ALBERT

Notes: Changes in dormancy of Spergula arvensis seeds were studied during pre-incubation at constant temperatures and under a temperature regime that condensed the annual temperature cycle into 73 days. Each day in the regime represented the mean day and night temperatures and day lengths of 5 successive days of an average year in The Netherlands. Incubation occurred in water or loamy sand, in darkness. Germination of the seeds was tested in water or KNO3 over a range of temperature. Seeds were irradiated with saturating doses of red light. In half of the treatments, pre-incubated seeds were dehydrated at the transfer to the conditions of the germination test. Breaking of dormancy occurred under conditions of 'spring'. It did not depend on exposure to low‘winter’temperatures, but was induced by rising 'spring’temperatures. Seeds developed secondary dormancy in late‘autumn'. The expression of the changes in dormancy that were induced during pre-incubation depended on the conditions of the germination test. Light, nitrate and dehydration stimulated germination. The experiments predicted that field emergence from nitrate-poor soils that have not been dehydrated will be restricted to a short period in autumn, whereas disturbance of nitrate-rich soils followed by a dry spell will stimulate germination of S. arvensis seeds from early spring to late autumn. The data presented good explanations for the cosmopolitan character and the serious weediness of this species. Its classification as a summer or winter annual is discussed.

Notes: Seeds of Sisymbrium officinale (L.) Scop, that are buried under natural conditions in soil pass annually through a seasonal pattern of changes in dormancy. Dormancy is broken in autumn-winter and re-induced in summer. To elucidate dormancy regulation in this species under natural conditions, a detailed analysis of the changes in sensitivity to some relevant germination factors was carried out Germination data fitted as logistic dose response curves showed that sensitivity to light and nitrate, both indispensable stimuli for germination of this species, varied with the seasons. Patterns of shifts in requirement for light and nitrate were remarkably similar. Sensitivity increased when both primary and secondary dormancy were alleviated, and it was reversed during induction of secondary dormancy. During alleviation of primary dormancy in spring 1991, the fluence response curves exhibited a biphasic character with responses occurring both in the very-low-fluence-range and in the low-fluence-range. The nitrate dose response data could all be fitted as monophasic curves, although responses might have occurred in two distinct ranges as well. From interpretation of curve parameters, it is postulated that dormancy is regulated by changes in the number of phytochrome and nitrate receptors, in shifts in the binding characteristics of the receptors and/or in shifts in the response chain initiated by the ligand-receptor interaction. Somewhere in this response chain, biosynthesis of gibberellins (GAs) is stimulated. By use of the GA biosynthesis inhibitor tetcyclasis, it was indirectly proven that the capacity to synthesize GAs indeed varied with the seasons. Sensitivity to GAs gradually increased from burial onwards and was not particularly related to changes in dormancy. Thus, except for the first few months of burial, GA sensitivity may not be regarded as a limiting factor in controlling dormancy in this species.

Notes: The characteristics of nitrogen acquisition, transport and assimilation were investigated in species of an Atlantic Forest succession over calcareous soil in south-eastern Brazil. Differences in behaviour were observed within the regeneration guilds. Pioneer species showed high leaf nitrogen contents, a high capacity to respond to increased soil nitrogen availability, a high capacity for leaf nitrate assimilation and were characterized by the transport of nitrate + asparagine. At the other end of the succession, late secondary species had low leaf nitrogen contents, little capacity to respond to increased soil nitrogen availability, low leaf nitrate assimilation and were active in the transport of asparagine + arginine. The characteristics of nitrogen nutrition in some early secondary species showed similarities to those of pioneer species whereas others more closely resembled late secondary species. Average leaf δ15N values increased along the successional gradient. The results indicate that the nitrogen metabolism characteristics of species may be an additional ecophysiological tool in classifying tropical forest tree species into ecological guilds, and may have implications for regeneration programmes in degraded areas.

Notes: Effects of dark incubation at different temperatures were studied on dormancy and respiratory activity of seeds of Sisymbrium officinale (L.) Scop. Because germination of this species absolutely depends on the simultaneous action of light and nitrate, changes in dormancy could be studied in darkness without the interference of early germination events. Upon the start of incubation rates of O2 uptake and CO2 release rose. This was followed by a gradual decrease until stable levels of O2 uptake and CO2 release were achieved. Seeds kept for prolonged periods at 24°C, showed neither a change in germination capacity nor in rates of O2 uptake and CO2 release. Respiratory quotients were 0.55–0.7. The initial rise in O2 uptake correlated with the rate of water uptake and with breaking of primary dormancy. However, the subsequent decline in O2 uptake was not generally linked to induction of secondary dormancy. An increased O2 uptake was not required during breaking of secondary dormancy. It is concluded that changes in dormancy are not generally related to changes in respiratory activity. However, germination strongly depends on respiration. The increase in O2 uptake started well before radicle protrusion. A far red irradiation only reversed this increase when it was given before germination escaped from its red light antagonising action. The contribution of different respiratory pathways was followed during prolonged incubation at 24°C in darkness. KCN at 1.5 mM was needed to inhibit the cytochrome pathway (CP) and benzohydroxamic acid (BHAM) at 30 mM to inhibit the alternative pathway (AP). These concentrations did not exert any side effects. Electron flow was predominantly via the CP, maximally 10% was via the AP. Flow through the CP declined during the first 6 days and residual respiration remained constant. Therefore, the contribution of residual respiration became relatively more important with prolonged incubation. KCN at concentrations that almost completely inhibited flow through the CP, did not dramatically reduce germination. BHAM already inhibited germination at concentrations that do not inhibit oxygen uptake.

Notes: Effects of light and temperature on gibberellin (GA)-induced seed germination were studied in Arabidopsis thaliana (L.) Heynh. with the use of GA-deficient (gal) mutants, mutants with a strongly reduced sensitivity to GA (gai) and with the recombinant gai/gal. Seeds of the gal mutant did not germinate in the absence of exogenous GAs, neither in darkness, nor in light, indicating that GAs are absolutely required for germination of this species. Wild-type and gai seeds did not always require applied GAs in light. The conclusion that light stimulates GA biosynthesis was strengthened by the antagonistic action of tetcyclacis, an inhibitor of GA biosynthesis. In wild-type, gal and gai/gal seeds light lowered the GA requirement, which can be interpreted as an increase in sensitivity to GAs. In gai and gai/gal seeds light became effective only after dormancy was broken by either a chilling treatment of one week or a dry after-ripening period at 2°C during some months. The present genetic and physiological evidence strongly suggests that temperature regulates the responsiveness to light in A. thaliana seeds. The responsiveness increases during dormancy breaking, whereas the opposite occurs during induction of dormancy (8 days at 15°C pre-incubation). Since light stimulates the synthesis of GAs as well as the responsiveness to GAs, temperature-induced changes in dormancy may indirectly change the capacities to synthesize GAs and to respond to GAs. GA sensitivity is also directly controlled by temperature. It is concluded that both GA biosynthesis and sensitivity to GAs are not the primary controlling factors in dormancy, but are essential for germination.

Notes: Atlantic cod Gadus morhua were collected from Smith Sound, Newfoundland in January 1999. Visual examination of females (n=150) and males (n=126) revealed that some large fish (42–79 cm) had underdeveloped gonads. Histological examination of underdeveloped ovaries indicated that the majority of these females were undergoing mass resorption of oocytes and would not have spawned in 1999. Fish in this condition included females that were aborting their first attempt at maturation and females that had spawned the previous year but were failing to re-ripen. Somatic and liver condition were significantly lower (P〈0·05) for fish undergoing mass oocyte resorption than ripening females, suggesting that the interruption in the maturation cycle may have been related to insufficient nutrient storage. In males, testes of some adult fish were considered to be non-reproductive as they showed no signs of ripening and probably would not have spawned in 1999. Liver condition was significantly higher (P〈0·05) for non-reproductive males than those that were ripening. Disruptions in male and female reproductive cycles may also have been related to water temperatures that were too cold (0–0·5° C) for successful gamete development. Immature gametes (perinucleolar oocytes in females; spermatogonia in males) showed no signs of breakdown in non-reproductive individuals, suggesting that they retained the potential to develop and spawn gametes in 2000.

Notes: Prespawning winter flounder, Pseudopleuronectes americanus Walbaum, manifest epidermal thickening as a secondary sexual characteristic, but with considerable individual variability. The correlation between epidermal thickness and fish size in post-spawned flounder is less apparent in prespawning flounders due to factors associated with sexual maturation. Thus, epidermal thickness in individual prespawning flounder displays significant correlation with gonadosomatic index and. in females, with the degree of final maturation of vitellogenic oocytes. However, both epidermal thickness and gonadosomatic index of individual flounders also display significant correlation with condition factor. It is proposed that body size and condition factor represent important primary physiological determinants influencing individual variability in seasonal epidermal thickness, and that factors associated with sexual maturation represent a secondary physiological determinant.

Notes: Filled gelatin capsules can be inserted in the stomach of non-anaesthetized flounder using a cheap, easy tube and plunger method.