Characteristics of photosynthetic carbon metabolism of spikelets in rice

In lemmas and paleae of rice, the amount of pyruvate, Pi dikinase (PPDK) protein increased dramatically 6 d after anthesis and this change was consistent with that in the activity of PPDK. Since lemmas and paleae at this stage also showed high activities of the other marker enzymes of C4 pathway including phosphot enolpyruvate carboxylase (Imaizumi et al. (1990) Plant Cell Physiol 31: 835–843), photosynthetic carbon metabolism with lemmas at this stage were characterized. In a 14C pulse-12C chase study by photosynthetic CO2 fixation, about 35% and 25% of 14C fixed in lemmas were incorporated initially into 3-phosphoglycerate (3-PGA) and C4 acids, respectively. This suggests that lemmas participate mainly in C3-type photosynthetic metabolism, but that lemmas may also participate in the metabolism of C4 acids to some extent. To clarify this possibility, large amounts of 14C-labeled C4 acids were synthesized in vivo by a light-enhanced dark CO2 fixation (LED) method and the fate of 14C in C4 acids in the light was investigated. The percentage distribution of 14C in C-4 position of malate was about 90% and 83% after 10 s of photosynthetic 14CO2 fixation and 110 s of LED, respectively. Some of the 14C incorporated into C4 acids was transferred into 3-PGA and sugar phosphates. The possibility of direct fixation of CO2 by phosphot enolpyruvate carboxylase and metabolic pathway of CO2 released by decarboxylation of malate produced were discussed.     

Development of an Oligidic Diet forin VitroRearing ofTrichogramma galloiZucchi andTrichogramma pretiosumRiley

The goal of this research was to develop an artificial diet for rearingTrichogramma galloiandTrichogramma pretiosum,which are important egg parasitoids of several pests in Brazil. The diet was based on different proportions of hemolymph ofHelicoverpa zealarvae, chicken egg yolk, powdered milk solutions, bovine fetal serum, and an extract fromHeliothis virescenseggs. The ideal volume of diet for rearingT. galloiwas also evaluated. The parasitoids showed different nutritional requirements for their development. The best proportion of diet components forT. galloiwas 70% hemolymph, 20% egg yolk, 10% fetal serum, and 0.2% streptomycin, and forT. pretiosumit was 70% hemolymph, 20% egg yolk, 5% fetal serum, 5% egg extract, and 0.2% streptomycin. Egg yolk was found to be essential for the development of both parasitoids, and the powdered milk solution was not an important component in the diet. Development was not obtained in diets with hemolymph concentrations lower than 40%. A 3- to 4-μl amount of diet was the ideal volume on which to rearT. galloiwith the techniques reported.     

Biological Attributes of the Nematode, Thripinema nicklewoodi, a Potential Biological Control Agent of Western Flower Thrips

Western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is the most important insect pest for greenhouse flower crops, but chemical control is often difficult because of the thrips' location in flowers and buds. Thripinema nicklewoodi (Tylenchida: Allantonematidae) is an entomoparasitic nematode that attacks and sterilizes WFT, but its biology and impact on WFT are poorly understood. Methods to propagate and study T. nicklewoodi with a microscope slide arena for observation and a rolled bean leaf arena for rearing were developed. On average, 21.4 nematodes were excreted per day by a parasitized female WFT. The sex ratio of the excreted nematodes was 6.0/1.0 (female/male). After dissection of adult WFT, a maximum of 11 ovoid-shaped first-generation nematodes in a female thrips and 6 in a male thrips were found. There were more second-generation nematodes in the adult female WFT (192.6) than in the adult male WFT (93.7). When 50 healthy first instar WFT were exposed to 4 parasitized female WFT in a rolled bean leaf, a 75.3% mean parasitization rate in the adult stage of the thrips was obtained. In contrast to previous reports, male WFT can be parasitized as readily as females. Parasitism reduced the longevity of both adult female and adult male WFT, and the degree of reduction was higher in adult male WFT. T. nicklewoodi, when presented with various WFT life stages (first instar, second instar, prepupa, pupa, adult female, and adult male), achieved the highest attack rate in first and second instars and prepupa. The free-living nematodes excreted by the hosts actively migrated to a trichome on leaf disks in the observation arena and moved up this structure. Then, the nematode actively waved the anterior part of its body while attaching itself to the trichome with the posterior part of its body. After a nematode contacted the leg of a thrips, the nematode immediately moved up along the leg toward the abdomen of the host. Increased understanding of the biology of T. nicklewoodi is important to better assess its potential for biological control of WFT.     

N‐ASSIMILATION IN THE NOXIOUS FLAGELLATE HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE): DEPENDENCE ON LIGHT,N‐SOURCE,AND PHYSIOLOGICAL STATE1

The capabilities of the diel vertically migrating flagellate Heterosigma carterae Hulburt for assimilating ammonium and nitrate into cell‐N in light and in darkness were studied using cells of different N‐status. Ammonium utilization in darkness, except by N‐replete cells, attained>50% of use in the light. However, the capacity to use nitrate was poor in darkness, and less than 20% of nitrate‐N that was taken up in darkness was then actually incorporated into cell‐N. The ability to assimilate N in darkness improved as N‐status (N:C) declined, concurrent with an increasing content of water‐soluble carbohydrate. This carbohydrate was used to support dark N‐assimilation. Cells held in darkness for over a day and that had halted nitrate‐uptake were still capable of taking up ammonium. Furthermore, the act of taking up ammonium appeared to make available a source of C to support nitrate uptake that was previously unavailable. The implications of these results for the ecophysiology of this organism and for the construction of mathematical models of algal growth are considered.     

Incorporation of 5-aminolevulinic acid into chlorophyll in darkness in barley

The incorporation of radioactive aminolevulinic acid (ALA) into chlorophyll (Chl) a and b , as well as protochlorophyllide (Pchlide) in light-grown barley seedlings ( Hordeum vulgare L. cv. Clipper) transferred to darkness is demonstrated.
In the experiments described, 6-day-old, glasshouse-grown seedlings were transferred to darkness and incubated in [¹⁴C]- or [³H]- ALA for 18 h.
Chl a and b were extracted and purified to constant specific radioactivity by HPLC and TLC of their magnesium-free derivatives, pheophytin a and b . The presence of label in the tetrapyrrole ring of the Chls was established by removal of the phytol chain by alkaline hydrolysis and determination of the specific radioactivity of the chlorin e ₆ and rhodin g ₇ derivatives.
Barley seedlings that had been grown in darkness for 5 days, transferred to light for 20 h, and then returned to darkness in the presence of radioactive ALA also incorporated label into Chl. However, this was only apparent in intact seedlings. Excised leaves from greened etiolated plants did not incorporate ALA into Chl in darkness. This was consistent with the finding of Apel et al. (K. Apel, M. Motzkus and K. Dehesh, 1984. Planta 161: 550–554) and may account for their failure to obtain evidence for a light-independent protochlorophyllide reductase in greening barley.
Although the incorporation of ALA into Chl compared to Pchlide was slight (5%), the presence of label in the tetrapyrrole nucleus of Chl a and b is unequivocal evidence of a light-independent pathway of Chl biosynthesis in barley that has been exposed to light during development. Limited entry of exogenous labelled ALA into the precursor pools leading to the dark reduction of Pchlide is postulated.     

CARBON ALLOCATION IN MACROCYSTIS PYRIFERA (PHAEOPHYTA): INTRINSIC VARIABILITY IN PHOTOSYNTHESIS AND RESPIRATION1

Measurements of net photosynthesis (PS, O₂ evolution), dark respiration (R, O₂ consumption), and light and dark carbon fixation (¹⁴C) were conducted on whole blades, isolated blade discs, sporophylls, apical scimitars and representative portions of stipe and holdfast of the giant kelp Macrocystis pyrifera L.C. Ag. On a dry weight basis, highest net PS rates were observed in apical scimitar segments and whole blades (3.81 and 3.07 mgC · g dry wt^?1· h^?1, respectively), followed by sporophylls (1.42 mgC·g dry wt^?1· h^?1) and stipe segments (0.15 mgC·g dry wt^?1· h^?1). No PS capacity was observed in holdfast material. Respiration rates showed similar ranking ranging from 1.22 mgC·g dry wt^?1·h^?1 for apical scimitar to 0.18–0.22 mgC·g dry wt^?1· h^?1 for holdfast material. Considerable within blade variability in both PS and R was also found. Steepest PS and R gradients on both an areal and weight basis were found within immature blades followed by senescent and mature blade material. Highest net PS rates were associated with the blade tips ranging from 3.08 (mature blades) to 10.3 mgC·dry wt^?1·h^?1 (immature blades). Highest rates of R generally occurred towards the basal portions of blades and ranged from 1.03–1.80 mgC·g dry wt^?1·h^?1 for immature blades. The variability within and between blades was high, with coefficients of variation approaching 50%. The observed patterns can be related to the decreasing proportionment of photosynthetic tissue and increasing proportionment of structural tissue as occurs from the blade tip to the blade base. Rates of light carbon fixation (LCF) revealed longitudinal profiles similar to oxygen measurements for the different blade types, with the absolute rates being slightly lower. Patterns of dark carbon fixation (DCF) were less easily interpreted. Highest rates of DCF (0.04–0.06 mgC·g dry wt^?1·h^?1) occurred at the basal portions of immature and senescent blades. Longitudinal profiles of total chlorophyll (a + c) on both an areal and weight basis were very similar to the profiles of PS. Normalized to chlorophyll a, PS displayed an unusual longitudinal profile in immature tissue; however, such profiles for mature and senescent tissues were similar to those for PS on an areal basis. It was demonstrated that it is difficult, if not impossible, to select single tissue discs that are representative of whole blades. The metabolic longitudinal profiles reveal a characteristic developmental pattern; the previous working definitions of immature, mature, and senescent blades, based on morphology and frond position thus have a physiological basis.     

Biological parameters of Thripobius semiluteus Bouček (Hym., Eulophidae), a larval endoparasitoid of Heliothrips haemorrhoidalis (Bouché) (Thysan., Thripidae)

Abstract:  The endoparasitoid Thripobius semiluteus Bouček was recently introduced to Italy from Israel for the biological control of Heliothrips haemorrhoidalis (Bouché). In this study, some aspects of the biology of T. semiluteus were determined in the laboratory. Developmental time (egg to adult), potential fecundity, realized fecundity, progeny, daily rate of deposition of eggs and several demographic growth parameters were evaluated. Studies of the longevity of fed and starved adults at seven temperatures (3, 10, 15, 20, 23, 25 and 30 ± 1°C) showed that fed T. semiluteus lived longest at 15°C (36.45 days) and shortest at 3°C (1.45 days). Longevity was reduced significantly at higher and lower temperatures than 15°C and when honey was not provided. Development time was measured at six temperatures. Pupae did not complete development at 10°C. The lower theoretical temperature threshold was 9.0°C; the optimum developmental temperature and the upper lethal threshold were 28.0°C and 34.1°C respectively. The most rapid development was found at 30°C, but waSPS suffered significantly higher mortality at this temperature than at other temperatures. Ovigeny index showed that T. semiluteus is synovigenic, with a mean realized fecundity of 78.8 eggs per female. The mean progeny was 68.2 adults per female on fed adults.