Biochemical Changes During Osmopriming of Leek Seeds

Osmotic priming treatments reduced both the mean time to germinationand the spread of germination for two leek seed-lots of highviability but differing vigour. In addition the differencesin germination performance between these two seed-lots was abolishedby the priming treatments. In the unprimed seed-lots, differencesin germination performance were reflected in differences inrates of protein biosynthesis in leek embryo tissue during germination.Osmopriming treatments abolished these differences upon subsequentgermination of osmotically primed seed and furthermore inducedhigh levels of protein biosynthesis in embryo tissue. DNA synthesiswas detectable in leek embryos during the priming period inthe absence of any cell division and was followed by a five-foldincrease in the rate of DNA synthesis in embryo tissue upongermination following priming at which time the rates of DNAsynthesis in these leek embryos was significantly greater thanthat found at any time over the first 4 d of germination inembryos of unprimed leek seeds. The increases in rates of bothprotein and DNA synthesis observed upon germination of primedseed occurred only after a 6–12 h lag period during whichtime there is little increase in these rates above those foundat the end of priming Analysis of nucleotide and nucleotide sugar levels in leek embryosboth during and after priming showed that only traces of GTPand CTP and low levels of ATP and UTP were present in embryosduring priming. After a 6 h lag period following the end ofpriming these levels increased sharply, probably via de novosynthesis. A similar pattern was found for UDP glucose levelsduring priming and subsequent germination. These results indicatethat there is considerable biochemical activity during primingand that the significant benefits in germination performanceof primed leek seeds is accompanied by marked increases in protein,DNA and nucleotide biosynthesis after a lag period of 6–12h following the end of the priming period Allium porrum, leek, seed, osmopriming, germination, protein synthesis, nucleic acids, nucleotides, nucleotide sugars     

THE INHERITANCE OF DIVERGENT MITOCHONDRIA IN THE LAND SNAIL, CEPAEA NEMORALIS

The mitochondrial genomes of Cepaea nemoralis can differ widelybetween individuals in the same population. Various hypothesishave been proposed to account for this diversity, includingunusually fast evolution and the retention of deep lineagesin sub-divided populations. Another possibility is that pulmonatemitochondria are inherited in the doubly uniparental mode, asin Mytilus, allowing separate maternal and paternal lineagesto coexist. In Mytilus, separate lineages may differ by as muchas 20% and may pre-date the origin of the species carrying them. Until now, mitochondrial inheritance has not been studied inany molluscan group except the bivalves. I have investigatedit in C. nemoralis through a series of matings, and assayedindividuals for evidence of heteroplasmy. In five matings, mitochondrialinheritance was maternal, and no heteroplasmic individuals weredetected. The maintenance of the divergent haplotypes can notbe explained by doubly uniparental inheritance. (Received 30 April 1999; accepted 6 July 1999)     

Conformation of Prostaglandins

ALTHOUGH different prostaglandins^* may have different pharmacological effects, in general the compounds have the same qualitative action on a given cell type. Investigation^1,2 has revealed structure-activity correlations and the importance of the orientation of the 11 and 15 hydroxyl groups³ is recognized. Molecular model building together with structure-activity data have suggested that prostaglandins are one of a number of classes of drugs and hormones that seem to fit stereochemically into a pre-existing (for example, polypeptide-nucleotide) receptor site^4,5. The restraints applied to the prostaglandin molecule to fix it as a stable conformational isomer, or conformer, are little understood and we now wish to indicate the significance of this conformation with respect to interaction with biological membranes.     

Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m^?2 s^?1. When measured at a standard temperature (17°C), rates of light-saturated photosynthesis (P_max) were higher in 5 °C-grown algae (c. 3.0 μmol O₂ m^?2 s^?1) than in 17 °C-grown algae (c. 0.9 μmol O₂ m_-2 s_-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 °C-grown algae than in algae grown at 17 °C. Light-limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low-light algae absorbed c. 75% of incident light, whereas 5 °C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin-Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0_max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m^?2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.