Leaf Soluble Protein Content Research Articles

Photosynthetic and physiological responses of native and exotic tidal woody seedlings to simulated tidal immersion

Hibiscus hamabo, a native tidal woody species, and Myrica cerifera, an exotic tidal woody species, have been widely planted on coastal beaches in subtropical China. However, whether there are differences in physiological response and tolerance to immersion between the two tidal species is still unknown. Our objectives were to evaluate differences in the photosynthetic and physiological responses to tidal immersion for the two species in the context of sea level rise. With increasing immersion, net photosynthesis, stomatal conductance, intercellular CO2 concentration, and light saturation point declined progressively for both species, whereas dark respiration and light compensation point showed the reverse trend. Lower variation was observed in H. hamabo than in M. cerifera for each index in the same treatment. Photosynthetic ability and utilization of light, especially under high light intensity, decreased for both species. Leaf soluble sugar and protein contents, and glycolate oxidase activity first increased and then decreased with increasing of immersion degree, with the higher values observed in the W4 (4 h duration, 15 cm depth) and W6 (6 h duration, 25 cm depth) treatments for H. hamabo, and W2 (2 h duration, 5 cm depth) and W4 treatments for M. cerifera. These findings indicate that H. hamabo has a better ability to keep the reduction of photosynthesis at a minimum through soluble substance regulated osmotic potential and avoiding excess light damage to the photosynthetic system through increased photorespiration, heat dissipation, chlorophyll fluorescence. Our results suggest that H. hamabo is more tolerant to tidal immersion than M. cerifera, and therefore it is better adapted to the anticipated sea level rise in future.

Physiological Response of <i>Pleioblastus fortunei</i> to Mercury Stress and Alleviatory Effects of Exogenous Silicon

A pot experiment was conducted to explore the physiological toxicity of mercury (Hg) and alleviatory effects of exogenous silicon (Si) onPleioblastus fortuneiby the determination of leaf membrane permeability, chlorophyll and soluble protein content, SOD and POD activity, root vigor, net photosynthetic rate. The results indicated that 20 mg/kg Hg2+treatment for 100 days caused no obvious physiological effect onPleioblastus fortuneiexcept for root vigor. As the concentration of Hg2+increased from 20 mg/kg to 500 mg/kg, the degree of physiological injury increased, and 500 mg/kg Hg2+exhibited significant physiological toxicity toPleioblastus fortunei. Application of 300 mg/kg Si had no apparent regulatory effect on physiological response ofSasa fortuneiin the presence of 20 mg/kg Hg2+, but significantly alleviated the toxicity of 500 mg/kg Hg2+. Si could prohibite the descent of SOD activity and the increase of POD activity caused by high concentration of Hg2+, thus maintain the metabolism balance of active oxygen.Pleioblastus fortuneican be considered as phytoremediation plant and Si to improve resistance of bamboos cultivated in Hg polluted area.

Response of rice nitrogen physiology to high nighttime temperature during vegetative stage.

The effects of night temperature on plant morphology and nitrogen accumulation were examined in rice (Oryza sativa L.) during vegetative growth. The results showed that the shoot biomass of the plants was greater at 27°C (high nighttime temperature, HNT) than at 22°C (CK). However, the increase in both shoot and root biomasses was not significant under 10 mg N/L. The shoot nitrogen concentrations were 16.1% and 16.7% higher in HNT than in CK under 160 and 40 mg N/L. These results suggest that plant N uptake was enhanced under HNT; however, the positive effect might be limited by the N status of the plants. In addition, leaf area, plant height, root maximum length, root and shoot nitrogen concentrations, soluble leaf protein content, and soluble leaf carbohydrate content were greater in HNT than in CK under 40 and 160 mg N/L, while fresh root volume, root number, and the content of free amino acid in leaf were not significantly different between HNT and CK regardless of nitrogen levels. Moreover, leaf GS activity under HNT was increased at 160 mg N/L compared with that under CK, which might partly explain the positive effect of HNT on soluble protein and carbohydrate content.

Ecophysiological studies of two andean forest contrasting species Abatia parviflora and Myrcianthes leucoxyla under Bogotá conditions, Colombia

The physiological response of high Andean forest contrasting plants, Myrcianthes leucoxyla, a shadow-facultative heliophyte, and Abatia parviflora, a heliophyte, was studied during the transition from dry season to wet season in Bogotá. Light response curves (A-PAR), water potential (Ψw), transpiration rate (E), stomatal conductance (gs), leaf soluble protein content and peroxidase activity were measured in this study in a 48h cycle. The values for E, gs, Ψw and Ψw predawn for M. leucoxyla were 0.07 to 4.89 µg/cm s, 0.02 to 0.5 cm s-1, -0.025 to -1.05 MPa, and-0.1 MPa, respectively. For A. parviflora E, gs, Ψw and Ψw predawn were 0.47 to 12.27 µg/cm s, 0.17 to 1.42 cm s-1, -0.05 to -0.3 MPa and -0.075 MPa, respectively. A. parviflora presented a tendency of stomatal closure at midday and peroxidase activity increased with the increasing solar radiation, this did not occur in M. leucoxyla. The light compensation point (Ic) in A. parviflora was about 18.10 µmol photon m-2s-1, typical for a heliophyte plant; while for M. leucoxyla it was 8.87 µmol photon m-2s-1, slightly above the maximal reported values for shadow plants and under the minimal reported values for light plants. The lowest photosynthetic rate (A) of M. leucoxyla (2.8 µmol CO2 m-2s-1) in comparison with A. parviflora (7.4 µmol CO2 m-2s-1) is compensated with a better photonic use efficiency (± 0.7792 mol C mol-1).

Do initial S reserves and mineral S availability alter leaf S-N mobilization and leaf senescence in oilseed rape?

Winter oilseed rape is sensitive to S limitation, however few studies have clearly assessed the impact of initial S reserves on the remobilization of leaf N-S compounds and senescence dynamics within the leaves in S limited plants. As a consequence, the impacts of high or low initial S reserves on these parameters, further cross-combined with either high or low S availabilities, were examined using a 15N and 34S double-labelling method associated with a study of gene expression of relevant tonoplastic sulphate transporters (BnSultr4;1 and BnSultr4;2) and a molecular indicator of leaf senescence (BnSAG12/BnCab).Plants with high initial S status and S limitation showed an optimal growth comparable to control plants. Moreover, in response to S limitation, leaf soluble protein content, total S, recently assimilated S (i.e., 34S) and the sulphate content in the oldest leaves declined, and the expression of genes encoding tonoplastic sulphate transporters were up-regulated. However, compared to control plants, S limitation delayed leaf senescence. These data suggested that in response to S limitation, plants with high initial S were able to sustain optimized leaf growth by increasing endogenous N and S remobilization independently of the leaf senescence process. In contrast, if these low S plants had no initial S reserves, leaf N-S remobilization was not sufficient to allow optimal growth.As a conclusion, our study supports a model where oilseed rape is able to compensate transiently for S limitation through a fine management of leaf N-S remobilization and a delayed leaf senescence dynamics.

The influence of cold acclimation on antioxidative enzymes and antioxidants in sensitive and tolerant barley cultivars

In order to better understand the role of cold acclimation in alleviating freezing injury, two barley cultivars with different cold tolerance, i.e. a sensitive cv. Chumai 1 and a tolerant cv. Mo 103, were used. The freezing treatment increased leaf soluble protein content more in the tolerant cultivar than in the sensitive one. Cold acclimation increased H2O2 content of the two cultivars during freezing treatment, especially in Mo 103. Glutathione and ascorbate contents during freezing and recovery were significantly higher in cold-acclimated plants than in non-acclimated ones. Activities of peroxidase, ascorbate peroxidase and glutathione reductase were also higher in cold-acclimated plants than non-acclimated plants during freezing treatment. However, there was no significant difference between cold-acclimated plants and the control plants in catalase activity. It may be assumed that cold acclimation induced H2O2 production, which in turn enhanced activities of antioxidative enzymes and synthesis of antioxidants, resulting in alleviation of oxidative stress caused by freezing.

Unintended molecular interactions in transgenic plants expressing clinically useful proteins: The case of bovine aprotinin traveling the potato leaf cell secretory pathway

We assessed the impact of subcellular targeting on the heterologous expression of a clinically useful protease inhibitor, bovine aprotinin, in leaves of potato, Solanum tuberosum. Transgenic potato lines targeting aprotinin to the cytosol, the ER or the apoplast were first generated, and then assessed for their ability to accumulate the recombinant protein. On-chip detection and quantitation of aprotinin variants by SELDI TOF MS showed the inhibitor to be absent in the cytosol, but present under different forms in the ER and the apoplast. No visible phenotypic effects of aprotinin were observed for the transgenic lines, but aprotinin retention in the ER was associated with a significant decrease of leaf soluble protein content. A 2-D gel assessment of control and transgenic lines revealed a possible link between this altered protein content and the down-regulation of proteins implicated in protein synthesis and maturation. These observations, supported by complementary 2-DE analyses with potato lines targeting aprotinin to the apoplast, suggest an aprotinin-mediated feedback in planta negatively altering protein anabolism. From a practical viewpoint, these data illustrate the importance of taking into account not only the characteristics of recombinant proteins expressed in heterologous environments, but also their possible effects on protein accumulation in the host plant factory.

Response to heat stress in warm season and cool season turf grass cultivars

In this study, we investigated differences between cool-season and warm season grasses when exposed to heat stress. The results show that Kentucky blue seed germination rate was the highest at 25oC (40-50%), decreased significantly at 30oC (23-30%) and dropped to 0 at 40oC. For the Bermuda cultivars, seed germination rate was two fold higher at 30oC then 25oC, and reached the highest at 40oC. The cool season perennial rye and Bent grass seeds germinated well between 25 and 30oC. Their germination rate was significantly lower at 40oC. After exposure to 38oC for 2 d, the chlorophyll content decreased significantly for Bermuda cultivars, remained stable for Bent grass and perennial rye, and increased to the greatest extentfor Kentucky blue. Leaf soluble protein contents increased significantly for Kentucky Blue, but remained stable for most of the other cultivars. Western blot with Hsp70 and dehydrin antibodies identified that the Bermuda cultivars had a dynamic changes in the profile of the heat and dehydration stress-related proteins. No similar changes were detected in Kenblue cultivars. High temperature induced dehydrin homolog proteins, but not the Hsp 70 in Perennial rye and Bent grass cultivars. Findings from this research can be used to differentiate cool season and warm season grass cultivars in terms of germination and survival ability under high temperature. Key words: seed germination, chlorophyll content, leaf soluble protein, heat shock protein, dehydrin protein.

Combined effects of water stress and high temperature on photosynthesis, nitrogen metabolism and lipid peroxidation of a perennial grass Leymus chinensis

Drought and high-temperature stresses have been extensively studied; however, little is known about their combined impact on plants. In the present study, we determined the photosynthetic gas exchange, chlorophyll fluorescence, nitrogen level, and lipid peroxidation of the leaves of a perennial grass (Leymus chinensis (Trin.) Tzvel.) subjected to three constant temperatures (23, 29 and 32 degrees C), and five soil-moisture levels (75-80%, 60-65%, 50-55%, 35-40% and 25-30% of field capacity, respectively). High temperature significantly decreased plant biomass, leaf green area, leaf water potential, photosynthetic rate (A), maximal efficiency of PSII photochemistry (F (v)/F (m)), actual PSII efficiency (Phi(PSII)), the activities of nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2), but markedly increased the ratio of leaf area to leaf weight (SLA), endopeptidase (EP; EC 3.4.24.11) activity, and malondialdehyde (MDA) content, especially under severe water stress conditions. The A and F (v)/F (m) were significantly and positively correlated with leaf-soluble protein content, and the activities of NR and GS. However, both photosynthesis parameters were significantly and negatively correlated with EP activity and MDA content (P < 0.05). It is suggested that high temperature, combined with severe soil drought, might reduce the function of PSII, weaken nitrogen anabolism, strengthen protein catabolism, and provoke lipid peroxidation. The results also indicate that severe water stress might exacerbate the adverse effects of high temperature, and their combination might reduce the plant productivity and distribution range of L. chinensis in the future.

Deficit irrigation effects on photosynthesis and the xanthophyll cycle in the tropical tree species Acacia auriculiformis in North Australia

The effect of water stress was examined in a clone of Acacia auriculiformis grown in irrigated and unirrigated sites during the wet and dry seasons in Darwin, northern Australia. During the dry season unirrigated plants had very low leaf water potential and thick leaf cuticles compared with irrigated plants. The plants were photoinhibited under these conditions and they showed greatly reduced Fv/Fm ratio and photosynthetic activity. Chlorophyll and leaf soluble protein contents decreased but carotenoid and xanthophyll, especially zeaxanthin, contents increased greatly compared with irrigated plants. Unirrigated plants showed large diurnal changes in photosynthesis and zeaxanthin and violaxanthin contents. Photosynthetic activity was 3–7‐fold less and zeaxanthin level 20–50‐fold higher than the values determined in the wet season or under irrigated conditions. The high level of xanthophyll cycling observed in the unirrigated or dry season plants was presumably associated with the dissipation of excess light energy and serves to protect the photosynthetic apparatus from photoinhibition.

Solar UV-B radiation on growth, photosynthesis and the xanthophyll cycle in tropical acacias and eucalyptus

The effects of solar ultraviolet-B (UV-B) radiation on the growth, photosynthesis and the xanthophyll cycle of four acacia and two eucalyptus species in Darwin, Australia, were examined. Solar UV-B radiation seemed to delay plant growth in all species examined even though it did not affect photosynthetic activity significantly. Under solar UV-B radiation, a reduced specific leaf area (SLA), and an increased leaf thickness and size of epidermis were observed in plants. Chlorophyll content decreased but leaf soluble protein content increased in plants under solar UV-B radiation. Solar UV-B radiation apparently had a strong effect on chlorophyll degradation rather than the size of the xanthophyll cycle pool. It seemed that xanthophyll formation was more strongly affected by photosynthetic photon flux density (PPFD) than by solar UV-B radiation. The contents of sugar, sugar alcohol and total sugar did vary dramatically between treatments in all the species examined. Overall, the effect of solar UV-B on plant growth and form was much less detrimental than reported for indoor experiments where high UV-B dosage (relative to growth irradiance) was used. Solar UV-B radiation did not cause any photodamage in acacia and eucalyptus plants examined. It had a significant effect on growth and metabolism such as plant height, canopy, leaf thickness and the contents of chlorophyll and soluble protein.

Effect of salinity in certain exzyme activity, physiological traits and yield of rice cultivars

A pot culture experiment was conducted at Agricultural College and Research Institute, Trichy during 1998 to 1999 with three levels of salinity viz. EC &lt; 1, 1-4, &gt; 4 dSm with four rice varieties viz. TRY1 and Co43. (Tolerant) and IR20 and ADT 39 (susceptible) to find out the effect of soil salinity on certain enzymatic activities, physiological attributes and yield. Growth and yield reductions were more at EC 4 dSm' than other treatments. Leaf soluble protein and chlorophyll content at flowering decreased with salinity and the reduction was more in the susceptible varieties than the resistant varieties. Proline content was increased with level of salinity and was higher in tolerant than the susceptible varieties. Amylase and ATPase activities increased toward salainity. Nitrate reductase activity was stimulated more at high salinity level in tolerant varieties than the susceptible varieties.

Cytoplasmic effects on photosynthesis and ribulose-1,5-bisphosphate carboxylase activity in Brassica species

Brassica genotypes representing four different species viz. B. nigra and B. campestris (both primary diploids), B. juncea and B. carinata (both allotetraploids) were examined for photosynthesis rate (Pn), ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, leaf soluble protein and chlorophyll content. B. nigra is the male and female parent of B. juncea and B. carinata, respectively. B. campestris is the maternal parent of B. juncea. Pn was significantly higher in B. nigra and B. carinata compared to the other two species. These two species also sustained Pn of the leaves for a longer period during ontogeny. When B. nigra was the male parent, the higher Pn of B. nigra was not inherited in B. juncea. On the other hand, the Pn and pattern of ontogenetic changes in B. campestris and B. juncea were more or less similar. In specific RuBPC activity on soluble protein basis, chlorophyll and soluble protein content B. carinata also followed B. nigra whereas, B. juncea followed B. campestris. These results indicated the possible maternal(cytoplasmic) influence on the inheritance of these traits.

Impact of fungicides on active oxygen species and antioxidant enzymes in spring barley ( Hordeum vulgare L.) exposed to ozone

Two modern fungicides, a strobilurin, azoxystrobin (AZO), and a triazole, epoxiconazole (EPO), applied as foliar spray on spring barley ( Hordeum vulgare L. cv. Scarlett) 3 days prior to fumigation with injurious doses of ozone (150–250 ppb; 5 days; 7 h/day) induced a 50–60% protection against ozone injury on leaves. Fungicide treatments of barley plants at growth stage (GS) 32 significantly increased the total leaf soluble protein content. Additionally, activities of the antioxidative enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate-peroxidase (APX) and glutathione reductase (GR) were increased by both fungicides at maximal rates of 16, 75, 51 and 144%, respectively. Guiacol-peroxidase (POX) activity was elevated by 50–110% only in AZO treated plants, while this effect was lacking after treatments with EPO. This coincided with elevated levels of hydrogen peroxide (H 2O 2) only in EPO and not in AZO treated plants. The enhancement of the plant antioxidative system by the two fungicides significantly and considerably reduced the level of superoxide (O 2 .−) in leaves. Fumigation of barley plants for 4 days with non-injurious ozone doses (120–150 ppb, 7 h/day) markedly and immediately stimulated O 2 .− accumulation in leaves, while H 2O 2 was increased only after the third day of fumigation. Therefore, O 2 .− itself or as precursor of even more toxic oxyradicals appears to be more indicative for ozone-induced leaf damage than H 2O 2. Ozone also induced significant increases in the activity of antioxidant enzymes (SOD, POX and CAT) after 2 days of fumigation in fungicide untreated plants, while after 4 days of fumigation these enzymes declined to a level lower than in unfumigated plants, due to the oxidative degradation of leaf proteins. This is the first report demonstrating the marked enhancement of plant antioxidative enzymes and the enhanced scavenging of potentially harmful O 2 .− by fungicides as a mechanism of protecting plants against noxious oxidative stress from the environment. The antioxidant effect of modern fungicides widely used in intense cereal production in many countries represents an important factor when evaluating potential air pollution effects in agriculture.

Low Night Temperature-Induced Changes in Photosynthesis and Rubber Accumulation in Guayule (Parthenium Argentatum Gray)

Three-year-old plants of Parthenium argentatum Gray cv. 11591 grown under natural photoperiod were exposed for 60 d to low night temperature (LNT) of 15 °C (daily from 18:00 to 06:00). Effects of the treatment on net photosynthetic rates (PN), rubber accumulation, and associated biochemical traits were examined. LNT initially reduced PN with a parallel decline in the activities of ribulose-1,5-bisphosphate carboxylase, fructose bisphosphatase, and sucrose phosphate synthase for 20-30 d. Later, LNT enhanced PN and the activities of photosynthetic enzymes. Associated with high PN in LNT-treated guayule plants was a two-fold increase in rubber content and rubber transferase activity per unit of protein. The initial decrease in PN in LNT-treated guayule was associated with low content of chlorophyll (a+b), large starch accumulation, and higher ratio of glucose-6-phosphate/fructose-6-phosphate. Photosystem 2 activity in isolated chloroplasts was initially decreased, but increased after 30 d. There was a significant increase in the leaf soluble protein content in LNT-treated plants. Hence the photosynthetic performance of plants grown at 15 °C night temperature for 50 d was superior to those grown under natural photoperiod in all parameters studied. The high photosynthetic capacity may contribute to superior rubber yields under LNT.

Insect clip cages rapidly alter photosynthetic traits of leaves

AbstractIn plant‐insect interaction experiments, a clip cage is frequently used to isolate insects or other small pests on a leaf. Clip cage effects on the physiology of the leaf could possibly confound experimental results. Our objective was to quantitate the effects of an insect clip cage of the type typically used for small pests such as whiteflies (Bemisia sp.), aphids (Aphis sp.) and mites (Urticae sp.) on the photosynthetic traits of cotton (Gossypium hirsutum L. cv. Coker 100A‐glandless) and muskmelon (Cucumis melo L. cv. Imperial 45) leaves. Clip cages that enclosed 11.3 cm2 of both the abaxial and adaxial sides of a leaf were attached to young fully expanded leaves. For the leaf tissue within the clip cage, incident radiation was decreased and leaf temperature was increased. After 24 h, chlorophyll content of tissue within the clip cage was significantly increased compared with non‐caged‐control samples taken from the opposite half of the same leaf. Three days after clip cages were attached to leaves, compared with controls, the tissue within the cage had a lower light‐saturated, steady‐state CO2 exchange rate (CER) and leaf soluble protein content. The cage effect on CER and soluble protein could be explained, at least in part, by decreased light‐saturated initial Rubisco activity for leaf tissue within the clip cage. We conclude that the clip cages caused physiological and biochemical alterations of leaves that could alter insect nutrition. Thus, it is suggested that clip cage effects on leaf physiology and microenvironment must be considered when interpreting results of plant‐insect interaction experiments.

Changes in the isozyme composition of antioxidant enzymes in response to aminotriazole in leaves ofArabidopsis thaliana

The changes in isozyme profiles of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) during severe deactivation of total CAT activity by aminotriazole (AT) treatment were investigated in the leaves ofArabidopsis thaliana (Columbia ecotype) in relation to H2O2-mediated oxidative stress. In spite of striking deactivation of total CAT activity by 0.1 mM AT, there were no significant differences in H2O2 levels or total leaf soluble protein contents including a Rubisco in both the control and AT-treated leaves. On the other hand, one specific protein band (molecular mass, 66 kD) was observed on the SDS-gel from leaf soluble proteins whose staining intensity was strikingly enhanced by AT treatment for 6 h. However, this band disappeared at 12 h. In the native-gel assays of CAT, POD, APX and GR isozymes, AT remarkably inhibited the expression of the CAT1 isozyme with no effects on CAT2 and CAT3, and generally had no effect on POD isozyme profiles. However, AT stimulated the intensity of activities of pre-existing APX1 and GR1 isozymes. In particular, it induced a new synthesis of one GR isozyme. Therefore, these results collectively suggest that a striking deactivation of total CAT activity by AT inA. thaliana leaves largely results from the suppression of CAT1 isozyme, and that APX1, GR1, and a newly synthesized GR isozyme could complement the role of CAT1 to metabolize H2O2 into non-toxic water.

Comparative growth and physiology of selected one-year-old red- and green-fruited European pear cultivars

Red-fruited pear trees are reported to be more difficult to grow, less vigorous and less productive than green-fruited pear trees. This study was undertaken to examine some hypotheses that have been proposed to explain the observed differences in red- vs. green-fruited pear trees. Several growth and gas exchange parameters plus ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, relative total soluble protein, and total chlorophyll were measured on potted, 1-yr-old greenhouse-grown trees of the green-fruited pear cultivars, ‘Bartlett’, ‘d'Anjou’, and ‘Clapp's Favorite’, and their respective red-fruited sports, ‘Red Bartlett’, ‘Red d'Anjou’ and ‘Kalle’. Green-fruited ‘d'Anjou’ trees had double the mean total leaf area of ‘Red d'Anjou’ ( P < 0.05). Specific leaf area of ‘Clapp's Favorite’ was 77% that of ‘Kalle’. The asymptotic maximum net photosynthetic rates ( P max) for red-fruited sports were 69% of those of their green-fruited parents. Stomatal conductance to water vapor of the sports was 78% of that of the parents under light-saturated conditions. Dark respiration of green-fruited ‘d'Anjou’ leaves was 77% of that of ‘Red d'Anjou’ leaves. Intercellular CO 2 concentration was not significantly different between green-fruited parents and red-fruited sports. Although the relative total soluble leaf protein content and total chlorophyll content did not differ significantly between green-fruited parents and red-fruited sports, both characteristics tended to be higher in the parental series, which was consistent with higher net photosynthesis ( P n) in the green-fruited parents than in the red-fruited sports. The ratio of chlorophyll a to chlorophyll b in “Red Bartlett” and ⋚d d'Anjou” was 62% and 54% of that in “Bartlett” and “d'Anjou”, respectively. Rubisco activity in the red-fruited sports was 60% of that in the green-fruited parents. On the basis of these observations, we cannot reject the hypothesis that lower chlorophyll content, particularly chlorophyll a, and lower P n contribute to the reduced vigor in trees of red-fruited sports compared to their green-fruited parents.

Sulfur Availability, Rubisco Content, and Photosynthetic Rate of Soybean

Understanding the role of S in soybean [Glycine max (L.) Merr.] growth is important because a deficiency of the S‐containing amino acids methionine and cysteine limits the nutritional value of soybean protein. As part of a broader study of S uptake and use, our objective was to quantify the effect of S availability on photosynthetic characteristics of soybean. Kenwood soybean was grown in a 3:1 mixture of Ida silt loam [fine‐silty, mixed (calcareous), mesic Typic Udorthent] and acid washed sand with varying amounts of S added as gypsum (CaSO4) in two greenhouse trials. Single‐leaf CO2‐exchange rate (CER), quantum efficiency, dark respiration, leaf S, leaf N, and Rubisco content were determined. There appeared to be a critical level of 35 mg S per kg mixture (about 85 mg S per plant) below which specific leaf S (mg m−2 leaf area) declined linearly with decreases in soil S availability. On average, the most S deficient plants had 70% lower CER, 42% less quantum efficiency, and 50% decline in dark respiration relative to plants receiving adequate S. Total leaf N and Rubisco content were linearly related to leaf S levels, and declined on average 62, and 95%, respectively, as S declined from approximately 120 to 40 mg S m−2 leaf area. There was a linear relation between CER and Rubisco content; however, the amount of nonstructural carbohydrates per unit leaf N increased two‐fold under S deficiency, suggesting that limitations on sink strength were greater than those on source capacity. Carbon dioxide exchange rate was linearly related to leaf S content at all sample dates, with a mean relation of 216 (μmol CO2 g−1 S s−1. The Rubisco fraction declined linearly from nearly 50 to &lt;10% of soluble protein, as leaf soluble protein content declined under S deficiency. We postulate that the decline in the Rubisco fraction may be a function of increased relative importance of housekeeping enzymes for survival as protein levels decline, and/or down‐regulation of Rubisco synthesis in response to a build up of carbohydrates in the source leaves under S deficiency.

743 PB 073 ANATOMICAL AND PHYSIOLOGICAL DIFFERENCES AMONG THREE SPECIES OF Fragaria

Several anatomical and physiological parameters were measured in 32 genotypes of fragaia, including the cultivated strawberry (frapria × ananassa) and its progenitor speck F. chiloensis and F. virginiana Measurements were made using potted. runner-propagated, &amp;month-old greenhouse-grown plants growing under long day (14/10) conditions. Significant differences in CO2 assimilation rates (leaf area and dry weight bases). leaf chlorophyll content, leaf soluble protein content, and leaf anatomy were found between subspecies of F. virginana as well as among species. Recessed stomata and greater water use efficiency were observed in F. virginana ssp glauca as well as in F. chiloensis genotypes. In addition, it appears that leaf anatomy characteristics, as studied using light microscopy, may he useful in corroborating taxonomic decisions based upon gross morphology in Fragaria.