Quantum yields for CO2 uptake in some diploid and tetraploid plant species

Abstract. Quantum (photon) yields for CO₂ uptake on an absorbed photon fluence rate (PFR) basis (φ_a) were determined for a number of diploid and tetraploid species under a range of experimental conditions. Little variation in φ_a was found either between species or across ploidy levels, which suggests that there are no intrinsic differences in the kinetics of CO₂ fixation. Variations in photosynthetic rate or quantum yield expressed on an incident PFR basis (φ_j) were found to be largely due to differences in leaf absorptance. On this basis these results do not support the biochemical evidence showing ploidy-related differences in the K_m (CO₂) of ribulose -1,5-bisphosphate carboxylase/oxygenase. However, there are obvious difficulties in relating in vitro enzyme kinetic data to in vivo studies and these problems are discussed.     

Germination of Rye Embryos Following Hydration-Dehydration Treatments: Enhancement of Protein and RNA Synthesis and Earlier Induction of DNA Replication

On germination of low viability embryos of rye, var. LovaszPatonai, the rate of protein synthesis increases during theearly hours of imbibition and high rates of DNA replicationcommence around the 9th hour. If embryos are imbibed for 3 or6 h then dehydrated back to their original weight, their rateof protein synthesis when next imbibed closely corresponds tothat of embryos germinated for a period equal to that of thehydration pre-treatment plus the duration of the second imbibition.Pre-treatment also enhances subsequent RNA synthesis and embryoshydrated for 9 h then dehydrated start major DNA synthesis atonce as water is again supplied. Many changes occurring duringthese periods of hydration pre-treatment must therefore be stableto subsequent dehydration. Damage occurs to areas that are firstactive in protein and RNA synthesis if pre-treatments extendbeyond 9 h and subsequent germination of the embryo is thenimpaired. The implications of these results are discussed inrelation to the effects of hydration pre-treatments upon enhancedgermination and the stability to dehydration of the productsof early RNA and protein synthesis.     

Studies on l-glutamate in insect haemolymph.

ABSTRACT. l -Glutamate when injected into the haemolymph of Lucilia sericata larvae and adult male Locusta migratoria was rapidly removed by uptake mechanisms to other tissues in the insect. Data from Lucilia larvae indicate that following uptake glutamate is metabolized and the metabolites are secreted back into the haemolymph. l -Aspartate injected into the haemolymph of Lucilia larvae was also rapidly removed. When both l -aspartate and l -glutamate were injected simultaneously, the rate of glutamate removal was significantly reduced. It is concluded that glutamate and aspartate share the same uptake mechanisms. l -Leucine injected into Lucilia larvae and Locusta was removed at a significantly slower rate than glutamate or aspartate.     

An algal pigment ratio as an indicator of the nitrogen supply to phytoplankton in three Norfolk broads

SUMMARY. A pigment ratio representing the ratio of carotenoid pigments to chlorophyll- a was calculated by dividing the optical density at 480 nm by that at 664 nm for a 90% acetone extract of phytoplankton. Its seasonal variation in three Norfolk broads was examined and, except for nitrogen-fixing species, it was found to vary independently of the algal species composition.
A good inverse correlation with the particulate nitrogen to carbon ratio was found. The seasonal variation in the pigment ratio was considerably affected by measurable lake concentrations of inorganic nitrogen supplied from ttie catchment. Other sources of nitrogen such as nitrogen fixation and release from the sediment were also indicated by changes in the ratio.
By comparison with the distinctions of extreme, moderate and no nitrogen deficiency drawn by Healey (1975) for the nitrogen/carbon ratio, values for the pigment ratio of < 1.4, 1.4–2.4 and > 2.4 were found to indicate no, moderate and extreme nitrogen deficiency respectively in the phytoplankton. The relation ship is attributed to the measurement of secondary carotenoids in response to nitrogen deficiency.