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Chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale L.) are persistent weeds, the aerial portions of which do not survive in winter. However, subterranean tissues remain viable and facilitate the rapid resumption of growth in early spring. The source of nutrients for growth prior to the establishment of foliage is the roots. Carbohydrate and N reserves are accrued during late summer and autumn, respectively. Hydrolysis of fructans during late autumn occurs coincidentally with increments in sucrose, the latter providing a readily accessible C pool. Nitrate, free amino acids and soluble protein all play substantial roles in nitrogen storage. Asparagine is the predominant amino acid in the free pool during winter, followed by glutamine, ornithine, serine, aspartic acid and glutamic acid. Storage reserves remain at peak levels throughout winter and deeline prior to the resumption of growth. The patterns observed here provide evidence that N is an important currency of storage metabolism and, thus, a framework has been provided for the examination of regulation of N storage in perennial weeds.

Exposure of dormant sugar maple seedlings to over 2000 h of winter temperatures of 5 °C and below was required for rapid and normal growth when seedlings were transferred to a warm greenhouse and extended photoperiods. Although chilling requirements were not fully satisfied until mid-March, a resurgence of metabolic activity occurred in early February. There was a marked shift in the potential for budbreak from the axillary to the terminal buds, and a surge in root growth occurred after a period of inactivity when the ground was frozen from late December to mid-January. The water content of the buds followed a pattern similar to that of the roots. It fell to a plateau in late fall well before the soil froze but began a steady increase with the resumption of active root growth in February. Inhibitory substances present in the buds did not exhibit significant changes during the overwintering period. However, cytokinin activity was observed beginning in February at the same time that root growth and bud succulence showed upward inflections. By the beginning of April there were two distinct peaks of activity which persisted through budbreak in early May.Seedlings that were brought into the greenhouse in the fall and never exposed to chilling temperatures did not break dormancy or show significant cytokinin activity or exhibit the physiological changes that occur under normal winter conditions.

During mid-development (25-40 d after pollination: DAP) of the castor bean seed the amount of abscisic acid (ABA) increases in both the endosperm and the embryo, declining substantially thereafter until there is little present in the mature dry (60 DAP) seed. Premature desiccation of the seed at 35 DAP also leads to a major decline in ABA within the embryo and endosperm. Partial water loss from the seed at 35 DAP which, like natural and premature desiccation, leads to subsequent germination upon return of the seed to full hydration, causes a much smaller decline in ABA levels. In contrast, ABA declines substantially in the non-dried (hydrated) control at 35 DAP, but the seeds do not germinate. Hence, a clear negative correlation between ABA content and germinability is not observed. Both drying, whether natural or imposed prematurely, and partial drying decrease the sensitivity of the isolated embryo to exogenous ABA by about 10-fold. The protein synthetic response of the castor bean embryo exposed to 01 mol m"3 ABA following premature desiccation exhibits some similarity to the response of the non-dried developing embryo—in both cases the synthesis of some developmental proteins is enhanced by ABA, and germination is suppressed. Germination of mature seeds is also suppressed by 01 mol m~3 ABA, but the same developmental proteins are not synthesized. In the cotyledons of prematurely-desiccated seed, some proteins are hydrolysed upon imbibition in 01 mol m 3 ABA, a phenomenon that occurs also in the cotyledons of similarly treated mature embryos, but not in developing non-dried embryos. Hence the embryo exhibits an 'intermediate' response upon rehydration in 01 mol m~3 ABA following premature desiccation; viz. some of the responses are developmental and some germinative. Following natural or imposed drying, the isolated embryo becomes relatively insensitive to 0 01 mol rrT 3 ABA: germination is elicited and post-germinative reserve breakdown occurs in the radicle and cotyledons. The reduced sensitivity of the embryo to ABA as a consequence of desiccation may be an important factor in eliciting the switch to germination and growth within the whole seed.

Application of 10−4 M benzyladenine to Phaseolus vulgaris germinated under etiolating conditions markedly delayed the onset of cotyledon senescence. Weight loss was curtailed, hydrolysis of starch and protein reserves was delayed, and the rate at which hydrolysis products were translocated out of the cotyledons was reduced in treated plants. Microsomal membranes of cotyledons from control seedlings acquired increasing proportions of gel phase lipid as senescence of the tissue intensified. The resulting mixture of liquid-crystalline and gel phase lipid within the membrane matrix renders the membranes leaky and may partially contribute to metabolite translocation out of the cotyledon storage cells during seedling development. This prospect is supported by the observation that in benzyladenine-treated plants the onset of gel phase lipid, and hence of membrane leakiness, was delayed in a manner that corresponded temporally with the decreased rate of metabolite translocation out of the cotyledons.

A comparison of the dye-binding method of Bradford (1976) with the Folin phenol method of Lowry et al. (1951) for the assay of protein in chlorophyllous tissue is described. Additions of chlorophyll to protein standards precluded reliable determinations with either method. Absorbance readings were increased by nearly 20% with the Bradford assay and by over 400% using the Lowry procedure. Trichloroacetic acid precipitation of the proteins effectively eliminated any significant interference by chlorophyll; however, the practice of washing the protein precipitate with 80% acetone to remove residual chlorophyll resulted in large protein losses. Eluting leaf tissue with acetone prior to extraction of protein increased protein yield significantly. Both assay procedures provide satisfactory measurement of leaf proteins once chlorophyll is removed. The dye-binding method is fast, simple, and more sensitive, but the Lowry procedure gives better linearity at high protein concentrations and better stability once color has developed.

Deleterious effects of salt stress on vegetative growth of tomato were most pronounced when plants were exposed to saline conditions during the early seedling stage. Growth rates remained severely restricted following removal of stress during this period, but plants stressed at later times resumed growth at rates similar to control values soon after they were returned to base nutrient solutions. While bud and flower formation were delayed by salt stress, the effect followed the previous trend and was most pronounced when plants were stressed during early vegetative growth. There were no indications that tomato declined in salt tolerance at the time of budding or flowering. The increase in water content of control plants during the early days of growth suggests that a rise in succulence is to be expected under nonstress conditions. However, imposition of stress during this period caused a marked decrease of water in the tissues, and contrary to the normal state, succulence declined during the sensitive see...

SUMMARY Balanced and unbalanced high-salt solutions were used to investigate the effects of osmotic stress on microbial activity in the rhizoplane and rhizosphere of barley. Bacteria in the root regions proved sensitive to both high ( - 1500 kPa) and low ( - 500 kPa) levels of each type of stress, but bacterial growth was most severely inhibited in the unbalanced treatments both of which contained high levels of sodium. Similar effects of stress were noted with barley. Distinct qualitative changes in microbial populations in the root zones were observed in the balanced stress treatments, but an increase in species diversity did not occur in the rhizoplane or rhizosphere following exposure to the unbalanced, high-sodium solutions. After five weeks of stress, a marked but transitory rise in rhizoplane counts accompanied death of the seedlings in the - 1500 kPa, high-sodium treatment indicating that at least some of the soil bacteria retain the potential for rapid growth at high salt concentrations.

SUMMARY Differential scanning calorimetry and electron spin resonance have been used to characterize the association of gibberellic acid4 and gibberellic acid, (a GA4/GA7 mixture) with phospholipid membranes. The GA4/GA7 mixture lowered the temperature and reduced the co-operativity of the main phase transition of liposomes prepared from dipalmitoylphosphatidylcholine (DPPC), distearylphosphatidylcholine (DSPC) and dipalmitoylphosphatidylglycerol (DPPG), and eliminated the pretransition. The reduction in co-operativity of the main transition was not accompanied by a reduction in transition enthalpy, indicating that the gibberellins simply perturb the bilayer rather than complex with the phospholipid molecules. Perturbation was markedly greater at pH values approaching the pKa of the gibberellin carboxyl group than at pH 7. Moreover, the negatively charged DPPG was less susceptible to perturbation than the zwitterionic phosphatidylcholines. Perturbation by GA8, a physiologically inert gibberellin, was virtually imperceptible. Electron spin resonance of GA4/GA7-treated liposomes of phosphatidylcholine (PC) and phosphatidylglycerol (PG) confirmed the results obtained by differential scanning calorimetry and also indicated that the gibberellins associate with the surface of the phospholipid membranes rather than penetrate into the interior of the bilayer. The data are consistent with the proposal that gibberellins can influence membrane behaviour by modulating the physical properties of the lipid bilayer.

Exposure of leaves to SO2 or bisulfite is known to induce peroxidation of thylakoid lipids and to inhibit photosynthetic electron transport. In the present study, we have examined the temporal relationship between bisulfite-induced thylakoid lipid peroxidation and inhibition of electron transport in an attempt to clarify the primary mechanism of SO2 phytotoxicity. Primary leaves of bean (Phaseolus vulgaris L. cv Kinghorn) were floated on a solution of NaHSO3, and the effects of this treatment on photosynthetic electron transport were determined in vivo by measurements of chlorophyll a fluorescence induction and in vitro by biochemical measurements of the light reactions using isolated thylakoids. Lipid peroxidation in treated leaves was followed by monitoring ethane emission from leaf segments and by measuring changes in fatty acid composition and lipid fluidity in isolated thylakoids. A 1 hour treatment with bisulfite inhibited photosystem II (PSII) activity by 70% without modifying Photosystem I, and this inhibitory effect was not light-dependent. By contrast, lipid peroxidation was not detectable until after the inhibition of PSII and was strongly light dependent. This temporal separation of events together with the differential effect of light suggests that bisulfite-induced inhibition of PSII is not a secondary effect of lipid peroxidation and that bisulfite acts directly on one or more components of PSII.

Changes in the anatomy, morphology, and stored food reserves of stratifying (5 °C) sugar maple embryos were followed from a strongly dormant state through germination. The correlation of cell division and cell elongation with radicle protrusion was also investigated. No morphological or anatomical changes were observed before first maturation of phloem elements on the 17th day of stratification. Mature xylem elements were first observed on day 37, and first germination was noted on day 38. Radicle protrusion was initiated by cell elongation, and cell division was not active for several days after emergence and a marked increase in lengths of the axes had occurred. Changes in amounts of protein, lipid, and starch were not observed during the stratification period, but mobilization of stored reserves was clearly evident with emergence of the radicles. Several of these key events appeared to be closely associated with previously described peaks and patterns of growth regulator activity.

Following imbibition and germination, levels of free abscisic acid (ABA) and water potentials in senescing bean cotyledons (Phaseolus vulgaris L. `Kinghorn') showed peaks on days 4 and 6 after planting and then declined as senescence intensified. Water potential displayed a final peak just prior to abscission which was not matched by a corresponding rise in abscisic acid, but this presumably reflected a generalized loss of synthetic capacity at that advanced stage of senescence. The changing water status of the tissue may be attributable to an imbalance between mobilization and transport of metabolites, with temporary water stress an apparent consequence of that asynchrony. These observations suggest that changes in the level of ABA were not directly related to advancing senescence but may have been a response to marked changes in water potential of the tissue.

Influence des conditions de stress induites par le sodium sur l'activite microbienne et la composition organique des exsudats racinaires de l'orge (Hordeum vulgare CV Clayton)

Investigations of the physiology of sugar maple seedlings have partially defined the phenological patterns associated with (1) root growth, (2) dormancy and budbreak, (3) changes in carbohydrate reserves and (4) the activity of endogenous hormones. Results are interpreted and discussed in relation to the problem of establishment of sugar maple seedlings on openfield sites in southern Ontario. The need to produce seedlings with the physiological characteristics, and in the developmental stage, most favorable to growth of a vigorous root system at time of planting is stressed. Future research is suggested.

Phenolics in sugar maple seeds were identified by colour reactions, u.v. spectroscopy and gas-liquid chromatography. Changes in their inhibitory activity during stratification were also followed using several bioassays. p-Coumaric, o-coumaric, and ferulic acids were found in all tissues. The highest concentrations were noted in the embryonic axis and testa, but total amounts per fruit were highest in cotyledons and pericarp. p-Coumaric acid was the principal phenolic in dry seeds, and it declined substantially in all tissues during the first half of stratification with little subsequent change thereafter. Decreases in o-coumaric and ferulic acids per seed were small by comparison, nevertheless losses ranged between 36 and 68% of the original concentrations. Bioassays confirmed that the three endogenous phenolics possessed marked inhibitory properties that diminished with the progress of stratification, but only the compound identified as p-coumaric acid showed major

Cytokinin and inhibitor activity were followed in the roots and stems of 2-year-old maple seedlings exposed to normal overwintering conditions from early November through April. The production of new roots was also monitored, and all measurements were repeated with dormant control seedlings placed in a greenhouse from the beginning of the experiment and provided with warm temperatures and extended photoperiods. The level of cytokinin-like substances increased in the roots and stems of the outside group in March after a large surge in root activity that began in late February and continued through April. Cytokinins peaked just before budbreak, with the highest levels detected in the lateral roots. Three bands of activity were present on the chromatograms at Rfs 0.1, 0.6, and 0.9. Large cytokinin peaks were also observed in the non-chilled seedlings and were associated with two periods of active root growth and abnormal bud flush in the fall and spring. Abscisic-acid-like activity was detected in the roots and stems of both greenhouse and exposed seedlings, but it remained essentially constant in the stems. Changes that occurred in the roots were not associated with emergence of the buds from the dormant condition.

The effects of salt stress on levels of soluble carbohydrate, amino acids and proteins in the shoots, roots and exudates of barley were studied under sterile conditions using balanced and unbalanced, high-salt solutions at −500, −1000 and −1500 kPa of osmotic stress. Moderate and severe stress with the unbalanced, high-sodium solutions proved toxic to barley, but plants exposed to the low-sodium, balanced solutions remained green and the stems remained turgid after 7 days of treatment. Both types of salinity increased the content of soluble carbohydrate in the shoots at all levels of stress and in the roots at −500 and −1000 kPa of stress. Carbohydrate in the exudates increased over 20-fold in response to balanced stress, but an apparent 3-fold increase in the exudates from the unbalanced treatments was not significant. Sucrose, glucose and fructose remained the principal sugars in the roots and shoots regardless of the type or intensity of stress, but their relative contents varied with treatment. Galactose, maltose, ribose and rhamnose were the major sugars in all exudates. Protein contents in the tissues fell at each level of balanced and unbalanced stress, but significant changes in protein were not detected in the exudates. Stress increased the size of the free amino acid pool in the shoots; however, it stimulated the reverse trend in the roots. With the exception of the −500 kPa low-sodium treatment, stress also induced a marked decline in the free amino acid content of the exudates, thus initiating a major limitation on the supply of a key group of metabolites in the rhizosphere.

Studies of salt tolerance of plants grown in balanced nutrient solutions revealed that growth rate was more a function of the duration of the applied stress than the rapidity with which a particular osmotic concentration was reached in the root medium.The low osmotic potentials initially attained by plants subjected to osmotic stress resulted from both a decrease in water content and an increase in ion concentration in the plant tissues. However, the importance of dehydration in the adjustment process decreased within a relatively short time, and ion uptake was noted to be the predominant factor in the adjustment of the plant sap throughout the vegetative period. With the exception of restrictions on growth, symptoms of ion toxicity were not observed with these balanced solutions, although exposure to stress in one of the treatment series lasted for 84 days.Substantial increases in osmotic potential on the removal of stress were apparently the result of passive diffusion of ions back to the substrate, rather than an increase in the water content of the tissues as previously reported. The cations K+ and Ca2+ provided the major contribution to changes in the osmotic potential of the foliar sap, but significant changes were noted in all of the ions measured.

Respiration and water uptake were previously shown to follow a three-phase pattern during the stratification period of Acer ginnala. The present study indicates that metabolism of several nitrogenous components also follows a multiphasic pattern during this period. However, total soluble nitrogen showed a rapid decline from day 9 to day 18 when respiration and water uptake were in what was essentially a plateau phase. This trend suggests that synthetic activities may be competing for substrates common to the respiratory pathway.The neutral fraction accounted for the major portion of the amino nitrogen pool and generally followed the pattern of total soluble nitrogen. The changes in the acidic and basic fractions were also phasic, but the patterns differed somewhat from that of the much larger neutral component. These results indicate that stratification is a highly active process composed of several well-defined phases.

Experiments with seeds of Acer ginnala support the view that stratification is a phasic process strongly influenced by both physical and metabolic events. Rates of imbibition indicate that the pericarp provides a significant restriction to water uptake by the embryo. Whole seeds required 30 days of stratification at 5 °C before first germination, but removal of the pericarp reduced the time to half that value. Tests showed that oxygen was not a limiting factor, and a water-soluble extract from pericarps did not increase stratification time of seeds with their pericarps removed and testas pricked. There was an apparent correlation between water uptake and respiration throughout the 30-day period, and both factors followed a similar three-phase pattern. These results are similar to those previously reported for Acer saccharum.

The endodermis, with its associated Casparian strip, is generally believed to act as an effective barrier to the passive movement of ions from the cortex to the xylem in young roots. However, several workers have suggested that the functional integrity of the endodermis might be somewhat impaired with the emergence of branch roots from the pericycle, thus providing pathways for the mass flow of water and ions into the stele. The present work was undertaken to examine the validity of this hypothesis.Sections of lateral roots embedded in glycol methacrylate were stained and examined by fluorescence microscopy, and a general picture of the relationship between branch root development and concomitant changes in the endodermis emerged. The endodermal cells of the parent root were found to maintain a continuous, unbroken, suberized layer over the surface of a very young lateral root, but with continued elongation there is a period when formation of the Casparian strip lags behind division of endodermal cells. It appears likely that, at this stage, water and ions can enter the stele of the parent root by mass flow.

Several factors affecting the stratification process in seeds of A. saccharum were investigated. Rates of imbibition and quantitative measurements of flow rate made with an osmometer indicate that the testa offers a severe restriction to water flow and that a significant portion of the stratification period is required for adequate water uptake. Respiration rates showed a close correlation with water uptake by the embryos throughout the stratification period. Whole seed needed 40–60 days to break dormancy; however, removal of the pericarps and tearing of the testas reduced the time needed by as much as two-thirds. Presoaking whole seed at 5 °C had a similar effect. Seeds with their pericarps removed and testas pricked and treated with gibberellic acid or kinetin provided the highest percentage germination and germinated in the shortest time. Additional tests showed that oxygen was not a limiting factor, and an inhibitor present in the pericarp evidently does not play a significant role in the dormancy mechanism. The restricted movement of water through the testa apparently controls and complements the metabolic block in the embryo and accounts for the prolonged stratification requirement.

An osmometer that can provide a direct estimate of permeability of various plant membranes under standardized conditions is described and potential applications suggested.

An automatic sand culture method that combines simplicity, economy, and versatility with the preferred technique of surface irrigation is described.

A new combination of embedding material and high contrast stain has provided the means for demonstrating, photographically, tangential sections of endodermal cells showing complete Casparian strips.

The growth potential of embryonic axes of Acer saccharum Marsh. increased during moist storage at 5 C but not at 20 C. During the period of increasing growth potential, the oxygen consumption of the axes remained constant. It was possible to distinguish three phases of the stratification-germination process at 5 C with respect to response of the axis to gibberellic acid and kinetin. From 0 to 10 days the growth regulators had no effect on elongation; from 10 to 60 days axis elongation was stimulated; and between day 60 and day 75, when germination had begun, the growth substances were inhibitory. The adenylate energy charge remained low (0.15) in axes of dry dormant seeds but increased to 0.78 following imbibition of water and 10 days of moist storage at 5 C. This phenomenon was not specifically related to low temperature stratification, since a rapid increase in the energy charge of the axes also occurred following imbibition and moist storage at 20 C. The excised axes would elongate in response to the growth substances only when a high energy charge (approximately 0.8) was maintained.

The effects of factorial combinations of N, P and Mg on some of the interrelationships among nutrient ions as they occurred in seedlings of slash pine were investigated. In similar studies, true interactions have not always been differentiated from apparent interactions, the result of comparing foliage concentrations in plants with widely divergent growth rates. To prevent this, nutrient solutions were formulated to produce conditions ranging only from slight deficiency through luxury consumption. This relatively narrow range of nutrition allowed actual interactions to be separated from those changes in foliage concentration that are primarily a result of large differences in growth.The needles were analyzed for total and soluble N and total P, K, Ca, Mg and Na. Each level of each nutrient variable had a significant effect on the concentration of 1 or more dissimilar elements. The familiar depressive effect of N on foliar P was observed; however this relationship was shown to be primarily the result of growth dilution rather than anion antagonism. Increased Mg did antagonistically reduce the uptake of Ca and, generally, K. Increments of P not required for growth stimulated uptake of N, Ca, Mg and K. No relationship was found between Mg supply and P accumulation.

A centrifugation procedure is described for producing different degrees of compaction in both wet and dry soils. To ensure uniform distribution of water in the test samples, appropriate quantities of crushed ice are mixed with the oven-dry soils 24 h prior to the centrifugation step.

On the occasion of its Silver Anniversary Meeting, the Canadian Society of Plant Physiologists was honored to host two international symposia on the topics of "New trends in phytochemistry" and "Plant senescence and postharvest physiology." The recent surge of interest in the chemistry of secondary plant products can be attributed, at least in part, to the economic challenge of and new developments in biotechnology. However, additional impetus for the discipline derives from a blurring of traditional distinctions between primary and secondary metabolites, and plant scientists and biochemists now recognize that many compounds heretofore labelled as nonessential products of secondary metabolism actually play crucial physiological and ecological roles in the growth, development, and survival of plants.The complexity and elegance of several of the physiological phenomena that characterize senescence and postharvest physiology of cells and tissues are no less compelling of our attention. Certainly, few other areas of research endeavor in the plant sciences hold more promise of socioeconomic benefit from the practical application of fundamental knowledge if we can but learn to control and manipulate some of the biochemical processes that occur in postharvest fruits, flowers, and vegetables.To each of the participants in the symposia, the Society offers its sincere thanks for presenting ideas and hypotheses that stimulated both discussion and controversy and will surely affect the course of future research. We also thank Dr. Ian de la Roche for his services as chief editor of these reports and we gratefully acknowledge the generous financial support from the Natural Sciences and Engineering Research Council of Canada that made it possible to convene these sessions.