Dynamics of Pollen Grain Germination in Two Cultivars of Malus domestica: the Influence of Actinomycin D on Fresh and Stored Pollen Grains

The pattern of germination has been detected in the presence or in the absence of Actinomycin D (AmD) in fresh and stored binucleate pollen grains of' Golden Delicious' (GD) and' Starkrimson' (S). Pollen tube growth consisted of two distinct phases, autotrophic and heterotrophic, in both fresh and stored pollen grains. The pollens of the two cultivars differ: (i) in the length of the first phase, being 3 h in GD and 2 h in S, and (ii) in the response to storage. As far as the response to storage is concerned the cultivar S seems to be more damaged than GD when the storage effect is evaluated as the first phase length; less damaged than GD when the effect is expressed as tube length

RNA-SYNTHESIS IN THE EMBRYO SUSPENSOR OF PHASEOLUS-COCCINEUS AT 2 STAGES OF EMBRYOGENESIS, AND THE EFFECT OF SUPPLIED GIBBERELLIC-ACID

RNA synthesis in giant cells containing polytene chromosomes in the embryo suspensor of Phaseolus coccineus was analyzed by autoradiography after [ 3H]-uridine treatment. Embryos at the heart-shaped stage of development and at a cotyledonary stage were studied. Discontinuous labelling of the polytene chromosomes was always observed. The chromosomes were subdivided into segments (chromosome regions) which behaved as functional units, since discontinuous labelling was never seen within any of the regions. It was found that most chromosome regions were engaged in RNA synthesis to different degrees at the two embryo developmental stages. Regions showing identical labelling patterns tended to lie close together in the chromosome arms and to keep their functional activity coordinated at both stages of embryo development. The chromosome regions bearing 18 S+25 S ribosomal genes were never simultaneously active in RNA synthesis and different regions were preferentially transcribed at each stage of embryo development. However, at both stages, all the chromosome regions bearing 5 S ribosomal genes showed comparable labelling frequencies. The effect on transcription of gibberellic acid (GA 3) treatments was also studied. At both embryo developmental stages, GA 3 enhanced the rate of RNA synthesis in the polytene suspensor cells. The frequency with which certain chromosome regions were transcribed was also increased significantly (P≤0.001) and this stimulatory effect was greater in embryos at the cotyledonary stage than in heart-shaped embryos. At the latter developmental stage, RNA synthesis was repressed by GA 3 in a few chromosome regions. These results are discussed briefly in relation to previous findings using different methods of studying the organization of polytene chromosomes and the functional activity of the embryo suspensor of Phaseolus coccineus

Arsenic-induced morphogenic response in roots of arsenic hyperaccumulator fern Pteris vittata.

On the assumption that arsenic induces stress morphogenetic responses involved in As tolerance and hyperaccumulation in the Pteris vittata fern, we analyzed the root system of young sporophytes grown in 250, 334, and 500 M As for five days and for 14 days. Anatomical and histological analyses were performed in plants grown for five days to evaluate the number, position, length and differentiation pattern of root hairs. AgNOR staining, employed to study nucleolus behavior in root apices, showed that arsenic influences nucleolar activity (evaluated by nucleolus size, number and absorbance) in the root meristem. In plants treated with 250 and 334 M As an acropetal shift of root hair development and an increase in hair length and density were observed, linked to an ectopic pattern of differentiation. The opposite trend was recorded in plants treated with 500 M As. It is worth noting the presence of living border-like cells, not yet observed in ferns, and their increase following As treatments. Analysis and vitality of border-like cells were surveyed after 14 days of treatments. In conclusion As treatments elicited a stress-induced morphogenic response which, by modifying the differentiation pattern, number and length of root hairs, modulating nucleolar activity and interacting with the rhizosphere by inducing border-like cell production, may adjust the rate of root uptake and its metabolic activity