bluuebunny/crossref_metadata_2025 huggingface dataset:
Accumulation of Glycinebetaine in Chloroplasts Provides Osmotic Adjustment During Salt Stress
Authors: Robinson SP , Jones GP
Published: January 2006

Glycinebetaine was determined in leaves and in isolated chloroplasts of spinach (Spinacia oleracea) by nuclear magnetic resonance spectroscopy. Some leakage of glycinebetaine from the chloroplasts occurred during the isolation so the concentration in chloroplasts in vivo could be up to 1.5 times higher than that measured in isolated chloroplasts. It was demonstrated that any contamination of the chloroplast preparations by glycinebetaine originating from other cellular compartments or from broken chloroplasts would have amounted to less than 10% of the measured values.
Leaf osmotic potential of salt-stressed plants was -2.09 MPa compared to -0.91 MPa in non-stressed controls. This was accompanied by a sixfold increase in glycinebetaine content in the leaf but the levels of choline and proline were not increased. In chloroplasts isolated from control leaves the calculated glycinebetaine concentration was 26 mM which was 10-fold higher than the concentration in the leaf as a whole but only contributed 7% of the osmotic potential of the chloroplast. Chloroplasts from salt-stressed plants contained up to 300 mM glycinebetaine which was 20 times the concentration in the leaf as a whole. The glycinebetaine concentration in chloroplasts from salt-stressed leaves was equivalent to an osmotic potential of -0.75 MPa and this contributed 36% of the osmotic potential of the chloroplast and 64% of the decrease in osmotic potential induced by salt stress. At least 30-40% of the total leaf glycinebetaine was localized in the chloroplast. The results demonstrate that glycinebetaine accumulates in chloroplasts to provide osmotic adjustment during salt stress and provide support for the hypothesis that glycinebetaine is a compatible cytoplasmic solute which may be preferentially located in the cytoplasm of cells.
Sensitivity of Photosystems II to NaCl in Relation to Salinity Tolerance. Comparative Studies With Thylakoids of the Salt Tolerant Mangrove, Avicennia marina, and the Salt-Sensitive Pea, Pisum sativum
Authors: Ball MC , Anderson JM
Published: January 2006

The sensitivity of photosystem II to NaCl was compared in thylakoids isolated from the salt-tolerant mangrove, Avicennia marina, and the salt-sensitive pea, Pisum sativum. There were no indications of fundamental differences in photosystem II between these two species. Rates of oxygen evolution declined linearly with increase in NaCl from 10 to 500 mol m-3, with both species being equally sensitive. The NaCl-induced changes in Chl a fluorescence characteristics of intact thylakoids were substantially reversed by addition of hydroxylamine, indicating that the water-oxidizing site of photosystem II is sensitive to the NaCl concentration. These results are consistent with NaCl-induced depletion of the 23 and 17 kDa proteins from photosystem II-enriched membrane sheets. While the inhibition of oxygen-evolving activity by 500 mol m-3 NaCl was substantially reversed in thylakoids kept in the dark, 500 mol m-3 NaCl induced marked photoinhibitory damage in illuminated thylakoids. Thus, accumulation of ions in the chloroplasts of either salt-tolerant or salt-sensitive species would probably result in rapid damage to photosystem II, particularly in the light.
Induction of Sensitivity to Gibberellic Acid in Wheat and Barley Caryopses: Effects of Dehydration, Temperature and the Role of the Embryo during Caryopsis Maturation
Authors: Nicholls PB
Published: January 2006

The development of gibberellic acid sensitivity, which is measured by the level of α-amylase activity, has been investigated by comparing enzyme levels in freshly detached wheat and barley caryopses cultured on moist filter paper for various times and temperatures with those in caryopses dried over 35% (w / w) glycerol-water solutions or in caryopses air-dried in detached ears at controlled temperatures and by comparing enzyme levels in de-embryonated caryopses with intact ones, both being cultured in aqueous buffer solutions. Similar amounts of enzyme were produced in caryopses held moist or dried, although the duration of the lag period, and the rate of accumulation of α-amylase were markedly influenced by the length and temperature of main treatments. Likewise similar amounts of enzyme were produced in de-embryonated and intact caryopses cultured in an aqueous buffer if the latter were de- embryonated prior to incubation in solutions of gibberellic acid. However, when intact or de-brushed (removal of the apical tip) caryopses were incubated with GA3, less α-amylase was found in these incubates than in those incubates containing de-embryonated caryopses. These observations were found in incubates of both sensitized freshly harvested and normal mature caryopses. It is concluded that drying is not essential for the development of gibberellic acid sensitivity in the wheat and barley caryopses.
Induction of Sensitivity to Gibberellic Acid in Developing Wheat Caryopses: Effect of Sugars in the Culture Medium
Authors: Nicholls PB
Published: January 2006

The influence of sugars in culture media on the development of the ability of the aleurone layer to respond to gibberellic acid was investigated by culturing detached wheat ears for 6 days and then measuring the hormone-induced α-amylase activity in incubates of endosperm halves derived from the cultured ears. Some response to gibberellic acid was found after ears had been cultured on water, or on solutions of either sorbitol or mannitol. Addition of mineral nutrients plus glutamine to these culture media reduced the response. Likewise, the addition of sucrose, glucose and/or fructose or galactose reduced the response, and a complete culture medium abolished the response, giving endosperm halves which were similar to those from ears retained on the plant. Supplying mannose to the culture medium yielded endosperm halves as responsive to gibberellic acid as those from fully air-dried caryopses. The separate effects of mannose and sucrose were concentration dependent in the range 1-10 mM. Adding mannose and/or glucose to GA3-containing incubates of endosperm halves did not alter the intensity of α-amylase activity in these incubates. The results were interpreted as an effect of the sugars on the metabolic status of the inflorescence.
Correlation Between Water-Use Efficiency and Carbon Isotope Discrimination in Diverse Peanut (Arachis) Germplasm
Authors: Hubick KT , Farquhar GD , Shorter R
Published: January 2006

Stable carbon isotope discrimination (Δ) showed both intraspecific and interspecific variations in leaves collected from field plants representing a wide range of peanut germplasm grown in similar environments. It was predicted, on the basis of theoretical models relating Δ and water-use efficiency (W), that there could be as much as 60% variation in W. The Δ of leaf material was used as a guide to select peanut genotypes for testing, in the glasshouse, for a correlation between Δ and W. Pot plants of nine peanut genotypes were grown in conditions of unlimited water availability or very restricted water supply. Water-use efficiency and Δ of leaves was measured on all plants. A strong correlation (r = -0.81) was found between Δ and W. Water-use efficiency actually varied as much as twofold. Carbon content and Δ were measured in all parts of some plants. The Δ values of all parts were highly correlated with and therefore well-represented by the Δ of the leaves. Calculation of W on a molar basis removes variation associated with carbon content of dry matter. On this basis, W was correlated with the discrimination against 13C of the whole plant. The link between Δ and W is not direct but the strong correlation between Δ and W suggests that other factors, which are discussed, do not interfere greatly. The data provide more evidence that Δ might be used as a selection technique for W in C3 species.
The Dependence of Quantum Yield on Wavelength and Growth Irradiance
Authors: Evans JR
Published: January 2006

The wavelength dependence of photosynthetic quantum yield was measured in a leaf disc oxygen electrode using narrow-band interference filters. Photorespiration was suppressed by measuring oxygen evolution in air containing ~ 1% CO2. Rates of oxygen evolution were determined as a function of absorbed irradiances between 0 and 100 �mol quanta m-2 s-1 and the slope was taken as the quantum yield. The wavelength-dependence previously observed in many species was confirmed for pea and spinach leaves. The maximum quantum yields obtained here and by others are close to 0.111 mol O2 mol-1 quanta for red light. Given the wavelength dependence of quantum yield and the spectral distribution of light, the quantum yields for various white lights were calculated to be around 85% of the red maximum. The quantum yields in white light were the same for plants grown at different irradiances. It is argued that the wavelength dependence of quantum yield reflects the distribution of quanta between the two photosystems with the quantum yield dropping at wavelengths strongly absorbed by chlorophyll b as this is mainly associated with photosystem II.
Effect of Stem Excision Under Water on Bulk Leaf Water Potential, Leaf Conductance, CO2 Assimilation and Stemwood Water Storage in Eucalyptus behriana F. Muell
Authors: Myers BA , Kuppers M , Neales TF
Published: January 2006

Cutting the stem, under water and above the lignotuber, of intact trees of Eucalyptus behriana caused rapid increases in the bulk leaf water potential (Ψ) in the canopy above. In eight separate experiments the mean increase in Ψ of 3.1 MPa in 1 h was associated with rapid and persistent decreases in leaf conductance (g), which have been ascribed to hydropassive changes in leaf turgor.
The water content of the stemwood increased by 1.8-2.0% as the bulk water potential increased by approximately 2.5 MPa. In the first hour after cutting the stems under water, the observed rate of water uptake by the cut stem was approximately six times the estimated transpiration rate of the leaves. This discrepancy is attributed to an increase in stem water content. The specific capacitance of the stemwood was estimated to be 0.008 g g-1 (dry weight) Mpa-1. The quantity of water available from storage in the stem was estimated to be less than 0.1 mm.
Continuous measurements of gas exchange on a leaf before, during and after stem-cutting showed that CO2 assimilation decreased in parallel with g, but in a manner that caused increases in intercellular CO2 concentration. This indicated that the rapid increases of bulk leaf turgor, induced by stem-cutting, affected photosynthetic capacity.
Organic Cosolutes as Stabilizers of Phosphoenolpyruvate Carboxylase in Storage: an Interpretation of Their Action
Authors: Selinioti E , Nikolopoulos D , Manetas Y
Published: January 2006

Phosphoenolpyruvate carboxylase (EC 4.1.1.3 1) is rapidly inactivated in dilute extracts from leaves of the C4 grass Cynodon dactylon (L.) Pers. Physiological osmotica (glycerol, betaine, proline, sorbitol and sucrose) and synthetic inert polymers like polyvinylpyrrolidone and polyethylene glycol prevent inactivation in a concentration-dependent manner. In a partially purified preparation (10.5 �mol CO2 min-1 mg-1), lability to inactivation and the minimum levels of cosolvents needed for complete protection become higher as the protein is diluted. Exogenous protein (bovine serum albumin) was much less effective than native protein in stabilising activity. The results could be interpreted on the basis of the exclusion volume theory and the assumption that the catalytic activity is mainly due to a polymeric form which is maintained only at high concentrations of the enzymic protein.
Effects of Water Stress and Simulated Grazing on Leaf Elongation and Water Relations of an East African Grass, Eustachys paspaloides
Authors: Toft NL , McNaughton SJ , Georgiadis NJ
Published: January 2006

Eustachys paspaloides was studied under conditions of water stress and simulated grazing (clipping) in the laboratory. Leaf and soil water potentials and leaf elongation rate (LER) were monitored during a 41-day drying period, and following rewatering. Water relations characteristics of tillers were derived from pressure-volume curves during the drought and recovery periods.
Water stress developed more slowly in clipped than in unclipped plants; predawn water potentials declined at mean rates of 0.13 and 0.38 MPa day-1 in clipped and unclipped plants, respectively. Consequently, leaf elongation of clipped plants continued approximately a week longer during the drying period than when plants were not clipped. Following rewatering, LER increased from zero to steady levels over 4 days.
Osmotic adjustment due to solute accumulation occurred in tillers of water-stressed plants. The difference in solute potential at full turgor between well-watered and stressed plants was 0.29 and 0.20 MPa for clipped and unclipped plants, respectively. The delay in permanent wilting afforded by lowered osmotic potential was about 1 day, indicating that osmotic adjustment is not a mechanism for reducing the effect of water stress on growth during long-term drought in Eustachys. However, osmotic adjustment may be an acclimation response to short-term drought during the growing season, and may aid in survival during the long dry season by limiting dehydration of the growing points.
Effect of Differential Sulfur Nutrition on the Specific Activity of ATP Sulfurylase in Mature Grain From Five Wheat Cultivars (Triticum aestivum L.)
Authors: Archer MJ
Published: January 2006

Wholemeal grists of five wheat cultivars (T. aestivum L.) - Gabo, Olympic, Stockade, Insignia and Summit - grown in sand culture supplied with low (10 �M), medium (375 �M) and high (875 �M) concentrations of sulfur, were analysed for their specific activities of ATP sulfurylase (EC 2.7.7.4, ATP:sulfate adenylyltransferase). Under sulfur deficient conditions, residual activities were significantly higher in Gabo, Olympic and Stockade. Olympic maintained significantly higher activities at both the medium and high sulfur concentrations. All cultivars except Summit showed significantly lower activities when the sulfur deficiency was corrected. The results are discussed in relation to grain yield per plant, yield components, grain N, S, P contents and Pelshenke quality data. Grain yield per plant and ATP sulfurylase activity were positively correlated at all sulfur levels.
Short Day Induction of Inflorescence Initiation in Some Winter Wheat Varieties
Authors: Evans LT
Published: January 2006

Experiments in the Canberra phytotron with several European winter wheat varieties, especially cv. Templar, have shown that their need for vernalisation at low temperature can be replaced entirely by growth in short days at 21/16°C for the same period. In fact, although wheat is usually classified as a long day plant, inflorescence initiation at 21/16°C in unvernalised plants was twice as rapid in 8 h photoperiods as in 16 h ones. Short day induction was fastest in photoperiods of less than 12 h and was relatively insensitive to irradiance. Inflorescence development following initiation was faster the longer the photoperiod. At high irradiance, anthesis eventually occurred in 8 h days, but not at lower irradiance. These wheats are therefore short-long day plants, and may appear to be indifferent to daylength if only their time to anthesis is observed. Although short days can replace low temperatures, there are several important differences in their modes of action, and short day induction is better not referred to as short day vernalisation. Vernalisation of developing grains in the ear was more effective in long days.
The Hydrogenase-Nitrogenase Relationship in a Symbiotic Cyanobacterium Isolated From Macrozamia communis L. Johnson
Authors: Daday A , Smith GD
Published: January 2006

The relationship between nitrogenase and hydrogenase activity in the cyanobacterial isolate from the corolloid roots of the cycad Macrozamia communis, grown both photoautotrophically and heterotrophically, has been investigated. The organism actively consumes hydrogen gas in both light and darkness in an oxygen-dependent reaction. The hydrogen consumption was substantially stimulated by light and was nickel-dependent. Nitrogenase activity was found not to be enhanced by hydrogen, either in the dark or light.
Why Did the Apparent Hydraulic Conductance of Plants Oscillate for Passioura and Tanner?
Authors: Sheriff DW
Published: January 2006

When using an apparatus to keep constant the position of the meniscus at the end of a cut petiole of phosphorus-deficient plants, Passioura and Tanner [Aust. J. Plant Physiol.12, 455-61 (1985)] observed oscillations in the applied balancing pressure. They ascribed these to oscillations in the hydraulic con- ductance of the plant. Their results are re-examined using an electric analogue, and it is suggested that oscillations resulted from the combination of hydraulic resistance and capacitance in the plant in conjunction with the apparatus they used. Measurement of the hydraulic resistance and of the period of oscillation makes possible an estimate of the hydraulic capacitance of the plant.
Carbon Dioxide Enrichment Increases Yield of Valencia Orange
Authors: Downton WJS , Grant WJR , Loveys BR
Published: January 2006

The response to elevated CO2 of 3-year-old fruiting Valencia orange scions (Citrus sinensis (L.) Osbeck) on citrange rootstock (C. sinensis × Poncirus trifoliata (L.) Raf.) was studied over a 12-month period under controlled environmental conditions. CO2 enrichment to approx. 800 �bar CO2 which com- menced just prior to anthesis shortened the period of fruitlet abscission. Trees enriched to 800 �bar CO2 retained 70% more fruit, which at harvest were not significantly smaller in diameter or lower in fresh weight than fruit from control trees grown at approx. 400 �bar CO2. Fruit from the CO2 enriched trees also did not differ from the controls in soluble solids content, dry weight, seed number or rind thickness. The progression of fruit coloration was more rapid for the CO2 enriched trees.
Dry weight of leaves and branches from the scion portion of the trees and the roots and stem of the rootstock portion did not differ between treatments at time of harvest. Leaf areas were also similar. However, specific leaf dry weight was 25% greater for the CO2 enriched treatment. Changes in dry matter partitioning resulted from the greater fruit yield (58% increase in dry weight) with CO2 enrichment.
Photosynthetic rates observed at intervals over the experimental period were always lower in the CO2 enriched treatment compared to controls when measured at the same partial pressure of CO2. However photosynthetic rates in the CO2 enriched cabinet were always higher because of the increased level of CO2. The extent of this difference between the treatments varied with fruit development and increased from 23% higher photosynthetic rates in the CO2 enriched chamber at the end of flowering to 77% higher rates when fruits were 5 cm in diameter and decreased to 18% higher rates when fruit coloration was well advanced. Flushes of leaves that developed during the experiment also showed similar photo- synthetic responses to CO2 enrichment and their photosynthetic rates declined as fruit matured.
These results indicate that crop yield by fruit trees will increase as global levels of CO2 continue to rise, at least in those species that experience source limitation during fruit development.
Effects of Sulfur Deficiency on the Synthesis and Accumulation of Proteins in the Developing Wheat Seed
Authors: Castle SL , Randall PJ
Published: January 2006

The effects of sulfur deficiency on the synthesis and accumulation of polypeptides in the developing wheat grain between 6 and 36 days after anthesis were examined by sodium dodecyl sul- fate-polyacrylamide gel electrophoresis. Wheat grain proteins were divided into two groups based on their solubility characteristics: (a) salt-soluble, and (b) salt-insoluble. Sulfur deficiency resulted in changes in the synthesis and accumulation of both groups of polypeptides, but the changes were more pronounced in the salt-insoluble group. In neither case were the changes as dramatic as those reported previously for sulfur deficient legume and barley seeds. In sulfur-deficient wheat plants, storage protein synthesis in developing seeds was detectable earlier than in plants grown with adequate sulfur.
Elicitation of Pisatin in Pea (Pisum sativum L.) By Copper-Asparagine Complexes
Authors: Cruickshank IAM , Dudman WF , Peoples MB , Smith MM
Published: January 2006

The early events in the mode-of-action of CuCl2 solutions in relation to pisatin elicitation were examined. Cu2+ ions were rapidly adsorbed to or taken up by pea endocarp tissue from CuCl2 solutions and large quantities of amino acids and sugars were rapidly released from the plant cells into the external solutions. Asparagine accounted for 56% of the amino-nitrogen while glucose represented 58% of the sugars. The concentration increases of asparagine and glucose relative to the water controls were approximately 140- and 180-fold respectively.
The enhanced pisatin elicitor activity of pea-Cu2+ -leachates (4 h, 20°C) obtained following the topical application of CuCl2 solutions to endocarp tissues was primarily due to the formation in the external solutions of Cu2+ -asparagine complexes. This was demonstrated by their isolation, identification and bioassay, and by the bioassay of synthetic Cu2+ -asparagine complexes. Cu2+ - complexes with other amino acids also present in pod leachates were prepared and their differential pisatin elicitor activity compared to asparagine. Only aspartic acid-complexes exhibited higher elicitor activity (109%) than Cu2+-asparagine. The other amino acids used resulted in pisatin concentrations 64 (homoserine) to 78% (glutamine) of that induced by asparagine.
Photosynthesis and Transpiration of Trees in a Eucalypt Forest Stand: CO2, Light and Humidity Responses
Authors: Wong SC , Dunin FX
Published: January 2006

Exchange of water vapour and CO2 was measured on a small group of trees in a 12-year-old regenerating forest dominated by Eucalyptus spp. in Kioloa State Forest, south-eastern New South Wales. The trees were growing in a weighing lysimeter (10.3 m2 ground area) with the dominant tree about 10 m high. A 12 m high enclosure made of polyethylene film was erected to enclose the trees on the lysimeter. Air was impelled in from the bottom of the enclosure by four fans at a total flow rate of 4.6 m3 s-1. Air samples for infrared gas analysers were taken 1, 4, 7 and 10 m above the ground. Pure CO2 (up to 100 litres min-1) was injected to obtain the response of rates of photosynthesis and transpiration at various levels of CO2 in the enclosure environment.
At normal ambient partial pressure of CO2, the photosynthetic rate of the canopy (28 �mol m-2 ground area s-1) was found to be saturated at about half of full sunlight. At midday, the foliage in the layers 1-4 m, 4-7 m and 7-10 m from the ground level contributed 20.7, 44.3 and 35% of the total carbon assimilated by the canopy, respectively. Canopy conductance was reduced with increasing vapour pressure difference between leaves and the air on the basis that internal partial pressure of CO2 was decreased. Light intensity required to saturate photosynthesis increased with increasing ambient partial pressure of CO2. At 680 �bar ambient partial pressure of CO2 and at saturating light intensity, there was a 50% increase in photosynthetic rate and a 30% reduction in transpiration rate, resulting in a reduction in transpiration ratio of about 80%. The apparent quantum yield derived at 340 and 680 �bar CO2 was 0.049 and 0.071, respectively. The light compensation point also decreased at higher ambient partial pressure of CO2.
The Effect of Soil Strength on the Growth of Young Wheat Plants
Authors: Masle J , Passioura JB
Published: January 2006

Wheat seedlings were grown in soil of various strengths, obtained by changing the bulk density or the water content of the soil. Leaf expansion and transpiration rate were monitored from emergence until the main stem had 5-7 leaves. Leaf area, and shoot and root dry weights, were negatively correlated with soil strength as measured by penetrometer resistance. The growth of roots was less affected than that of shoots. Leaf expansion was reduced before the first leaf was fully expanded. Relative rates of leaf expansion thereafter were consistently lower at high soil strength, although not always significantly. High soil strength also produced substantially smaller stomatal conductances. All effects were the same whether variations of soil strength were brought about by changes in water content or in bulk density.
Three possible causes of reduced shoot growth were examined: (1) a limiting supply of nutrients; or (2) of water, because of a restricted root system; or (3) a reduced carbon supply because of a higher carbon demand from the roots, or because of the low stomatal conductance. We conclude that these are all unlikely explanations for the onset of the effects of soil strength, which were independent of soil phosphorus content, of leaf water potential, and of the amount of carbon reserves in the seed. We suggest that growth of the shoot is primarily reduced in response to some hormonal message induced in the roots when they experience high soil strength.
Effect of Oxygen Supply on Nitrogenase Activity of Nitrate- and Dark-Stressed Soybean (Glycine max (L.) Merr.) Plants
Authors: Carroll BJ , Hansen AP , Mcneil DL , Gresshoff PM
Published: January 2006

Nitrate and dark stress were used to induce decline in nitrogenase activity of root nodules of soybeans (Glycine max (L.) Merr. cv. Bragg). Response to this treatment and to various oxygen concentrations was assessed by short-term acetylene reduction assays. Decreases in oxygen partial pressure reduced nitrogenase activity substantially in unstressed soybean nodules and even further in nodules of nitrate- or dark-stressed plants. Increasing oxygen concentrations from 21 to 60% severely restricted nitrogenase activity in control plants, but stimulated activity in soybeans exposed to 10 mol m-3 nitrate or darkness for 2 days. Less stressed plants (treated with 7.5 mol m-3 nitrate) were stimulated less by high oxygen tension. Soybeans deprived of light for 4 days were symbiotically inactive and did not respond to raised O2 concentrations. Bacteroids isolated from these plants had lost their autonomous activity but recovered in the presence of succinate, indicating substrate deprivation. The data presented suggest that suboptimal oxygen concentration near the bacteroids is an important factor limiting nitrogenase activity in nitrate-or dark-stressed soybeans.
The Molecular Mechanism of Photoinhibition — Facts and Fiction
Authors: Critchley C
Published: January 2006

In this paper, the evidence supporting two different models for the molecular mechanism of photoinhibition is discussed. One hypothesis centres around the suggestion that photoinhibition is due to the loss of the herbicide-binding Dl polypeptide of photosystem II. The other model suggests that damage to a functional group in the reaction centre is the primary cause of photoinhibition. In order to put the apparent controversy into context, recent developments in our understanding of the structure and function of the photosystem II reaction centre are described. Interpretation and judgement of all available evidence suggest primary photoinhibitory damage to be incurred by the reaction-centre chlorophyll P680 destabilising the apoprotein(s) and eventually resulting in their proteolytic degradation and removal from the photosystem II complex and the thylakoid membrane.
Adaptation to Sun and Shade: a Whole-Plant Perspective
Authors: Givnish TJ
Published: January 2006

Whole-plant energy capture depends not only on the photosynthetic response of individual leaves, but also on their integration into an effective canopy, and on the costs of producing and maintaining their photosynthetic capacity. This paper explores adaptation to irradiance level in this context, focusing on traits whose significance would be elusive if considered in terms of their impact at the leaf level alone. I review traditional approaches used to demonstrate or suggest adaptation to irradiance level, and outline three energetic tradeoffs likely to shape such adaptation, involving the economics of gas exchange, support, and biotic interactions. Recent models using these tradeoffs to account for trends in leaf nitrogen content, stornatal conductance, phyllotaxis, and defensive allocations in sun v. shade are evaluated.
A re-evaluation of the classic study of acclimation of the photosynthetic light response in Atriplex, crucial to interpreting adaptation to irradiance in many traits, shows that it does not completely support the central dogma of adaptation to sun v. shade unless the results are analysed in terms of whole-plant energy capture. Calculations for Liriodendron show that the traditional light compensation point has little meaning for net carbon gain, and that the effective compensation point is profoundly influenced by the costs of night leaf respiration, leaf construction, and the construction of associated support and root tissue. The costs of support tissue are especially important, raising the effective compensation point by 140 �mol m-2 s-1 in trees 1 m tall, and by nearly 1350 �mol m-2 s-1 in trees 30 m tall. Effective compensation points give maximum tree heights as a function of irradiance, and shade tolerance as a function of tree height; calculations of maximum permissible height in Liriodendron correspond roughly with the height of the tallest known individual. Finally, new models for the evolution of canopy width/height ratio in response to irradiance and coverage within a tree stratum, and for the evolution of mottled leaves as a defensive measure in understory herbs, are outlined.
Acclimation by the Thylakoid Membranes to Growth Irradiance and the Partitioning of Nitrogen Between Soluble and Thylakoid Proteins
Authors: Evans JR
Published: January 2006

Three characteristics of shade plants are reviewed. Firstly, they have relatively more chlorophyll b and the associated light-harvesting chlorophyll a/b-protein complex (LHC). Two currently accepted reasons for this are not supported by quantitative analysis. Instead, the reduced protein cost of complexing chlorophyll in LHC and the turnover of the 32 kDa herbicide binding protein are considered.
Secondly, shade plants have low electron transport capacities per unit of chlorophyll. This is primarily related to a reduction in the amount of electron transport components such as the cytochrome f complex and the ATPase. The nitrogen cost of the thylakoid membranes per unit of light absorbed is thereby reduced, but the irradiance range over which light is used with high efficiency is also reduced.
Thirdly, shade plants have less RuP2 carboxylase and other soluble proteins for a given amount of chlorophyll. However, while the ratio of RuP2 carboxylase protein to thylakoid protein declined, the ratio of the RuP2 carboxylase activity to electron transport activity increased. For several species, the relationship between the rate of CO2 assimilation and leaf nitrogen content depends on the irradiance during growth.
Photosynthetic Acclimation and Photoinhibition of Terrestrial and Epiphytic CAM Tissues Growing in Full Sunlight and Deep Shade
Authors: Adams III WW
Published: January 2006

Light response curves of O2 exchange and fluorescence from photosystem II at 77K were examined in several species possessing crassulacean acid metabolism (CAM) growing under natural conditions of varying irradiance. All of the species exhibited considerable acclimation to low irradiance, but the epiphytes Dendrobium speciosum and Pyrrosia confluens were unable to acclimate fully to full sunlight. Although Opuntia stricta possessed a reduced quantum yield under full sunlight conditions, its photosynthetic capacity, unlike that of D. speciosum and P. confluens, was very high, and was probably due, at least in part, to the higher level of CAM activity present in this species. Shade tissues of O. stricta, however, were quite susceptible to photoinhibition by high light, as indicated by reductions in 77K fluorescence.
Fronds of P. confluens growing in full sunlight were clearly photoinhibitedr However, the light environment in the epiphytic habitat is rarely static, and considerable recovery from photoinhibition in a sun population of P. confluens fronds was observed near the summer solstice when the canopy shielded this population from direct sunlight for most of the day. Such seasonal and diurnal changes in irradiance may be important to the survival of epiphytic species with a limited capacity for CAM activity.
Effects of Photoinhibition Induced by Water Stress on Growth and Yield of Grain Sorghum
Authors: Ludlow MM , Powles SB
Published: January 2006

The significance of photoinhibition induced by water stress for growth and grain yield of sorghum was investigated by shading water-stressed plants for a 7-day period during panicle development. Thereafter, shading was removed, stressed plants were rewatered, and all plants were kept well-watered until physiological maturity.
Shading water-stressed plants for a 7-day period increased grain number and grain yield of primary heads by 10- and 13-fold, respectively. Even though plants were severely stressed, photoinhibition was only 20%. Moreover, reduction of photoinhibition by shading did not improve carbon supply to the developing panicle. Therefore, the response of grain yield to shading was attributed to a 15% higher average leaf water potential in shaded plants, which arose despite attempts to keep water status similar in shaded and unshaded plants.
The effect of water stress on the primary head was so severe that many plants produced secondary heads. The grain yield from these secondary heads compensated for the low yield of primary heads so that the total dry matter production and total grain yield of water-stressed plants were similar to those of unstressed plants. In view of the ability of this relatively determinate species to compensate for potential yield losses, as well as the mechanisms to avoid water stress, high temperatures and excessive absorption of light, it seems unlikely that photoinhibition induced by water stress will be of agronomic significance in grain sorghum.
Effect of Temperature on Photoinhibition and Recovery in Actinidia deliciosa
Authors: Greer DH
Published: January 2006

Photoinhibition of photosynthesis was induced in intact leaves of kiwifruit (Actinidia deliciosa) grown in natural light not exceeding a photon irradiance (PI) of 300 �mol m-2 s-1 by exposing them to a PI of 1500 �mol m-2 s-1. The temperature was held constant during the high-light exposure between 5 and 35°C. Recovery was followed at temperatures between 10 and 35°C, after photoinhibition was induced by a 240 min exposure to high light. The kinetics of photoinhibition and recovery were followed by chlorophyll fluorescence at 692 nm and 77K.
Photoinhibition occurred at all temperatures but was greatest at low temperatures. Temperature affected the severity of photoinhibitory damage but not the kinetics of photoinhibition. Recovery was also temperature-dependent with little or no recovery occurring below about 20°C and rapid recovery at 30-35°C. The extent of photoinhibition also affected the rates of recovery which were reduced as the severity of photoinhibition increased.
An analysis of the rate constants for energy transfer within photosystem II indicated that kiwifruit leaves have some capacity to prevent photoinhibition by increasing the amount of non-radiative energy dissipation. However, the analysis also indicates that this protection mechanism was not wholly effective since the primary photochemical reactions apparently become inactivated during exposure of these leaves to high light.
Quantitative Assessment of the Degree to Which Ribulosebisphosphate Carboxylase/Oxygenase Determines the Steady-State Rate of Photosynthesis During Sun-Shade Acclimation in Helianthus annuus L
Authors: Woodrow IE , Mott KA
Published: January 2006

The degree to which ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) determines or limits the steady state rate of CO2 assimilation during sun-shade acclimation in sunflower (Helianthus annuus) was examined and expressed as a 'flux control coefficient'. The coefficients were calculated according to the procedure developed by Woodrow et al. (1987) [In: Proc. Congress on Rubisco, (Ed. R. G. Jensen.) (Tucson: U.S.A.)] an outline of which is presented in this paper. The analysis shows that the Rubisco control coefficient, and therefore the degree of flux control exerted by this enzyme, increases with increasing light intensity until, at saturating light, Rubisco is the principal determinant of the photosynthetic rate. There was however a marked difference in the range of light intensities over which changes in flux control occurred between the plants at various stages of acclimation.
Photosynthetic Characterisation of Rice Varieties in Relation to Growth Irradiance
Authors: Tu ZP , Lin XZ , Huang QM , Cai WJ , Feng HY , Ye LY
Published: January 2006

The growth irradiances in the primary habitats of newly popularised Chinese rice 'Gui-Chao 2' and modern U.S. rice varieties 'Bellemont' and 'Lemont' are quite different, with only 2-8 h sunshine per day in Guangzhou, China, and 8-12 h sunshine per day in Texas, U.S.A. The U.S. varieties Bellemont and Lemont adapted to higher photon irradiance, showing increase of photosynthesis and increase of leaf thickness under high photon irradiance (1000 �mol photons m-2 s-1). Bright light reduced leaf chlorophyll content less in Bellemont than in Gui-Chao 2. The Chinese variety Gui-Chao 2 seemed adapted to low photon irradiance, showed delayed leaf senescence and retained higher photosynthetic rate after 20 days shading treatment. Thus, the yield reduction under shading of Gui-Chao 2 was less than that of Bellemont. After treatment for 9 days at 1000 �mol photons m-2 s-1, the quantum yield and light- and CO2-saturated photosynthesis of Gui-Chao 2 was lower than that of Lemont, suggesting possible photoinhibition in Gui-Chao 2 under high irradiance. It was proposed that these varieties represent two light-intensity ecotypes of rice. The possible application of this research to rice breeding and agricultural cultivation is discussed.
On the Role of Photosynthetic Responses in Constraining the Habitat Distribution of Rainforest Plants
Authors: Field CB
Published: January 2006

Two rainforest species that differ in the range of light environments encountered by an individual provide a model system for illustrating implications of diurnal variation and spatial heterogeneity of the light environment within single canopies. The two species are similar in the acclimation of leaf-level photosynthetic characteristics to the leaf's past light environment, but are distinguished by the limited ability of the high-light species to decrease dark respiration in response to growth under shade. Over 24 h, total carbon gain from a leaf increases with increasing light, but may increase or decrease with increasing nitrogen. Intermediate nitrogen levels and photosynthetic capacities yield maximum daily carbon gain in only a narrow range of light environments. The ratio of daily photosynthesis to leaf nitrogen is a complex function of nitrogen, photosynthetic characteristics, and light availability in a microsite. Nitrogen levels in real leaves may be close to the optima, but leaf nitrogen levels are clumped relative to the optima. Daily carbon gain from a canopy of fixed total nitrogen tends to increase as the leaf area of the canopy decreases, a trend caused by two factors. First, photosynthetic capacity is a nearly linear function of leaf nitrogen up to the highest nitrogen levels observed in nature. Second, only leaves with nitrogen levels above a substantial threshold are competent to generate positive rates of net photosynthesis. Differences between the species in canopy architecture and leaf duration have counteracting effects on long-term nitrogen-use efficiency.
Intercellular Invertase in Developing Peach Mesocarp
Authors: Ugalde TD , Chalmers DJ , Jerie PH
Published: January 2006

Acid invertase (β-fructofuranosidase, EC 3.2.1.26) was extracted from peach mesocarp (Prunus persica (L.) Batsch) using a range of extraction conditions. The enzyme always was attached to insoluble particles in the crude homogenate and was bound by a mechanism that could not have arisen during extraction. The activity in the insoluble fraction made up (essentially) all of the total activity extracted from the tissue and was the same as the activity shown by whole tissue slices placed directly into the assay solution. These results demonstrate that most of the acid invertase in developing peach mesocarp is located outside the cell. The amount of this enzyme, as measured in vitro, did not change during development at times when the rate of dry matter increase was changing rapidly. Either the action of intercellular invertase is not associated with the control of dry matter accumulation in peach mesocarp, or control is effected through activity of the enzyme in vivo, not its synthesis or degradation.
Growth and Photosynthetic Responses to Manganese and Copper Deficiencies in Wheat (Triticum aestivum) and Barley Grass (Hordeum glaucum and H. leporinum)
Authors: Kriedemann PE , Anderson JE
Published: January 2006

Wheat and barley grass were raised as seedlings in aerated solution cultures under high-pressure sodium vapour lamps in a growth cabinet. Manganese and copper were provided over a wide span of concentrations to induce a range in deficiency symptom expression. Plant response was documented in terms of biomass gain, in vivo chlorophyll fluorescence, CO2-saturated O2 evolution by leaf slices, single leaf H2O/CO2 exchange and A(pI) curves (assimilation as a function of intercellular CO2 partial pressure) at saturating light.
Photosynthetic dysfunction due to trace element deficiency lowered O2 evolution (both area and chlorophyll basis) and slowed down leaf gas exchange. Both initial slope and CO2-saturated phases of A(pi) curves were similarly affected in the two species under either Cu or Mn deficiency.
Induction kinetics of in vivo chlorophyll fluorescence proved distinctive for both species. Mn deficiency was often manifest as increased constant-yield (Fo) in combination with much reduced variable fluorescence (Fv). Increased ratio of Fo/ Fv was confirmed as a useful index for early diagnosis of Mn deficiency regardless of leaf Cu status.
Barley grass (both H. glaucum Steud. and H. leporinum Link) was more tolerant of low Mn and Cu status than wheat, especially in terms of growth and photosynthetic response to Mn deficiency. Wheat plants made little growth once Mn supply was reduced to 10% of control level whereas barley grass was only moderately constrained.
The Response of Six Eucalyptus Species and Casuarina obesa to the Combined Effect of Salinity and Waterlogging
Authors: van der Moezel PG , Watson LE , Pearce-Pinto GVN , Bell DT
Published: January 2006

Seedlings of Eucalyptus camaldulensis, E. comitae-vallis, E. kondininensis, E. lesouefii, E. platycorys, E. spathulata and Casuarina obesa were grown in a glasshouse under non-saline drained, saline drained, non-saline waterlogged, and saline waterlogged conditions for 3 months. Measurements were taken of seedling height, seedling survival and the concentration of Na, K, Ca, Mg and Cl in plant tissues. Production of specialised roots containing aerenchyma in E. camaldulensis and C. obesa enabled these species to tolerate non-saline waterlogged conditions. Saline, but freely drained conditions reduced seedling growth for all species but only E. kondininensis recorded seedling deaths. C. obesa was the species most tolerant of saline waterlogged conditions with no seedling deaths and a lower reduction in growth compared to the Eucalyptus species. Exclusion of Na and Cl, together with the production of specialised roots by C. obesa are suggested as the probable factors relating to the high seedling tolerance in saline waterlogging. The species with highest tolerance to non-saline waterlogging were more tolerant of saline waterlogged conditions. The importance of this result for evaluating trees to be used in the rehabilitation of secondary salinised land in Australia is discussed.
Vegetative Activity of the Main Stem Terminal Bud Under Photoperiod and Flower Removal Treatments in Soybean
Authors: Caffaro SV , Nakayama F
Published: January 2006

Effects of photoperiod and flower removal on vegetative activity of the main stem apical bud were examined for an indeterminate ('Williams') and a determinate ('Bragg') soybean cultivar.
Plants grew under long day conditions until the V2 stage. Then, they were subjected to three photoperiodic treatments: (1) short days of 9 h of solar radiation during all the experiment (SD); (2) 10 short days followed by long days until the end of the experiment (SD + LD); and (3) long days during all the experiment (LD). From the moment anthesis was reached, half of the plants of each photoperiodic treatment were periodically deflowered.
Flower removal induced an additional but limited vegetative growth of the main stem apex, due to the elongation of the youngest internodes. This effect was only seen under SD because long day applications (SD+LD and LD) induced a high flower abortion. On the contrary, long days stimulated internode elongation, leaf expansion and, under LD, delayed anthesis which resulted in enhanced vegetative activity of apical buds and a greater production of nodes and branches. Thus, a close but inverse relation was observed between flower induction and vegetative structure differentiation by apical buds. As in Bragg, Williams may stop vegetative activity of buds by their simple transition to a terminal raceme hence, only posterior differentiated internode elongation will be either limited or stimulated depending on SD or LD conditions, respectively.
The involvement of Microbial Epiphytes in Uptake Measurements with the Giant-celled Alga Chara australis
Authors: Wilson MR , Hush JM , Walker NA
Published: January 2006

The giant-celled algae Chara and Nitella have been used extensively in studies of the transport of ions and other solutes. Before this report, uptake measurements were made without a detailed consideration of the effects of microbial epiphytes living on the external surface of the algal cell wall. Examination of the cell walls of Chara and Nitella with the scanning electron microscope revealed the presence of an often dense microflora consisting of diatoms, many types of bacteria, and even fungi. The contribution of this microflora to uptake measurements made with radiotracers was estimated by using isolated Chara cell wall cylinders internally filled with a silicone compound. For the Chara tested by us, the microflora was shown to make a substantial contribution to the uptake of urea, uric acid and glycine measured for untreated internodes. It was shown that, by briefly soaking Chara internodes in an artificial pond water, pH 8.5, containing 3 mM EGTA and then wiping their surfaces with a Kimwipe (a lint-free paper tissue), the microbial epiphytes can be quickly and simply removed. This treatment could be very useful in radiotracer studies of giant-celled algae in which the activity of the surface microflora complicates measurements of solute uptake.