Effects of water and nitrogen (N) supply on growth and photosynthetic response of B. carinata were examined in this study. Plant growth and related characteristics varied significantly in response to the availability of water and nitrogen. B. carinata maximized the utilization efficiency of the most limiting resources by developing physiological adaptations, such as changes in root and leaf development. The utilization of water and N was tightly linked with the availability of each resource. Instantaneous water-use efficiency (WUE) was always greater in plants with high-N nutrition [50, 100, and 150 kg(N) ha-1] than in the low-N-treated plants
[0 kg(N) ha-1] in all watering treatments. Instantaneous N-use efficiency (PNUE) decreased significantly with increasing water stress in all N treatments. Seed yield is significantly related to PNUE (p>0.05) but not WUE (p<0.05). The positive relationship between leaf net photosynthetic rate (PN) and seed yield suggests that PN can be used as an important tool for selection of new strains with high seed yield. and X. Pan ... [et al.].
Environmental conditions that promote photorespiration are considered to be a major driving force for the evolution of C4 species from C3 ancestors. The genus Flaveria contains C3 and C4 species as well as a variety of intermediate species. In this study, we compare the water-use efficiency of intermediate Flaveria species to that of C3 and C4 species. The results indicate that under both well-watered and a drought-stress condition, C3-C4 and C4-like intermediacy in Flaveria species improve water-use efficiency as compared to C3 species. and M. C. Dias, W. Brüggemann.
After the formulation of the photosynthetic unit (PSU) concerning the cooperation of 2400 chlorophyll molecules in the reduction of one molecule of C02 by Emerson and Arnold in 1932, the search for a morphological expression of the functional unit began. The quantasome hypothesis is an attempt to relate the structure visible in the electron microscope, the quantasome, and the PSU. The term 'quantasome' was introduced by Park and Calvin as a name for grana subunits. The quantasomes were regarded as the main integral parts of the grana lamellae in the protein lipid layers. Yet it soon became clear that a morphological mit such as the quantasomes did not exist. Nevertheless, the term was still used in various applications till the eighties.
The carbon dioxide concentrating system in C4 photosynthesis allows high net photosynthetic rates (PN) at low internal carbon dioxide concentrations (Ci), permitting higher PN relative to stomatal conductance (gs) than in C3 plants. This relation would be reflected in the ratio of Ci to external ambient (Ca) carbon dioxide concentration, which is often given as 0.3 or 0.4 for C4 plants. For a Ca of 360 µmol mol-1 that would mean a Ci about 110-140 µmol mol-1. Our field observations made near midday on three weedy C4 species, Amaranthus retroflexus, Echinochloa crus-galli, and Setaria faberi, and the C4 crop Sorghum bicolor indicated mean values of Ci of 183-212 µ mol mol-1 at Ca = 360 µmol mol-1. Measurements in two other C4 crop species grown with three levels of N fertilizer indicated that while midday values of Ci at high photon flux were higher at limiting N, even at high nitrogen Ci averaged 212 and 196 µmol mol-1 for Amaranthus hypochondriacus and Zea mays, respectively. In these two crops midday Ci decreased with increasing leaf to air water vapor pressure difference. Averaged over all measurement days, the mean Ci across all C4 species was 198 µmol mol-1, for a Ci/Ca ratio of 0.55. Prior measurements on four herbaceous C3 species using the same instrument indicated an average Ci/Ca ratio of 0.69. Hence midday Ci values in C4 species under field conditions may often be considerably higher and more similar to those of C3 species than expected from measurements made on plants in controlled environments. Reducing gs in C4 crops at low water vapor pressure differences could potentially improve their water use efficiency without decreasing PN.
High temperature is a common constraint during anthesis and grain-filling stages of wheat leading to huge losses in yield. In order to understand the mechanism of heat tolerance during monocarpic senescence, the present study was carried out under field conditions by allowing two well characterized Triticum aestivum L. cultivars differing in heat tolerance, Hindi62 (heat-tolerant) and PBW343 (heat-susceptible), to suffer maximum heat stress under late sown conditions. Senescence was characterized by measuring photosynthesis related processes and endoproteolytic activity during non-stress environment (NSE) as well as heat-stress environment (HSE). There was a faster rate of senescence under HSE in both the genotypes. Hindi62, having pale yellow flag leaf with larger area, maintained cooler canopy under high temperatures than PBW343. The tolerance for high temperature in Hindi62 was clearly evident in terms of slower green-leaf area degradation, higher stomatal conductance, higher stability in maximum PSII efficiency, Rubisco activity and Rubisco content than PBW343. Both the genotypes exhibited lower endopeptidase activity under HSE as compared to NSE and this difference was more apparent in Hindi62. Serine proteases are the predominant proteases responsible for protein degradation under NSE as well as HSE. Flag leaf of both the genotypes exhibited high-molecular-mass endoproteases (78 kDa and 67 kDa) isoforms up to full grain maturity which were inhibited by specific serine protease inhibitor in both the environments. In conclusion, the heat-tolerant Hindi62 exhibited a slower rate of senescence than the heat-susceptible PBW343 during HSE, which may contribute towards heat stability. and S. Chauhan ... [et al.].
The thermoluminescence signals from leaflets of the same pea plant varied gradually according to their developmental stage. The AG emission, due to a back flow of electrons towards photosystem 2 (PS2) along a cyclic/chlororespiratory pathway, was stronger in mature leaves than in the growing ones. These age-related variations could be explained by a higher capacity of cyclic electron flow in mature leaves.
The coffee plant is native to shaded environments and its seedlings are often produced in shaded nurseries. However, some nursery managers, in an effort to improve the acclimation of seedlings to field conditions after transplantation, produce seedlings in full sun exposure. In this study, the morphological and physiological parameters of arabica coffee (Coffea arabica) seedlings produced in full sun (T1) and in shade (T2) were examined. The biomass accumulation and relative growth rate of T1 and T2 seedlings were similar. The T1 seedlings had less biomass allocation to shoots, a lower leaf mass ratio and a lower leaf area ratio; however, they had a greater net assimilation rate (rate of increase in plant mass per unit leaf area), which was associated with a greater net photosynthetic rate. There were no alterations in the concentrations of total chlorophylls or in the chlorophyll a/b ratio when comparing T1 and T2 seedlings. No indications of photoinhibition or photooxidative damage were observed in the T1 plants, which were shown to have a more robust antioxidant system than the T2 plants. Seedlings transferred from shade to full sun (T3) were not capable of utilising the incident extra light to fix CO2. These seedlings showed a remarkable nocturnal retention of zeaxanthin and a significantly increased deepoxidation state of the xanthophyll cycle, even at predawn, but the activity of antioxidant enzymes was lower than in the T1 and T2 plants. Despite the acclimation capacity of T3 seedlings to the new light environment, they exhibited chronic photoinhibition and considerable photooxidative damage throughout the seven days following the transfer to full sun exposure. We further discuss the practical implications of producing coffee seedlings in full sunlight and under shade. and G. A. B. K. Moraes ... [et al.].