Analysis of mycorrhizal associations formed by Cistus incanus transformed root clones with Terfezia boudieri isolates.

One clone (M-2), out of several Agrobacterium rhizogenes transformed root clones of Cistus incanus, formed ecto- or endomycorrhiza in vitro with two isolates of Terfezia boudieri collected in Israel. All other clone-fungal isolate combinations formed ectomycorrhiza. The endomycorrhiza-forming isolate secreted smaller amounts of auxin than an ectomycorrhiza-forming isolate. Addition of 2,4-dichlorophenoxyacetic acid (2,4-D) led to ectomycorrhiza formation by the M-2 clone on low P medium. Endomycorrhizas were formed by both M-2 and a control clone with the same T. boudieri isolates on high P medium with 2,4-D. The M-2 clone of C. incanus exhibited greater sensitivity to exogenous auxins (IAA and 2,4-D) than other clones, and clonal sensitivity to auxin was increased tenfold under low P conditions. Results are discussed in relation to phosphate and auxin influence on T. boudieri-C. incanus interaction.

Homokaryotic and heterokaryotic hyphae in Terfezia.

Mycelia of Terfezia pfeilii (Ascomycetes) were obtained by two methods, i.e., from the sterile hyphae of fresh fruit bodies or by germinating ascospores. Nuclear staining revealed the existence of multinucleate cells in all mycelia. Paired nuclei were observed only in mycelia obtained from sterile hyphae proliferation, while single nuclei were found in mycelia originating from singly germinated spores. Co-cultivation of mycelia from two different ascospores apparently facilitated plasmogamy, resulting in mycelia with paired nuclei. Terfezia boudieri cultures originating from sterile hyphae also exhibit paired nuclei, indicating the possible existence of a long-term heterokaryon. The timing of plasmogamy and karyogamy in Terfezia is discussed.

Nature of the phytochrome effect on the binding of glycolate oxidase to peroxisomes in vitro.

The attachment of glycolate oxidase to the peroxisomal fraction derived from etiolated barley leaves (Hordeum vulgare L. cr. Dvir) is affected by light. The effect of red irradiation is reversed by subsequent far-red irradiation, indicating the involvement of phytochrome. This phytochrome effect is assumed to be related to phytochrome binding. Indeed, prevention by filipin (1.2·10(-6) mol g(-1) f wt) or cholesterol of phytochrome binding to membranes abolishes the effect of light on the interaction between glycolate oxidase and the peroxisomal fraction. Glycolate oxidase binding is affected by addition of quasi-ionophores such as gramicidin and filipin at a concentration of 0.6·10(-3) mol g(-1) f wt. This fact indicates that peroxisome-glycolate oxidase interaction may be affected by membrane potential. Since both ion transport and membrane potential are known to be affected by phytochrome, it is proposed that phytochrome acts in the light-induced modulation of glycolate oxidase attachment as a quasi-ionophore.

Effects of filipin and steroids on phytochrome pelletability.

Red light given to dark-grown etiolated leaves of Hordeum vulgare L. in vivo or to crude homogenates increases the phytochrome content of the 20,000 g pellet on centrifugation. The steroids cholesterol and stigmasterol inhibit this red light-induced phytochrome pelletability. Filipin (a polyene antibiotic, which is known to combine with steroids) inhibits red light-induced phytochrome pelletability. Filipin and steroids at the appropriate concentration applied together prevent the inhibition caused by either when applied alone. These results suggest that phytochrome may bind to a steroid component of membranes. The phospholipid phosphatidyl choline dipalmitoyl has no effect on red light-induced phytochrome pelletability. Preliminary evidence demonstrates a direct association of soluble phytochrome in its active form and steroids. The physiological significance of red light-induced pelletability and the primary mechanism of phytochrome action are discussed in terms of a hypothetical steroid-binding site.

Spectral characteristics of phytochrome in vivo and in vitro.

The absorption maximum of the far-red absorbing form of phytochrome in the difference spectrum for phototransformation (Pfr λmax) was investigated in vivo and in in vitro pellets from dark grown Hordeum vulgare L. primary leaves. Exposure of pellets in Honda medium from tissue pre-irradiated with red light to far red light gave a Pfr λmax of 734 nm, a slightly longer wavelength than was seen in vivo (730 nm). After incubation as the red absorbing form of phytochrome (Pr) for 2 h at 0° C irradiation with red light showed that Pfr λmax had shifted to shorter wavelength (716 nm) in Honda medium. Further incubation as Pfr for 2 h at 0° C and irradiation with far red light showed that Pfr λmax had shifted to longer wavelength (726 nm). Similar shifts were also seen in other media, although the peak positions were different. Phytochrome remained pelletable throughout these experiments and Pfr λmax is compared to that of soluble phytochrome in similar media. The results are interpreted as indicating changes in molecular environment of the putative phytochrome membrane receptor site and that Pfr λmax can be used to probe the nature of this binding.

Glycolate oxidase content of microbodies as affected by nitrate.

Glycolate oxidase is loosely held by microbodies obtained from etiolated barley (Hordeum vulgare L.) leaves depleted of nitrate. Defined centrifugation conditions cause the complete detachment of the enzyme from the microbodies. Addition of nitrate to these plants brings about a greater retention of glycolate oxidase by the microbodies. Synthesis of a nitrate-induced protein seems to be responsible for the enhanced retention of glycolate oxidase. Catalase, on the contrary, is strongly attached to the microbodies under all nutritional and experimental conditions considered.

Light and hormones: interchangeability in the induction of nitrate reductase.

Suitable concentrations of kinetin and gibberellic acid permit induction of nitrate reductase in leaves of tobacco in the dark. Hormone sprays eliminate the need for light induction of the enzyme. The concentration of gibberellic acid required for optimal induction varies according to the concentration of kinetin supplied.

Mediation of phytochrome in the inductive action of low temperature on dark germination of lettuce seed at supra-optimal temperature.

The induction of dark germination in light-requiring lettuce (Lactuca sativa) seed at supraoptimal temperatures by cold treatment (in darkness) was partly reversed by a brief far-red irradiation made at time of transfer, and even more so when the irradiation was made at the beginning of the cold pretreatment. When the inhibitory far-red irradiation was followed by additional cold treatment, the promotion was greatly restored. The promotive effects of brief irradiations with red light were further enhanced by a following cold period, before transfer to the supraoptimal temperature. These results are interpreted as indicating that the active (far-red absorbing) form of phytochrome is pre-existing in the dry seed, and interacts with a co-factor which is built-up during imbibition. The rate of build-up of this co-factor, as well as of the dark inactivation of active phytochrome increase with temperature. The products of the interaction pass through a photo-labile thermo-stable phase, before becoming photo-stable as well.