Alternate partial root-zone irrigation reduces bundle-sheath cell leakage to CO2 and enhances photosynthetic capacity in maize leaves

The physiological basis for the advantage of alternate partial root-zone irrigation (PRI) over common deficit irrigation (DI) in improving crop water use efficiency (WUE) remains largely elusive. Here leaf gas exchange characteristics and photosynthetic CO(2)-response and light-response curves for maize (Zea mays L.) leaves exposed to PRI and DI were analysed under three N-fertilization rates, namely 75, 150, and 300 mg N kg(-1) soil. Measurements of net photosynthetic rate (A(n)) and stomatal conductance (g(s)) showed that, across the three N-fertilization rates, the intrinsic WUE was significantly higher in PRI than in DI leaves. Analysis of the CO(2)-response curve revealed that both carboxylation efficiency (CE) and the CO(2)-saturated photosynthetic rate (A(sat)) were significantly higher in PRI than in DI leaves across the three N-fertilization rates; whereas the N-fertilization rates did not influence the shape of the curves. The enhanced CE and A(sat) in the PRI leaves was accompanied by significant decreases in carbon isotope discrimination (Δ(13)C) and bundle-sheath cell leakiness to CO(2) (Φ). Analysis of the light-response curve indicated that, across the three N-fertilization rates, the quantum yield (α) and light-saturated gross photosynthetic rate (A(max)) were identical for the two irrigation treatments; whilst the convexity (κ) of the curve was significantly greater in PRI than in DI leaves, which coincided with the greater CE and A(sat) derived from the CO(2)-response curve at a photosynthetic photon flux density of 1500 μmol m(-2) s(-1). Collectively, the results suggest that, in comparison with the DI treatment, PRI improves photosynthetic capacity parameters CE, A(sat), and κ of maize leaves and that contributes to the greater intrinsic WUE in those plants.     

Does nitrogen supply affect the response of wheat (Triticum aestivum cv. Hanno) to the combination of elevated CO(2) and O(3)?

Spring wheat (Triticum aestivum cv. Hanno) was grown at ambient (350 micromol mol(-1)) or elevated CO(2) (700 micromol mol(-1)) in charcoal/Purafil-filtered air (CFA <5 nmol mol(-1)) or ozone (CFA +75 nmol mol(-1) 7 h d(-1)) at three levels of N supply (1.5, 4 and 14 mM NO(-3)), to test the hypothesis that the combined impacts of elevated CO(2) and O(3) on plant growth and photosynthetic capacity are affected by nitrogen availability. Shifts in foliar N content reflected the level of N supplied, and the growth stimulation induced by elevated CO(2) was dependent on the level of N supply. At 60 d after transfer (DAT), elevated CO(2) was found to increase total biomass by 44%, 29%, 12% in plants supplied with 14, 4 and 1.5 mM NO(-3), respectively, and there was no evidence of photosynthetic acclimation to elevated CO(2) across N treatments; the maximum in vivo rate of Rubisco carboxylation (V(cmax)) was similar in plants raised at elevated and ambient CO(2). At 60 DAT, ozone exposure was found to suppress plant relative growth rate (RGR) and net photosynthesis (A) in plants supplied with 14 and 4 mM NO(-3). However, O(3) had no effect on the RGR of plants supplied with 1.5 mM NO(-3) and this effect was accompanied by a reduced impact of the pollutant on A. Elevated CO(2) counteracted the detrimental effects of O(3) (i.e. the same ozone concentration that depressed RGR and A at ambient CO(2) resulted in no significant effects when plants were raised at elevated CO(2)) at all levels of N supply and the effect was associated with a decline in O(3) uptake at the leaf level.     

The rate-limiting step for CO(2) assimilation at different temperatures is influenced by the leaf nitrogen content in several C(3) crop species

Effects of nitrogen (N) supply on the limiting step of CO(2) assimilation rate (A) at 380 μmol mol(-1) CO(2) concentration (A(380) ) at several leaf temperatures were studied in several crops, since N nutrition alters N allocation between photosynthetic components. Contents of leaf N, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) increased with increasing N supply, but the cyt f/Rubisco ratio decreased. Large leaf N content was linked to a high stomatal (g(s) ) and mesophyll conductance (g(m) ), but resulted in a lower intercellular (C(i) ) and chloroplast CO(2) concentration (C(c) ) because the increase in g(s) and g(m) was insufficient to compensate for change in A(380) . The A-C(c) response was used to estimate the maximum rate of RuBP carboxylation (V(cmax) ) and chloroplast electron transport (J(max) ). The J(max) /V(cmax) ratio decreased with reductions in leaf N content, which was consistent with the results of the cyt f/Rubisco ratio. Analysis using the C(3) photosynthesis model indicated that A(380) tended to be limited by RuBP carboxylation in plants grown at low N concentration, whereas it was limited by RuBP regeneration in plants grown at high N concentration. We conclude that the limiting step of A(380) depends on leaf N content and is mainly determined by N partitioning between Rubisco and electron transport components.     

Interaction of temperature and irradiance effects on photosynthetic acclimation in two accessions of Arabidopsis thaliana

The effect of temperature and irradiance during growth on photosynthetic traits of two accessions of Arabidopsis thaliana was investigated. Plants were grown at 10 and 22?°C, and at 50 and 300?μmol photons?m(-2)?s(-1) in a factorial design. As known from other cold-tolerant herbaceous species, growth of Arabidopsis at low temperature resulted in increases in photosynthetic capacity per unit leaf area and chlorophyll. Growth at high irradiance had a similar effect. However, the growth temperature and irradiance showed interacting effects for several capacity-related variables. Temperature effects on the ratio between electron transport capacity and carboxylation capacity were also different in low compared to high irradiance grown Arabidopsis. The carboxylation capacity per unit Rubisco, a measure for the in vivo Rubisco activity, was low in low irradiance grown plants but there was no clear growth temperature effect. The limitation of photosynthesis by the utilization of triose-phosphate in high temperature grown plants was less when grown at low compared to high irradiance. Several of these traits contribute to reduced efficiency of the utilization of resources for photosynthesis of Arabidopsis at low irradiance. The two accessions from contrasting climates showed remarkably similar capabilities of developmental acclimation to the two environmental factors. Hence, no evidence was found for photosynthetic adaptation of the photosynthetic apparatus to specific climatic conditions.     

Estimation of canopy average mesophyll conductance using δ(13) C of phloem contents

Conductance to CO(2) inside leaves, known as mesophyll conductance (g(m)), imposes large limitations on photosynthesis. Because g(m) is difficult to quantify, it is often neglected in calculations of (13)C photosynthetic discrimination. The 'soluble sugar method' estimates g(m) via differences between observed photosynthetic discrimination, calculated from the δ(13)C of soluble sugars, and discrimination when g(m) is infinite. We expand upon this approach and calculate a photosynthesis-weighted average for canopy mesophyll conductance ((c) g(m)) using δ(13)C of stem phloem contents. We measured gas exchange at three canopy positions and collected stem phloem contents in mature trees of three conifer species (Pseudotsuga menziesii, Thuja plicata and Larix occidentalis). We generated species-specific and seasonally variable estimates of (c)g(m) . We found that (c)g(m) was significantly different among species (0.41, 0.22 and 0.09 mol m(-2) s(-1) for Larix, Pseudotsuga and Thuja, respectively), but was similar throughout the season. Ignoring respiratory and photorespiratory fractionations ((c)Δ(ef)) resulted in ≈30% underestimation of (c)g(m) in Larix and Pseudotsuga, but was innocuous in Thuja. Substantial errors (~1-4‰) in photosynthetic discrimination calculations were introduced by neglecting (c)g(m) and (c)Δ(ef) . Our method is easy to apply and cost-effective, captures species variation and would have captured seasonal variation had it existed. The method provides an average canopy value, which makes it suitable for parameterization of canopy-scale models of photosynthesis, even in tall trees.     

Growth and photosynthetic responses to salinity of the salt-marsh shrub Atriplex portulacoides

BACKGROUND AND AIMS: Atriplex (Halimione) portulacoides is a halophytic, C(3) shrub. It is virtually confined to coastal salt marshes, where it often dominates the vegetation. The aim of this study was to investigate its growth responses to salinity and the extent to which these could be explained by photosynthetic physiology. METHODS: The responses of young plants to salinity in the range 0-700 mol m(-3) NaCl were investigated in a glasshouse experiment. The performance of plants was examined using classical growth analysis, measurements of gas exchange (infrared gas analysis), determination of chlorophyll fluorescence characteristics (modulated fluorimeter) and photosynthetic pigment concentrations; total ash, sodium, potassium and nitrogen concentrations, and relative water content were also determined. KEY RESULTS: Plants accumulated Na(+) approximately in proportion to external salinity. Salt stimulated growth up to an external concentration of 200 mol m(-3) NaCl and some growth was maintained at higher salinities. The main determinant of growth response to salinity was unit leaf rate. This was itself reflected in rates of CO(2) assimilation, which were not affected by 200 mol m(-3) but were reduced at higher salinities. Reductions in net photosynthetic rate could be accounted for largely by lower stomatal conductance and intercellular CO(2) concentration. Apart from possible effects of osmotic shock at the beginning of the experiment, salinity did not have any adverse effect on photosystem II (PSII). Neither the quantum efficiency of PSII (Phi(PSII)) nor the chlorophyll fluorescence ratio (F(v)/F(m)) were reduced by salinity, and lower mid-day values recovered by dawn. Mid-day F(v)/F(m) was in fact depressed more at low external sodium concentration, by the end of the experiment. CONCLUSIONS: The growth responses of the hygro-halophyte A. portulacoides to salinity appear largely to depend on changes in its rate of photosynthetic gas exchange. Photosynthesis appears to be limited mainly through stomatal conductance and hence intercellular CO(2) concentration, rather than by effects on PSII; moderate salinity might stimulate carboxylation capacity. This is in contrast to more extreme halophytes, for which an ability to maintain leaf area can partially offset declining rates of carbon assimilation at high salinity.     

Internal conductance to CO(2) diffusion and C(18)OO discrimination in C(3) leaves

(18)O discrimination in CO(2) stems from the oxygen exchange between (18)O-enriched water and CO(2) in the chloroplast, a process catalyzed by carbonic anhydrase (CA). A proportion of this (18)O-labeled CO(2) escapes back to the atmosphere, resulting in an effective discrimination against C(18)OO during photosynthesis (Delta(18)O). By constraining the delta(18)O of chloroplast water (delta(e)) by analysis of transpired water and the extent of CO(2)-H(2)O isotopic equilibrium (theta(eq)) by measurements of CA activity (theta(eq) = 0.75-1.0 for tobacco, soybean, and oak), we could apply measured Delta(18)O in a leaf cuvette attached to a mass spectrometer to derive the CO(2) concentration at the physical limit of CA activity, i.e. the chloroplast surface (c(cs)). From the CO(2) drawdown sequence between stomatal cavities from gas exchange (c(i)), from Delta(18)O (c(cs)), and at Rubisco sites from Delta(13)C (c(c)), the internal CO(2) conductance (g(i)) was partitioned into cell wall (g(w)) and chloroplast (g(ch)) components. The results indicated that g(ch) is variable (0.42-1.13 mol m(-2) s(-1)) and proportional to CA activity. We suggest that the influence of CA activity on the CO(2) assimilation rate should be important mainly in plants with low internal conductances.     

Small decreases in SBPase cause a linear decline in the apparent RuBP regeneration rate, but do not affect Rubisco carboxylation capacity

The response of net photosynthetic CO(2) uptake (A) to increasing leaf intercellular CO(2) concentration (c(i)) was determined in antisense Nicotiana tabacum plants, derived from six independent transformation lines, displaying a range of sedoheptulose-1, 7-bisphosphatase (SBPase) activities. The maximum in vivo ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation (V(c,max)) and RuBP regeneration (J(max)) rates were calculated from the steady-state measurements of the A to c(i) response curves. In plants with reductions in SBPase activity of between 9% and 60%, maximum RuBP regeneration capacity declined linearly (r(2)=0.79) and no significant change in apparent in vivo Rubisco activity (V(c,max)) was observed in these plants. No correlation between V(c,max) and a decrease in capacity for RuBP regeneration was observed (r(2)=0.14) in the SBPase antisense plants. These data demonstrate that small decreases in SBPase activity limit photosynthetic carbon assimilation by reducing the capacity for RuBP regeneration.     

Circumvention of over-excitation of PSII by maintaining electron transport rate in leaves of four cotton genotypes developed under long-term drought

We investigated the patterns of response to a long-term drought in the field in cotton cultivars (genotypes) with known differences in their drought tolerance. Four cotton genotypes with varying physiological and morphological traits, suited to different cropping conditions, were grown in the field and subjected to a long-term moderate drought. In general, cotton leaves developed under drought had significantly higher area-based leaf nitrogen content (N (area)) than those under well irrigation. Droughted plants showed a lower light-saturated net photosynthetic rate (A (sat)) with lower stomatal conductance (g (s)) and intercellular CO (2) concentration (C (i)) than irrigated ones. Based on the responses of A (sat) to g (s) and C (i), there was no decreasing trend in A (sat) at a given g (s) and C (i) in droughted leaves, suggesting that the decline in A (sat) in field-grown cotton plants under a long-term drought can be attributed mainly to stomatal closure, but not to nonstomatal limitations. There was little evidence of an increase in thermal energy dissipation as indicated by the lack of a decrease in the photochemical efficiency of open PSII (F (v)'/F (m)') in droughted plants. On the basis of electron transport (ETR) and photochemical quenching (q (P)), however, we found evidence indicating that droughted cotton plants can circumvent the risk of excessive excitation energy in photosystem (PS) II by maintaining higher electron transport rates associated with higher N (area), even while photosynthetic rates were reduced by stomatal closure.     

The lack of mitochondrial complex I in a CMSII mutant of Nicotiana sylvestris increases photorespiration through an increased internal resistance to CO2 diffusion

The cytoplasmic male sterile II (CMSII) mutant lacking complex I of the mitochondrial electron transport chain has a lower photosynthetic activity but exhibits higher rates of excess electron transport than the wild type (WT) when grown at high light intensity. In order to examine the cause of the lower photosynthetic activity and to determine whether excess electrons are consumed by photorespiration, light, and intercellular CO(2), molar fraction (c(i)) response curves of carbon assimilation were measured at varying oxygen molar fractions. While oxygen is the major acceptor for excess electrons in CMSII and WT leaves, electron flux to photorespiration is favoured in the mutant as compared with the WT leaves. Isotopic mass spectrometry measurements showed that leaf internal conductance to CO(2) diffusion (g(m)) in mutant leaves was half that of WT leaves, thus decreasing the c(c) and favouring photorespiration in the mutant. The specificity factor of Rubisco did not differ significantly between both types of leaves. Furthermore, carbon assimilation as a function of electrons used for carboxylation processes/electrons used for oxygenation processes (J(C)/J(O)) and as a function of the calculated chloroplastic CO(2) molar fraction (c(c)) values was similar in WT and mutant leaves. Enhanced rates of photorespiration also explain the consumption of excess electrons in CMSII plants and agreed with potential ATP consumption. Furthermore, the lower initial Rubisco activity in CMSII as compared with WT leaves resulted from the lower c(c) in ambient air, since initial Rubisco activity on the basis of equal c(c) values was similar in WT and mutant leaves. The retarded growth and the lower photosynthetic activity of the mutant were largely overcome when plants were grown in high CO(2) concentrations, showing that limiting CO(2) supply for photosynthesis was a major cause of the lower growth rate and photosynthetic activity in CMSII.     

The photosynthetic limitation posed by internal conductance to CO2 movement is increased by nutrient supply

The internal conductance to CO(2) supply from substomatal cavities to sites of carboxylation may pose a large limitation to photosynthesis, but little is known of how it is affected by nutrient supply. Knowing how internal conductance responds to nutrient supply is critical for interpreting the biochemical responses from A-C(i) curves. The aim of this paper was to examine the response of g(i) and photosynthetic parameters to nutrient supply in glasshouse-grown seedlings of the evergreen perennial Eucalyptus globulus Labill. Seedlings were grown with five different nutrient treatments and g(i) was estimated from concurrent measurements of gas exchange and fluorescence. Internal conductance varied between 0.12 and 0.19 mol m(-2) s(-1) and the relative limitation of photosynthesis due to internal conductance was greater than the stomatal limitation. In most species these two limitations are rather similar, but in E. globulus stomatal limitations were abnormally low due to high stomatal conductance (0.31 to 0.39 mol m(-2) s(-1)). The large positive response of photosynthesis to nutrient supply was not matched by changes in internal conductance, and thus the relative limitation of photosynthesis due to internal conductance increased with increasing nutrient supply. Failure to account for finite internal conductance led to estimates of V(cmax) that were 60% of the true value, which, in turn, led to an underestimation of in vivo Rubisco specific activity (as V(cmax)/Rubisco content). The specific activity of Rubisco in E. globulus (21 mol mol(-1) s(-1)) was close to the maximum published estimates, and thus, despite these leaves containing a large fraction of N as Rubisco (38-44%) there was no evidence that Rubisco activity was down-regulated or that the enzyme was in excess.     

Salicylic acid treatment via the rooting medium interferes with stomatal response, CO2 fixation rate and carbohydrate metabolism in tomato, and decreases harmful effects of subsequent salt stress

Salicylic acid (SA) applied at 10(-3) m in hydroponic culture decreased stomatal conductance (g(s)), maximal CO(2) fixation rate (A(max) ) and initial slopes of the CO(2) (A/C(i)) and light response (A/PPFD) curves, carboxylation efficiency of Rubisco (CE) and photosynthetic quantum efficiency (Q), resulting in the death of tomato plants. However, plants could acclimate to lower concentrations of SA (10(-7) -10(-4) m) and, after 3 weeks, returned to control levels of g(s), photosynthetic performance and soluble sugar content. In response to high salinity (100 mm NaCl), the pre-treated plants exhibited higher A(max) as a function of internal CO(2) concentration (C(i) ) or photosynthetic photon flux density (PPFD), and higher CE and Q values than salt-treated controls, suggesting more effective photosynthesis after SA treatment. Growth in 10(-7) or 10(-4) m SA-containing solution led to accumulation of soluble sugars in both leaf and root tissues, which remained higher in both plant parts during salt stress at 10(-4) m SA. The activity of hexokinase (HXK) with glucose, but not fructose, as substrate was reduced by SA treatment in leaf and root samples, leading to accumulation of glucose and fructose in leaf tissues. HXK activity decreased further under high salinity in both plant organs. The accumulation of soluble sugars and sucrose in roots of plants growing in the presence of 10(-4) m SA contributed to osmotic adjustment and improved tolerance to subsequent salt stress. Apart from its putative role in delaying senescence, decreased HXK activity may divert hexoses from catabolic reactions to osmotic adaptation.     

Comparison of the photosynthetic characteristics of three submersed aquatic plants

Light- and CO(2)-saturated photosynthetic rates of the submersed aquatic plants Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum were 50 to 60 mumol O(2)/mg Chl.hr at 30 C. At air levels of CO(2), the rates were less than 5% of those achieved by terrestrial C(3) plants. The low photosynthetic rates correlated with low activities of the carboxylation enzymes. In each species, ribulose 1,5-diphosphate carboxylase was the predominant carboxylation enzyme. The apparent K(m)(CO(2)) values for photosynthesis were 150 to 170 mum at pH 4, and 75 to 95 mum at pH 8. The K(m)(CO(2)) of Hydrilla ribulose 1,5-diphosphate carboxylase was 45 mum at pH 8. Optimum temperatures for the photosynthesis of Hydrilla, Myriophyllum, and Ceratophyllum were 36.5, 35.0, and 28.5 C, respectively. The apparent ability of each species to use HCO(3) (-) ions for photosynthesis was similar, but at saturating free CO(2) levels, there was no indication of HCO(3) (-) use. Increasing the pH from 3.1 to 9.2 affected the photosynthetic rate indirectly, by decreasing the free CO(2). With saturating free CO(2) (0.5 mm), the maximum photosynthetic rates were similar at pH 4 and 8. Carbonic anhydrase activity, although much lower than in terrestrial C(3) plants, was still in excess of that required to support HCO(3) (-) utilization.Hydrilla and Ceratophyllum had CO(2) compensation points of 44 and 41 mul/l, respectively, whereas the value for Myriophyllum was 19. Relatively high CO(2) compensation points under 1% O(2) indicated that some "dark" respiration occurred in the light. The inhibition of photosynthesis by O(2) was less than with terrestrial C(3) plants. Glycolate oxidase activity was 12.3 to 27.5 mumol O(2)/mg Chl.hr, as compared to 78.4 for spinach. Light saturation of photosynthesis occurred at 600 to 700 mueinsteins/m(2).sec in each species grown under full sunlight. Hydrilla had the lowest light compensation point, and required the least irradiance to achieve the half-maximal photosynthetic rate.Field measurements in a Hydrilla mat indicated that in the afternoon, free CO(2) dropped to zero, and O(2) rose to over 200% air saturation. Most photosynthetic activity occurred in the morning when the free CO(2) was highest and O(2) and solar radiation lowest. The low light requirement of Hydrilla probably provides a competitive advantage under these field conditions.     

The effects of O3 fumigation during leaf development on photosynthesis of wheat and pea: An in vivo analysis

Previous studies have shown that short exposure of plants to high doses of ozone decreases subsequent photosynthesis; initially by reducing carboxylation capacity. This study tests the hypothesis that this is also the primary cause of loss of photosynthetic capacity in leaves affected by development under a low level of ozone. Triticum aestivum and Pisum sativum plants were exposed from germination to ozone in air (80 nmol mol^-1 for 7 hours per day, for 18 days. Leaves that had completed lamina expansion at this time were free of visible injury and light absorptance was unaffected. However, some significant changes in photosynthetic gas exchange were evident. Photosynthetic CO2 uptake at light saturation was decreased significantly by 35% in T. aestivum but was unchanged in P. sativum. The reduction in photosynthesis of T. aestivum was accompanied by a 31% decline in the maximum velocity of carboxylation measured in vivo. Decreased stomatal conductance did not contribute to this reduction of photosynthesis because there was no significant change in the stomatal limitation to CO2. Processes directly dependent upon photochemical reactions; that is, the quantum yield of CO2 uptake and capacity for regeneration of ribulose 1,5-bisphosphate were not affected by O3 fumigation in either species. This suggests that for wheat, the quantitative cause of decreased photosynthetic rate in vivo is a decrease in the quantity of active ribulose-1,5- bisphosphate carboxylase-oxygenase.     

青藏高原药用植物唐古特山莨菪和唐古特大黄光合作用对强光的响应

与唐古特大黄相比,唐古特山莨菪的表观光合量子效率(AQY)较高,但最大净光合速率(Pmax)较低。在光强小于1200μmolm-2s-1时,后者用于碳同化的电子传递占总光合电子传递的比例(JC/JF)比前者高,而分配于光呼吸的电子传递(JO/JF)及Rubisco氧化和羧化速率的比值(VO/VC)则相反;光强大于1200μmolm-2s-1以后两种植物的这些参数都趋向稳定。随光强增加,后者叶片吸收光能分配于热耗散(D)的增加斜率较前者高,表明两高山植物对强辐射的适应方式略有不同。加强光呼吸途径的耗能代谢和PSII天线热耗散份额是唐古特山莨菪适应高原强辐射的主要方式,而提高叶片光合能力则是唐古特大黄的一种适应方式。     

The biochemistry of Rubisco in Flaveria

C(4) plants have been reported to have Rubiscos with higher maximum carboxylation rates (kcat(CO(2))) and Michaelis-Menten constants (K(m)) for CO(2) (K(c)) than the enzyme from C(3) species, but variation in other kinetic parameters between the two photosynthetic pathways has not been extensively examined. The CO(2)/O(2) specificity (S(C/O)), kcat(CO(2)), K(c), and the K(m) for O(2) (K(o)) and RuBP (K(m-RuBP)), were measured at 25 degrees C, in Rubisco purified from 16 species of Flaveria (Asteraceae). Our analysis included two C(3) species of Flaveria, four C(4) species, and ten C(3)-C(4) or C(4)-like species, in addition to other C(4) (Zea mays and Amaranthus edulis) and C(3) (Spinacea oleracea and Chenopodium album) plants. The S(C/O) of the C(4) Flaveria species was about 77 mol mol(-1), which was approximately 5% lower than the corresponding value in the C(3) species. For Rubisco from the C(4) Flaverias kcat(CO(2)) and K(c) were 23% and 45% higher, respectively, than for Rubisco from the C(3) plants. Interestingly, it was found that the K(o) for Rubisco from the C(4) species F. bidentis and F. trinervia were similar to the C(3) Flaveria Rubiscos (approximately 650 microM) while the K(o) for Rubisco in the C(4) species F. kochiana, F. australasica, Z. mays, and A. edulis was reduced more than 2-fold. There were no pathway-related differences in K(m-RuBP). In the C(3)-C(4) species kcat(CO(2)) and K(c) were generally similar to the C(3) Rubiscos, but the K(o) values were more variable. The typical negative relationships were observed between S(C/O) and both kcat(CO(2)) and K(c), and a strongly positive relationship was observed between kcat(CO(2)) and Kc. However, the statistical significance of these relationships was influenced by the phylogenetic relatedness of the species.     

Manipulation of light and CO2 environments of the primary leaves of bean (Phaseolus vulgaris L.) affects photosynthesis in both the primary and the first trifoliate leaves: involvement of systemic regulation.

Possible involvement of systemic regulation of the photosynthetic properties of young leaves by the local environments and/or photosynthate production of the mature leaves were examined using Phaseolus vulgaris plants. When primary leaves (PLs) were treated with air containing 150 microL CO2 L(-1) with the other plant parts in ambient air at a photosynthetic photon flux density (PPFD) of 300 micromol photon m(-2) s(-1), decreases in the photosynthetic rate measured at 360 microL CO2 L(-1) and a PPFD of 300 micromol photon m(-2) s(-1) (A360) were markedly retarded in both PLs and the first trifoliate leaves (TLs) as compared to plants treated with 400 microL CO2 L(-1). Conversely, when PLs were treated with 1000 microL CO2 L(-1), decreases in A360 were accelerated in both PLs and TLs. Shading of PLs accelerated the decrease in PL A360, and delayed the decrease in TLs. In the CO2 treatments, changes in A360 in TLs were mainly attributed to the changes in ribulose bisphosphate (RuBP) carboxylation rate, while the shading of PLs caused increases in both the RuBP carboxylation and regeneration rates in TLs. The ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco) activity on chlorophyll basis, an indicator of sun/shade acclimation, differed both among PLs and among TLs in accordance with the redox state of photosystem II (PSII) in PLs. Although carbohydrate contents of TLs were not affected by any manipulation of PLs, changes in the photosynthetic capacities of TLs acted to compensate for changes in PL photosynthesis. These results clearly indicate that the CO2 and shade treatments of PLs not only affect photosynthetic properties of the PLs themselves, but also systemically affected the photosynthetic properties of TLs. Possible roles of the redox state and photosynthate concentration in PLs in regulation of photosynthesis in PLs and TLs are discussed.