Priming relieves dormancy in lettuce seeds independently of changes in osmotic constituents

The relationship was studied between germination and dormancy of lettuce seeds ( Lactuca sativa L. cv. Musette) and both soluble amino nitrogen metabolism and osmotic potential. Germination at 15°C in darkness coincided with a rise in the levels of free amino acids and total soluble amino nitrogen compounds and in the activity of glutamine synthetase (GS, EC nr. 6.3.1.2). In further experiments GS activity was used as indicator of soluble amino nitrogen metabolism. GS activity increased after the start of growth indicated by an increasing intolerance to desiccation. At 30°C seeds did not germinate, unless dormancy was broken beforehand during incubation at 2° or 15°C (priming). The alleviation of dormancy occurred much earlier than the rise in the activity of GS. Priming at 15°C in polyethylene glycol instead of water retarded the breaking of dormancy and at –1.28 MPa even stimulated the induction of secondary dormancy, but did not prevent a continued rise in the activity of GS. GS activity was also not reduced during induction of secondary dormancy by dehydration of primed seeds, which antagonized the beneficial effect of priming. Psychrometric measurements showed that osmotic potential (Ψ_π) of the seeds remained constant during prolonged priming in polyethylene glycol at 15°C. During incubation in water, Ψ_π increased both prior to and after the moment of germination to less negative values. It is concluded that changes in the level of dormancy in lettuce seeds occur independently of soluble amino nitrogen metabolism and of changes in Ψ_π.     

The effect of exposure to microgravity on the development and structural organisation of plant protoplasts flown on Biokosmos 9

Preparatory experiments for the IML-1 (International Microgravity Laboratory) mission to be flown on the Space Shuttle in January, 1992, were performed on a 14 day flight on Biokosmos 9 (Kosmos 2044) in September 1989. The purpose of the experiment was to study the effect of weightlessness on protoplast regeneration. Problems with late access to the space vehicle meant that the newly isolated protoplasts from hypocotyl cells of rapeseed (Brassica napus L. cv Niklas) and suspension cultures of carrot (Daucus carota L, cv Nobo) had to be stored at 4 degrees C for 36 h prior to the launch of the biosatellite, in order to delay cell wall regeneration until the samples were in orbit. In the flight samples and the ground controls, a portion of the total number of protoplasts regenerated cell walls. The growth of flight rapeseed cells was only 56% compared to the ground control; the respective growth of carrot cells in orbit was 82% of the ground control. Analysis demonstrated that the peroxidase activity and the amount of protein was lower in the flight samples than in the ground controls. The number of different isoenzymes was also decreased in the flight samples. A 54% decrease in the production of cellulose was found in rapeseed, and a 71% decrease in carrot. Hemicellulose production was also decreased in the flight samples compared to the ground controls. Ultrastructural analysis of the cell aggregates from the protoplasts cultured in orbit, demonstrated that hydrolysis and disappearance of reserve starch occurred in the flight cell plastids. The mitochondria were more varied in appearance in the flight samples than in the ground control cells. An increased frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds was also observed. Fluorescence analysis showed a decrease of the calcium content in cell cultures under space flight compared to the ground controls. One general effect of the stay onboard the space vehicle was a retardation of the regeneration processes. Callus cultures obtained from the flight samples grew very slowly compared to callus regenerated from the ground controls, and two years after the Biokosmos 9 flight there appears to be no further growth in the samples exposed to microgravity. Callus cultures from the ground controls, however, continue to grow well. A simulation experiment for IML-l performed in January 1990 at ESTEC (European Space Technology Center), The Netherlands, has resulted in regenerated plants. These observations are discussed and compared to the results obtained on Biokosmos 9.     

The effect of temperature on the germination-promoting activities of cytokinin and gibberellin applied to celery seeds (Apium graveolens)

Celery seeds (Apium graveolens L. cv. Lathom Blanching) made dormant by high temperature pretreatment (28–40°C) during imbibition in the dark, germinated at 22°C in the light after treatment with benzyladenine (BA). This BA-induced promotion of germination increased with increasing pre-treatment temperature from 32 to 38°C. whether BA was given before or after pretreatment. A mixture of gibberellins A₄ and A₇ (GA_4/7) given before a 4 day high temperature pretreatment at 32°C partially inhibited the germination-promoting activity of GA_4/7 given after. It is suggested that gibberellin induces the formation of a thermola-bile product which is necessary for germination, the precursor of which has a limited source.     

The effect of 8 days of microgravity on regeneration of intact plants from protoplasts

The growth and development of protoplasts of rapeseed (Brassica napus L. cv Line) and carrot (Daucus carota L. cv. Navona) were studied onboard the Space Shuttle‘Discovery’during an 8-day International Microgravity Laboratory [IML-l) mission in January 1992. The Flight experiments were carried out in‘Biorack'. a fully controlled cell biological experimental facility. under microgravity conditions and in a l-g centrifuge. Parallel experiments were performed in a‘Biorack’module on the ground. After retrieval, some samples were subcultured on appropriate media and analysed for callus growth and regeneration to intact plants. The remainder were used for biochemical analysis. Samples fixed on board the Space Shuttle were kept in l% glutaraldehyde fixative at 4°C for 3–7 days for microscopy analysis after retrieval. Protoplasts exposed to microgravity conditions showed a delay in cell wall synthesis. Cells were swollen in appearance and formed cell aggregates with only few cells. Callus were obtained from protoplasts cultured under microgravity (Fogl). on the l-g centrifuge on board the shuttle (Flg), under normal l-g conditions on the ground (G1g) and on a centrifuge on the ground giving 1.4 g (Gl.4g). Regeneration of intact rapeseed plants was obtained from Flg. Glg and G1.4g. However, no plants were regenerated from protoplasts exposed to microgravity (Fog). Biochemical analysis indicated that the microgravity samples (Fog displayed a reduced packed cell volume, an increased concentration of soluble proteins per cell, and a reduced specific activity of peroxidase in the cytoplasm. Morphometric analysis of fixed samples demonstrated that 3-day old protoplasts under microgravity conditions were significantly larger than protoplasts kept on the l-g centrifuge in space. UItrastructural analysis by transmission electron microscopy showed that protoplasts exposed to microgravity conditions for 3 days had larger vacuoles and a slightly reduced starch content compared to Flg cells. Cell aggregates formed under microgravity conditions (Fog) had an average of 2–I cells per aggregate while aggregates formed under Flg had 8–12 cells.     

Biopriming of maize seeds with plant growth-promoting bacteria isolated from the earthworm Aporrectodea molleri: effect on seed germination and seedling growth

Earthworms have become a potential source of multi-beneficial bacteria and effective bioinoculants. Seed biopriming is an efficient inoculation method to apply bacteria prior to sowing, which enhances the chances of bacterial candidates to colonize the rhizosphere and/or establish a liaison with the plant. In this study, we evaluated plant growth-promoting traits of bacterial strains isolated from the earthworm’s Aporrectodea molleri chloragogenous tissue. In addition, we investigated their prospective use as biopriming agents to enhance Zea mays germination and seedling growth. Results were subjected to principal component analysis for potential correlations between the studied parameters. The bacterial strains displayed different in vitro plant growth-promoting characteristics and were efficient when applied in vivo as they significantly increased maize germination rate (26–78%), root elongation (67–84%), seedlings fresh weight and dry weight. Aeromonas encheleia TC22 was the most significant strain to influence germination due to its high ability to produce indole-3-acetic acid, and along with Pseudomonas azotoformans TC1, they were the most proficient at enhancing seedling root elongation and biomass, which was significantly correlated with their in vitro plant growth-promoting traits. Our findings indicate that isolates TC22 and TC1 are potent bio-primers for maize seeds and should be tested further for their use as biopriming inoculants.     

The effects of mechanically-induced stress and plant growth regulators on the growth of lettuce,cauliflower and bean (Phaseolus vulgaris L.) plants

The plant growth regulators, gibberellic acid (GA₃), ethephon and chlormequat chloride (CCC) were sprayed on young lettuce, cauliflower and bean (Phaseolus vulgaris) plants, which had either been given or not been given a mechanically-induced stress (MIS) treatment. MIS was applied by brushing the plants with paper for 1.5 minutes each day. GA₃ increased extension growth of bean and leaf length of lettuce in unbrushed plants as much as in brushed ones. CCC and ethephon were less effective at reducing the height of brushed bean plants compared to unbrushed ones. The effects of CCC on the growth of cauliflower and lettuce plants was not influenced by brushing, whereas unbrushed plants responded more readily to ethephon than did brushed ones. The effects of CCC on growth were generally similar to those of MIS whereas the effects of ethephon were in many ways different to MIS.The results are discussed in relation to the use of PGR and MIS treatments for modifying plant growth.     

The effect of income on the extraction of non-timber tropical forest products: Model,hypotheses, and preliminary findings from the Sumu Indians of Nicaragua

We use microeconomic theory to frame hypotheses about the effects of income on the use of non-timber rain forest products. We hypothesize that an increase in income: (a) encourages foraging specialization, resulting in the extraction of fewer goods; (b) increases the share of household income from occupations besides foraging; (c) produces a yearly value from the extraction of nontimber forest goods of about $50 per hectare; and (d) produces depletion of forest goods entering commercial channels and sustainable extraction of goods facing cheaper industrial substitutes. To examine these hypotheses we present worldwide ethnographic information and preliminary findings from field work carried out among the Sumu Indians of Nicaragua. Field work suggests that higher income produces: (a) foraging specialization with animals rather than with plants; (b) a decline in the economic importance of forest goods in household income; (c) and a rise in the value of non-timber goods removed from the forest to about $35/ha/year. We did not have time to test hypothesis d.