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PubMed1999

Inhibition of photosynthesis and bleaching of zooxanthellae by the coral pathogen Vibrio shiloi.

Vibrio shiloi is the causative agent of bleaching (loss of endosymbiotic zooxanthellae) of the coral Oculina patagonica in the Mediterranean Sea. To obtain information on the mechanism of bleaching, we examined the effect of secreted material (AK1-S) produced by V. shiloi on zooxanthellae isolated from corals. AK1-S caused a rapid inhibition of photosynthesis of the algae, as measured with a Mini-PAM fluorometer. The inhibition of photosynthesis was caused by (i) ammonia produced during the growth of V. shiloi on protein-containing media and (ii) a non-dialysable heat-resistant factor. This latter material did not inhibit photosynthesis of the algae by itself but, when added to different concentrations of NH4Cl, enhanced the inhibition approximately two- to threefold. Ammonia and the enhancer were effective to different degrees on zooxanthellae isolated from four species of coral examined. In addition to the rapid inhibition of photosynthesis, AK1-S caused bleaching (loss of pigmentation) and lysis of zooxanthellae. Bleaching was more rapid than lysis, reaching a peak (25% bleached algae) after 6 h. The factors in AK1-S responsible for bleaching and lysis were different from those responsible for the inhibition of photosynthesis, because they were heat sensitive, non-dialysable and active in the dark. Thus, the coral pathogen V. shiloi produces an array of extracellular materials that can inhibit photosynthesis, bleach and lyse zooxanthellae.

Ammonium Chloride↗
PubMed2000

Photosynthesis, plant growth and N allocation in transgenic rice plants with decreased Rubisco under CO2 enrichment.

Ribulose-1,5-bisphosphate carboxylase (Rubisco) efficiency for CO2-saturated photosynthesis was examined in leaves of rice (Oryza sativa L.). The amount of Rubisco in a leaf was calculated to be 30-55% in excess for the light-saturated rate of photosynthesis at 100 Pa CO2. Long-term exposure to CO2 enrichment decreased the amount of Rubisco protein. However, N was not reallocated from decreased Rubisco to other components limiting photosynthesis, and the decrease in Rubisco was simply due to a decrease in total leaf-N content by CO2 enrichment. Thus, rice plants did not optimize N allocation into Rubisco at elevated CO2. Transgenic rice plants with decreased Rubisco were obtained by transformation with the rbcS antisense gene. The transformant with 65% wild-type Rubisco was selected as a plant with optimal Rubisco content for CO2-saturated photosynthesis at the level of a single leaf. This selected transgenic plant had 20% lower rates of photosynthesis at normal CO2 (36 Pa), but 5-15% higher rates of photosynthesis at elevated CO2 (100 Pa) for a given leaf N content. However, such transgenic plants did not necessarily show greater production of biomass even under conditions of CO2 enrichment. Although they had a higher N-use efficiency for plant growth under such conditions during the middle stage of growth, the growth rate was lower during the early stage of growth. Thus, improvement of N-use efficiency by a single leaf did not necessarily lead to greater production of biomass by the whole plant.

Carbon Dioxide↗
PubMed2005

Effects of elevated CO2 on the capacity for photosynthesis of a single leaf and a whole plant, and on growth in a radish.

The atmospheric concentration of CO2 will probably rise to about 700 micromol mol(-1) by the end of this century. The effects of elevated growth CO2 on photosynthesis are still not fully understood. Effects of elevated growth CO2 on the capacity for photosynthesis of a single leaf and a whole plant were investigated with the radish cultivar White Cherish. The plants were grown under ambient ( approximately 400 micromol mol(-1)) or elevated CO2 ( approximately 750 micromol mol(-1)). The rates of net photosynthesis per leaf area with a whole plant and a single leaf of plants of various ages (15-26 d after planting) were measured under ambient and elevated CO2. The rates of photosynthesis were increased by 20-28% by elevated CO2. There was no effect of elevated growth CO2 on the rate of photosynthesis, clearly indicating no downward acclimation of photosynthesis to elevated CO2. Elevated CO2 increased dry weight accumulation by >27%. The effect of elevated CO2 on other growth characteristics will also be shown.

Carbon Dioxide↗
PubMed2003

Midday depression of net photosynthesis in the tropical rainforest tree Eperua grandiflora: contributions of stomatal and internal conductances, respiration and Rubisco functioning.

High midday temperatures can depress net photosynthesis. We investigated possible mechanisms underlying this phenomenon in leaves of Eperua grandiflora (Aubl.) Benth. saplings. This tropical tree establishes in small gaps in the rainforest canopy where direct sunlight can raise midday temperatures markedly. We simulated this microclimate in a growth chamber by varying air temperature between 28 and 38 degrees C at constant vapor pressure. A decrease in stomatal conductance in response to an increase in leaf-to-air vapor pressure difference (deltaW) caused by an increase in leaf temperature (Tleaf) was the principal reason for the decrease in net photosynthesis between 28 and 33 degrees C. Net photosynthesis decreased further between 33 and 38 degrees C. Direct effects on mesophyll functioning and indirect effects through deltaW were of similar magnitude in this temperature range. Mitochondrial respiration during photosynthesis was insensitive to Tleaf over the investigated temperature range; it thus did not contribute to midday depression of net photosynthesis. Internal conductance for CO2 diffusion in the leaf, estimated by combined gas exchange and chlorophyll fluorescence measurements, decreased slightly with increasing Tleaf. However, the decrease in photosynthetic rate with increasing Tleaf was larger and thus the difference in CO2 partial pressure between the substomatal cavity and chloroplast was smaller, leading to the conclusion that this factor was not causally involved in midday depression. Carboxylation capacity inferred from the CO2 response of photosynthesis increased between 28 and 33 degrees C, but remained unchanged between 33 and 38 degrees C. Increased oxygenation of ribulose-1,5-bisphosphate relative to its carboxylation and the concomitant increase in photorespiration with increasing Tleaf were thus not compensated by an increase in carboxylation capacity over the higher temperature range. This was the principal reason for the negative effect of high midday temperatures on mesophyll functioning.

Carbon Dioxide↗
PubMed2004

Characteristics of photosynthesis and stomatal conductance in the shrubland species manuka (Leptospermum scoparium) and kanuka (Kunzea ericoides) for the estimation of annual canopy carbon uptake.

Responses of photosynthesis to carbon dioxide (CO2) partial pressure and irradiance were measured on leaves of 39-year-old trees of manuka (Leptospermum scoparium J. R. Forst. & G. Forst.) and kanuka (Kunzea ericoides var. ericoides (A. Rich.) J. Thompson) at a field site, and on leaves of young trees grown at three nitrogen supply rates in a nursery, to determine values for parameters in a model to estimate annual net carbon uptake. These secondary successional species belong to the same family and commonly co-occur. Mean (+/- standard error) values of the maximum rate of carboxylation (hemi-surface area basis) (Vcmax) and the maximum rate of electron transport (Jmax) at the field site were 47.3 +/- 1.9 micromol m(-2) s(-1) and 94.2 +/- 3.7 micromol m(-2) s(-1), respectively, with no significant differences between species. Both Vcmax and Jmax were positively related to leaf nitrogen concentration on a unit leaf area basis, and the slopes of these relationships did not differ significantly between species or between the trees in the field and young trees grown in the nursery. Mean values of Jmax/Vcmax measured at 20 degrees C were significantly lower (P < 0.01) for trees in the field (2.00 +/- 0.05) than for young trees in the nursery with similar leaf nitrogen concentrations (2.32 +/- 0.08). Stomatal conductance decreased sharply with increasing air saturation deficit, but the sensitivity of the response did not differ between species. These data were used to derive parameters for a coupled photosynthesis-stomatal conductance model to scale estimates of photosynthesis from leaves to the canopy, incorporating leaf respiration at night, site energy and water balances, to estimate net canopy carbon uptake. Over the course of a year, 76% of incident irradiance (400-700 nm) was absorbed by the canopy, annual net photosynthesis per unit ground area was 164.5 mol m(-2) (equivalent to 1.97 kg C m(-2)) and respiration loss from leaves at night was 37.5 mol m(-2) (equivalent to 0.45 kg m(-2)), or 23% of net carbon uptake. When modeled annual net carbon uptake for the trees was combined with annual respiration from the soil surface, estimated net primary productivity for the ecosystem (0.30 kg C m(-2)) was reasonably close to the annual estimate obtained from independent mensurational and biomass measurements made at the site (0.22 +/- 0.03 kg C m(-2)). The mean annual value for light-use efficiency calculated from the ratio of net carbon uptake (net photosynthesis minus respiration of leaves at night) and absorbed irradiance was 13.0 mmol C mol(-1) (equivalent to 0.72 kg C GJ(-1)). This is low compared with values reported for other temperate forests, but is consistent with limitations to photosynthesis in the canopy attributable mainly to low nitrogen availability and associated low leaf area index.

Carbon↗
PubMed2006

Wintertime photosynthesis and water uptake in a boreal forest.

Warm air in combination with frozen soil is a major cause of wintertime drought damage in evergreen plants in subalpine and boreal environments. We analyzed diurnal tree stem diameter variation (SDV), which reflects soil water uptake, canopy-level water vapor flux (Fw), stand photosynthesis (Ps), photosynthetically active radiation (PAR), soil and air temperatures (Ts and T air, respectively) and soil liquid water content (theta) to determine under what conditions photosynthesis is possible in wintertime and how crucial water uptake from soil is for photosynthesis. Measurements were made under field conditions in a Scots pine forest in southern Finland during winter 2002-2003. We found four wintertime periods when there was measurable Ps and SDV, the latter always starting 2-7 days after photosynthesis and both usually ending on the same day. Stand photosynthesis began when T air reached 3-4 degrees C and ended when T air dropped below -7 degrees C. The trees appeared to rely on stored stem water first and started taking up water from the soil a few days later, when the transpirational demand became strong enough. The more difficult it was to access soil water because of low Ts or low theta, the longer the trees used water stored in their stems. Even partial stem freezing did not prevent photosynthesis or soil water uptake.

Carbon Dioxide↗
PubMed2005

Base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics.

The nutritional benefits that mycorrhizal associations provide to plants may be constrained by acidic soil conditions resulting in decreased photosynthetic function. Sugar maple (Acer saccharum) and red maple (Acer rubrum) seedlings were grown on a native acidic (pH 4.1) soil both unamended and amended with base cations (pH 6.2). In a second study a fungicide treatment was included. Foliar nutrition, mycorrhizal colonization, photosynthesis and their relationships were assessed. On the native soil, red maple maintained higher levels of mycorrhizal colonization and photosynthesis than sugar maple but showed little response to base cation amendments. Mycorrhizal colonization and photosynthesis of sugar maple increased significantly in response to base cation amendments. Correlations were observed among mycorrhizal colonization, foliar nutrition and photosynthesis. The fungicide treatment indicated that 50% of the base cation-induced increase in sugar maple photosynthesis was mycorrhiza related. The results suggest that base cation stimulation of mycorrhization and photosynthesis of sugar maple on acid soils are coupled by foliar nutrient dynamics. Red maple exhibits much less sensitivity to these same edaphic conditions.

Acer↗
PubMed2004

An evaluation of the effects of exogenous ethephon, an ethylene releasing compound, on photosynthesis of mustard (Brassica juncea) cultivars that differ in photosynthetic capacity.

BACKGROUND: The stimulatory effect of CO2 on ethylene evolution in plants is known, but the extent to which ethylene controls photosynthesis is not clear. Studies on the effects of ethylene on CO2 metabolism have shown conflicting results. Increase or inhibition of photosynthesis by ethylene has been reported. To understand the physiological processes responsible for ethylene-mediated changes in photosynthesis, stomatal and mesophyll effects on photosynthesis and ethylene biosynthesis in response to ethephon treatment in mustard (Brassica juncea) cultivars differing in photosynthetic capacity were studied. RESULTS: The effects of ethephon on photosynthetic rate (PN), stomatal conductance (gS), carbonic anhydrase (CA) activity, 1-aminocyclopropane carboxylic acid synthase (ACS) activity and ethylene evolution were similar in both the cultivars. Increasing ethephon concentration up to 1.5 mM increased PN, gS and CA maximally, whereas 3.0 mM ethephon proved inhibitory. ACS activity and ethylene evolution increased with increasing concentrations of ethephon. The corresponding changes in gs and CA activity suggest that the changes in photosynthesis in response to ethephon were triggered by altered stomatal and mesophyll processes. Stomatal conductance changed in parallel with changes in mesophyll photosynthetic properties. In both the cultivars ACS activity and ethylene increased up to 3.0 mM ethephon, but 1.5 mM ethephon caused maximum effects on photosynthetic parameters. CONCLUSION: These results suggest that ethephon affects foliar gas exchange responses. The changes in photosynthesis in response to ethephon were due to stomatal and mesophyll effects. The changes in gS were a response maintaining stable intercellular CO2 concentration (Ci) under the given treatment in both the cultivars. Also, the high photosynthetic capacity cultivar, Varuna responded less to ethephon than the low photosynthetic capacity cultivar, RH30. The photosynthetic capacity of RH30 increased with the increase in ethylene evolution due to 1.5 mM ethephon application.

Carbon Dioxide↗
PubMed2000

[Reorganization of the chloroplast thylakoid system during decay of acquired thermotolerance of photosynthesis and aging of wheat leaves].

A 3 hours heating at 39 degrees C of 14-day old wheat plants increases the termotolerance of photosynthesis, and also the length and number of thylakoids in chloroplast in mature leaves. The acquired termotolerance disappears within 10 days. Simultaneously the intensity of photosynthesis and the length of thylakoids decrease. Reduction of photosynthesis ability and of thylakoid membranes occurs in the first leaves of non-hardened plants during 14-29 days after sowing. The intensity of photosynthesis in plants of both variants positively correlates with the length of grana membranes and with the total length of membranes of all thylakoids. Besides, a positive correlation was detected between the intensity of photosynthesis and the share of small (2-7 thylakoids) grana and the length of their membranes in non-hardened plants. The level of thermotolerance of photosynthesis in leaves in heat hardened plants correlates positively with the length of grana membranes and with the total length of all thylakoid membranes and the share of small grana.

Adaptation, Physiological↗
PubMed2004

Modulation of osmotic stress effects on photosynthesis and respiration by temperature in mesophyll protoplast of pea.

Exposure of mesophyll protoplast of pea to osmotic stress decreases the rate of photosynthesis while stimulating marginally the respiratory rate of mesophyll protoplasts. The interaction of osmotic and temperature stress during the modulation of photosynthetic and respiratory rates of pea (Pisum sativum var Azad P1) mesophyll protoplasts was investigated. The protoplasts were exposed to either iso-osmotic (0.4 M) or hyper-osmotic (1.0 M) concentration of sorbitol at 15 degrees and 25 degrees C. The rates of photosynthesis and respiration were studied. At optimum temperature of 25 degrees C, there was a decrease in photosynthesis (< 10%) at hyper-osmoticum (osmotic effect), whereas respiration increased marginally (by about 15%). Low temperature (15 degrees C) aggravated the sensitivity of both respiration and photosynthesis to osmotic stress. At 15 degrees C, the decrease in photosynthesis due to osmotic stress was > 35%, while the respiratory rate was stimulated by 30%. The relative proportion of cytochrome pathway decreased by about 50% at both 15 degrees C and 25 degrees C while that of alternative pathway increased, more so, at 15 degrees C, when the mesophyll protoplasts were subjected to hyper-osmoticum stress. The titration experiments showed that extent of engagement of alternative pathway was higher, the slope value was slightly higher for 15 degrees C compared to 25 degrees C. Low temperature modulates the effect of hyper-osmoticum stress on photosynthesis and respiration, and results in increased participation of alternative pathway.

Cell Respiration↗
PubMed2001

Effects of Photosynthesis on Bacterial Phosphatase Production in Biofilms.

The fraction of bacteria displaying phosphatase activity within natural photosynthetic biofilms was examined in relation to phosphorus limitation and algal photosynthesis. An artificial substrate that forms a fluorescent precipitate was used in conjunction with the nucleic acid stain DAPI to enumerate extracellular phosphatase expression by biofilm bacteria exposed to different photosynthetic activities and phosphorus supplies. The proportion of bacteria displaying phosphatase activity changed in response to the presence or absence of algal photosynthesis. In general, phosphate-deprived biofilms had positive linear trends in bacterial phosphatase activity (p <0.001), with greater proportions of bacteria displaying phosphatase under photosynthetic inhibition compared to active photosynthesis. Under sufficient phosphate supplies, biofilms had negative linear trends (p <0.05) or were lower in the proportion of bacteria displaying phosphatase activity in the presence of algal photosynthesis, whereas bacterial phosphatase activity was generally maintained when photosynthesis was inhibited. it is suggested that the amount of extracellular organic carbon released within the biofilm matrix during photosynthesis indirectly affected bacterial phosphatase synthesis.

Journal Article↗
PubMed2000

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale.

The relative stimulation of photosynthesis by elevated carbon dioxide in C(3) species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C(3) species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 degrees C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 - 25 degrees C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 degrees C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide.

Journal Article↗
PubMed2001

Growth temperature can alter the temperature dependent stimulation of photosynthesis by elevated carbon dioxide in Albutilon theophrasti.

Stimulation of photosynthesis in response to elevated carbon dioxide concentration [CO2] in the short-term (min) should be highly temperature dependent at high photon flux. However, it is unclear if long-term (days, weeks) adaptation to a given growth temperature alters the temperature-dependent stimulation of photosynthesis to [CO2]. In velveltleaf (Albutilon theophrasti), the response of photosynthesis, determined as CO2 assimilation, was measured over a range of internal CO2 concentrations at 7 short-term measurement (12, 16, 20, 24, 28, 32, 36 degrees C) temperatures for each of 4 long-term growth (16, 20, 28 and 32 degrees C) temperatures. In vivo estimates of VCmax, the maximum RuBP saturated rate of carboxylation, and Jmax, the light-saturated rate of potential electron transport, were determined from gas exchange measurements for each temperature combination. Overall, previous exposure to a given growth temperature adjusted the optimal temperatures of Jmax and VCmax with subsequently greater enhancement of photosynthesis at elevated [CO2] (i.e., a greater enhancement of photosynthesis at elevated [CO2] was observed at low measurement temperatures for A. theophrasti grown at low growth temperatures compared with higher growth temperatures, and vice versa for plants grown and measured at high temperatures). Previous biochemical based models used to predict the interaction between rising [CO2] and temperature on photosynthesis have generally assumed no growth temperature effect on carboxylation kinetics or no limitation by Jmax. In the current study, these models over predicted the temperature dependence of the photosynthetic response to elevated [CO2] at temperatures above 24 degrees C. If these models are modified to include long-term adjustments of Jmax and VCmax to growth temperature, then greater agreement between observed and predicted values was obtained.

Journal Article↗
PubMed1977

Quantum yields for oxygenic and anoxygenic photosynthesis in the cyanobacterium Oscillatoria limnetica.

A comparison of the quantum yield spectra of the oxygenic (H(2)O as the electron donor) with the anoxygenic (H(2)S as the electron donor) photosynthesis of the cyanobacterium, Oscillatoria limnetica reveals that anoxygenic photosynthesis is driven by photosystem I only. The highest quantum yields of the latter (maximum; 0.059 CO(2) molecules/quantum of absorbed light) were obtained with wavelengths which preferentially excite photosystem I (<550, >650) in which chlorophyll a and carotenoids are the major pigments. The addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea had no effect on anoxygenic photosynthesis, and no enhancement in quantum efficiency was observed by a superimposition of light preferentially exciting photosystem II.Oxygenic photosynthesis efficiently utilizes only a narrow range of the absorption spectrum (550-650 nm) where light is provided in excess to photosystem II via phycocyanin. The quantum yield (0.033 CO(2) molecules/quantum of absorbed light) is lower than the theoretical yield by a factor of 3, possibly due to inefficient light transfer from photosystem II to I. Thus, 3-fold enhancement of oxygenic photosynthesis by superimposition of photosystem I light, and low quantum yields for anoxygenic photosynthesis, were obtained in this region. These results are consonant with the suggestion that such a cyanobacterium represents an intermediate stage in phototrophic evolution.

Journal Article↗
PubMed2000

DNA sequence analysis of the photosynthesis region of Rhodobacter sphaeroides 2.4.1.

This paper describes the DNA sequence of the photosynthesis region of Rhodobacter sphaeroides 2.4.1 (T). The photosynthesis gene cluster is located within a approximately 73 kb Ase I genomic DNA fragment containing the puf, puhA, cycA and puc operons. A total of 65 open reading frames (ORFs) have been identified, of which 61 showed significant similarity to genes/proteins of other organisms while only four did not reveal any significant sequence similarity to any gene/protein sequences in the database. The data were compared with the corresponding genes/ORFs from a different strain of R.sphaeroides and Rhodobacter capsulatus, a close relative of R. sphaeroides. A detailed analysis of the gene organization in the photosynthesis region revealed a similar gene order in both species with some notable differences located to the pucBAC = cycA region. In addition, photosynthesis gene regulatory protein (PpsR, FNR, IHF) binding motifs in upstream sequences of a number of photosynthesis genes have been identified and shown to differ between these two species. The difference in gene organization relative to pucBAC and cycA suggests that this region originated independently of the photosynthesis gene cluster of R.sphaeroides.

Base Sequence↗
PubMed1992

Photosynthesis and water relations of the floodplain tree, boxelder (Acer negundo L.).

During summer, gas exchange and water relations were measured in mature boxelder (Acer negundo L.) trees growing on a floodplain in central Indiana, USA. A shallow (< 1.25-m deep) water table and repeated flooding kept the soil water potential above -0.5 MPa at all times. Net photosynthesis and stomatal conductance were influenced primarily by light and, to a lesser extent, by leaf temperature, but showed no relationships with leaf-to-air water vapor gradient or leaf water potential. Throughout the summer, there was no midday stomatal closure on any measurement day, and leaf water potential at dawn and minimum daily leaf water potential remained above -0.4 and -1.4 MPa, respectively. Nevertheless, there was a seasonal decline in leaf osmotic potentials at saturation and turgor-loss point. Seasonal changes in maximum daily net photosynthesis and stomatal conductance, minimum daily leaf water potential and soil-to-leaf hydraulic conductance were not related to seasonal changes in soil water potential, air or soil temperature, or water table depth. Seasonal responses of net photosynthesis to intercellular CO(2) indicated that net photosynthesis was controlled primarily by nonstomatal factors. High soil water and a shallow water table may have kept soil-to-leaf hydraulic conductance large (5-9 mmol m(-1) s(-1) MPa(-1)) throughout the summer, permitting the trees to keep their stomata open, yet maintain leaf turgor and high net photosynthesis during the hot, low-humidity afternoons. This could also account for the dominance of nonstomatal influences on net photosynthesis.

Journal Article↗
PubMed1993

Leaf area and net photosynthesis during development of Prunus serotina seedlings.

We used the plastochron index to study the relationship between plant age, leaf age and development, and net photosynthesis of black cherry (Prunus serotina Ehrh.) seedlings. Leaf area and net photosynthesis were measured on all leaves >/= 75 mm of plants ranging in age from 7 to 20 plastochrons. Effects of plant developmental stage on leaf area and net photosynthesis were evaluated for leaves of differing age (horizontal series), leaves on plants of constant age (vertical series), and leaves of constant age (oblique series). Regression techniques were used to estimate leaf area from leaf blade dimensions. The best equations for predicting leaf area had R(2) values of 0.991-0.992 and used linear or logarithmic functions of both leaf length and width. Suitable, but less precise, equations with R(2) values of 0.946-0.962 were developed from either leaf length or leaf width. Leaf area development in black cherry seedlings was similar to that in other indeterminate species. Leaves of young plants reached full expansion at a lower leaf plastochron age than leaves of older plants. Maximum net photosynthesis per unit leaf area occurred 2-3 plastochrons before full leaf expansion. There was strong ontogenetic drift in net photosynthesis with leaf age; net photosynthesis decreased as plant age increased in leaves of the same plastochron age. Plots of the oblique series were particularly useful in providing information about interaction effects.

Journal Article↗
PubMed1992

Spatial Distribution of Photosynthesis during Drought in Field-Grown and Acclimated and Nonacclimated Growth Chamber-Grown Cotton.

Inhomogeneous photosynthetic activity has been reported to occur in drought-stressed leaves. In addition, it has been suggested that these water stress-induced nonuniformities in photosynthesis are caused by "patchy" stomatal closure and that the phenomenon may have created the illusion of a nonstomatal component to the inhibition of photosynthesis. Because these earlier studies were performed with nonacclimated growth chamber-grown plants, we sought to determine whether such "patches" existed in drought-treated, field-grown plants or in chamber-grown plants that had been acclimated to low leaf water potentials (psi(leaf)). Cotton (Gossypium hirsutum L.) was grown in the field and subjected to drought by withholding irrigation and rain from 24 d after planting. The distribution of photosynthesis, which may reflect the stomatal aperture distribution in a heterobaric species such as cotton, was assayed by autoradiography after briefly exposing attached leaves of field-grown plants to (14)CO(2). A homogeneous distribution of radioactive photosynthate was evident even at the lowest psi(leaf) of -1.34 MPa. "Patchiness" could, however, be induced by uprooting the plant and allowing the shoot to air dry for 6 to 8 min. In parallel studies, growth chamber-grown plants were acclimated to drought by withholding irrigation for three 5-d drought cycles interspersed with irrigation. This drought acclimation lowered the psi(leaf) value at which control rates of photosynthesis could be sustained by approximately 0.7 MPa and was accompanied by a similar decline in the psi(leaf) at which patchiness first appeared. Photosynthetic inhomogeneities in chamber-grown plants that were visible during moderate water stress and ambient levels of CO(2) could be largely removed with elevated CO(2) levels (3000 muL L(-1)), suggesting that they were stomatal in nature. However, advanced dehydration (less than approximately 2.0 MPa) resulted in "patches" that could not be so removed and were probably caused by nonstomatal factors. The demonstration that patches do not exist in drought-treated, field-grown cotton and that the presence of patches in chamber-grown plants can be altered by treatments that cause an acclimation of photosynthesis leads us to conclude that spatial heterogeneities in photosynthesis probably do not occur frequently under natural drought conditions.

Journal Article↗