Effects of phosphate deficiency on assimilate partitioning in barley seedlings

Photosynthesis and assimilate partitioning were measured in barley (Hordeum vulgare L.) seedlings raised from seed with mineral nutrient solution containing either 0 or 1 mmolar orthophosphate (P_i). Carbon assimilation rates and leaf extension rates were inhibited about 40% by low P_i treatment. Starch and sucrose levels were similar in P_i-depleted compared to control leaves during most of the photoperiod. These results indicated that low P_i treatment inhibited carbon export from the primary leaf. Acid extractable P_i decreased about 60% in P_i-depleted barley leaves after a dark to light transition. In similar experiments with control barley and tobacco (Nicotiana tabacum L.) leaves acid extractable P_i decreased about 25% and 15%, respectively. These findings provided preliminary evidence for a diurnal variation in leaf P_i content. Photosynthetic intermediate levels were lower and extractable enzyme activities were the same or higher in low P_i compared to control leaves. These observations suggested that photosynthetic intermediate pools turnover more quickly in low P_i than in P_i-sufficient leaves.     

Genotypic and within canopy variation in leaf carbon isotope discrimination and its relation to short-term leaf gas exchange characteristics in cassava grown under rain-fed conditions in the tropics

In a field rain-fed trial with 15 cassava cultivars, leaf gas exchanges and carbon isotope discrimination (Δ) of the same leaves were determined to evaluate genotypic and within-canopy variations in these parameters. From 3 to 7 months after planting leaf gas exchange was measured on attached leaves from upper, middle, and lower canopy layers. All gas exchange parameters varied significantly among cultivars as well as canopy layers. Net photosynthetic rate (P _N) decreased from top canopy to bottom indicating both shade and leaf age effects. The same trend, but in reverse, was found with respect to Δ, with the highest values in low canopy level and the lowest in upper canopy. There were very significant correlations, with moderate and low values, among almost all these parameters, with P _N negatively associated with intercellular CO₂ concentration (C _i), ratio of C _i to ambient CO₂ concentration C _i/C _a, and Δ. Across all measured leaves, Δ correlated negatively with leaf water use efficiency (WUE = photosynthesis/stomatal conductance, g _s) and with g _s, but positively with C _i and C _i/C _a. The later parameters negatively correlated with leaf WUE. Across cultivars, both P _N and correlated positively with storage root yield. These results are in agreement with trends predicted by the carbon isotope discrimination model.     

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: I. At High Soil Water Potential

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), stomatal resistance (r_s), leaf water potential (ψ), osmotic potential (π), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. var. Pa 602A), sorghum (Sorghum bicolor [L.] Moench var. RS610), and tobacco (Nicotiana tabacum L. var. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were high. In all three crops the r_s, measured with a ventilated diffusion porometer, the ψ, measured with the pressure chamber, the π, measured with a vapor pressure osmometer, and the calculated P, decreased from sunrise to reach minimum values near midday and then increased again in the afternoon. The diurnal range of all the variables was greater for leaves in the upper canopy than for those in the lower canopy. P was observed to decrease with decreasing ψ, but never became zero. Sorghum had a higher P at a ψ of, say −10 bars, than did maize, and maize had a higher P than tobacco at the same ψ. Moreover, at the same ψ the upper leaves in all canopies had a higher P than the lower leaves. When compared at high irradiances, r_s did not increase as ψ declined to −13, −15, and −10 bars or as P declined to 0.3, 3.5, and 1.2 bars in maize, sorghum, and tobacco, respectively. The relation between r_s and I in the upper, nonsenescent leaves of all three crops fits a hyperbolic curve, but the response varied with species and leaf senescence. The adaxial and abaxial epidermises had the same response of r_s to I in maize and sorghum, whereas in tobacco the adaxial epidermis had a higher r_s than the abaxial epidermis at all values of I. At equal values of I, tobacco had the lowest leaf resistance (r_l) and maize had the highest r_l. Senescent maize leaves had nonfunctional stomata, whereas the lowermost sorghum leaves had higher stomatal resistances on average than the other leaves.     

Gas Exchange Characteristics of the Flue-Cured Tobacco (Nicotiana Tabacum L.) Cultivars Grown under Two Production Systems

The net photosynthetic rate (P _N), intercellular CO₂ concentration (C _i), stomatal conductance (g _s), transpiration rate (E), water use efficiency (WUE), and leaf biomass production of four American flue-cured tobacco (Nicotiana tabacum L.) cultivars K 326, K 358, and Speight G 28 were compared with three local Indian cultivars 16/103, Special FCV, and PCT-7, during 1994 and 1995 crop seasons under irrigated and rainfed production systems (Northern light soils, NLS, and Karnataka light soils, KLS) in India. By comparison, the American tobacco cv. K 326 showed the highest P _N and g _s. A positive correlation was found between P _N and biomass production in all the varieties tested (r = 0.55 in NLS and 0.73 in KLS). The American cultivars were superior than the local cultivars in their biomass production and P _N under Indian farming conditions.     

A study on the relationship between leaf conductance,CO2 concentration and carboxylation rate in various species

Leaf conductance g_L is strongly influenced by environmental factors like CO₂, irradiance and air humidity. According to Ball et al. (1987), g_L is correlated with an index calculated as the product of net CO₂ exchange rate A and ambient water vapour concentration W_a, divided by ambient CO₂ concentration c_a. However, this empirical model does not apply to high values of g_L observed at c_a below CO₂ compensation concentration . Therefore, we applied modified indices in which A is replaced by estimates for the rate of carboxylation. Such estimates, P₁ and P₂, were determined by adding to A the quotient of and the sum of gas phase resistance r_g and intracellular resistance for CO₂ exchange r_i, P₁ = A+/(r_g + r_i), or the quotient of and r_i, P₂ = A + /r_i. If P₂ is chosen, c_a in the Ball index has to be replaced by the intercellular CO₂ concentration c_i. By using the modified indices P₁·W_a/c_a and P₂·W_a/c_i, we analysed data from the C₃ species Nicotiana tabacum and Nicotiana plumbaginifolia, the C₃–C₄ intermediate species Diplotaxis tenuifolia, and the C₄ species Zea mays. The data were collected at widely varying levels of irradiance and CO₂ concentration. For all species uniform relationships between g_L and the new indices were found for the whole range of CO₂ concentrations below and above . Correlations between g_L and P₁·W_a/c_a were closer than those between g_L and P₂·W_a/c_i because P₁/c_a implicitly contains g_L. Highly significant correlations were also obtained for the relationships between g_L and the ratios P₁/c_a and P₂/c_i.     

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: II. At Low Soil Water Potential

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), leaf resistance (r₁), leaf water potential (ψ), osmotic potential (π), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. cv. Pa602A), sorghum (Sorghum bicolor [L.] Moench cv. RS 610), and tobacco (Nicotiana tabacum L. cv. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were low. The r₁, measured with a ventilated diffusion porometer, of the leaves in the upper canopy decreased temporarily after sunrise [~0530 hours Eastern Standard Time] as I increased, but then r₁ increased again between 0700 and 0830 hr Eastern Standard Time as the ψ, measured with a pressure chamber, decreased rapidly from the values of −7, −4 and −6 bars at sunrise to minimal values of −18, −22 and −15 bars near midday in the maize, sorghum, and tobacco, respectively. The π, measured with a vapor pressure osmometer, also decreased after sunrise, but not to the same degree as the decrease in ψ, so that a P of zero was reached in some leaves between 0730 and 0800 hours. The lower (more negative) π of leaves in the upper canopy than those in the lower canopy gave the upper leaves a higher P at a given ψ than the lower leaves in all three species; leaves at intermediate heights had an intermediate P. This difference between leaves at the three heights in the canopy was maintained at all values of ψ. The r₁ remained unchanged over a wide range of P and then increased markedly at a P of 2 bars in maize, −1 bar in sorghum, and near zero P in tobacco: r₁ also remained constant until ψ decreased to −17, −20, and −13 bars in leaves at intermediate heights in maize, sorghum, and tobacco, respectively. In all three species r₁ of leaves in the upper canopy increased at more negative values of ψ than those at the base of the canopy, and in tobacco, leaves in the upper canopy wilted at more negative values of ψ than those in the lower canopy.     

Effect of surplus glucose on physiological and biochemical characteristics of sugar beet leaves in relation to the age of the leaf and the whole plant

Effect of surplus glucose on physiological and biochemical parameters of leaves of different age was investigated in sugar beet (Beta vulgaris L., subsp. saccharifera) plants in the stages of vegetative growth (SVG). Early and late SVG were differentiated by the ratio between the weights of roots and aboveground organs (0.10 and 0.35, respectively). The excess of Glu was produced by incubation of the disks excised from detached leaves in water or 0.1 M Glu at radiant flux density of 250 μmol/(m² s) with the light regime pattern described as night/day/night/light (8/16/8/3 h). In all the leaf disks incubated in water and glucose solution, the content of Glu and other soluble carbohydrates considerably increased as compared with their content in the leaves they were taken from. After disk incubation in water and glucose solution, the content of chlorophyll (a + b) rose as compared with its level in respective leaves in early SVG; in late SVG, it declined. In early SVG, the rate of the O₂ photosynthetic evolution (Ph) in the ageing leaves under saturating concentration of NaHCO₃ after incubation in water and Glu solution declined more considerably than in young leaves. In late SVG, incubation of leaf disks in water and Glu solution weakly affected P _n. The rate of O₂ dark consumption in the leaf disks of all the types of treatment increased after incubation in water and especially in Glu solution. Activity of soluble carbonic anhydrase (sCA) in the extracts from young leaves in early SVG after their incubation in water and Glu solution was essentially the same, but after the incubation of ageing leaves in Glu solution, it reliably decreased. In late SVG, sCA activity sharply decreased after incubation in water and Glu solution irrespective of the leaf age. In late SVG, activity of Rubisco in the young leaves did not change after their incubation in water but decreased after incubation of the leaves of the three ages in Glu solution. In early SVG, nonphotochemical fluorescence quenching (NPQ) in the young intact leaf was lower than in the ageing leaf, and after leaf incubation in water and Glu solution, it rose. In late SVG, the value of NPQ was greater than in early SVG and, in contrast to the leaves of early SVG, it declined after leaf incubation; in water, this decline was more pronounced than in the Glu solution. In early SVG, efficient quantum yield of photosystem II (PSII) was much greater than in late SVG and it declined in the leaves incubated with Glu. It was concluded that surplus Glu can maintain biosynthetic processes in the young leaves of young sugar beet plants (trophic function). A decline in the level of chlorophyll and the activities of sCA and Rubisco in the course of leaf development and senescence is considered as a symptom of the suppression of biosynthesis of proteins of chlorophyll-protein complexes and the enzymes (Rubisco and sCA).     

Changes of epicuticular wax induced by enhanced UV-B radiation impact on gas exchange in Brassica napus

The epicuticular wax covering on plant surface plays important roles in protecting plants against UV radiation. However, the role of epicuticular wax in affecting leaf gas exchange under enhanced ultraviolet-B (UV-B) radiation remains obscure. In the present study, different aged leaves of Brassica napus were used to analyze the responses of crystal structure and chemical constituents of epicuticular wax to UV-B radiation and the effects of such responses on gas exchange indices. Enhanced UV-B radiation significantly decreased the amount of esters in all leaves except the first leaf, amount of secondary alcohols in the second, third and fourth leaves, and amount of primary alcohols in the second and third leaves, while increased the amounts of ketones and aldehydes in the first leaf. Enhanced UV-B level had no significant effect on the amounts of alkanes and total wax in all leaves. Exposure to UV-B radiation resulted in wax fusion on adaxial leaf and stomata opening on abaxial leaf. Fusions of plates and rods on adaxial leaf surface covered most of the stomata, thereby influencing the photosynthesis in the upper mesophyll of leaves. Enhanced UV-B level significantly reduced the net photosynthesis rate (P _N) but increased the stomata conductance (g _s), concentrations of intercellular CO₂ (C _i ), and transpiration rate (E) in all leaves. Both UV-B radiation and the wax fusion induced by enhanced UV-B radiation resulted in different stomata status on abaxial and adaxial leaf surface, causing decrease of P _N, and increase of g _s, C _i and E in leaves.     

Distribution pattern of gas exchange in the area of maize leaf blades during the generative phase

Net photosynthetic CO₂ uptake (P _N ) and transpiration (E) rates through adaxial and abaxial leaf surfaces were measured gasometrically on the area of maize leaf blades of different insertion levels in the phase of male florescence and in the phase of spadices development. The distribution pattern of gas exchange on the area of all measured leaf blades found in the phase of male florescence (significantly lower value in the basal parts) was changed in the phase of spadices development: P_N andE of abaxial surfaces of older leaves,i.e. 9th, 10th (under which the spadices were growing) and 11th, rapidly increased in the basal parts in comparison with the middle ones and positively influenced the gas exchange of the whole leaves. It appears that P_N may be maintained or increased in the older leaves in the phase of spadices development to prevent shortage of photosynthates.     

Determinant of photosynthetic capacity in rice leaves under ambient air conditions

At the grain-filling stage, net photosynthetic rate (P _N), stomatal conductance (g _s), and ribulose-1,5-bisphosphate carboxylation efficiency (CE) were correlated in order to find the determinant of photosynthetic capacity in rice leaves. For a flag leaf, P _N in leaf middle region was higher than in its upper region, and leaf basal region had the lowest P _N value. The differences in g _s and CE were similar. P _N, g _s, and CE gradually declined from upper to basal leaves, showing a leaf position gradient. The correlation coefficient between P _N and CE was much higher than that between P _N and g _s in both cases, and P _N was negatively correlated with intercellular CO₂ concentration (C _i). Hence the carboxylation activity or activated amount of ribulose-1,5-bisphosphate carboxylase/oxygenase rather than g_s was the determinant of the photosynthetic capacity in rice leaves. In addition, in flag leaves of different tillers P _N was positively correlated with g _s, but negatively correlated with C _i. Thus g _s is not the determinant of the photosynthetic capacity in rice leaves.The study was supported by the State Key Basic Research and Development Plan (No.G1998010100).     

Image analysis of the leaf vascular network: physiological considerations

The study of leaf vascular systems is important in order to understand the fluid dynamics of water movement in leaves. Recent studies have shown how these systems can be involved in the performance of photosynthesis, which is linked to the density of the vascular network per unit of leaf area. The aim of the present study was to highlight the correlation between a leaf vein density (V_D) and net photosynthetic rate (P_N), which was undertaken using a digital camera, a stereoscopic microscope, and a light source. The proposed hypothesis was tested, for the first time, on the leaves of two cultivars of Vitis vinifera (L.). A significant difference was found between the V_D of mature leaves of the two cultivars. V_D was also significantly correlated with the maximum leaf P_N. These findings support the hypothesis that the vascular system of grape leaves can be correlated with leaf photosynthesis performance.     

Influence of phosphorus and nitrogen on photosynthetic parameters and growth in <Emphasis Type="Italic">Vicia faba</Emphasis> L.

The influence of phosphorus (P) and nitrogen (N) supply on biomass, leaf area, photon saturated photosynthetic rate (P_max), quantum yield efficiency (α), intercellular CO₂ concentration (C_i), and carboxylation efficiency (CE) was investigated in Vicia faba. The influence of P on N accumulation, biomass, and leaf area production was also investigated. An increase in P supply was consistently associated with an increase in N accumulation and N productivity in terms of biomass and leaf area production. Furthermore, P increased the photosynthetic N use efficiency (NUE) in terms of P_max and α. An increase in P supply was also associated with an increase in CE and a decrease in C_i. Under variable daily meteorological conditions specific leaf nitrogen content (N_L), specific leaf phosphorus content (P_L), specific leaf area (δ_L), root mass fraction (R_f), P_max, and α remained constant for a given N and P supply. A monotonic decline in the steady-state value of R_f occurred with increasing N supply. δ_L increased with increasing N supply or with increasing N_L. We tested also the hypothesis that P supply positively affects both N demand and photosynthetic NUE by influencing the upper limit of the asymptotic values for P_max and CE, and the lower limit for C_i in response to increasing N.     

Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (ψ₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ψ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.     

Leaf orientation,photorespiration and xanthophyll cycle protect young soybean leaves against high irradiance in field

In order to fully understand the adaptive strategies of young leaves in performing photosynthesis under high irradiance, leaf orientation, chloroplast pigments, gas exchange, as well as chlorophyll a fluorescence kinetics were explored in soybean plants. The chlorophyll content and photosynthesis in young leaves were much lower than that in fully expanded leaves. Both young and fully expanded leaves exhibited down-regulation of the maximum quantum yield (F_V/F_M) at noon in their natural position, no more serious down-regulation being observed in young leaves. However, when restraining leaf movement and vertically exposing the leaves to 1200 μmol m⁻² s⁻¹ irradiance, more pronounced down-regulation of F_V/F_M was observed in young leaves; and the actual photosystem II (PS II) efficiency (Ф_PSII) drastically decreased with the significant enhancement of non-photochemical quenching (NPQ) and ‘High energy’ quenching (q_E) in young leaves. Under irradiance of 1200 μmol m⁻² s⁻¹, photorespiration (P_r) in young leaves measured by gas exchange were obviously lower, whereas the ratio of photorespiration/gross photosynthetic rate (P_r/P_g) were higher than that in fully expanded leaves. Compared with fully expanded leaves, young leaves exhibited higher xanthophyll pool and a much higher level of de-epoxidation components when exposure to high irradiance. During leaf development, the petiole angle gradually increased all the way. Especially, the midrib angle decreased with the increasing of irradiance in young leaves; however, no distinct changes were observed in mature leaves. The changes of leaf orientation greatly reduced the irradiance on young leaf surface under natural positions. In this study, we suggested that the co-operation of leaf angle, photorespiration and thermal dissipation depending on xanthophyll cycle could successfully prevent young leaves against high irradiance in field.     

CO2 and water vapour exchange through adaxial and abaxial surfaces of tobacco leaves of different insertion level

CO₂ uptake (P _N ) and water vapour efflux (E) through adaxial and abaxial surfaces were measured separately and the corresponding diffusive resistances for water vapour (r ₁) were calculated in leaves of different insertion levels during vegetative growth of tobacco plants. Relatively higher values of the abaxialP _N/E ratio in comparison with the adaxial one were found in agreement with relatively higherE _ad/E _ab coefficients and the distribution of the gas exchange in plants in all measurements carried out. Because of the more rapid decrease of theP _N rates as compared with theE rates theP _N/E ratios of both surfaces decreased gradually from young to old leaves. The decreasing values ofE _ad/E _ab andP _N,ab/P _N,ab coefficients showed thatr _1,ab increased with the age of the leaves more quickly thanr _1,ab.     

Polysomes from expanded tobacco leaves

The isolation of intact polysomes from leaves of tobacco (Nicotiana tabacum L.) is dependent on the age and state of development of leaves. Undegraded polysomes from young leaves in the early stages of expansion can be isolated easily by extracting the leaves in ice-cold extraction buffer (200 mM tris(hydroxymethyl)aminomethylmethane(Tris)-HCl, pH 9.0; 400 mM KCl; 200 mM sucrose; 35 mM MgCl₂). Medium-size leaves give best yields of undegraded polysomes when extractions are carried out in the above buffer and in the presence of ethyleneglycol-bis-(β-amino-ethyl ether)-N,N′-tetracetic acid (EGTA) and mercaptoethanol. Isolation of polysomes from large, nearly fully expanded (mature) leaves requires all of the above plus diethyldithiocarbamate (DIECA) in the extraction medium. An extraction medium consisting of 25 mM EGTA, 0.01 M mercaptoethanol, 25 mM DIECA and 0.5% of the nonionic detergent, Nonidet-P40 (NP 40) was found to be very suitable for extraction of polysomes from all developmental stages of leaves. The polysomes extracted in the above medium showed active translation of protein in the wheat-germ in-vitro protein-synthesizing system. The translational products were similar when translations were carried out directly with polysomes or polysomal RNA, or polysomal poly(A)⁺ RNA from tobacco leaves. Poly(A)^? polysomal RNA was a poor template in the in-vitro wheat-germ system.     

Photosynthesis of plant régénérants. Specificity ofin vitro conditions and plantlet response

Regenerants from tobacco(Nicotiana tabacum L. cv. White Burley) leaf segments cultivatedin vitro in vessels with solid agar medium under usual conditions (plantlets) grew under very low irradiance (I = 40 μxmol m?2 s?1), very high relative humidity (more than 90%) and decreased CO₂ concentration (c_a) during light period. In comparison with seedlings of a similar number of leaves and similar total leaf area grown in sand and nutrient solution, the plantlets had lower dry mass of shoots and roots per plant and thinner leaves almost without trichomes and epicuticular waxes. Due to a low transpiration rate under high relative humidity the water potential of plantlet leaves was higher than that of seedling leaves and the difference in water potential between leaves and medium was lowei. The rate of water loss from leaves detached from plantlets was considerably faster than that from seedlings under the same conditions (I = 110 μrnol m^?2; s^?1, temperature 30 °C, relative humidity 50 %). Net photosynthetie rates (P_n) of leaves of plantlets and seedlings measured under saturating I, natural ca and the leaf temperature 20 °C were similar, nevertheless the shape of curves relating Pn to c» indicated some differences in photosynthetie parameters(e.g. saturation of Pn under lower ca> higher CO2 compensation concentration in plantlets than in seedlings). Similarly compensation and saturating I were lower in plantlets than in seedlings. The shape of transpiration curves as well as the expressive linear phases of P_N(ca) and P_N(I) curves of plantlet leaves indicated ineffective stomatal control of gas exchance. These results were confirmed by microscopic observations of stomatal movementsin situ     

Potato virus X induces DNA damage in leaf nuclei of the host plant Nicotiana tabacum L. var. xanthi

We employed the comet assay (single cell gel electrophoresis) to evaluate induced DNA damage in nuclei isolated from tobacco leaves (Nicotiana tabacum var. xanthi) inoculated with Potato virus X (PVX). The highest DNA damage, expressed by the tail moment value, was observed in the inoculated leaves and decreased in the 1^st to 4^th systemic leaves. DNA damage increased with the time after the inoculation (from day 3 to day 21) and was higher in nuclei isolated from a part of the leaf at the petiole compared to nuclei isolated from the leaf tip. A Pearson moment correlation (r = 0.94) between the induced DNA damage and the PVX titres expressed by ELISA absorbance values was observed. The PVX infection did not induce a significant increase in the rate of somatic mutations evaluated by appearance of dark green, yellow, and double green/yellow sectors on the heterozygous pale green leaves of N. tabacum var. xanthi.     

Nitrogen enhanced photosynthesis of Miscanthus by increasing stomatal conductance and phosphoenolpyruvate carboxylase concentration

Miscanthus is one of the most promising bioenergy crops with high photosynthetic nitrogen-use efficiency (PNUE). It is unclear how nitrogen (N) influences the photosynthesis in Miscanthus. Among three Miscanthus genotypes, the net photosynthetic rate (P _N) under the different light intensity and CO₂ concentration was measured at three levels of N: 0, 100, and 200 kg ha^?1. The concentrations of chlorophyll, soluble protein, phosphoenolpyruvate carboxylase (PEPC), ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit, leaf anatomy and carbon isotope discrimination (Δ) in the leaf were analyzed to probe the response of photosynthesis in Miscanthus genotypes to N levels. P _N in all genotypes rose significantly as N application increased. The initial slope of response curves of P _N to C _i was promoted by N application in all genotypes. Both stomatal conductance and C _i were increased with increased N supply, indicating that stomatal factors played an important role in increasing P _N. At a given C _i, P _N in all genotypes was enhanced by N, implying that nonstomatal factors might also play an important role in increasing P _N. Miscanthus markedly regulated N investment into PEPC rather than the Rubisco large subunit under higher N conditions. Bundle sheath leakiness of CO₂ was constant at about 0.35 for all N levels. Therefore, N enhanced the photosynthesis of Miscanthus mainly by increasing stomatal conductance and PEPC concentration.     

Soil salinity effects on transpiration and net photosynthetic rates,stomatal conductance and Na+ and Cl− contents in durum wheat

Leaf gas exchange, plant growth and leaf ion content were measured in wheat (Triticum durum L. cv. HD 4502) exposed to steady- state salinities (1.6, 12.0 and 16.0 dS nr⁻¹) for 8 weeks. Salinity reduced leaf area and number of tillers, and increased Na⁺ and Cl⁻ concentrations in leaves. Leaf- to- leaf gradients of these ions were observed. The oldest leaf contained 6 to 8 times more Na⁺ and Cl⁻ than the flag leaf. Net photosynthetic rate (P_N), transpiration rate (E) and stomatal conductance (g_S) were the highest in flag leaf, declined in the middle and fully expanded leaves, and were minimum in the oldest leaves. These processes were reduced by salinity with similar leaf- to- leaf gradients. Intercellular CO₂ concentrations in the older leaves were higher than in the flag leaf in non-saline plants, and increased similarly with salinity. Leaf age was the major factor in reducing P_N, and senescence processes were promoted by salinity.