Influence of low temperature on germination and endogenous growth regulator contents in Scots Pine (Pinus silvestris L.) seeds

Twenty days-long stratification of Scots pine seeds results in the seeds germinating in similar high percentage in darkness as in light. The period of stratification enough to overcome the "barrier" of light is connected with simultaneous increase of gibberellin contents, especially with the appearance of the new groups of gibberellins qualitatively similar to those occurring in pine tissues under the influence of red and white light. It was also found that seedlings grown from stratificated pine seeds produce the increased amounts of gibberellins.

Redifferentiation of moss protonemata: an experimental and immunofluorescence study of brood cell formation

The formation of ovoid or spherical brood cells from chloronemal filaments by swelling and symmetrical subapical divisions preceded by phragmosomes, but not preprophase bands, is described in the mosses Physcomitrella patens, Dicranoweisia cirrata, Bryum tenuisetum, Bryum bicolor, and Rhytidiadelphus loreus. This is a widespread phenomenon that occurs in protonemal colonies cultured for long periods of time or allowed to dry out. It involves the redifferentiation of highly polarized chloronemal cells with a net axial array of microtubules into nonpolar cells containing microtubules with no preferred orientation. Brood cells in some species become thick walled and retain their viability for long periods even in a desiccated state. When transferred to new medium they immediately regenerate protonemata from new filaments of no fixed position. Experiments using activated charcoal, which prevents brood cell formation, and transferring protonemata or spores onto old medium in which brood cells had been produced previously, indicate that the redifferentiation process is triggered by substances released into the medium by protonemata. Addition of abscisic acid, an endogenous growth regulator in mosses, causes precocious brood cell formation in young cultures and is very likely the natural compound triggering their development and inducing their tolerance to desiccation. Key words: abscisic acid, activated charcoal, redifferentiation, desiccation tolerance, microtubules, polarity, protonema, regeneration.

Roles of endogenous and exogenous growth regulators in dormancy of Utricularia vulgaris

The roles of endogenous and exogenous growth regulators on dormancy control of Utricularia vulgaris were investigated by extraction and bioassay of endogenous levels of four classes at various developmental stages and by measuring the effects of synthetic regulators on these stages. The bioassays used were oat coleoptile for auxins, abscisic acid and other inhibitors; lettuce hypocotyl for gibberellins; and soybean callus for cytokinins. Two weeks before turion formation and during innate dormancy abscisic acidlike and bound gibberellinlike levels were high while free gibberellinlike and auxinlike levels were low. Abscisic acid exogenously applied to actively growing plants rapidly induced turion formation even under noninductive environmental conditions. Kinetin rapidly and completely caused sprouting in innately dormant turions but would not promote continued vegetative growth. These plants formed new turions within 2 weeks of sprouting. During imposed dormancy, when turions rapidly sprouted, there was a low level of abscisic acidlike inhibitor and high levels of gibberellinlike and auxinlike compounds. Turions collected during this state could be maintained in a dormant condition by incubation with abscisic acid even at high temperatures which normally induce sprouting. During sprouting the endogenous growth regulator pattern was similar to that described for imposed dormancy. A model of the environmental and growth regulator factors which control dormancy is presented.