Particularities of the carbohydrate content in pollen and pollen tubes of a tomato variety

CARRIZO GARCÍA C., GUARNIERI M., PACINI E.

Parma, Italia

Jornada; Reunión Anual de los Grupos de Trabajo ‘Biología Celular y Molecular’ y ‘Biotecnología y Diferenciación’ de la Sociedad Botánica Italiana; 2009

Sociedad Botánica Italiana

A wide range of carbohydrates are found in ripe pollen grains, which accomplish several functions during pollen presentation, dispersal and germination. Then, the regulation of the carbohydrates metabolism is relevant for male fertility and/or pollen performance. We have studied the carbohydrate content in mature pollen grains and its fluctuations during pollen tubes growth in the tomato (Solanum lycopersicum L.) cv. Platense in order to analyze its possible relation with pollen and pollen tubes performance. The profile of soluble carbohydrates and starch content in mature pollen grains was studied at different moments of the flowering season in two consecutive years. The content of soluble carbohydrates can change among samples, in the carbohydrates found and their concentration. Reducing sugars predominate, being glucose and fructose the most abundant; small concentrations of Fru-6P/Glc-6P, UDP-Glc, and maltosaccharides were also recorded. The constant presence of maltosaccharides is a novel feature. Sucrose was absent in pollen in one season, but present in the other, being a minor percetange in contrast to reducing sugars. Starch amount is always very low, almost invariable. No significant variations in pollen viability were recorded along each season, then the carbohydrate metabolism of the pollen analyzed may evidence certain plasticity to allow constant adjustments to environmental conditions to maintain fertility. A study of pollen germination and pollen tube growth was done in the first season, when sucrose was absent in pollen grains. In vitro assays were done using a culture medium without carbohydrate supply to define and describe the autotrophic/ous phase of pollen tube growth, and to analyze the fluctuations of endogenous structural or stored carbohydrates. There was a definite autotrophic phase of growth in which pollen tubes elongated continuously until a certain length. The most substantial changes in the carbohydrates were registered in soluble carbohydrates and total pectins, being more important in the first minutes, when the germination started. There was callose in the ripe pollen grains, but its amount rose slightly along the pollen tubes growth (when callose walls were formed). Total pectins were the most abundant pollen tube wall component. Starch amount did not change significantly along the period analyzed. The fluctuations of the different carbohydrates suggested that another type of substances must be connected with the carbohydrates metabolism. Despite the lack of sucrose in pollen grains, substance considered the main nutrient for pollen tubes, pollen germination and pollen tube growth could be sustained with the pollen reserves in an autotrophic way, whatever their nature could be. The analysis made have evidenced some peculiar features in the tomato Platense, and have also shown that the different carbohydrates analyzed (for reserve or structural), except for starch, seem to be actively involved in pollen and pollen tubes metabolism.