Water Darkness Research Articles

EXTENDING THE POSTHARVEST LIFE OF WOODY CUT STEMS

The postharvest life under various handling procedures was determined for nine species of woody cut stems: Buddleja davidii Franch. ‘Royal Red’, Buxus sempervirens L., Hydrangea quercifolia W. Bartram, Ilex crenata Thunb., Ilex L. ‘Nellie R. Stevens’, Ligustrum sinense Lour., Myrica cerifera (L.) Small, Pyracantha coccinea M. Roem., and Viburnum tinus L. ‘Spring Bouquet’. 1-methylcyclopropene (1-MCP) and 50°C distilled (DI) water produced the longest vase life for Buddleja, 6.6 and 6.4 d, respectively, compared to the control of 5.6 d. The 10% sucrose pulse and 1-MCP produced the longest vase life for Viburnum of 15.0 and 13.5 d, respectively, compared to the control of 10.0 d, while vase life of stems placed in 50°C DI and tap water was shorter. Ambient (20°C) DI water was optimal for Myrica (9.9 weeks), while stems pulsed with 10% sucrose had the shortest vase life of 2.2 weeks. Optimum storage (5°C), light level and duration by species were: Buddleja – dark in water for up to 1 week; Buxus – light in water for up to 3 weeks; Hydrangea – cannot be stored; Ilex crenata – light or dark in water for up to 3 weeks; Ilex ‘Nellie R. Stevens’ – light in water for up to 3 weeks; Ligustrum – dark in water for up to 3 weeks; Myrica – either light or dark in water for up to 3 weeks; Pyracantha – any condition for up to 3 weeks and Viburnum – either light or dark in water for up to 1 week. The use of floral foam adversely affected vase life of all species except Buxus. Myrica vase life was longest with 0% sucrose in the vase solution, while Ligustrum, Ilex ‘Nellie R. Stevens’ and Viburnum vase life was longest with either 2 or 4% sucrose. Sucrose in the vase solution had no effect on Buddleja, Buxus, Hydrangea, Ilex crenata or Pyracantha vase life.

Contrasting effects of submergence in light and dark on pyruvate decarboxylase activity in roots of rice lines differing in submergence tolerance.

Submergence tolerance of 13 doubled haploid lines of rice and their parents (submergence tolerant FR13A and submergence intolerant CT6241) was assessed using 2-week-old seedlings. Plants were scored for leaf senescence and percentage of seedlings that survived up to 15 d submergence, followed by a 12 d recovery period. Seven lines proved to be submergence tolerant, and six relatively intolerant. In all lines, activity of pyruvate decarboxylase (PDC), extracted from the apical 3-5 cm of root axes, decreased by 46-96 % and 38-76 %, respectively, during 5 or 10 d submergence under natural day/night conditions, compared with pre-submergence values (100 %). However, when the enzyme was extracted at night, submergence increased PDC activity of all rice lines (approx. 112 % on average), compared with pre-submergence values (100 %). The stimulating effect of the dark period on PDC activity was reproduced and amplified by submerging rice seedlings for up to 5 d in continuous darkness in water containing sub-ambient concentrations of oxygen (2.3 mg l(-1)). Such increased PDC activity was also observed in seedlings exposed to anoxia for 6 h (approx. 6-175 % higher than pre-submergence values). Irrespective of tolerance class, submergence decreased soluble protein concentrations under all conditions and sampling times. No positive correlation was found between PDC activity and tolerance of the various rice lines to submergence. However, PDC activity was slightly higher in submergence intolerant lines, compared with tolerant lines, under both dark submergence and anoxia. Such differences in PDC activity between the two groups of rice lines were not observed when they were submerged under the natural diurnal cycle. Increased PDC activity in roots at night demonstrated a probable incidence of tissue hypoxia or anoxia during submergence during each dark period.

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A3 (GA3). Soluble sugars in the imbibition solutions influenced the depth of skotodormancy. Ten-day DS seeds, imbibed in 50–500 mm sucrose or 100–500 mm glucose and given terminal GA3 germinated completely and germinated about 80% when imbibed in 100 mm galactose, mannose, lactose, or maltose. In contrast, terminal R applied to 10-day DS seeds caused only 20–50% germination. If given R at day 0 and imbibed for 10 days in darkness in 500 mm sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germinated about 50% in darkness in water. These seeds responded to terminal R or GA3 with complete germination. When seeds were given FR at day 0, germination responses following terminal R or GA3 were significantly lower when the duration of DS was increased from 7–10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either solutions of 50 or 100 mm sucrose and KNO3, either terminal R or GA3 treatment gave complete or near complete germination. It is concluded that seed exposure to certain soluble sugars and/or nitrate during a 10-day DS protected certain substrates and thereby extended the sensitivity of the seeds to terminal R or GA3 treatment. The study provides substantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy.

The bottom of the ocean: three abysses

ABSTRACTThis testimony is the result – better, the tale – of some sea and ocean descents made by a novelist to gather information for writing two of his books. The first one is The meadow under the sea published by Mondadori, 1974, and thereafter in various other editions, in Italian and other languages. The second is The Blue Whale, Mondadori, 1988, which went through several Italian editions.The present piece concerns impressions and events of contacts with the marine and oceanic floor in the Mediterranean sea, along Atlantic beaches and the Indian Ocean, off Tromelin, Madagascar.The last voyage takes the novelist to a peculiar situation, where water's darkness overturns the image, comes through the bathysphere port‐hole and the observer looks inside himself, a view that corresponds to a mythical history of the ocean floor.

PROTEIN PATTERNS DURING GERMINATION OF Lactuca sativa `Empire'.

Lettuce seeds were germinated at 20 C in the dark in water and sampled at various intervals during the first 18h of germination to determine quantitative and qualitative differences in proteins. The soluble protein fraction was partitioned into albumins and globulins by dialysis and the proteins of the globulin fraction were visualized by SDS-PAGE. Heat stable proteins were obtained by boiling the proteins, cooling on ice, and resuspending in buffer.The soluble protein content remained constant during the first 8h of germination. Thereafter protein content decreased and was 6% of the amount present in unimbibed seed in 21 day old seedlings. The ratio of heat stable to heat unstable proteins decreased during the germination process. No differences in banding patterns were observed when the soluble protein fraction were run on SDS-PAGE. However, on gels run with the globulin fraction a 57 kD protein appeared 4 and 8 h after imbibition and had disappeared by 12 h after imbibition. The role of proteins and heat-stable proteins during germination and prevention of dessication during early seedling growth is discussed.

Joint Action of Gibberellic Acid and Coumarin in Germination

THE stimulatory effect of gibberellic acid on germination has been recently observed1–3 and the possible modes by which this is brought to pass have been discussed by Brian4. Coumarin is well known as a germination inhibitor5,6 and is also known to induce light sensitivity in certain seeds not normally requiring light for their germination7. It seemed of interest therefore to determine whether gibberellic acid, like light, could reverse inhibition in coumarin treated seeds. Lettuce seeds, variety Grand Rapids, were allowed to germinate for 48 hr. at 25° C. in the dark in water, or solutions of coumarin, gibberellic acid (sodium salt), or mixtures of the two. The results are shown in Table 1.