Relationship of leaf anatomy with photosynthetic acclimation of Valeriana jatamansi was studied under full irradiance [FI, 1 600 μmol(PPFD) m-2 s-1] and net-shade [NS, 650 μmol(PPFD) m-2 s-1]. FI plants had thicker leaves with higher respiration rate (RD), nitrogen content per unit leaf area, chlorophyll a/b ratio, high leaf mass per leaf area unit (LMA), and surface area of mesophyll cell (Smes) and chloroplasts (Sc) facing intercellular space than NS plants. The difference between leaf thickness of FI and NS leaves was about 28 % but difference in photon-saturated rate of photosynthesis per unit leaf area (PNmax) was 50 %. This indicates that PNmax can increase to a larger extent than the leaf thickness with increasing irradiance in V. jatamansi. Anatomical studies showed that the mesophyll cells of FI plants had no open spaces along the mesophyll cell walls (higher Sc), but in NS plants wide open spaces along the mesophyll cell wall (lower Sc) were found. Positive correlation between Sc and PNmax explained the higher PNmax in FI plants. Increase in mesophyll thickness increased the availability of space along the mesophyll cell wall for chloroplasts (increased Sc) and hence PNmax was higher in FI plants. Thus this Himalayan species can acclimate to full sunlight by altering leaf anatomy and therefore may be cultivated in open fields. and S. Pandey, R. Kushwaha.
Increase in both atmospheric CO2 concentration [CO2] and associated warming are likely to alter Earths' carbon balance and photosynthetic carbon fixation of dominant plant species in a given biome. An experiment was conducted in sunlit, controlled environment chambers to determine effects of atmospheric [CO2] and temperature on net photosynthetic rate (P N) and fluorescence (F) in response to internal CO2 concentration (C i) and photosynthetically active radiation (PAR) of the C4 species, big bluestem (Andropogon gerardii Vitman). Ten treatments were comprised of two [CO2] of 360 (ambient, AC) and 720 (elevated, EC) µmol mol-1 and five day/night temperature of 20/12, 25/17, 30/22, 35/27 and 40/32 °C. Treatments were imposed from 15 d after sowing (DAS) through 130 DAS. Both F-P N/Ci and F-P N/PAR response curves were measured on top most fully expanded leaves between 55 and 75 DAS. Plants grown in EC exhibited significantly higher CO2-saturated net photosynthesis (Psat), phosphoenolpyruvate carboxylase (PEPC) efficiency, and electron transport rate (ETR). At a given [CO2], increase in temperature increased P sat, PEPC efficiency, and ETR. Plants grown at EC did not differ for dark respiration rate (RD), but had significantly higher maximum photosynthesis (P max) than plants grown in AC. Increase in temperature increased Pmax, RD, and ETR, irrespective of the [CO2]. The ability of PEPC, ribulose-1,5-bisphosphate carboxylase/oxygenase, and photosystem components, derived from response curves to tolerate higher temperatures (>35 °C), particularly under EC, indicates the ability of C4 species to sustain photosynthetic capacity in future climates. and V. G. Kakani, G. K. Surabhi, K. R. Reddy.
In the dimorphic stag’s hom fem, Platycerium coronarium (Koenig ex Mueller) Desv., photosynthetic characters and chlorophyll (Chl) contents were deteiinined in both nést and pendulous fronds at different stages of ontogeny and at different positions along the longest length of each frond. Area-specific radiant energy- saturated net photosynthetic (P^) and dark respiration rates, dry mass-specific Chl content and quantum yield increased during frond development and decreased when senescence set in. Radiant energy-saturated and dry-mass specific Chl content were greatest in the youngest tissues of each frond. In addition to the functions ascribed to the nést (water and nutrient collection) and pendulous (reproduction) fronds, the results indicate the important roles of both frond types in providing Chemical energy to the growth and survival of the plant.
Contents of chlorophylls and carotenoids in yellow-green mutant Biao 810S were approximately half those in control type 810S. Biao 810S had fewer grana lamellae and looser structure than 810S, lower volume of starch granules in chloroplasts, but under high temperature and high irradiance the net photosynthetic rate (PN) of Biao 810S was higher than that of 810S. The chlorophyll fluorescence parameter Fv/Fm of Biao 810S was little higher and photochemical quenching qP was obviously higher than those of 810S. No significant differences in PN and biomass were observed in their hybrid combination. The yellow-green mutant phenotype may be a useful genetic marker of P(T)GMS rice used for hybrid seed production. and L.-J. Ou ... [et al.].
Photosynthetic parameters were studied in Arbutus unedo L. trees growing at either ambient (AC) or elevated EC (mean 465 µmol mol-1) CO2 concentration near a natural CO2 vent in Orciatico, Italy Diurnal courses of net photosynthetic rate (PN), ratio of variable to maximum chlorophyll fluorescence (Fv/Fm), and quantum yield of electron transport through photosystem 2 (Φ2) were measured on sun and shade leaves. The contents of N, C, Ca, K, P, and chlorophyll (Chl) and specific leaf area (SLA) in these leaf categories were also determined. A morning peak and midday depression of PN were found for both AC and EC sun leaves. Long-term EC caused little or no down-acclimation of PN in sum leaves. The estimate of total daily CO2 uptake was lower in AC leaves than in EC leaves. In shade leaves, it reached up to 70 % of the value of sun leaves. The Fv/Fm ratio showed decreasing trend in the morning, reached a minimum at midday (90 % of dawn value), and then increased in the afternoon. The EC had no effect on Fv/Fm either in sun or shade leaves. Plants grown near the CO2 spring had lower Chl content, higher SLA, and higher Ca and K contents than plants grown under AC. and M. Barták, A. Raschi, R. Tognetti.
To quantify photosynthetic response of wheat to the combination of a fungal brown rust infection and a post-infection drought, four treatments were compared: no stress (control), fungal stress (FS), water stress (WS), and twofold stress (WS×FS). Predawn leaf water potential (Ψwp) was similar in FS and WS treatments over a 3-week period. In the WS treatment, net photosynthetic rate (PN) and stomata CO2 conductance (gs) diminished concomitantly with a constant intercellular CO2 concentration (Ci) close to 200 µmol mol-1. In the FS treatment, a reduction of PN occurred with an increase in respiration rate (doubling of the CO2 compensation concentration) and in Ci but with no water loss modification. Healthy leaves of infected plants (FS) showed a reduction of PN as well, with constant gs and increased Ci. In the twofold stress treatment (WS×FS), leaves showed reduced PN in relation to the lower Ψwp. Deleterious effects of both drought and fungal infection on the final area of leaves and dry matter were additive. and O. Bethenod, L. Huber, H. Slimi.
Air-grown tobacco (Nicotiana tabacum L.) plants were transferred for one week into a low oxygen atmosphere (2 kPa O2, LO) to study both immediate and long-term effects of the suppression of photorespiration on net photosynthetic rate (PN), plant morphology, and chloroplast ultrastructure. The PN and the leaf conductance for CO2 increased upon exposure of attached tobacco leaves to LO. These results may suggest that under LO, external CO2 is used to consume the radiant energy normally utilized in photorespiration by net CO2 assimilation at the expense of an increased rate of transpiration. The increase in the coefficient of nonphotochemical fluorescence quenching indicates that under LO, (surplus) radiant energy is also dissipated as heat. Prolonged LO-treatment of tobacco resulted in a decrease in the PN (measured in air) and in a reduction in the number of starch grains in the chloroplasts. Concomitantly, large lipid globuli appeared in the chloroplasts and the distance between the thylakoids forming the grana decreased. These changes in the ultrastructure of chloroplasts may have contributed to the decline in the PN. The LO-treated plants were considerably smaller than the control plants maintained in air. This appears to have resulted from a reduction in the rate of leaf area expansion at the expense of an increase in the specific mass of the leaves. This long-term response to LO-treatment may allow the plants to conserve water. and A. Migge ... [et al.].
The tested tree species included pioneer species Acacia mangium, early succession stage species Schima superba, mesophyte intermediate-succession species Machilus chinensis, and shade-tolerant plant or late-succession species Cryptocarya concinna which occur in the lower subtropical forest community. A comparison with the current ambient level of UV-B radiation (UV-B) showed the leaf net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (g s) of the four species ranged from significantly decreased to no significant change. Additionally, the thickness of palisade and mesophyll in leaves of four tree species were decreased sharply by enhanced UV-B. The thickness of spongy parenchyma in leaves was also decreased except for M. chinensis. UV-B increased the leaf width of A. mangium but its leaf length, leaf thickness, and dry mass per unit area were not affected. Significantly increased stomata width was observed in A. mangium leaf epidermis in response to UV-B. Significantly decreased stomata width and significantly increased stomata density of leaf abaxial epidermis in M. chinensis were also observed. The stomata density of abaxial epidermis of C. concinna was remarkably increased by enhanced UV-B. The height and branch biomass of A. mangium and the height of S. superba were reduced visibly by enhanced UV-B. The four plant species could be classified into three groups of UV-B sensitiveness by hierarchical cluster analysis. A. mangium was sensitive to enhanced UV-B, while C. concinna showed more tolerance. and X. A. Cai ... [et al.].
We investigated the photosynthetic induction time-course in species of different ecological groups grown in contrasting forest irradiance environments, gap and understorey, exposed to different darkness times in order to verify the plant capacity to exploit irradiance heterogeneity. Photosynthetic induction was studied in leaves of Bauhinia forficata and Guazuma ulmifolia (early succession species, ES), and Esenbeckia leiocarpa and Hymenaea courbaril (late succession species, LS). T50 and T90 (time estimates to attain 50 and 90 % of maximum net photosynthetic rate, respectively) varied according to the time of previous exposure to darkness and growth irradiance. In both darkness times of 10 and 30 min, T50 was lower in the LS-than ES-species. These results, jointly with significant higher induction state of the leaves after 10 min of darkness, suggest that the LS-species has a higher potential to sunfleck utilization compared to ES-species, both grown in the understorey. After 10 and 30 min of darkness the differences between ecological groups were not clearly detected in the gap for T50 and T90, indicating that eco-physiological characteristics of each ecological group did not influence the induction time of the species evaluated herein. Thus the capacity to show phenotypic plasticity is not exclusive to an ecological group, but it is rather a more intrinsic feature related to the differential capacity of individuals. and M. T. Portes, T. H. Alves, G. M. Souza.