Pigment contents of chloroplasts and net photosynthetic rate were dramatically reduced in maize leaves suffering from iron deficiency. However, the reduction in photosynthesis was probably not caused by decreased contents of chlorophylls and carotenoids and by photon absorption; the primary limiting factor for photosynthesis may rather be the decrease of electron transport activity in photosystem 1. Iron-deficient leaves suffered serious acceptor-side photoinhibition, and more than 60 % of absorbed photons were dissipated, while less than 40 % was used in photochemical reaction. Thermal energy dissipation depending on xanthophyll cycle and D1 protein turnover was enhanced when acceptor-side photoinhibition occurred in iron-deficient maize leaves. and Chuang-Dao Jiang, Hui-Yuan Gao, Qi Zou.
Net CO2 assimilation rate (PN), stomatal conductance (gs), transpiration rate (E), and water use efficiency (WUE) in four perennial C3 species (grasses: Dactylis glomerata, Festuca rupicola, dicots: Filipendula vulgaris, Salvia nemorosa) grown for 231 d in open-top chambers at ambient (CA, 350 µmol mol-1) or elevated (CE, 700 µmol mol-1) CO2 concentrations were compared. When measured at CE, PN was significantly higher in CE plants of all four species than in the CA ones. The increase in PN was less prominent in the two grasses than in the two dicots. The E was significantly higher in the CE-grass F. rupicola and CE-dicot F. vulgaris than in the CA plants. There was no change in E owing to CE in the other grass and dicot. The gs in F. vulgaris and F. rupicola increased, while there was a decrease in D. glomerata and no change in S. nemorosa. WUE increased in all species grown in CE: four- to five-fold in the dicots and less than two-fold in the grasses. The increase in WUE was primarily due to an increase in PN and not to a decrease in E. and K. Szente, Z. Nagy, Z. Tuba.
Diurnal and seasonal fluctuations in water potential (Ψ), stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) were monitored in Capparis spinosa L., a Mediterranean plant growing during summer, i.e. at the period considered the most stressful for local plant life. In spite of the complete absence of rain, Ψ exhibited a modest drop at midday (-2.7 MPa), but was fully recovered overnight, indicating sufficient access to water sources. The stomata remained open throughout the day and season and the high E resulted in leaf temperatures up to 3.9 °C below air temperature. Additionally, PN of the fully exposed leaves was higher than 25 μmol m-2 s-1 for more than 10 h per day throughout the summer growth period. No symptoms of photooxidative stress were shown, as judged by maximum photosystem 2 photochemical efficiency (Fv/Fm) and the function of xanthophyll cycle. Indeed, diurnal inter-conversions of the xanthophyll cycle components were modest during the summer and a more intensive function of the cycle was only evident during leaf senescence in autumn. In comparison with a semi-deciduous and an evergreen sclerophyll co-existing in the same ecosystem, C. spinosa assimilated up to 3.4 times more CO2 per m2 during its growth period (May to October) and up to 1.8 times more on an annual basis. and E. Levizou, P. Drilias, A. Kyparissis.
In order to investigate the effect of large isoform of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activase (RuBPCO-A) on photosynthesis, cDNA of the enzyme (rca) was transferred to rice cultivars (Oryza sativa f. japonica cv. Nipponbare) under the control of RuBPCO small subunit gene promoter (rbcS) via Agrobacterium tumefaciens-mediated transformation. Transgenic rice plants were identified by polymerase chain reaction (PCR) and Southern and Western blot analyses. Net photosynthetic rate (PN ) values of the T1 transgenic lines 34 (T34) and 40 (T40) were 45.26 and 46.32 % higher than that of the control plants, respectively. At the same time, their carboxylation efficiency and RuBPCO initial activity, quantum yield of electron transport in photosystem 2 (ΦPS2), and steady state photochemical fluorescence quenching (qP) increased. In addition, heading time of the transgenic rice was advanced. Thus increasing the amount of large isoform of RuBPCO-A in the transgenic rice might have a stimulatory effect on both photosynthesis and plant growth. and H. R. Wu ... [et al.].
Spartina maritima (Curtis) Fernald, Spartina densiflora Brong, Arthrocnemum perenne (Miller) Moss, and Arthrocnemum fruticosum (L.) Moq are very frequent halophytes on the coasts of SW Europe. The first two are perennial Gramineae with C4 metabolism; the last two are perennial Chenopodiaceae with C3 metabolism. Controlled garden experiments were carried out with the four species to compare their physiological response, i.e., water potential (Ψ), net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll fluorescence of photosystem (PS) 2 under saline and non-saline conditions. S. maritima behaves as an osmoconformer species, the other three as osmoregulators. In the four species, PN, E, and gs improved following freshwater irrigation. The variations in PN might be related with biochemical changes (which appear not to affect PS2), but not with significant stomatal fluctuations, which are associated with a lower water use efficiency in the case of Arthrocnemum. The species were segregated into two groups (not depending on their C3 or C4 photosynthetic pathway), in relation with the topographic level of this species in natural conditions: the relative responses of PN in S. maritima and A. perenne were lower than those of S. densiflora and A. fruticosum. The salt-tolerance index supports such segregation. S. densiflora demonstrated the best competitive possibilities against salt-tolerant glycophytes, with its more flexible response in saline or brackish environments, which explains its spreading along the rivers draining into the estuaries of the SW Iberian Peninsula. and F. J. J. Nieva ... [et al.].
The response of gas exchange and chlorophyll fluorescence along with changes in simulated rainfall were studied in water stressed plants Hedysarum fruticosum var. mongolicum (H.f.m.). Net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (Ψleaf), and apparent carboxylation efficiency (PN/Ci) were significantly increased with the increase of rainfall. However, they did not change synchronously. The complete recovery of both PN and PN/Ci appeared 3 d after watering while gs and Ψleaf were recovered 1 d after treatment. Gas exchange characters increased sharply from 5 to 15 mm rainfall and then maintained steady state with increasing rainfall. During the initial phase of water recovery, photosystem 2 (PS2) activity was not affected and its complete recovery occurred also 3 d after rainfall. Hence the recovery of PN was attributed to both opening of stomata and increase in carboxylation efficiency. Furthermore, PS2 activity was really impaired by water stress and could recover to the normal status when the water stress disappeared. and S. L. Niu ... [et al.].
The influence of air humidity on leaf-air gas exchange and leaf water potential (4^) was investigated during daily courses in control and water stressed potted young plants of Copaifera langsdorffii. When leaf-air water vapour concentration difference (AW) increased during the day, stomatal conductance (g^) and net photosynthetic rate (P]vj) decreased under both soil moistures. Moderate AW induced lower values of g^ and Pn unwatered than control plants, High AW in atmosphere produced strong depression in g^ (from 0.22 to 0,01 mol m'^ s’’) and (from 6.5 to 0.7 pmol m'2 s'*) in control plants around midday, with recuperation of T'. Expected conductance tese) was calculated as fimction of AW, which was useful for discriminating soil to atmosphere water stress. In špite of momentary T or soil water stress, P^, g^, and water use efficiency decreased when AW increased during day course.
Optical characteristics, contents of photosynthetic pigments, total soluble sugars, and starch, rates of gas exchange, chlorophyll (Chl) a fluorescence, and leaf water relations were analysed in three Vitis vinifera L. cultivars, Tinto Cão (TC), Touriga Nacional (TN), and Tinta Roriz (TR), grown in Mediterranean climate. Chl content was significantly lower in TC than in TN and TR leaves, while the Chl a/b ratio was higher. TR had the lowest net photosynthetic rate, stomatal conductance, and contents of soluble sugars and starch than TN and TC. In spite of low Chl content, TC showed the lowest photon absorbance and the highest photochemical efficiency of photosystem 2. TC had the lowest predawn and midday leaf water potential. The capability for osmotic adjustment was similar among cultivars and the calculated modulus of elasticity was higher in TC leaves. The typical lighter green leaves of TC seemed to be an adaptive strategy to high irradiance and air temperature associated to water stress. and J. Moutinho-Pereira ... [et al.].
The net photosynthetic rate (PN), intercellular CO2 concentration (Ci), stomatal conductance (gs), 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 PN and gs. A positive correlation was found between PN 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 PN under Indian farming conditions. and P. Srinivas, B. N. Smith, P. M. Swamy.
Short-term responses of four carrot (Daucus carota) cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) to CO2 concentrations (Ca) were studied in a controlled environment. Leaf net photosynthetic rate (PN), intercellular CO2 (Ci), stomatal conductance (gs), and transpiration rate (E) were measured at Ca from 50 to 1 050 μmol mol-1. The cultivars responded similarly to Ca and did not differ in all the variables measured. The PN increased with Ca until saturation at 650 μmol mol-1 (Ci= 350-400 μmol mol-1), thereafter PN increased slightly. On average, increasing Ca from 350 to 650 and from 350 to 1 050 μmol mol-1 increased PN by 43 and 52 %, respectively. The PNvs.Ci curves were fitted to a non-rectangular hyperbola model. The cultivars did not differ in the parameters estimated from the model. Carboxylation efficiencies ranged from 68 to 91 μmol m-2 s-1 and maximum PN were 15.50, 13.52, 13.31, and 14.96 μmol m-2 s-1 for Cascade, CC, Oranza, and RCC, respectively. Dark respiration rate varied from 2.80 μmol m-2 s-1 for Oranza to 3.96 μmol m-2 s-1 for Cascade and the CO2 compensation concentration was between 42 and 46 μmol mol-1. The gs and E increased to a peak at Ca= 350 μmol mol-1 and then decreased by 17 and 15 %, respectively when Ca was increased to 650 μmol mol-1. An increase from 350 to 1 050 μmol mol-1 reduced gs and E by 53 and 47 %, respectively. Changes in gs and PN maintained the Ci:Ca ratio. The water use efficiency increased linearly with Ca due to increases in PN in addition to the decline in E at high Ca. Hence CO2 enrichment increases PN and decreases gs, and can improve carrot productivity and water conservation. and S. Kyei-Boahen ... [et al.].