Showing papers in "Physiologia Plantarum in 1976"

Mineral Requirements for Growth and Callus Initiation of Tissue Explants Excised from Mature Coconut Palms (Cocos nucifera) and Cultured in vitro

Abstract: Growth of stem, leaf, and inflorescence explants from mature coconut (Cocos nucifera L.) palms on a new mineral formulation (Y3) was superior to that on the minerals of White, Heller, or Murashige and Skoog. Cell division in the upper part of cultured explants gave rise to a layer of white callus within a month. The effects of omitting entirely or altering the concentration of individual elements in the Y3 formulation were investigated. It was concluded that growth on White's and Heller's minerals was seriously limited by deficiencies in macro-elements, i.e. nitrogen (particularly ammonium), potassium and phosphorus, as well as micro-elements, i.e. iron, iodine and molybdenum. The Murashige and Skoog formulation, on the other hand, was deficient only in certain micro-elements (particularly iodine).

Sources of Nitrogen Supporting Growth and Embryogenesis in Cultured Wild Carrot Tissue

Abstract: This paper seeks to calarify conflicting reports on the nitrogen requirements for in vitro embryogenesis in Daucus carota. Tissue derived from petiole explants of the wild strain of this species were tested with a variety of sources of cellular nitrogen under conditions otherwise favorable for in vitro embryogenesis. The use of very small, sieved and well-washed inocula reduced the carry-over of soluble materials with the inoculum. Embryo yield was quantified by direct counting of samples. Nitrate at concentrations ranging from 5 to 95 mM KNO3 supportes only weak growth and very low embryogenesis under the exacting conditions of these experiments. As little as 0.1 mM NH4Cl added to a nitrate medium allows some embryogenesis and 10 mM NH4Cl is near optimal when KNO3 is in the range of 12 to 40 mM concentration. Glutamine, glutamic acid, urea and alanine can individually partially replace NH4Cl as a supplement to KNO3. Glutamine, alanine, and possibly glutamic acid can serve as sole sources of nitrogen supporting both good growth and embryogenesis. It was concluded that a reduced nitrogen source is required, at least as a supplement to nitrate, for rapid growth and for in vitro embryogenesis of cultured wild carrot tissue. The relationship of pH of the culture medium to growth and embryogenesis was explored and optima observed at approximately pH 5.4 for both processes.

Effects of cadmium on respiration rate and activities of several enzymes in soybean seedlings

Abstract: Soybean (Glycine max L. cv. Columbus) seedlings grown in culture solution were treated with cadmium as CdSO/sub 4/. Final concentrations of cadmium (Cd/sup 2 +/) in the solution were 0, 0.45, 0.90, and 1.35 ..mu..M. Soybean leaves, analyzed 10 days after Cd/sup 2 +/ was added to the culture solution, showed increased respiration rate and activities of malate dehydrogenase, acid phosphatase, ribonuclease, deoxyribonuclease, and peroxidase but decreased activity of carbonic anhydrase. Increased activity of hydrolytic enzymes and peroxidase reflects a general senescence response while the carbonic anhydrase decrease is consistent with an antagonism between cadmium and endogenous zinc. Chlorosis, epinasty, abscission of leaves, and decreased growth rate occurred in seedlings treated with 1.35 ..mu..M Cd/sup 2 +/.

Water Stress Induced Alterations of the Stomatal Response to Decreases in Leaf Water Potential

Abstract: Young growth-chamber-grown cotton plants were subjected to a series of eight periods of soil water stress, which served as a preconditioning treatment. After preconditioning, water was withheld and changes in the stomatal resistance and leaf water potential were determined and compared with similar well watered control plants. The stomatal response of stress preconditioned plants adjusted such that the diffusion resistance of the lower surface of the leaf did not reach a value greater than 20 s cm−1 until the leaf water potential dropped 14 bars below that required to reach the same resistance on previously unstressed plants. The resistance—leaf water potential relation for the adaxial surface was unaltered by the preconditioning treatment. Adjustment of the osmotic potential of the guard cells on the abaxial surface provides at least a partial explanation of this change in response. The lack of adjustment of stomatal response on the adaxial surface of the leaves was correlated with a lack of adjustment in osmotic potential of guard cells on that surface.

Effect of Zinc Nutrition on Photosynthesis and Carbonic Anhydrase Activity in Cotton

Abstract: Photosynthesis, respiration, carbonic anhydrase activity and chlorophyll concentrations were correlated with zinc nutrition in cotton (Gossypium hirsutum L.). The critical zinc level during early plant growth was 13 μg/g dry weight in recently matured leaves (blade three). Photosynthesis and chlorophyll concentration required a minimum Zn of 13 and 14 μg/g dry weight, respectively, in blade three for maximum activity and synthesis. Respiration was not influenced by zinc status. Carbonic anhydrase activity increased curvilinearly as zinc status improved from deficiency to adequacy.

The Critical Oxygen Pressures for Respiration in Intact Plants.

Abstract: Two methods for determining critical respiratory oxygen pressure in whole plants are described. By a polarographic method involving the use of cylindrical platinum electrodes the following critical oxygen pressures for root respiration were found: Rice (cv. Norin 36). 0.024 atm: Rice (cv. Norm 37). 0.026 atm: Eriophorum angustifolium. 0.02 atm. These values contrast markedly with those obtained in vitro, and support earlier criticisms of in vitro measurements: they call into question the use of such data in the modelling of root aeration. When the results were assessed by an electrical analogue system, it was concluded that the respiratory activity in the intact root does not follow the normally accepted hyperbolic relationship with oxygen partial pressure. The experimental data were simulated most closely by assuming the critical oxygen pressure to be a function of respiratory responses in the low porosity (high diffusional impedance) tissues of the root meristem and stele, and respiratory activity in the moderately porous root cortex to be unaffected at values greater than 0.001 atm. A critical oxygen pressure of 0.025–0.04 atm for E. angustifolium was found from analyses of the gas phase oxygen in the leaves of whole plants after submergence in the dark. It was concluded that the higher value found by this method was most likely a function of respiratory responses in root tissue remote from the leaf and should not be regarded as the critical oxygen pressure for leaf respiration. The form of the oxygen concentration vs. time plot again suggested a very much lower critical oxygen pressure for certain of the plant tissues.

The Physiology of Rooting Populus Cuttings

Abstract: The changing levels of carbohydrates and the rates of photosynthesis in rooting Populus cuttings are described. The cuttings were planted in a sand medium, in controlled environment conditions. There was no evidence to support the view that failure to root in P. tremula was caused by insufficient carbohydrate reserves. In leafless hardwood cuttings, the carbohydrate levels were initially very high (14–19%) but fell rapidly (to 5–10%) as roots, callus or shoots developed. In leafy softwood cuttings, a steady accumulation of carbohydrate reserves was observed, rising from 5–10% on planting to 15–25% when roots had developed. One of the differences between the easy-to-root P. × euramericana and the hard-to-root P. tremula was the apparent downward transport of assimilates in P. × euramericana softwood cuttings.

Apical Growth Cessation and Shoot Tip Abscission in Salix

Abstract: Time course of apical shoot growth and shoot tip abortion in northern ecotypes (lat. 69°39′N, long. 18°37′E) of Salix pentandra and S. caprea have been investigated. In trees more than 15 years old growing under natural climatic conditions apical growth cessation and shoot tip abortion normally occurred in June-July when the day length still was 24 h. Application of GA3, in spring to the apex effectively delayed growth cessation and shoot tip abortion. Application of kinetin was without effect. First-year seedlings of both species grew continuously at temperatue of 9 to 24°C in 24 h photoperiod. Short days induced apical growth cessation, but two to four (S. pentandra) or three to five (S. caprea) weeks of 12 h photoperiod were required to stop the elongation growth. The results indicated that the critical photoperiod for apical growth cessation in the used ecotype of S. pentandra was 16 to 18 h at 18°C. Short days had a minor effect only on the formation of apical leaf primordia in small seedlings. Development of axillary buds and radial growth were stimulated by short days when compared with long days. Small seedlings of both species (3 to 8 cm high at the start) formed terminal buds in short days, but in large seedlings (more than about 15 cm high) apical growth cessation was accompanied by shoot tip abortion. Abscisic acid applied to the apex or through a leaf did not induce growth cessation in S. pentandra seedlings grown in continuous light. The growth retardants CCC, B-9 and Phosphon D reduced growth rate under continuous light and induced shoot tip abortion in some plants. The effect of CCC was counteracted by GA3. Apical growth cessation in short days was significantly delayed by a single GA1 application.

Seasonal Changes in the Cytokinin Content of Ginkgo biloba Leaves

Abstract: During the course of the growing season Ginkgo biloba leaves undergo both quantitative and qualitative changes in their cytokinin content. In young expanding leaves the major cytokinins cochromatograph with zeatin and zeatin riboside. In mature and aging leaves most of the cytokinin activity was due to slow moving compounds (paper chromatography) which could be hydrolysed by β-glucosidase. After hydrolysis the active compounds co-chromatographed with zeatin and zeatin riboside respectively. This indicates that both zeatin glucoside and zeatin riboside glucoside are present in the mature leaves. It is suggested that these glucosides are formed when the xylem transported cytokinins are metabolized (inactivated) in the leaves.

Variation of Alkaloid Production in Nicotiana rustica Callus Cultures

Abstract: Callus cultures have been established from the seed, root and leaf of Nicotiana rustica L. var. brasilia in a synthetic medium containing 1 μM 2,4-D and μM kinetin. These callus tissues behaved similarly not only in growth and organogenesis but also in nicotine production. The nicotine contents of callus cultures, which were in the order of 0.25–0.58% of dry weight during a few passages subsequent to callus induction, rapidly decreased to trace amounts in succeeding subcultures in association with the decline of the root-regenerating activity. On the other hand, free cells prepared from a callus tissue in the third passage developed into individual clones showing wide differences in growth and nicotine production. One of these clones gave rise to a relatively stable strain which is capable of producing nicotine at a high rate (0.29% of dry weight) in the absence of organization. The significance of these findings is discussed in connection with some results which have been reported for other callus cultures of Nicotiana species.

Hormonal Control of Germination under Saline Conditions of Three Halophytic Taxa in the Genus Suaeda

Abstract: The interaction between hormones and salinity on seed germination of three halophytic taxa in the genus Suaeda: S. maritima (L.) Dum. var. flexilis Focke and var. macrocarpa Moq., and S. depressa (Pursh) Wats, was studied. Exogenous applications of kinetin and gibberellic acid (GA3) were applied in order to determine if either of these growth-promoting hormones would promote germination in the two dormant taxa, Suaeda depressa and S. maritima var. flexilis and to see if osmotically induced dormancy by NaCl could be alleviated. Our results indicate that gibberellic acid is capable of breaking dormancy in these species with dormant seeds, but kinetin proved to be ineffective. A seed dormancy that was induced by osmotic stress could also be alleviated by treatments with gibberellic acid. Endogenous concentrations of both cytokinins and gibberellins were measured in seeds exposed to osmotic stress (0.85 M NaCl), and we found a reduction in cytokinin activity in these three taxa. Gibberellin-like activity was reduced in S. depressa when seeds were soaked in 0.85 M NaCl.

Nitrogenase Activity in Relation to Intracellular Organisms in Sphagnum Mosses

Abstract: Electron microscopic studies of Sphagnum lindbergii (Schimp.) and S. riparium (Angstr.) have revealed the presence of intracellular organisms such as blue-green algae, green algae, bacteria and fungi. Nitrogenase activities of these Sphagnum mosses were found to be related mainly to the presence of intracellular Nostoc filaments. The appearance of nitrogen-fixing blue-green algae within bryophytes is thus not restricted to liverworts. The association is likely to be of ecological importance as it seems to occur in very acid habitats generally lacking blue-green algae. Possible interrelations between the moss, the blue-green algae and different types of bacteria are discussed.

Effects of Salt Stress on Growth, Nodulation and Nitrogen Fixation in Cowpea and Mung Beans

Abstract: The effects of salt stress on growth, nodulation, and nitrogen accumulation in cowpea (Vigna sinensis) and mung beans (Vigna aureus) were studied in sand culture. Salinity (NaCl) retarded the growth of leaves, stem and roots of both the crops. Root growth of mung beans was more sensitive to the increase in salt stress than that of cowpea. The relative growth rates of stressed plant parts declined initially but were subsequently higher than those of control for a period, suggesting that the plants tended to adapt to unfavourable environment even while being stressed. The total nodule number, weight and nitrogen content per plant decreased due to salt treatment, which interfered with the initiation of nodules but not with their further development. There was a considerable fall in the nitrogen fixation efficiency of mung beans under saline environment; it was not so in cowpea.

Amelioration of Chilling Injuries in Cucumber Seedlings by Abscisic Acid

Abstract: Exposure of cucumber seedlings (Cucumis sativus L.) to chilling temperature resulted in injuries such as increased leakage of cellular materials, loss of water and wilting. In addition, the development of the seedlings after the exposure to chilling was impaired. Abscisic acid applied to the seedlings prior to chilling significantly ameliorated these injuries.

Two sites of hormonal action during germination of Chenopodium album L. seeds

Abstract: During the overall germination process in the light-requiring seeds of Chenopodium album L. two sites of hormonal action can be distinguished. The start of visible growth is induced in darkness by the gibberellins 4 and 7 (GA4+7) or by ethylene. Added cytokinins are inactive although 8-14C-kinetin shows rapid penetration into the seed and rapid turnover. The induction of growth by GA4+7 and the uptake of 8-methylene-14C-GA3 are enhanced at lower pH values. Prolonged incubation in darkness results in a decreased responsiveness of the seeds towards GA4+7 and ethylene. A second site of hormonal action is located during the progress of growth inside the covering structures. ABA inhibits radicle growth, while GA4+7, GA3, kinetin, zeatin and ethylene reduce the inhibition.

Attachment of Rhizobium to Legume Roots as the Basis for Specific Interactions

Abstract: Experiments were conducted to elucidate the basis of the observation that different strains of Rhizobium infect particular legumes. Rhizobia specific for a variety of legumes were grown with 13PO2−4 and exposed to pea roots (Pisum sativum L.), R. leguminosarum 128C53, which nodulates pea, did not attach to the roots in greater numbers than those strains of rhizobia incapable of infecting pea roots. A complex of R. leguminosarum 128C53 conjugated to a fluorochrome-labeled antibody exhibited a striking attachment to the tips of pea root hairs, where infection normally occurs, but this fluorescent complex also bound to the root hairs of Canavalia en siformis DC., Lupinus polyphyllus Lindl., Trifolium pratense L., and Medicago sativa L., which are not infected by this bacterium. A reproducible, quantitative technique developed for studying interactions between fluorochrome-labeled lectins and rhizobia revealed no relationship between lectin-Rhizobium interactions and the capacity to infect a plant. The data are interpreted as suggesting that simple attachment of Rhizobium to a legume root is not the basis of host-symbiont specificity in this system.

Effects of Flavonoids on the Polar Transport of Auxins

Abstract: The effect of some flavonoids on the polar transport of auxins was investigated in hypocotyl sections of dark grown seedlings of cucumber, Cucumis sativus L., by means of 14C labelled auxins. In experiments of 4–6 h duration quercitrin, morin, dihydroquercetin, naringin, sulfuretin and ferulic acid increased the polarity of the transport of indol-3yl-acetic acid (stimulation of basipetal, inhibition of acropetal transport). Naringenin, genistein and pinobanksin, on the other hand, decreased the polarity of this transport. For NAA no increase in the polarity of the transport could be observed, but all the substances tested inhibited the basipetal transport. There was no simple correlation between the effects on the polar transport and the effects on IAA oxidase.

Temperature and Humidity Effects on Net Photosynthesis and Transpiration of Citrus

Abstract: Maximum rates of net photosynthesis for Citrus sinensis (L.) Osbeck and Citrus paradisi Macf. cultivars were observed at the lowest temperature (22°C) under which these subtropical species were examined. Net photosynthesis decreased with higher temperatures or greater vapor pressure differences between leaf and air. The reduction in net photosynthesis due to higher temperatures was associated with reductions in mesophyll conductance to CO2; whereas, the effects of greater vapor pressure differences on net photosynthesis were associated with changes in total leaf conductance to water vapor. Actual water-use efficiency was reduced at higher temperatures and greater vapor pressure differences, but intrinsic water-use efficiency, calculated for a constant vapor pressure difference, increased with increases in vapor pressure difference indicating a possible adaptive mechanism for conditions of high evaporative demand. Day-today increases in net photosynthesis, total leaf conductance to water vapor and mesophyll conductance were observed as plants were subjected to the same temperature and humidity treatments on progressive days. Growing plants under higher irradiances increased their photosynthetic rates and mesophyll conductance to CO2 but leaf conductance to water vapor was unaffected by irradiance pretreatment. Consequently, acclimation to radiation can only account for a small part of the day-to-day changes in gas exchange. Other possible explanations for these day-to-day changes were discussed. Significant differences were not observed among trees of ‘Campbell Valencia’ orange, ‘Parent Navel’ orange and ‘Frost Marsh’ grapefruit in responses of net photosynthesis and leaf conductance to temperature and humidity.

Regeneration of Plants from Cell Suspensions Frozen at −20, −70 and −196°C

Abstract: Cell suspensions of carrot, Datura, tobacco and soybean subjected to −20°C, −70°C and −196°C in the presence of a suitable cryoprotective agent, and stored for various lengths of time have been revived. After revival these cells divided to form callus masses. Direct immersion in liquid nitrogen invariably killed the cells, whereas cooling at the rate of 1 or 2°C/min, or pre-freezing briefly at −20 and −70°C, followed by freezing at −196°C retained the viability. Depending on the plant species up to 70% of the cell clumps could withstand ultra-cooling. Tobacco and Datura cell suspensions were more sensitive to cold treatment than were those of carrot. Actively growing cell suspensions containing small cell-clumps revived rapidly, while filtered cell-suspensions of free cells only occasionally survived. Calli of tobacco and carrot obtained from frozen suspensions have been regenerated into plants.

Salinity and the Hydraulic Conductance of Roots

Abstract: The effect of salinity on hydraulic conductance of intact roots of tomato (Lycopersicon esculentum Mill.) and sunflower (Helianthus annuus L.) was determined in split-root experiments using salinized nutrient solutions. Experiments were conducted in controlled climate chambers under two or three relative humidity levels and four solution osmotic potential levels. The relationship between water flux through roots (Jv) and total water potential difference between the leaves and the root medium (Δψ) was linear, usually with a small intercept. Thus, the root hydraulic conductance (L) was not affected by salinity within the range of fluxes obtained in these experiments, with L= 0.036 mm h−1 bar−1 for tomato and L= 0.0167 mm h−1 bar−1 for sunflower. Our results agreed with theoretical analysis of coupled water and ion uptake. From Cl− and Na+ uptake data, the reflection coefficient (o) for tomato roots was calculated as 0.956, which was compatible with the near-zero intercept. A large intercept for sunflower could not be readily explained. Relative humidity strongly affected root growth, with more rapid growth under low humidity conditions. Transpiration of sunflower plants was reduced by 20% when the relative humidity was increased from 34% to 84%, whereas transpiration in tomato was reduced 50%.

Nitrate Uptake during Recovery from Nitrogen Deficiency

Abstract: Two-week-old nitrogen-deficient wheat plants attained a high rate of nitrate uptake on the first day of exposure to nutrient solutions supplemented with KNO3. Ammonium uptake from similar solutions supplemented with NH4NO3 was also high during the first day of exposure, but nitrate uptake from this solution was lower than from the KNO3 treatment. During the next two to three days there was a progressive decrease in uptake of both nitrogen ions. A steady increase in uptake then occurred as the plants fully recovered from the nitrogen-deficient state. The transient low nitrate uptake after three or four days of exposure to KNO3 was not due to an excessive accumulation of nitrate in the tissue, nor to a failure in nitrate reduction as indicated by the rate of nitrate accumulation relative to the uptake rate. Nitrogen supplied as 15N-nitrite during the low uptake period was effectively incorporated into organic forms and effectively translocated to the shoots. Failure of the root tissue to increase in soluble carbohydrates during illumination was characteristic of the low uptake period. This contrasted with an increase in root soluble carbohydrates in the light during rapid uptake associated with full recovery from the nitrogen-deficient state. It is concluded that carbohydrate translocation to the root system was insufficient during the intermediate recovery period for optimal nitrate uptake, although it was sufficient for effective reduction and translocation of nitrate and reduced nitrogen. Ammonium uptake from NH4NO3 was restricted during darkness by the third day whereas there was little difference between light and dark periods in nitrate uptake from KNO3 until about the sixth day of recovery. The extent to which ammonium restricted nitrate uptake increased progressively for two or three days following which a lessening influence seemed evident, and the effects were not directly associated with the rate of ammonium uptake.

Changes in Chloroplast Lipids during the Development of Photosynthetic Activity in Barley Etio-Chloroplasts

Abstract: The content of monogalactosyl diglyceride, digalactosyl diglyceride, sulfoquinovosyl diglyceride and phosphatidyl glycerol of gel-filtrated etio-chloroplasts isolated from greening barley seedlings was determined. The development of photosynthetic electron transport, measured as anthraquinone autooxidation, was simultaneously determined with an oxygen electrode. During the first hour of irradiation of the etiolated seedlings the lipid content of the plastids decreased rapidly. The decrease is interpreted as a chlorophyll sensitized photooxidation of the fatty acids of the diglycerides. With artificial electron donors an oxygen uptake was detected after 10 min of greening. With no donors added, a DCMU sensitive oxygen uptake was detected after 2 h. The level of DCMU inhibition increased as the plastid developed and total inhibition was obtained after 5 h. Between 2 and 6 h of greening the lipid content of the plastids stayed constant. During this greening period there was a correlation between the appearance of a DCMU sensitive electron transport and the accumulation of the trans-3-hexadecenoic acid of phosphatidyl glycerol. The trans-3-hexadecenoic acid was present already in the dark-grown seedlings but an increase in content did not occur until after 3 h. The lipid content increased after 6 h of greening. This increase coincided well in time with the formation of grana. The fatty acid composition of the individual lipids, with the exception of phosphatidyl glycerol, and the monogalactosyl diglyceride to digalactosyl diglyceride ratios did not change fundamentally during the greening.

Effect of Salinity on the Photosynthesis of the Halophyte Salicornia rubra and Distichlis stricta

Abstract: The photosynthesis and biomass production of two contrasting species, Salicornia rubra and Distichlis stricta from the same habitat, were studied under different light intensities and osmotic conditions. Application of NaCl increased the biomass and succulence of Salicornia and decreased that of Distichlis. Ethylene glycol, EG mol. wt. 62.07, and 1:1 NaCl-EG killed Salicornia and affected Distichlis adversely. The CO2 uptake of both the species increased with increasing light intensity and was strongly influenced by the application of NaCl. All concentrations of NaCl stimulated the CO2 uptake of Salicornia, but decreased that of Distichlis. NaCl significantly decreased the light compensation point of Salicornia but had no effect on that of Distichlis. The CO2 efflux of the two species at 4.52 klx was not significantly different. The rate of CO2 uptake of both the species declined with time at all levels of treatment. Salicornia had a more rapid decline in CO2 uptake in absence of NaCl, whereas that of Distichlis was relatively unaffected by it. Although the tissue Na concentration of the two species increased with increasing NaCl concentration in the medium, the increase in Salicornia was 3.0 to 5.5 times greater than that of Distichlis. Increasing NaCl concentration decreased the chlorophyll concentration of Salicornia and increased that of Distichlis. This resulted in higher ratios of photosynthesis/chlorophyll concentration in Salicornia as against lower ratios in Distichlis. The tissue OP (osmotic potential) of both the species decreased with decreasing OP of the medium. In Salicornia the tissue OP decrease was concurrent with an increase in the CO2 uptake, whereas the CO2 uptake of Distichlis declined with decreasing OP of the medium despite a decrease in its tissue OP. It is concluded that Salicornia requires NaCl for its normal development, whereas Distichlis is adversely affected by it. Both species however, are better adapted to osmotic stress due to natural osmotic agents like NaCl, than to the osmotic stress due to artificial osmotic agents like ethylene glycol.

Anthurium andraeanum Plantlets Produced from Callus Tissues Cultivated in vitro

Abstract: During the last 3 years a method has been developed to reproduce Anthurium andraeanum Lind. through callus cultures. The procedural sequence is as follows: callus induction on excised leaf fragments, callus subculture on solid and in liquid media, adventitious sprout formation in callus on solid media, and rooting of excised sprouts. Recently 20 adult genotypes were propagated by this method.

Carbohydrate Metabolism and Frost Hardiness in Pine and Spruce Seedlings Grown at Different Photoperiods and Thermoperiods

Abstract: Large changes occur in carbohydrate contents of pine (Pinus silvestris L.) and spruce (Picea abies (L.) Karst.) seedlings cold-hardened by photoperiod or by combined photo- and thermo-period. The largest change is in sucrose content, which is almost doubled after six weeks short-day (6/18 h) treatment; and more than doubled (spruce) or more than tripled (pine), when also temperature is lowered (10/5°C). Development of frost hardiness is strongly correlated with the change in carbohydrate contents. At dehardening, the carbohydrate content decreases rapidly, especially in pine, and the raffinose formed during the rest period disappears within 2–4 weeks. Frost hardiness decreases in parallel. The content of soluble carbohydrates may thus play a role in frost hardiness, although it is not the only factor. Bud formation at cold acclimation is not directly correlated with the changes in carbohydrate content and hardiness.

Role of Photosynthetic Electron Transfer in Light Activation of Calvin Cycle Enzymes

Abstract: The effect of light in activating fructose-1,6 biphosphate phosphatase (E.C. 3.1.3.11), sedoheptulose-1,7, biphosphate phosphatase (E.C. 3.1.3.11), ribulose-5 phosphate kinase (E.C. 2.7.1.19), ribulose-1,5 biphosphate carboxylase (E.C. 4.1.1.39) and (NADPH) glyceraldehyde-3 phosphate dehydrogenase (E.C. 1.2.1.13) in intact spinach chloroplasts in the presence of antimycin A, tetramethylethylenediamine (TMEDA) or chlorophenyl-1,1-dimethylurea (CMU) was examined. Antimycin A and TMEDA were added as stimulating agents for photosynthetic electron transfer in intact chloroplasts while CMU was added for its inhibitory characteristics. Light exerted its control through the mediation of the photosynthetic electron transfer. Antimycin A and TMEDA promoted the light activation. CMU nullified the light activation as well as the stimulatory effect of antimycin A and TMEDA. Thus the control by light of the activities of the Calvin cycle enzymes involves a reduced agent formed by the photosynthetic electron transport chain. From the presently available evidence, it seems appropriate to hypothesize that the light activation of the enzymes is not a single mechanism. In fact three types of enzymes can be distinguished: Ru-5 P kinase and (NADPH) G-3 P dehydrogenase, maximal activation of which appears within the first minute of illumination and is promoted by antimycin A and by TMEDA; F-1,6 P2 phosphatase and S-1,7 P2 phosphatase, ferredoxin-dependent enzymes, activation of which is slightly slower but is also promoted by antimycin A and by TMEDA; finally Ru-1,5 P2 carboxylase, activation of which is still slower and characterized by the absence of any response to antimycin A as well as to TMEDA.

A Role for Auxin and Auxin Transport Inhibitors on the Ca Content of Artificially Induced Parthenocarpic Fruits

Abstract: Artificially induced parthenocarpic fruits of apples, pears and tomatoes, as well as seeded fruits treated with 2,3,5-triiodobenzoic acid, frequently show symptoms of Ca deficiency and a low Ca content. It was concluded that auxins, probably produced by the seeds, play a significant role in Ca translocation into fruits. Exogenous indoleacetic acid but not 4-chlorophenoxyacetic acid applications could replace the effect of seeds in this respect. Auxin transport, rather than auxin accumulation, seems to be necessary for Ca transport, as can be concluded from the effect of auxin transport inhibitors.

Chemical Forms of Manganese and Zinc in Phloem Exudates

Abstract: Investigations were performed to study the chemical form in which manganese and zinc are transported in sieve tubes. As a test plant Ricinus communis was used. From this plant phloem sap can be obtained in a rather pure state. The plants received labelled manganese or zinc. In the experiments on manganese translocation a radioactive phosphorus isotope was added to the nutrient solution to test if complex compounds of the cation contain also phosphorus. Components of the phloem exudate were determined by means of physicochemical separation methods. Almost all zinc but only a part of the manganese were bound to organic compounds. The major part of the manganese was in ionic form. The molecular weight of the complexing com-pound(s) of manganese was estimated to be between 1000 and 5000 and of zinc between 1000 and 1500. The complexes probably contain some phosphorus. The charge of the zinc complex is negative.

Occurrence of a Cytokinin Glucoside in the Leaves and in Honeydew of Salix babylonica

Abstract: Honeydew and leaf extracts from Salix babylonica indicate that large quantities of cytokinin are present in the leaves and are transported through the phloem of this plant during late autumn The active compound in the extracts could be hydrolysed with β-glucosidase, whereafter it showed the same chromatographic behaviour as zeatin It is proposed that cytokinins in the leaves are converted to the glucoside and then redistributed to the rest of the plant organs where it is stored

Manipulation of IAA‐Oxidase Activity and Auxin‐Deficiency Symptoms in Intact Cotton Plants with Manganese Nutrition

Abstract: Cotton (Gossypium hirsutum L. cv. Deltapine 15) seedlings were grown in solution culture in which the Mn2+ level was varied. Following an initial period, a series of shifts in manganese nutrition were employed, each lasting 14 days. Appearance was observed and fresh weight, IAA oxidase (IAAO), peroxidase and IAAO inhibitor levels were determined. After the initial 3 weeks of treatment, growth was negatively correlated with IAAO (or peroxidase) activity. All shifts in manganese nutrition resulted in predicted changes in IAAO activity, growth and plant appearance during a second 2-week period of the experiment. Continuously deficient plants exhibited highest leaf abscission and IAA oxidase activity, and lowest growth of all treatments. Plants shifted from deficient to control levels of Mn2+ exhibited a marked decline in IAAO activity, increase in growth and absence of leaf abscission. Plants shifted from borderline deficiency to deficient Mn2+ exhibited a major increase in IAAO activity, reduction in growth and extensive leaf abscission. Control and borderline toxicity plants maintained normal IAAO activity, growth, and appearance. During a final 2-week period, symptom expression was intensified. In particular, the initial borderline deficiency plants shifted to deficient levels of Mn2+ abscised most of those leaves that expanded after the shift in treatment. In addition, shifts of some plants to toxic Mn2+ levels during the third phase of the experiment produced a complete cycle of manipulation. Plants initially deficient in Mn2+ with high IAAO and low growth recovered growth and declined in IAAO when shifted to control Mn2+ and then suffered severe inhibition of growth and toxicity symptoms when shifted to high Mn2+. In all cases changes in enzyme activity, growth, leaf abscission and similar symptoms were most strongly expressed in the youngest tissue or that with the greatest potential for growth during the interval of a particular treatment. Since total growth, IAAO, leaf abscission, internode length and similar symptoms were consistently manipulated in both directions (increase or decrease in intensity or degree) by raising or lowering Mn2+ levels in the plant culture medium, we conclude that there is a causal relationship between IAAO and these responses that involves destruction of auxin.