Developmental changes of plant in the regulation of photosynthate distribution of leaves were studied in hydroponically cultivated rice by the 14CO2 tracer technique and analysis of the activity of the regulatory enzymes, sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), and pyruvate kinase (PK). The distribution of primary photosynthates into sugars, amino acids, organic acids, sugar phosphates, proteins, and polysaccharides was determined by column chromatography. The relative primary photosynthate distribution to the sugar phosphate fraction was significantly larger in the 5th leaf than in the 6th one. Correspondingly, the Vmax of PEPC was significantly higher in the 5th than in the 6th leaf, while no significant differences between leaves were detected in the other enzymes. As a consequence, the ratio of the Vmax of SPS and PEPC was lower in the 5th than in the 6th leaf. As the 5th leaf develops before panicle initiation in rice, it predominantly supports vegetative growth, while the 6th leaf develops after panicle initiation and thus contributes mainly to reproductive growth. We conclude that the physiological properties of each leaf are regulated developmentally. When the 6th leaf became fully expanded (corresponding to the panicle initiation stage of plant), the distribution pattern of 14C was transiently changed in the 5th leaf, indicating that individual organs that are mainly involved in vegetative development are affected to some extent by the whole-plant-level physiological transformation that occurs at the transition from the vegetative to the reproductive stage. and T. Shinano ... [et al.].
Alterations in photosynthetic capacity of primary leaves of wheat seedlings in response to ultraviolet-B (UV-B; 280-320 nm; 60 µmol m-2 s-1) exposure alone and in combination with photosynthetically active radiation (PAR; 400-800 nm; 200 µmol m-2 s-1) during different phases of leaf growth and development were assessed. UV-B exposure resulted in a phase-dependent differential loss in photosynthetic pigments, photochemical potential, photosystem 2 (PS2) quantum yield, and in vivo O2 evolution. UV-B exposure induced maximum damage to the photosynthetic apparatus during senescence phase of development. The damages were partially alleviated when UV-B exposure was accompanied by PAR. UV-B induced an enhancement in accumulation of flavonoids during all phases of development while it caused a decline in anthocyanin content during senescence. The differential changes in these parameters demonstrated the adaptation ability of leaves to UV-B stress during all phases of development and the ability was modified in UV-B+ PAR exposed samples. and M. K. Pradhan ... [et al.].
mRNA expression patterns of genes for metabolic key enzymes sucrose phosphate synthase (SPS), phosphoenolpyruvate carboxylase (PEPC), pyruvate kinase, ribulose 1,5-bisphosphate carboxylase/oxygenase, glutamine synthetase 1, and glutamine synthetase 2 were investigated in leaves of rice plants grown at two nitrogen (N) supplies (N0.5, N3.0). The relative gene expression patterns were similar in all leaves except for 9th leaf, in which mRNA levels were generally depressed. Though increased N supply prolonged the expression period of each mRNA, it did not affect the relative expression intensity of any mRNA in a given leaf. SPS Vmax, SPS limiting and PEPC activities, and carbon flow were examined. The ratio between PEPC activity and SPS Vmax was higher in leaves developed at the vegetative growth stage (vegetative leaves: 5th and 7th leaves) than in leaves developed after the ear primordia formation stage (reproductive leaves: 9th and flag leaves). PEPC activity and SPS Vmax decreased with declining leaf N content. After using 14CO2 the 14C photosynthate distribution in the amino acid fraction was higher in vegetative than in reproductive leaves when compared for the same leaf N status. Thus, at high PEPC/SPS activities ratio, more 14C photosynthate was distributed to the amino acid pool, whereas at higher SPS activity more 14C was channelled into the saccharide fraction. Thus, leaf ontogeny was an important factor controlling photosynthate distribution to the N- or C-pool, respectively, regardless of the leaf N status. and T. Shinano ... [et al.].
Orcuttieae is a small tribe of C4 grasses endemic to seasonal pools in the southwestern U.S., comprising the basal genus Neostapfia, Tuctoria, and the most derived group, Orcuttia. Growth is initiated underwater, and when pools dry, species undergo a metamorphosis replacing aquatic foliage with terrestrial foliage. O. californica and O. viscida exhibit CAM-like diel fluctuations in acidity in the aquatic foliage. Pulse-chase studies showed that although CO2 was fixed into malic acid in the dark, an overnight chase in the dark revealed that most label was not retained in organic acids, indicating a role other than CAM. Terrestrial foliage exhibited a very different diel fluctuation; acids accumulated during the day, and diminished overnight. Malic acid predominated and was secreted on the surface of the leaf in a manner similar to another arid land species. This terrestrial daytime acid accumulation may not be related to photosynthetic pathway but may play an anti-herbivore function. No acid fluctuations were observed in either N. colusana or T. greenei.
Among various C4 plants we found a wide range in the level of inactivation of phosphoenolpyruvate carboxylase (PEPC) at low temperature (0 °C). The activity of the 2-fold diluted enzyme in crude leaf extracts after 60 min incubation (compared to zero time incubation) at pH 7.5, remained above 87 % at low temperatures for the species Setaria verticillata, Portulaca oleracea, and Saccharum officinarum, and between 11 and 17 % in the species Cynodon dactylon and Atriplex halimus. The enzyme exhibited intermediate levels of inactivation (42 to 58 %) for the species Amaranthus sp., Zea mays, Salsola kali, and Digitaria sanguinalis. The enzyme activity for S. verticillata was unaffected between pH 5.7 and 8.4 during incubation at room and low temperatures. Under similar conditions, the activity of the enzyme from C. dactylon was stable between pH 5.7 and 7.0 and decreased at pH above 7.0, but for Z. mays it was enhanced between pH 5.7 and 6.8 and decreased at pH above 7.0. and G. Zervoudakis ... [et al.].
Field gas exchange and water potential in the leaves of a C3 dicot, Plantago asiatica L., and a C4 monocot, Eleusine indica Gaertn., which dominate in trampled vegetation in eastern Japan were surveyed during the growing periods for two consecutive years. Net photosynthetic rate (PN) of E. indica increased with photosynthetic photon flux density (PPFD) and leaf temperature (TL). PN was not saturated at PPFDs above 1500 µmol m-2 s-1 and at TL above 30 °C. On a sunny day in mid summer, maximum PN was two times higher in E. indica than in P. asiatica [42 vs. 20 µmol(CO2) m-2 s-1], but their transpiration rate (E) and the leaf water potential (ΨL) were similar. Soil-to-leaf hydraulic conductance, which probably plays a role in water absorption from the trampled compact soil, was higher in E. indica than in P. asiatica. The differences in photosynthetic traits between E. indica explain why E. indica communities more commonly develop at heavily trampled sites in summer than the P. asiatica communities. and T. Kobayashi, K. Okamoto, Y. Hori.
Differences in leaf δ13C among four dominant species as well as the species-specific response to the fluctuations of either soil moisture or monthly mean temperature were examined along a secondary succession sere with a time scale from 3 to 149 y on the Loess Plateau in north-western China. We used leaf δ13C as a surrogate for water use efficiency (WUE) of the mentioned dominant species. Bothrichloa ischaemun as a dominant species in the final succession stage belongs to C4 photosynthesis pathway, while the other three dominant species occurring in the first three succession stages belong to C3 pathway. The overall trend of leaf δ13C variation among the three C3 species was Artemisia gmelinii (in the third stage) and Lespedeza davurica (in the second stage) > Artemisia scoparia (in the first stage). This suggests that species with higher WUE (more positive leaf δ13C) would have substantial competitive advantages in the context of vegetation succession. Furthermore, species with highest WUE (i.e. C4 pathway) have great potential to be dominant in the final succession stage in the habitats (such as the study area) undergoing strong water stress in growing season. The evolution of WUE among the dominant species occurring in different succession stages strongly depends on the time scale of given stage since abandonment. The longer the time scale is, the more significant the differences among them in terms of leaf δ13C, hence WUE. Our results support the notions that leaf δ13C may be more positive when water supply is less favourable.
The effects of continuous soil hypoxia on stomatal conductance (g^ and net photosynthetic rate (P^) ů* seedlings of Taxodium disíichum, Quercus lyrata, and Q. falcata var. pagodaefolia were studied under controlled environment. Soil oxygen deficiency induced significant stomatal closure and reduction of in oak species within 1-3 d. This response pattem continued resulting in average daily values of g^ reduced 85 and 40 % within 14 d in g. falcata and Q. lyrata as compared to control plants, respectively. Ehiring the same period Pn reduced 96 and 71 % in 0. falcata and Q. lyrata as compared to control plants, respectively. In T. distichum, however, gg and Pff were reduced 18 and 33 % by day 8. Significant recoveiy of gg and was noted in T. distichum. By day 14, gg had recovered to 91 % and to 92 % of control plants. In oak species, however, remained significantly lower than in control plants without any apparent recovery. The regain of photosynthetic activity and stomatal functioning in flood-tolerant species appears to be an important flood- tolerance characteristic allowing these species to fimction under flooded soil.
In crowns of chestnut trees the absorption of radiant energy is not homogeneous; leaves from the south (S) side are the most irradiated, but leaves from the east (E) and west (W) sides receive around 70 % and those from north (N) face less than 20 % of the S irradiation. Compared to the S leaves, those from the N side were 10 % smaller, their stomata density was 14 % smaller, and their laminae were 21 % thinner. N leaves had 0.63 g(Chl) m-2, corresponding to 93 % of total chlorophyll (Chl) amount in leaves of S side. The ratios of Chl a/b were 2.9 and 3.1 and of Chl/carotenoids (Car) 5.2 and 4.8, respectively, in N and S leaves. Net photosynthetic rate (PN) was 3.9 µmol(CO2) m-2 s-1 in S leaves, in the E, W, and N leaves 81, 77, and 38 % of that value, respectively. Morning time (10:00 h) was the period of highest PN in the whole crown, followed by 13:00 h (85 % of S) and 16:00 h with 59 %. Below 500 µmol m-2 s-1 of photosynthetic photon flux density (PPFD), N leaves produced the highest PN, while at higher PPFD, the S leaves were most active. In addition, the fruits from S side were 10 % larger than those from the N side. and J. Gomes-Laranjo ... [et al.].