Meccanismi ormonali di controllo della dormienza del tubero di patata

Bioinvestigations on the mechanisms which control potato tuber dormancy are of basic importance, for both fresh market or processing products and seed tubers. Despite many years of research, the physiology of dormancy is not yet clear. Some recent results, achieved by several experimental approaches, represent a significant progress. Some hormonal classes are involved in this phenomenon, but current literature is often contradictory, therefore the role of these molecules must be studied in depth. Our research focused on auxins, a group of natural plant growth regulators which includes indoleacetic acid, the most studied and widespread auxin in higher plants, and the subject of our work. Changes of hormonal concentration in different tuber parts were analyzed by physic o -chemical techniques throughout dormancy and early sprouting. Further investigations by immunohystochemical techniques led to tissue-localization of indoleacetic acid during the above said experimental period. Early results from tubers of cv "Monalisa", from which all buds were excised and analyzed, suggested that auxin could induce bud outgrowth, because its concentration in buds rose during dormancy and early sprouting. Further and more accurate analyses were then planned, to be carried out on tubers from two different cultivars ("Agata" and "Merit", which markedly differ for dormancy length). In this work, only buds from the apical part of the tuber were sampled: these sprout earlier, therefore we assume that they undergo the most relevant physiological changes during the time of our experiments. Results from the latter work are in striking contrast with the previous ones, because indoleacetic acid concentration decreases in the apical buds of tubers of both cultivars, throughout dormancy and early sprouting. Immunostaining of indoleacetic acid confirms that the hormone is far more abundant in dormant than in sprouting buds: the apical meristem and the underlying, differentiating, vascular tissues of dormant buds show high levels of indoleacetic acid. The research dealing with "Agata" and "Merit" tubers yielded accurate and detailed results, which allowed us to put forward the following hypothesis on the role of indoleacetic acid in tuber dormancy control: the hormone would play a positive role on dormancy overcoming, by enhancing cell division and expansion in the bud apical meristem and differentiation of vascular tissues. In this way, auxin would cause a progressive increase of bud tissue mass and enhance the flow of nutrients and growth factors to the bud. Dormancy length undoubtedly depends on several endogenous signals, but indoleacetic acid is a key factor in the control of this phenomenon.