Formación de cuatro generaciones de tubérculos sin follaje en «Solanum tuberosum» L.

Abstract

En el presente trabajo se informa acerca de los experimentos realizados para verificar cuántas generaciones de tubérculos pueden formarse sin follaje, y determinar así si el estímulo o capacidad de tuberizar se agota por la falta de follaje. Para tal fin se eligieron tubérculos de aproximadamente 300 g del cultivar Katahdin y se colocaron con un solo brote en cajones de madera cubiertos con vermiculita, en condiciones de ± 20°C én oscuridad. La vermiculita se mantuvo húmeda mediante riegos periódicos. Una vez obtenidos los tubérculos de la primera generación se repitió la operación para obtener con igual procedimiento las siguientes generaciones. Se lograron cuatro generaciones de tubérculos producidos sin follaje. En la Figura 1 se detalla el peso de los tubérculos. En los tubérculos de la cuarta generación sin follaje, la brotación ocurría en forma normal. Luego de colocados en la vermiculita húmeda también presentaban el crecimiento de los brotes normales. Luego de aproximadamente tres meses en estas condiciones todos los tubérculos se ablandaron por hidrólisis de sus reservas y decaían completamente, no formando los tubérculos correspondientes a la quinta generación. Se realizaron cortes anatómicos de los tubérculos y se trataron en una solución de yodo, yoduro de potasio. Como testigos se utilizaron cortes de un tubérculo de la ¿primera generación sin follaje. En la Figura 2 se detallan los cortes realizados, en los cuales no se observa almidón en los de la cuarta generación, pero sí en los de la primera generación, que después forman tubérculos en los brotes. Los resultados indicarían que la no formación de tubérculos de la quinta generación se debería a la ausencia de algún factor de la formación de almidón después que se han hidrolizado las reservas del tubérculo anterior, correspondiente a la cuarta generación sin follaje. Los resultados indicarían que la formación de tubérculos constituiría un proceso de dos etapas : la iniciación de la tuberización que se debería a la acción de una fitohormona, actuando sobre la polaridad de las células del rizoma, y la segunda etapa estaría internamente relacionada a los factores de la formación del almidón, enzimas, cofactores energéticos, etc.

The present paper deais with the research conducted to study the number of generations of potato tubers that can be formed without foliage, and also to find out whether the stimulus or tuberization capacity is exhausted by lack of foliage, Tubers of the Katahdin cultivar of ± 300 g were chosen and placed with only one sprout in wooden trays on vermiculite, at rooin temperatura ± 20° C, in darkness. Vermiculite was kept hurnid by periodic watering. Once the tubers of the first generation were obtained (after sprouting) the process Was repeated to obtaiu further generations. Four generations of tubers without foliage were obtained. Fig. 1 shows the weight of the tubers of the four generations. With tubers of the fourth generation without foliage the sprouting and growth of shoots were normal. After approximately three months of treatment all the tubers were softened by hydrolysis of their storage tissues and decayed, not forming the tubers corresponding to the fifth generation. Tubers were sectioned aud treated with an iodine solution. Sectións of a tuber of the first generation without foliage were used as controls. Fig. 2 shows the thin sectións in which starch was not present in the tubers of the fourth generation, but it was in those of the controls that afterwards formed tubers on the etiolated shoots. The results would indícate that the non-formation of tubers of the fifth generation would be due to the lack of some factor of the starch formation after the storage tisúes of the fourth generation without foliage had hydrolyzed, With tubers formed with foliage underthe action of light and photosynthesis Claver (1961) obtained six series of tubeTS of the first generation after the removal of those already formed. This would indícate the possibility of the need of some factor of light or photosynthesis for the tuberization or for the synthesis of starch. After four generations of tubers without foliage in darkness, the tubers wlll die. This is related to the difference found in plants from true seeds and sprouts cultivated «in vitro». It was demonstrated that sprouts are able to generate tubers under light and dark-conditions. On the other hand, seedlings only form tubers under light conditions. Metabolic regulation of starch by light would be accomplished through photosynthesis. The conceutrátión of phosplioglyceric acid (3-PGA) increases d líing photosynthesis and would actívate the enzyme which produces an active form of glucose, adenosine diphosphoglucose (ADPG), and consequently starch. Ghosh and Preiss (1965). Bodlaender and Marinus (1969) inform that the mother tuber is not necessary fór the tuberization process. In the present work we have shown that the foliage is not indispensable for the formation of tubers up to the fourth generation, corroborating that tuberization is a normal phase in the development of potato plants. The resulta also indicate that tuber formation is a two-stage process: initiation of tuberization, due to the action of the plant hormone on the change of polarity in the sub-apical región of the rhizomes (stolons) and secondly, a stage closely related to the factors of starch deposition, enzymes, energetic cofactors, etc. Catchpole and Hillman (1969) conclude that ethylene plays a role in tuber initiation and that starch deposition occurs in a second stage.