Showing papers on "Shoot published in 1991"

Effects of source‐sink relations on photosynthetic acclimation to elevated CO2

Abstract: . While photosynthesis of C3 plants is stimulated by an increase in the atmospheric CO2 concentration, photosynthetic capacity is often reduced after long-term exposure to elevated CO2. This reduction appears to be brought about by end product inhibition, resulting from an imbalance in the supply and demand of carbohydrates. A review of the literature revealed that the reduction of photosynthetic capacity in elevated CO2 was most pronounced when the increased supply of carbohydrates was combined with small sink size. The volume of pots in which plants were grown affected the sink size by restricting root growth. While plants grown in small pots had a reduced photosynthetic capacity, plants grown in the field showed no reduction or an increase in this capacity. Pot volume also determined the effect of elevated CO2 on the root/shoot ratio: the root/shoot ratio increased when root growth was not restricted and decreased in plants grown in small pots. The data presented in this paper suggest that plants growing in the field will maintain a high photosynthetic capacity as the atmospheric CO2 level continues to rise.

Root Restriction as a Factor in Photosynthetic Acclimation of Cotton Seedlings Grown in Elevated Carbon Dioxide

Abstract: Interactive effects of root restriction and atmospheric CO2 enrichment on plant growth, photosynthetic capacity, and carbohydrate partitioning were studied in cotton seedlings (Gossypium hirsutum L.) grown for 28 days in three atmospheric CO2 partial pressures (270, 350, and 650 microbars) and two pot sizes (0.38 and 1.75 liters). Some plants were transplanted from small pots into large pots after 20 days. Reduction of root biomass resulting from growth in small pots was accompanied by decreased shoot biomass and leaf area. When root growth was less restricted, plants exposed to higher CO2 partial pressures produced more shoot and root biomass than plants exposed to lower levels of CO2. In small pots, whole plant biomass and leaf area of plants grown in 270 and 350 microbars of CO2 were not significantly different. Plants grown in small pots in 650 microbars of CO2 produced greater total biomass than plants grown in 350 microbars, but the dry weight gain was found to be primarily an accumulation of leaf starch. Reduced photosynthetic capacity of plants grown at elevated levels of CO2 was clearly associated with inadequate rooting volume. Reductions in net photosynthesis were not associated with decreased stomatal conductance. Reduced carboxylation efficiency in response to CO2 enrichment occurred only when root growth was restricted suggesting that ribulose-1,5-bisphosphate carboxylase/oxygenase activity may be responsive to plant source-sink balance rather than to CO2 concentration as a single factor. When root-restricted plants were transplanted into large pots, carboxylation efficiency and ribulose-1,5-bisphosphate regeneration capacity increased indicating that acclimation of photosynthesis was reversible. Reductions in photosynthetic capacity as root growth was progressively restricted suggest sink-limited feedback inhibition as a possible mechanism for regulating net photosynthesis of plants grown in elevated CO2.

The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source‐sink relations and respiration

Abstract: . Herbaceous C3 plants grown in elevated CO2 show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO2-enriched herbaceous plants and decrease for CO2-enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root: shoot ratios due to elevated CO2 show no alteration in the whole-plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold-adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO2-enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented in support.

On the relationship between specific root length and the rate of root proliferation: a field study using citrus rootstocks

Abstract: summary This study tested two hypotheses: (1) species with roots that have a high length to dry mass ratio or specific root length (SRL) also have the potential for high rates of root growth in small volumes of favourable soil and (2) variation in average root diameter fully accounts for variation in SRL. To minimize differences among shoots, the study used 13-year-old ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] trees budded to rootstocks representing a range of genotypes. Soil cores 7.4 cm in diameter and 14.2 cm deep were extracted from beneath the canopy, and the soil was sieved free of roots and replaced. Root length, diameter and dry weight of the roots in the disturbed soil and adjacent undisturbed soil were evaluated 5, 10, 19 and 40 weeks following soil replacement. The disturbed soil had a higher water content than the undisturbed soil for the first three sampling dates. Averaged across rootstocks, root length density increased in a linear fashion in the disturbed soil and was comparable to that in the undisturbed soil by 40 weeks. Mean root diameter of the fibrous roots (< 2 mm) declined with age. Rootstocks with the highest SRL had the most rapid rate of root proliferation (cm cm−3 wk−1) (r= 0.94) and the greatest rate of water extraction at 19 weeks (r= 0.79). Although variation in root diameter contributed to rootstock variation in SRL, the data also suggested that rootstocks of high SRL had roots with lower tissue density than those of low SRL (P < 0.05). The potential trade-offs of constructing root systems of high SRL are discussed.

Contribution of the VA mycorrhizal hyphae in acquisition of phosphorus and zinc by maize grown in a calcareous soil

Abstract: An investigation was carried out to test whether the mechanism of increased zinc (Zn) uptake by mycorrhizal plants is similar to that of increased phosphorus (P) acquisition. Maize (Zea mays L.) was grown in pots containing sterilised calcareous soil either inoculated with a mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappe or with a mixture of mycorrhizal fungi, or remaining non-inoculated as non-mycorrhizal control. The pots had three compartments, a central one for root growth and two outer ones for hyphal growth. The compartmentalization was done using a 30-μm nylon net. The root compartment received low or high levels of P (50 or 100 mg kg−1 soil) in combination with low or high levels of P and micronutrients (2 or 10 mg kg−1 Fe, Zn and Cu) in the hyphal compartments. Mycorrhizal fungus inoculation did not influence shoot dry weight, but reduced root dry weight when low P levels were supplied to the root compartment. Irrespective of the P levels in the root compartment, shoots and roots of mycorrhizal plants had on average 95 and 115% higher P concentrations, and 164 and 22% higher Zn concentrations, respectively, compared to non-mycorrhizal plants. These higher concentrations could be attributed to a substantial translocation of P and Zn from hyphal compartments to the plant via the mycorrhizal hyphae. Mycorrhizal inoculation also enhanced copper concentration in roots (135%) but not in shoots. In contrast, manganese (Mn) concentrations in shoots and roots of mycorrhizal plants were distinctly lower, especially in plants inoculated with the mixture of mycorrhizal fungi. The results demonstrate that VA mycorrhizal hyphae uptake and translocation to the host is an important component of increased acquisition of P and Zn by mycorrhizal plants. The minimal hyphae contribution (delivery by the hyphae from the outer compartments) to the total plant acquisition ranged from 13 to 20% for P and from 16 to 25% for Zn.

Effects of CO2 Enrichment and Nitrogen Stress on Growth, and Partitioning of Dry Matter and Nitrogen in Wheat and Maize

Abstract: Atmospheric CO2 levels are increasing, but little is known about how this will affect tissue concentrations and the partitioning of agriculturally important nutrients such as nitrogen (N) within crop plants. To investigate this, a glasshouse experiment was conducted in which wheat, a C3 species, and maize, a C4 species, were grown for 8 weeks at high CO2 (1500 cm3 m-3) on N supplies ranging from deficient (0.5 mol m-3) to more than adequate for maximum growth (25 mol m-3). Wheat responded to both CO2 enrichment and N supply; maize responded only to N supply. CO2-enriched wheat produced about twice the dry matter of control plants at all levels of N supply. Tiller and ear numbers were increased by CO2 enrichment irrespective of N supply. Enriched wheat plants had a lower Leaf Area Ratio but higher Net Assimilation Rate and Relative Growth Rate than control plants. There was no effect of CO2 enrichment on specific leaf weight. The enriched plants had lower shoot to root dry matter ratios than the controls at 6 mol m-3 N and higher. Shoot to root dry matter ratios of both wheat and maize increased with increasing N supply. CO2-enriched wheat plants accumulated more N than the controls but the proportional increase in N content was not as great as that in dry matter, with the result that concentrations of total-N and nitrate-N were lower in all organs of enriched plants, including ears. Nitrate reductase activity was lower in enriched than in control wheat plants. N-use efficiency by wheat was increased by CO2 enrichment. From a practical point of view, the study indicates that critical total-N and NO3-N concentrations used to diagnose the N status of wheat will need to be reassessed as global CO2 levels increase. Elevated CO2 may also reduce the protein content of grain and thus the baking quality of hard wheats.

Effects of soil temperature on root and shoot growth traits and iron deficiency chlorosis in sorghum genotypes grown on a low iron calcareous soil

Abstract: Iron deficiency chlorosis (FeDC) is a common disorder for sorghum [Sorghum bicolor (L.) Moench] grown on alkaline calcareous soils. Four sorghum genotypes were grown in growth chambers on a low Fe (1.3 μg/g DTPA-extractable), alkaline (pH 8.0), calcareous (3.87% CaCO3 equivalent) Aridic Haplustoll to determine effects of different soil temperatures (12, 17, 22 and 27°C at a constant 27°C air temperature) on various root and shoot growth traits and development of FeDC. As soil temperature increased, leaf chlorosis became more severe, and shoot and root dry weights, root lengths, and leaf areas increased markedly. Shoot/root ratios, shoot weight/root length, leaf area /shoot weight and leaf area /root weight and root length also increased while root length/root weight decreased as soil temperature increased. Severe FeDC developed in all genotypes even though genotypes had previously shown different degrees of resistance to FeDC. Genotypes differed in most growth traits, especially dry matter yields, root lengths, and leaf areas, but most traits did not appear to be related to genotype resistance to FeDC. The most FeDC resistant genotype had the slowest growth rate and this may be a mechanism for its greater resistance to FeDC.

Achievable productivities of certain CAM plants: basis for high values compared with C3 and C4 plants.

Abstract: CAM species, which taxonomically are at least five times more numerous than C4 species, often grow-slowly, as is the case for various short-statured cacti and many epiphytes in several families, However, slow growth is not a necessary corollary of the CAM photosynthetic pathway, as can be appreciated by considering the energetics of CO2 fixation. For every CO2 fixed photosynthetically, C3 plants require 3 ATP and 2 NADPH, whereas the extra enzymatic reactions and compartmentation complexity for C4 plants require 4 or 5 ATP and 2 NADPH, and CAM plants require 5.5-6.5 ATP and 2 NADPH. Photorespiration in C8 plants can release some of the CO2 , fixed and also has an energetic-cost, whereas photorespiration is much less in C4 and CAM plants. Therefore, CAM plants can perform net CO2 fixation 15% more efficiently than C3 , plants, although 10% less efficiently than C4 plants. Using a simple model that assumes 8 photons per CO2 fixed and a processing time per excitation of 5 ms, a maximum instantaneous rate for net CO2 , uptake of 55 μmol m-2 s-1 is predicted. Measured maximal rates average 48μmol m-2 s-1 for leaves of six C3 species with the highest rates and 64 μmol m-2 s-1 for six such C4 species; CAM plants take up CO2 mainly at night, which is not directly related to the instantaneous rate of photon absorption. Net CO2 uptake integrated over 24 h, which is more pertinent to productivity than are instantaneous CO2 uptake rates, is similar for the three pathways, although the higher water-use efficiency of CAM plants can be an advantage during drought. Canopy architecture is crucial for the distribution of the photosynthetic photon flux density (PPFD) over the shoot, which determines net CO2 uptake per unit ground area and hence determines productivity. Maximal productivity for idealized canopies under optimal conditions is predicted to be about 100 Mg d. wt ha-1 yr-1 (1 Mg = 1 tonne), whereas actual values of environmental factors in the field approximately halve this prediction. The influence of environmental factors on net CO2 uptake can be quantified using an environmental productivity index (EPI), which predicts the fractional limitation on net CO2 uptake and is the product of a water index, a temperature index, and a PPFD index (nutrient effects can also be included). Using EPI with a ray-tracing technique to determine the PPFD index and taking into account respiration and carbon incorporated structurally, maximal productivity of CAM plants is predicted to occur at leaf or stem area indices of 4-5. In experiments designed using such shoot area indices, annual above-ground dry-weight productivities averaging 43 Mg ha-1 yr-1 have recently been observed for certain agaves and plutyopuntias. In comparison, the measured average annual productivity of the most productive plants is 49 Mg ha-1 yr-1 for six agronomic C4 species, 35 Mg ha-1 yr-1 for sis agronomic C3 species, and 39 Mg ha-1 yr-1 for six C3 tree species. Thus, CAM plants are capable of similar high productivities, which can become especially advantageous in regions of substantial water stress. Recognition of the high potential productivity of certain CAM species under optimal environmental conditions, exceeding that of most C3 species, may increase the cultivation of such CAM plants in various areas in the future. CONTENTS Summary 183 I. Introduction 184 II. Biochemistry of C3 , C4 , and CAM plants 185 III. CO2 uptake rates 188 IV. Canopy architecture and light absorption 193 V. Measured biomass productivity 198 VI. Conclusions 200 Acknowledgement 202 References 202.

The fate of carbon in pulse-labelled crops of barley and wheat

Abstract: Wheat (cv. Gutha) and barley (cv. O'Connor) were grown as field crops on a shallow duplex soil (sand over clay) in Western Australia with their root systems contained within pvc columns. At four stages during growth, the shoots were pulse-labelled for 1.5h with14CO2; immediately prior to labelling, the soil was isolated from the shoot atmosphere by pvc sheets. After labelling, the soil atmosphere was pumped through NaOH to trap respired CO2 and after 2.5, 5, 7.5 and 24 h from the start of labelling, columns were destructively sampled to recover14C from the roots, soil and shoot.

Redistribution of carbon and nitrogen compounds from the shoot to the harvesting organs during maturation in field crops

Abstract: The present paper alms at determining how carbon (C) and nitrogen (N) compounds are redistributed from leaves to harvesting organs during maturation in several major field crops. In order to illustrate these processes in the case of C and N compounds, 6 major crops in Hokkaido were grown and compared during maturation. The results obtained were as follows. 1) The N-redistribution rate during maturation was in the order of wheat, soybean and potato > maize > rice. The percentage of distributed nitrogen among the different nitrogenous fractions in leaves and stems was remained constant during maturation, suggesting that each nitrogen compound was equally decomposed. 2) The composition of protein amino acids was similar regardless of organs or crops. The composition of free amino acids differed widely among organs and crops, and differed from that of protein amino acids. Therefore during the translocation of amino acids from leaves to harvesting organs through stems, the composition of free amino ac...

Response to Anoxia in Rice and Wheat Seedlings: Changes in the pH of Intracellular Compartments, Glucose-6-Phosphate Level, and Metabolic Rate.

Abstract: 31P nuclear magnetic resonance spectroscopy was used to measure intracellular pH in living tissues. Oxygen deprivation caused fast cytoplasmic acidification from pH 7.4 to 7.0 in shoots of rice, Oryza sativa L. var arborio, a species highly resistant to anoxia. Acidification was complete after 10 minutes of anoxia. Alkalinization of both cytosplasm and vacuole followed thereafter. In the anoxia intolerant wheat shoots, Triticum aestivum L. var MEK, the same treatment caused a sharper cytoplasmic acidification, from pH 7.4 to 6.6, which occurred during a period of 2 hours. Cytoplasmic acidification continued with progress of anoxia and there was no vacuolar alkalinization comparable to the one observed in rice. In wheat oxyen, withdrawal also caused the reduction of both glucose-6-phosphate level and of metabolic rate. It also induced heavy losses of inorganic phosphate from tissues. Conversely, in rice, glucose-6-phosphate level and metabolic rate were increased and inorganic phosphate leakage from tissues was completely absent. These results are discussed in relation to the mechanisms of plant resistance to anoxia.

Micropropagation of Withania somnifera from germinating seeds and shoot tips

Abstract: Shoot multiplication was achieved in vitro from shoot tips of aseptically germinated seedlings of Withania somnifera L. using low concentrations of 6-benzyladenine (BA), viz. 2.2, 4.4 and 8.9 μM. Maximum number of shoots were obtained when 2.3 μM 2,4-dichlorophenoxyacetic acid (2,4-D) or 2.5 μM indolebutyric acid (IBA) was added to medium containing 4.4 μM BA during initiation of shoot multiplication, but not when added later. Direct multiple shoot initiation was also obtained from germinating seeds in the presence of BA alone. Rooting was successful in excised shoots grown on growth regulator-free MS medium. Rooted shoots were successfully established in soil in a greenhouse.

Adventitious shoot regeneration from in vitro leaves of several pear cultivars (Pyrus communis L.)

Abstract: An efficient adventitious shoot regeneration system was developed for pear (Pyrus communis L.), using leaves from in vitro proliferating shoots. Under optimal conditions, bud regeneration frequencies of ‘Comice’, ‘Passe-Crassane’, ‘Williams’ and ‘Conference’ ranged from 60% to 97%, with the mean number of shoots per regenerating leaf ranging from 3.2 to 6.6. Despite the great variability in responses of the different cultivars, in general an initial dark exposure of at least 20 days was required. Ammonium and total nitrogen proved to play an essential role: intermediate NH4 + concentrations were suitable for regeneration. The balance between NH4 + and NO3 - also influenced regeneration; optimal regeneration occured on media with a 1:3 NH4 +/NO3 - ratio. TDZ at 1 μM was less efficient than higher concentrations, whatever the NAA level. Finally, length and growth regulator composition of the two phases (induction and expression) influenced the regeneration rate of ‘Conference’.

Effect of applied and internal hormones on vitrification and apical necrosis of different plants cultured in vitro

Abstract: Development of vitrification and apical necrosis was followed in Camellia sinensis, Gerbera jamesonii, Malus domestica and hybrid Populus tremula x P. alba shoots cultured in vitro on Murashige & Skoog (MS) medium with different concentrations of growth regulators. High humidity in the culture vessels and excess of BA in the medium were found to be the major factors influencing vitrification. Lack of exogenous cytokinin in the medium during successive subcultures induced apical necrosis in poor-rooting species (Malus domestica, Camellia sinensis). The level of internal phytohormones (ABA, IAA, IPA, 2iP, Z, ZR) was determined in the apple shoots by means of ELISA. The content of internal cytokinins in the vitrified apple shoots was several times greater than in normal ones, which supports the hypothesis that excess of cytokinins, inducing rapid divisions of cells in meristems in the atmosphere with high humidity, is responsible for vitrification. Apical necrosis of the plantlets that appeared after cultivation on cytokinin-free medium is the result of deficiency in endogenous hormones in apple shoots and this being confirmed by analysis of endogenous hormones in apple shoots.

Cation and Chloride Partitioning through Xylem and Phloem within the Whole Plant of Ricinus communis L. under Conditions of Salt Stress

Abstract: Uptake and partitioning through the xylem and phloem of K + , Na+, Mg2 + , Ca2+ and CU were studied over a 9 d interval during late vegetative growth of castor bean (Ricinus communis L.) plants exposed to a mean salinity stress of 128 mol m~3 NaCl. Empirically based models of flow and utilization of each ion within the whole plant were constructed using information on ion increments of plant parts, molar ratios of ions to carbon in phloem sap sampled from petioles and stem internodes and previously derived information on carbon flow between plants parts in xylem and phloem in identical plant material. Salient features of the plant budget for K+ were prominent deposition in leaves, high mobility of K+ in phloem, high rates of cycling through leaves and downward translocation of K+ providing the root with a large excess of K+. Corresponding data for Na+ showed marked retention in the root, lateral uptake from xylem by hypocotyl, stem internodes and petioles leading to low intake by young leaf laminae and substantial cycling from older leaves back to the root. The partitioning of the anionic component of NaCl salinity, Cl~, contrasted to that of Na+ in that it was not substantially retained in the root, but deposited more or less uniformly in stem, petiole and leaf lamina tissues. The flow pattern for Mg2 + showed relatively even deposition through the plant but some preferential uptake by young leaves, generally lesser export than import by leaf laminae, and a return flow of Mg2 + from shoot to root considerably less than the recorded increment of the root. Ca2 + partitioning contrasted with that of the other ions in showing extremely poor phloem mobility, leading to progressive preferential accumulation in leaf laminae and negligible cycling of the element through leaves or root. Features of the response of Ricinus to salinity shown in the present study were discussed with data from similar modelling studies on white lupin (Lupinus albus L.) and barley (Hordeum vulgare L.).

Characterization of Na+ exclusion mechanisms of salt‐tolerant reed plants in comparison with salt‐sensitive rice plants

Abstract: Salt-tolerant reed plants (Phragmites communis Trinius) and salt-sensitive rice plants (Oryza sativa L. cv. Kinmaze) were grown in salinized nutrient solutions up to 50 mM NaCl, and growth, Na+ contents and kinetics of 22Na+ uptake and translocation were compared between the species to characterize the salt tolerance mechanisms operating in reed plants. When both plants were grown under the same salinity, Na+ contents of the shoots were lower in reed plants, although those of the roots were quite similar. The shoot base region of both species accumulated Na+ more than the leaf blades did. Sodium-22 uptake and pulse-chase experiments suggested that the lower Na+ transport rate from root to shoot could limit excessive Na+ accumulation in the reed shoot. There was a possibility that the apparently lower 22Na+ transport rate to the shoot of reed plants was due to net downward Na+ transport from shoot base to root.

Sagebrush carbon allocation patterns and grasshopper nutrition: the influence of CO2 enrichment and soil mineral limitation.

Abstract: Artemisia tridentata seedlings were grown under carbon dioxide concentrations of 350 and 650 μl l-1 and two levels of soil nutrition. In the high nutrient treatment, increasing CO2 led to a doubling of shoot mass, whereas nutrient limitation completely constrained the response to elevated CO2. Root biomass was unaffected by any treatment. Plant root/shoot ratios declined under carbon dioxide enrichment but increased under low nutrient availability, thus the ratio was apparently controlled by changes in carbon allocation to shoot mass alone. Growth under CO2 enrichment increased the starch concentrations of leaves grown under both nutrient regimes, while increased CO2 and low nutrient availability acted in concert to reduce leaf nitrogen concentration and water content. Carbon dioxide enrichment and soil nutrient limitation both acted to increase the balance of leaf storage carbohydrate versus nitrogen (C/N). The two treatment effects were significantly interactive in that nutrient limitation slightly reduced the C/N balance among the high-CO2 plants. Leaf volatile terpene concentration increased only in the nutrient limited plants and did not follow the overall increase in leaf C/N ratio. Grasshopper consumption was significantly greater on host leaves grown under CO2 enrichment but was reduced on leaves grown under low nutrient availability. An overall negative relationship of consumption versus leaf volatile concentration suggests that terpenes may have been one of several important leaf characteristics limiting consumption of the low nutrient hosts. Digestibility of host leaves grown under the high CO2 treatment was significantly increased and was related to high leaf starch content. Grasshopper growth efficiency (ECI) was significantly reduced by the nutrient limitation treatment but co-varied with leaf water content.

Low-temperature accumulation of alcohol dehydrogenase-1 mRNA and protein activity in maize and rice seedlings.

Abstract: Low-temperature stress was shown to cause a rapid increase in steady-state levels of alcohol dehydrogenase-1 message (Adh1) and protein activity (ADH1) in maize (Zea mays) (B37N, A188) and rice (Oryza sativa) (Taipei 309, Calmochi 101) seedlings. Maize roots and rice shoots and roots from 7-day seedlings shifted to low temperature (10°C) contained as much as 15-fold more Adh1 mRNA and 8-fold more ADH1 protein activity than the corresponding tissues from untreated seedlings. Time-course studies showed that these tissues accumulated Adh1 mRNA and ADH1 activity severalfold within 4- to 8-hour, levels plateaued within 20 to 24 hours, and remained elevated at 4 days of cold treatment. Within 24 hours of returning cold-stressed seedlings to ambient temperature, Adh1 mRNA and ADH1 activity decreased to pretreatment levels. Histochemical staining of maize and rice tissue imprints showed that ADH activity was enhanced along the lengths of cold-stressed maize primary roots and rice roots, and along the stems and leaves of rice shoots. Our observations suggest that short-term cold stress induces Adh1 gene expression in certain plant tissues, which, reminiscient of the anaerobic response, may reflect a fundamental shift in energy metabolism to ensure tissue survival during the stress period.

Seedling Quality of Southern Pines

Abstract: Seedling quality is related to a seedling’s ability to survive prolonged environmental stresses and produce vigorous growth following outplanting This complex concept includes both a seedling’s “physiological readiness” to grow and suitable morphological features that will allow the seedling to overcome site limitations Seedling ontogeny (genetically coded course of development) and phenology (response to environment) alter seedling physiology (processes), and fluctuations in physiology are, in turn, manifested in seedling morphology (structure) Morphological criteria for assessing seedling quality — shoot height, root-collar diameter, and root and shoot architecture — can be manipulated by nursery cultural practices However, to implement these practices, nursery personnel must understand seedling growth dynamics and allometry (interrelationship of shoot and root growth over time) Physiological criteria for assessing quality include water relations, nutrition, carbohydrates, and dormancy and cold hardiness Water and nutritional status, responsive to environmental changes, also can be influenced by nursery practices and, in turn, affect carbohydrate production and storage and, in part, dormancy and cold hardiness Inappropriate or ill-timed cultural practices can produce seedlings of inferior morphological grade that perform poorly in the field Moreover, careless handling during lifting, packaging, storing, and planting can degrade high-quality seedlings such that field survival and growth suffer To predict quality before planting, nursery managers and foresters can subject seedlings to morphological, physiological, and/or performance tests The better morphological tests are based on diameter, alone or in combination with height Physiological tests include mitotic index, carbohydrate concentration, and cold hardiness, and performance tests include root-growth potential and budbreak with or without stressing Future tests may rely on infrared thermography and spectroradio-metry, chlorophyll a fluorescence, volatile-compound emissions, and biochemical markers

Development of yield loss models in relation to reductions of components of soybean infected with Phakopsora pachyrhizi

Abstract: Epidemics of soybean rust (Phakopsora pachyrhizi) were manipulated by applying protectant fungicides at weekly intervals to different plant growth stages. Effects of disease on plant growth and yield components were monitored at different growth stages. Reduction of shoot weights was different among the cultivars. The number of pods per plant measured at soybean growth stage R6 was reduced as much as 40% in the diseased plants, but the number of seeds per pod was not affected, indicating that disease affected the attainable yield by reducing pod set (...)

Micro- and Cutting Propagation of Silver Maple. I. Results with Adult and Juvenile Propagules

Abstract: Clonal micropropagation studies with silver maple (Acer saccharinum L.) included experiments with var- ious shoot. explant types, cytokinins, and stock plant maturation levels. These trials led to successful explant estab- lishment, axillary shoot proliferation, rooting of microshoots, and establishment of plantlets in the greenhouse. Overall, the best cytokinin tested was the phenylurea derivative TDZ. Shoot proliferation on juvenile explants was poor with kinetin, 2iP, and BA. Only zeatin at 10 µ M was comparable to TDZ. TDZ at 10 nM was optimal for both juvenile and adult nodal explants. Juvenile explants that were held in vitro for 4 months commonly had at least 60 axillary shoots that could be subculture or excised for rooting. Microshoots rooted within 2 weeks. Following rooting, silver maple plantlets could be transplanted into a growing medium and placed directly onto a greenhouse bench. Studies were also conducted on rooting stem cuttings (macropropagation). Single nodes from juvenile plants rooted under intermittent mist, regardless of auxin application; however, shoot-tip cuttings from adult trees rooted best when auxin in ethanol solution was applied. Chemical names used: N- phenyl- N' -1,2,3 -thiadiazol-5-ylurea (thidiazuron, TDZ), N- (2-furanylmethyl)-1H-purin-6-amine (kinetin), isopentenyladenine (2iP), benzyladenine (BA), (E)-2-methyl-4-(1H-purin- 6-ylamino)-2-buten-1-ol (zeatin). Silver maples are valued in the landscape because of their at- tractive foliage with its typical "maple" shape and silvery under- side, the graceful inverted vase shape of the mature trees, rapid growth that provides summer shade in a reasonably short time, and adaptability to a wide variety of soil types. The rapid juvenile growth rate is an attribute where fast shade is required (Dirr, 1977) and is also desirable in species grown under short-rotation culture conditions for the production of energy (Ranney et al., 1986). -Appropriate selection and documentation of performance for woody biomass species that grow well on secondary farmland are important to the energy future of the United States. As fossil fuels become depleted, renewable resources can be used to con- vert the sun's energy into biomass. Silver maple has been se- lected as a model species for research under the Short Rotation Woody Crops (SRWC) program, sponsored by the U.S. Dept. of Energy's Biofuels and Municipal Waste Technology Divi- sion, because of its rapid juvenile growth and other attributes as a potential woody biomass species (Ranney et al., 1986). Research that uses clonal planting stock offers advantages for the study of tree genotypes, as compared to using seedlings from open-pollinated seed orchards. Individual tree seedlings can present problems because the components of genotype and en- vironment are very difficult to separate when one is attempting to interpret the performance of a particular phenotype. Members of clones are genetically identical and, as such, can allow for

Absorption of atmospheric NO2 by spruce (Picea abies L. Karst.) trees

Abstract: summary When spruce (Picea abies L., Karst.) branches were exposed to 5.2–18.7 nl NO2 l−1the flux to the shoots increased linearly with increasing NO2 concentrations. At NO2 concentrations below 2.6 nl l−1uptake of NO2 by the shoots was not observed. The measured flux of NO2 to the shoots was found to be lower than the NO2 flux predicted from the shoot conductance to diffusion of H2O. These results are consistent with the existence of internal resistances for NO2 influx, e.g. production and emission of NO2 by the leaves. However, emission of NO2 was not observed. When the NO2 flux to the shoots was plotted versus transpiration rate, a linear increase was found with an y-axis intercept. The intercept may be interpreted as the NO2 flux to the cuticle and the bark; its value increased with increasing atmospheric NO2 concentrations. The flux of NO2 to the shoots showed diurnal variation with high levels in the light and low levels during darkness. NO2 flux to the branches was dependent on light intensity. This dependency can largely be explained by light dependent changes in shoot conductance. Daytime light intensity determined also the night-time shoot conductance and, hence, the NO2 flux to the branches during the night. The ratio of NO2 flux to transpiration rate was higher in the dark than in the light. Whether this observation can be explained by a light dependency of internal resistances remains to be elucidated. The absorption of NO2 by the shoots enhanced the in vitro NR activity of the needles, while NiR and GS activities were not increased significantly. One day after exposure to NO2 concentrations of 60 nl l−1, nitrate reductase (NR) activity was three times higher than that of untreated controls. However, after three days of NO2 exposure the NR activity declined to the level of untreated controls. Apparently, the increased in vitro NR activity upon NO2 fumigation is a transient phenomenon in spruce needles. The regulatory events that may modulate NR activity of the needles, when exposed to atmospheric NO2, are discussed.

Growth and mineral absorption in maize seedlings as affected by increasing NaCl concentrations

Abstract: The influence of NaCl solutions of decreasing osmotic potentials (¥π = ‐0.44 and ‐0.88 MPa) on seedling growth and on the concentration of the most important macro‐ and micro‐nutrients in the shoots and roots of maize (Zea mays L., cv. Summer II) grown in Hoagland's solution in a growth chamber was studied. Salt stress was imposed on six‐day‐old seedlings for a three day period. Increasing NaCl concentrations induced a reduction in the leaf water potential and a significant decrease in the length and dry weight of the shoots, whereas these two parameters decreased in the roots only at the lowest osmotic potential. Although the absorption and accumulation of nutrients upon salt stress differed in the two treatments depending on the plant tissue and nutrient, almost all of the macronutrients decreased in the roots and shoots, showing the lowest values at ¥π = ‐0.88 MPa. Sodium and Cl increased continuously, much more in the roots than in the shoots. A different response was seen in the shoots and r...

Pathogenicity, distribution, sources of inoculum, and infection courts of Botryosphaeria dothidea on pistachio.

Abstract: A panicle and shoot blight disease caused by Botryosphaeria dothidea is reported for the first time on pistachio in California. The disease was prevalent in northern counties (Butte, Tehama, and Glenn) and sporadic in southern counties (Madera, Fresno, Kings, and Kern). In early spring, symptoms of panicle and shoot blight resulted from continued activity of the pathogen in buds infected the previous summer and fall. Shoot blight symptoms included dark brown to black lesions at the base of current-season shoots, followed by the wilting and drying of leaves, which remained attached to their shoots. Particle and shoot infections caused perennial cankers (...)

Stimulation of shoot regeneration from cotyledons of Helianthus annuus by the ethylene inhibitors, silver and cobalt

Abstract: The effects of CoCl2, AgNO3 and ethylene released by exogenous 2-chloroethylphosphonic acid (Ethephon), were studied on shoot regeneration from cotyledons of Helianthus annuus cv. E8206R, a poorly regenerative cultivar. Inhibition of ethylene biosynthesis by CoCl2, at concentrations of 20 μK, provoked a substantial enhancement of shoot regeneration (30 %): the control was poorly regenerative. However, CoCl2 had no effect when Ethephon was supplied. Inhibition of ethylene action by AgNO3, at concentrations of 10–25 μM, caused a significant increase in plant regeneration: 25 % instead of 1.2 % in the control. Furthermore, addition of Ethephon to AgNO3-treated tissues failed to reduce the stimulation of shoot regeneration caused by AgNO3. On the basis of these findings, it is suggested that ethylene inhibits the regeneration process from cotyledons of sunflower.

Ethylene Evolution from Maize (Zea mays L.) Seedling Roots and Shoots in Response to Mechanical Impedance.

Abstract: The effect of mechanical impedance on ethylene evolution and growth of preemergent maize (Zea mays L.) seedlings was investigated by pressurizing the growth medium in triaxial cells in a controlled environment. Pressure increased the bulk density of the medium and thus the resistance to growth. The elongation of maize primary roots and preemergent shoots was severely hindered by applied pressures as low as 10 kilopascals. Following a steep decline in elongation at low pressures, both shoots and roots responded to additional pressure in a linear manner, but shoots were more severely affected than roots at higher pressures. Radial expansion was promoted in both organs by mechanical impedance. Primary roots typically became thinner during the experimental period when grown unimpeded. In contrast, pressures as low as 25 kilopascals caused a 25% increase in root tip diameter. Shoots showed a slight enhancement of radial expansion; however, in contrast to roots, the shoots increased in diameter even when growing unimpeded. Such morphological changes were not evident until at least 3 hours after initiation of treatment. All levels of applied pressure promoted ethylene evolution as early as 1 hour after application of pressure. After 1 hour, ethylene evolution rates had increased 10, 32, 70, and 255% at 25, 50, 75, and 100 kilopascals respectively, and continued to increase linearly for at least 10 hours. When intact corn seedlings were subjected to a series of hourly cycles of pressure, followed by relaxation, ethylene production rates increased or decreased rapidly, illustrating tight coupling between mechanical impedance and tissue response. Seedlings exposed to 1 microliter of ethylene per liter showed symptoms similar to those shown by plants grown under mechanical impedance. Root diameter increased 5 times as much as the shoot diameter. Pretreatment with 10 micromolar aminoethoxyvinyl glycine plus 1 micromolar silver thiosulfate maintained ethylene production rates of impeded seedlings at basal levels and restored shoot and root extension to 84 and 90% of unimpeded values, respectively. Our results support the hypothesis that ethylene plays a pivotal role in the regulation of plant tissue response to mechanical impedance.

Micropropagation and tissue culture of Eucalyptus—a review

Abstract: Micropropagation has the potential to provide very high multiplication rates of selected tree genotypes, with resulting short-term silvicultural gains. Aseptic cultures have been established from seeds, seedlings, shoots, flowers and lignotubers. Callus cultures have been established from a wide range of tissue sources for at least 30 species of Eucalyptus. Plant regeneration from callus was successful for 12 of these species. Micropropagation through axillary proliferation, or adventitious shoot proliferation on nodal explants, or both, has been successful. An agar-based medium of Murashige and Skoog with a low auxin/cytokinin ratio is most commonly used for shoot multiplication. Vitrification and shoot senescence remain problems. Gibberellic acid was added in some media to stimulate shoot elongation. Various media are used for in vitro root initiation. Suspension and protoplast cultures have been achieved and plants have been regenerated from protoplasts. In vitro techniques are presently being applied to Eucalyptus to achieve genetic transformations.

Role of the Root Apoplasm for Iron Acquisition by Wheat Plants

Abstract: The role of the root apoplasm for iron acquisition was studied in wheat (Triticum aestivum L. cv Ares) grown in nutrient solution under controlled environmental conditions. To obtain different levels of Fe in the root apoplasm, plants were supplied in the dark for 5 hours (preloading period) with various (59)Fe-labeled Fe compounds [Fe(III) hydroxide; microbial siderophores: Fe rhodotorulic acid (FeRDA) and ferrioxamin (FeDesferal(3)), and synthetic Fe chelate (FeEDDHA)], each at a concentration of 5 micromolar. Large pools of apoplasmic Fe were formed after supplying Fe(III) hydroxide or FeRDA, but no such pools were observed after supplying FeDesferal or FeEDDHA. Depending on plant Fe nutritional status (preculture +/- 0.1 millimolar FeEDTA), apoplasmic Fe was used to different extent for translocation to the shoot. Under Fe deficiency, a much greater fraction of the apoplasmic Fe was utilized than in Fe-sufficient plants, as a result of the different rates of phytosiderophore release. Because of the diurnal rhythm in release of phytosiderophores in Fe-deficient plants, the utilization of the apoplasmic Fe for translocation into the shoot started 2 hours after onset of the light period and was dependent on the concentration of Fe in the apoplasm, which followed the order: Fe(III) hydroxide >> FeRDA >> FeDesferal = FeEDDHA. From these results, it can be concluded that in soil-grown plants the apoplasmic Fe pool loaded by various indigenous Fe compounds such as siderophores in the soil solution can be an important Fe source in graminaceous species, particularly during periods of limited Fe supply from the soil.

Regeneration of Gossypium hirsutum and G. barbadense from shoot apex tissues for transformation

Abstract: A method of regenerating cotton plants from the shoot apical meristem of seedlings was developed for use with particle gun and Agrobacterium-mediated transformation. This method was developed to circumvent the problems of genotype restriction and chromosomal damage frequently encountered in cotton regeneration in tissue culture through somatic embryogenesis. In this procedure, the cells of the shoot meristem are targeted for transformation. Normal and fertile plants of Gossypium barbadense Pima S-6, and 19 cultivars of G. hirsutum were regenerated using this method. Shoot regeneration from these tissues was direct and relatively rapid. A MS based, hormone-free medium could be used with all the varieties tested.