The photosynthetic response of 8 cotton (Gossypium hirsutum L.) genotypes to changing irradiance was investigated under field conditions during the 1998 through 2000 growing seasons. Equations developed to describe the response of net photosynthetic rate (PN) to photosynthetic photon flux density (PPFD) demonstrated that, across all irradiances, the two okra leaf-type genotypes photosynthesized at a greater rate per unit leaf area than all of the six normal leaf-type genotypes. This superior photosynthetic performance of the okra leaf-type genotypes can be partially explained by their 13 % greater leaf chlorophyll content relative to that of the normal leaf-type genotypes. The 37 % reduction in leaf size brought upon by the okra leaf trait may have concentrated the amount of photosynthetic machinery per unit leaf area. Nevertheless, the lack of sufficient canopy leaf surface area suppressed the potential yield development that could accompany the higher PN per unit leaf area.
A list of plant species documented over the past 25 years to exhibit Crassulacean Acid Metabolism (CAM) is presented. The list compiles all available information on these species including their growth habits, succulent parts, carbon isotope discrimination values, CAM types, CAM inducers, and CAM modifications.
In Sedum wrightii grown in a growth chamber, detached leaves could survive for at least 120 d with a high rate of success for propagule formation. The pattern of gas exchange, associated with CAM, may be important in extending the period during which the detached leaf remains physiologically active. The added benefit for the developing propagule, still attached to the "parent" leaf, is an additional source of water and saccharide reserves over an extended period necessary for rooting. Drought survival of propagules may be determined by the amount of water-storing tissue in the detached leaf.
The epiphytic fern Platycerium bifurcatum grows in different habitats characterized by drought and high irradiance stress. The plant shows diurnal malate oscillations, indicative for CAM expression only in cover leaves, but not in sporotrophophyll. In P. bifurcatum cover leaves exposed to high irradiance and desiccation, the decrease in both CO2 assimilation (PN) and stomatal conductance (gs) was accompanied with occurrence of diurnal malate oscillations. Exogenously applied abscisic acid (ABA) induced the decrease in PN and gs, but no clear change in malate oscillations. The measurements of the maximum quantum efficiency of photosystem 2 (Fv/Fm) under high irradiance showed distinct photoinhibition, but no clear changes in Fv/Fm due to desiccation and ABA-treatment were found. and G. Rut ... [et al.].
Goldspur apple (Malus pumila cv. Goldspur) is one of the main fruit trees planted in semiarid loess hilly areas. The photosynthetic efficiency in leaves of eight-year-old trees were studied under different soil water conditions with a Li-6400 portable photosynthesis system and a Li-Cor1600 portable steady state porometer in order to explore the effects of soil water stress on photosynthesis and the suitable soil water content (SWC) for water-saving irrigation of apple orchards. The results showed that the leaf net photosynthetic rate (P N), transpiration rate (E), water-use efficiency (WUE), stomatal conductance (gs), intercellular CO2 concentration (Ci), and stomatal limiting value (Ls) displayed different threshold responses to soil water variation. When SWC was within a range of about 60%-86% of field capacity (FC), PN and E were maintained in a relative steady state. At an elevated level but below 60% of FC, both PN and E decreased evidently with decreasing soil moisture. The SWC needed to support WUE in a relatively steady state and at a high level was in the range of about 50%-71% of FC. When SWC was less than 48% of FC, g s and Ls declined with decreasing soil moisture, while Ci increased rapidly. Based on the analysis of the stomatal limitation of photosynthesis using two criteria (Ci and Ls) suggested by Farquhar and Sharkey, it was implied that the predominant cause of restricting PN had changed from stomatal limitation to nonstomatal one under severe water stress. In terms of water-saving irrigation for enhancing water-use efficiency, it was concluded that in semiarid loess hilly areas, the suitable range of SWC for water-saving irrigation in goldspur apple orchards is in the range of about 50%-71% of FC, and the most severe degree of soil water stress tolerated for photosynthesis is about 48% of FC. and S. Y. Zhang ... [et al.].
The occurrence of shade and drought stress either individually or simultaneously causes altered morphophysiological and molecular responses in crops. Nevertheless, responses of crop plants to combined shade and drought stress are unique as compared to those of individually occurring stress which urges need to study and identify distinctions, commonalities, and the interaction between responses of plants to these concurrent stress factors. In the present review, we outlined currently available knowledge on responses of plants to shade and drought stress on a shared as well as the unique basis and tried to find a common thread potentially underlying these responses. Then, we briefly described some plausible mitigation strategies to cope with these stresses along with future perspectives. A deeper insight into plant responses to co-occurring shade and drought stress will help us to generate crops with broad-spectrum stress tolerance and increased resilience to such stresses in high planting densities or intercropping systems, thus, ensuring food security.
A filamentous freshwater cyanobacteriuni, identifíed as Oscillatoria annae, has two different phycoerythrins. One of them contains only phycoerythrobilin chromophores, thus being a typical C-phycoerythrin. The other has both phycoerythrobilin and phycourobilin chromophores and is therefore related to CU- phycoerythrins (cyanobacterial phycoerythrins containing urobilin). The stoichiometry of the chromophore prosthetic groups in CU-phycoerythrin from O. annae is 1:1, therefore the (ap)-polypeptide monomer of this phycoerythrin carries three phycoerythrobilin and three phycourobilin prosthetic groups. The pigment is believed to be a new t3T)e of CU-phycoerythrin.
Ten day old pea plants {Pisum sativum L., cv. Ran) were ušed to analýze the effects of Cu2+ ions on the dry mass, chlorophyll, carotenoid and proline contents, rates of photosynthesis (En) and transpiration {E), stomatal resistance {r^, carboxylation enzymes activities (RuBPC, PEPC), RNA and protein syntheses and changes in chloroplast structure. Cu^^ treated plants showed lower chlorophyll a and carotenoids contents, and higher than Controls. Pii, E and protein synthesis were significantly reduced. Four days after metal treatment P^ was 5-7 % at 500 and 1000 pM Cu2+ from the Controls, was reduced and E was increased by all ušed metal concentrations. The lower RuBPC activity after the 4 d treatment by 1000 pM Cu2+ could be due to the inhibition of de novo protein synthesis. The higher proline content was probably due to the same reason. Cu2+ ions did not change RNA synthesis in pea leaves. We foímd complete disintegration of chloroplast lamellar systém 4 d after 1000 pM Cu2+ treatment, which confirmed the observed ftmctional changes.