regenerate (Regrowth site). Litter had no effect on emergence of planted E. incrassata seeds, but emergence differed between sites. Overall, the percentage of seeds that germinated and emerged was substantial (mean 35.2% ± 25.9%). Seedling shoot biomass did not differ between sites or litter treatments. Although seedlings grown in Pasture litter suffered higher mortality rates, overall mortality rates were low (mean 13.2% ± 15.5%), suggesting that leaf litter has little effect on recruitment rates during winter and spring. We conclude that leaf litter does not affect emergence or growth in young E. incrassata seedlings during winter and spring, when most establishment occurs. Our results emphasize the difficulty in predicting litter effects on recruitment.