Aluminium toxicity is an important factor limiting crop productivity in acid soils and toxic effects of this metal are primarily root related. The aim of this paper was to study responses to Al toxicity in two Cuban rice cultivars and the relation with Al localization at root of seedlings. Different AlCl3 levels were employed to impose stress condition.

Aluminium toxicity is an important factor limiting crop productivity in acid soils and toxic effects of this metal are primarily root related. The aim of this paper was to study responses to Al toxicity in two Cuban rice cultivars and the relation with Al localization at root of seedlings. Different AlCl3 levels were employed to impose stress condition. Root apical segments were processed to optic microscopy by a Progressive Low Temperature Method (PLT) and they were included in Lowycril resin. The stained sections were viewed with Optic Microscopy (Zeiss) and photographed with Digital Camera Coupled to microscopy. Haematoxylin were employed to Al localization. Adventitious roots number was increased while the root elongation was reduced in seedlings exposed to Al. Different modifications were observed at the structure of epidermal and cortical cells in cross section. It provoked an increased at root diameter. These changes were accompanying by deformed roots and seedlings exposed to Al exhibited more root curvature than control seedlings and it could be consider a visual indicator to Al toxicity in rice plants. Differential Al localization and these results evidenced the toxic effect of Al in rice root cells and it evidenced that J-104 cultivar is more sensible to Al toxicity than INCA LP-7 cultivar.

Aluminium toxicity significantly limits crop productivity in acid soils and its effects are primarily root-related. The aim of this paper was to study the effects of aluminium on the morphology and cell structure of rice roots. Different AlCl3 levels were employed to impose stress conditions. Apical root segments were processed using a Progressive Low Temperature Method (PLT) and Lowycril resin, so that the samples could be cut. The stained sections were viewed and photographed using a Zeiss Optic microscope with an attached digital camera. Root elongation was reduced in seedlings exposed to Al, accompanied by deformed roots. Some structural changes were detected in epidermal and cortical cells. Reduced length accompanied by radial expansion contributed to cell elongation inhibition in different cellular types. Thickened cell walls and a vacuole size increase were also observed. These results provide evidence of the structural changes provoked in rice root cells by toxic levels of aluminium, as well as the morphological changes observed in Al-stressed rice roots in our laboratory.

Qualitative changes of root tissues, as a result of high temperature (38 o C for 1.5 h) were studied in two tomato (Lycopersicon esculentum Mill.) seedlings with different heat tolerance degrees. Seven days after rice seeds started to germinate, the heat treatment was applied to rootlets of each variety, which were isolated in pots containing water and later put on the stove for 1.5 h at 38 o C, whereas the control treatment consisted of leaving the other group of rootlets under laboratory conditions while applying high temperature. Afterwards, rootlet samples were taken and processed through light microcopy, including epon resin and 2 µm-wide sections were cut and stained with toluidine blue, observed and photographed under a microscope with a digital camera. Longitudinal sections of rootlets showed that high temperature increased vacuole size and expanded cell walls, among other disorders; such changes became more evident at the heat stress tolerant variety. RESUMEN. Los cambios cualitativos en los tejidos radiculares, como consecuencia de la alta temperatura empleada en este trabajo (38 o C durante 1.5 horas), fueron estudiados en plantulas de dos variedades de tomate (Lycopersicon esculentum Mill.), con diferentes grados de tolerancia a altas temperaturas. A los siete dias de puestas a germinar las semillas de arroz, se aplico el tratamiento de alta temperatura a las radiculas de cada varie- dad, que fueron puestas en recipientes con agua, por separa- do, y colocadas en la estufa durante 1.5 h a 38 0 C y el tratamien-

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