Gas Exchange and Carbon Partitioning in the Leaves of Celery (Apium graveolens L.) at Various Levels of Root Zone Salinity

Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress.     

Mannitol Synthesis in Higher Plants : Evidence for the Role and Characterization of a NADPH-Dependent Mannose 6-Phosphate Reductase

Mannitol is a major photosynthetic product in many algae and higher plants. Photosynthetic pulse and pulse-chase ¹⁴C-radiolabeling studies with the mannitol-synthesizing species, celery (Apium graveolens L.) and privet (Ligustrum vulgare L.), showed that mannose 6-phosphate (M6P) and mannitol 1-phosphate were among the early photosynthetic products. A NADPH-dependent M6P reductase was detected in these species (representing two different higher plant families), and the enzyme was purified to apparent homogeneity (68-fold with a 22% yield) and characterized from celery leaf extracts. The celery enzyme had a monomeric molecular mass, estimated from mobilities on sodium dodecyl sulfate-polyacrylamide gels, of 35 kilodaltons. The isoelectric point was pH 4.9; the apparent K_m (M6P) was 15.8 millimolar, but the apparent K_m (mannitol 1-phosphate) averaged threefold higher; pH optima were 7.5 with M6P/NADPH and 8.5 with mannitol 1-phosphate/NADP as substrates. Substrate and cofactor requirements were quite specific. NADH did not substitute for NADPH, and there was no detectable activity with fructose 6-phosphate, glucose 6-phosphate, fructose 1-phosphate, mannose 1-phosphate, mannose, or mannitol. NAD only partially substituted for NADP. Mg²⁺, Ca²⁺, Zn²⁺, and fructose-2,6-bisphosphate had no apparent effects on the purified enzyme's activity. In vivo radiolabeling results and the enzyme's kinetics, specificity, and distribution (in two-plant families) all suggest that NADPH-dependent M6P reductase plays an important role in mannitol biosynthesis in higher plants.     

Differential effects of dimethyl sulfoxide and sodium butyrate on α-fetoprotein,albumin, and transferrin production by rat hepatomas in culture

Summary Radioimmunoassay was used to determine α-fetoprotein (AFP), albumin, and transferrin production (ng/10⁵ cells/24 h) by two cell lines (7777 and 8994) derived from chemically induced rat hepatomas. α-Fetoprotein production was high (2000 to 4400) in 7777, but was very low (0.2 to 0.4) in 8994. Albumin production varied from 0.4–0.8 (7777) to 14–26 (8994). Both lines produced substantial amounts of transferrin (180 to 240 by 7777 and 29 to 42 by 8994). Addition of dimethyl sulfoxide (DMSO, 1 to 4%) or sodium butyrate (BA, 0.5 to 2.0 mM) to the medium inhibited growth in both lines, but 8994 was more sensitive to these agents than 7777. Dimethyl sulfoxide treatment (2 to 4%) resulted in a dose-related decrease (<10% of control at 4% DMSO) in AFP, albumin, and transferrin production by 7777, but in 8994, DMSO (1 to 2%) resulted in an increase, (up to sixfold) in albumin and transferrin production, without affecting AFP production. By contrast, BA (2 to 4 mM) stimulated the production of all three proteins in both lines, most notably that of albumin (up to sixfold) by 7777 and that of AFP (up to 20-fold) by 8994. It is concluded that both DMSO and BA can enhance the expression of differentiated functions of the hepatoma cell, and that DMSO at the same time can suppress the expression of an oncofetal function. However, neither DMSO nor BA is selective in its effects on specific genes (i.e., normal, adult vs. oncofetal genes), and it appears that their effects may be the result of a more general phenomenon, the expression of which may be related to the stage of differentiation of the cell.     

Production of polyclonal antibodies in rabbits is simplified using perforated plastic golf balls.

Production of polyclonal antibodies in the lumen of a perforated golf ball implanted surgically under the skin of a rabbit offers advantages over conventional techniques. Less stress is placed on the rabbit because bleeding is eliminated, complete adjuvants are not used and animal handling is minimized. The technique also offers the advantage that large amounts of antibody-containing fluid can be removed easily from the ball. In this report we describe the surgical protocol and demonstrate use of this technique to produce high-titered antibodies to plant and plant viral proteins.     

5'-Nucleotide phosphodiesterase: features of the substrate binding site as deduced from specificity and kinetics of some novel substrates

Phosphonate monoesters and phosphate diesters with systematically varied substituents and leaving groups were synthesized and tested as substrates for homogeneous 5'-nucleotide phosphodiesterase from bovine intestine. The enzyme was shown to hydrolyze phosphorothioate and phosphonoamidate compounds but at significantly lower rates than comparable oxy compounds. The effects of bulk and structure of the ester or phosphonate substituents were also investigated. Dibenzyl phosphate, an ester of an aliphatic alcohol, was a poor substrate. The enzyme did not hydrolyze aliphatic monoesters of phosphonates, regardless of bulk. Kinetic parameters of several nitrophenyl phosphonomonoesters and phosphodiesters are presented. The results suggest that synthetic nonnucleotide substrates can bind in two different modes, only one of which is productive. Incidence of nonproductive binding, with consequent kinetic effects, is increased by increasing the symmetry of the substrates.     

Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on development within the host

The monogenean Protopolystoma xenopodis has been established in Wales for >40 years following introduction with Xenopus laevis from South Africa. This provides an experimental system for determining constraints affecting introduced species in novel environments. Parasite development post-infection was followed at 15, 20 and 25°C for 15 weeks and at 10°C for ?1 year and correlated with temperatures recorded in Wales. Development was slowed/arrested at ?10°C which reflects habitat conditions for >6 months/year. There was wide variation in growth at constant temperature (body size differing by >10 times) potentially attributable in part to genotype-specific host-parasite interactions. Parasite density had no effect on size but host sex did: worms in males were 1·8 times larger than in females. Minimum time to patency was 51 days at 25°C and 73 days at 20°C although some infections were still not patent at both temperatures by 105 days p.i. In Wales, fastest developing infections may mature within one summer (about 12 weeks), possibly accelerated by movements of hosts into warmer surface waters. Otherwise, development slows/stops in October-April, delaying patency to about 1 year p.i., while wide variation in developmental rates may impose delays of 2 years in some primary infections and even longer in secondary infections.     

Environmental constraints influencing survival of an African parasite in a north temperate habitat: effects of temperature on egg development

Factors affecting survival of parasites introduced to new geographical regions include changes in environmental temperature. Protopolystoma xenopodis is a monogenean introduced with the amphibian Xenopus laevis from South Africa to Wales (probably in the 1960s) where low water temperatures impose major constraints on life-cycle processes. Effects were quantified by maintenance of eggs from infections in Wales under controlled conditions at 10, 12, 15, 18, 20 and 25°C. The threshold for egg viability/ development was 15°C. Mean times to hatching were 22 days at 25°C, 32 days at 20°C, extending to 66 days at 15°C. Field temperature records provided calibration of transmission schedules. Although egg production continues year-round, all eggs produced during >8 months/ year die without hatching. Output contributing significantly to transmission is restricted to 10 weeks (May-mid-July). Host infection, beginning after a time lag of 8 weeks for egg development, is also restricted to 10 weeks (July-September). Habitat temperatures (mean 15·5°C in summer 2008) allow only a narrow margin for life-cycle progress: even small temperature increases, predicted with 'global warming', enhance infection. This system provides empirical data on the metrics of transmission permitting long-term persistence of isolated parasite populations in limiting environments.     

Tinted Semi‐Transparent Solar Panels Allow Concurrent Production of Crops and Electricity on the Same Cropland

Agrivoltaics describes concurrent agricultural production of crops and photovoltaic generation of electricity on the same cropland. By using tinted semi‐transparent solar panels, this study introduces a novel element to transform the concept of agrivoltaics from just solar‐sharing to selective utilization of different light wavelengths. Agrivoltaic growth of basil and spinach is tested. When compared with classical agriculture, and based on the feed‐in‐tariff of the experimental location, agrivoltaic co‐generation of biomass and electricity is calculated to result in an estimated financial gross gain up to +2.5% for basil and +35% for spinach. Marketable biomass yields do not change significantly for basil, while a statistically significant loss is observed for spinach. This is accompanied by a relative increase in the protein content for both plants grown under agrivoltaic conditions. Agrivoltaics implemented with tinted solar panels improve the biomass production per unit amount of solar radiation up to 68%, with up to 63% increase in the ratio of leaf and stem biomass to root. Agrivoltaics can enrich the portfolio of farmers, mitigate risks associated with climate, and vastly enhance global photovoltaics capacity without compromising agricultural production.