Zlatko Giba

Effect of nitric oxide - releasing compounds on phytochrome - controlled germination of Empress tree seeds

Using different nitric oxide releasing compounds and appropriate controls we have obtained data strongly suggesting the involvement of nitric oxide in the phytochrome controlled germination of Paulownia tomentosa seeds. Direct detection of nitric oxide, under various experimental conditions, was performed by a spin-trapping technique combined with electron paramagnetic resonance (EPR) spectroscopy. The addition of methylene blue prevented light-induced and NO donors-potentiated germination of P. tomentosa seeds. This inhibition could be completely overcome by addition of gibberellin. The promotive effect of nitrite was pH dependent, maximally pronounced at the pH range where nitrite undergoes dismutation and liberates nitric oxide. Under these conditions, nitrite exerted its efficacy at the same concentrations at which nitric oxide releasing compounds such as sodium nitroprusside (SNP), S-nitroso acetylpenicillamine (SNAP), and 3-morpholinosydnonimine (SIN-1), were the most effective. Likewise, the potentiation of P. tomentosa seed germination could be achieved by chemical reduction of nitrite with Na2S2O4 during which liberation of nitric oxide could be detected.

Nitrogen oxides as environmental sensors for seeds

Nitrates have long been known to promote seed germination in many species, and various proposals have been made regarding the role of nitrates in this process. One hypothesis suggests a possible ecological role for nitrate, providing the seeds with a report of soil nitrogen status and the proximity of already established plants. However, nitrogen oxides (NO, NO 2 ), which are present in the soil, also may be information carriers that indicate not only soil nitrate content, but also microbial activity and, therefore, soil quality. Because of annual variation of soil trace gas fluxes, seeds could be provided with information on seasonal and climate changes in their surroundings. Thus, nitrogen oxides would be the outer information carriers providing the seeds with integral data about many important factors required for successful germination and seedling establishment.

Sucrose effects on in vitro fruiting and seed production of Centaurium pulchellum

The effect of sucrose on fruiting, seed production, and seed germination of lesser centaury [Centaurium pulchellum (Sw.) Druce] was examined using explants of flowers and flower buds. Sucrose concentrations in the culture medium ranged from 0.003 to 0.3 M. It has been shown that the number of auxiliary buds, capsules dimension, number of viable seeds per capsule and seed dimensions increased with the increase of sucrose concentrations. The highest values were recorded at sucrose concentrations higher than 0.03 M, except for seeds size, which were larger at sucrose concentration ranging from 0.003 to 0.1 M. The germination of in vitro produced seeds was affected by previous culture history: a higher germination percentage was obtained in seeds that were raised from explants originally grown on medium with sucrose concentrations higher than 0.003 M.

Seeking the Role of NO in Breaking Seed Dormancy

In the course of evolution, higher plants developed a special reproductive organ, the seed, which ensures their spatio-temporal distribution and perpetuation of the species. The fate of the future plant is almost completely determined when the seed “decides” to germinate. A number of dormancy mechanisms serve to detect surrounding conditions and define the appropriate point in time for germination. To ensure survival of the future seedling, environmental conditions have to be detected, integrated, and translated through different signaling molecules at the seed level, even before germination starts. One of the ten smallest molecular species known, nitric oxide, is now recognized as an endogenous mediator of seed germination, external dormancy-breaking agent, and outer information carrier that provides the seeds with integral information on the factors most important for plant growth and development.

Stimulation of empress tree seed germination by liquid smoke

The germination of Empress tree (Paulownia tomentosa Steud.) seeds is phytochrome-controlled. Liquid smoke could not induce germination in darkness but red light irradiation of liquid smoke imbibed seeds induced a high percentage of germination. Maximum germination was achieved at liquid smoke concentration of 0.1% (v/v) when present during the imbibition phase or during the phase of phytochrome activity. The light requirement of these seeds could be completely substituted by exogenously applied gibberellins. In the presence of liquid smoke, optimal concentrations of GA3, GA4, and GA9 necessary for inducing germination were several times lower than in the controls, while that of GA7 was equally active when applied at a concentration one order of magnitude lower. The inhibitory effect of the applied growth retardants was strongly reduced and liquid smoke, in the presence of retardants, allowed light-induced germination, if applied simultaneously or after retardants treatment.

THE EFFECT OF ORGANIC NITRATES IN PHYTOCHROME‐CONTROLLED GERMINATION OF Paulownia tomentosa SEEDS

The long light irradiation requirement in Paulownia tomentosa (empress tree) seeds can be substituted by organic nitrates such as nitroglycerine, isosorbide di‐ and mononitrate, and pentaerythri‐tyl tetranitrate and a pulse of red light (5 min). The most effective was nitroglycerine (0.1 mM). Its effect depended on the time of application, i.e. a simultaneous presence of Pfr and these compounds was required. The effect decreased with delayed time of application after red light pulse. In seeds imbibed in nitroglycerine, an escape from far‐red light reversible action was similar to that obtained for seeds which can be induced to germinate by a brief exposure to red light. However, the application of nitroglycerine to seeds after a far‐red light pulse was ineffective. The effectiveness of organic nitrates also depended on the number of nitro groups in the compound. Isosorbide mononitrate was less effective than isosorbide dinitrate. Substances with structures similar to nitroglycerine, such as glycerol and glyceryl triacetate, in combination with the pulse of red light, failed to reduce the long light requirement.

Gibberellic Acid Nitrite Stimulates Germination of Two Species of Light-Requiring Seeds via the Nitric Oxide Pathway

Abstract: We used two species of light‐requiring seeds, Paulownia tomentosa, which have absolute light requirement (no germination in darkness), and Stellaria media seeds, which germinate in darkness to a certain extent because of presence of preformed active phytochrome, to obtain results strongly suggesting that gibberellic acid nitrite stimulates seed germination via its capability as a functional NO donor. Exogenous application of gibberellic acid nitrite stimulates gibberellin‐insensitive Stellaria media seed germination in darkness as do a wide variety of NO donors. Pure gibberellic acid could replace the light requirement of P. tomentosa seeds, thus enabling them to germinate in darkness. Gibberellic acid nitrite did not have this effect. A stimulative effect from gibberellic acid nitrite could be detected only after exposure of these seeds to short, 10 min, pulse of red light. Taken together, these results suggest that gibberellic activity of gibberellic acid nitrite is lost after nitrosation but, regarding to the presence of −O‐NO moiety in the molecule, gibberellic acid nitrite shares stimulative properties in seed germination with other compounds with NO‐releasing properties.

Interaction of gibberellins and fusicoccin in growth retardant- and far red light-inhibited germination of lettuce seeds

Germination of lettuce seeds cv. May Queen iscompletely prevented either with 10 µM tetcyclacisor with continuous FR illumination. GA3 and the N-substituted phtalimide, AC 94,377, werepartially effective in overcoming tetcyclacis-inducedinhibition but ineffective on photoinhibited seeds. FCcompletely reversed tetcyclacis inhibition and inducedca. 60% germination in continuous FR light. Aninteraction between FC and GA3 (as well asbetween FC and AC 94,377) was evident in stimulationof germination under both inhibitory conditions.Interaction was calculated as a ratio of thepercentage of seeds germinated under the simultaneousaction of stimulators compared to their additiveeffect. This was 2.54 for tetcyclacis- and 2.95 forphotoinhibited seeds. It is concluded that thistype of interaction is promotive synergism. Themagnitude of the interaction was highest if theapplication of FC was delayed after GA3application, and the optimal time lag was 6 h fortetcyclacis-inhibited, or 24 h for photoinhibited seeds.

Effect of photoperiod during growth of Chenopodium rubrum mother plants on properties of offspring

Using in vitro culture, we determined the effect of photoperiod during growth of Chenopodium rubrum mother plants on vegetative and reproductive development of offspring. Photoperiod during flowering induction of mother plants (the first 6 d after the germination) has the key influence on seed germination and offspring growth, while offspring flowering and seed maturation is determined by photoperiod their mothers experienced during, and shortly after, flowering induction. The mechanism can be through changes in seed protein pattern which we found dependent on photoperiod experienced by mother plants.