Carbohydrate Status of Tulip Bulbs during Cold-Induced Flower Stalk Elongation and Flowering

Abstract

The effect of a cold treatment on the carbohydrate status of the scales and flower stalk of Tulipa gesneriana 1. cv Apeldoorn bulbs during growth after planting was studied and compared with bulbs not given cold treatment. Bulbs were stored dry for 12 weeks at 5'C (precooled) or 17°C (noncooled). Only the 5°C treatment led to rapid flower stalk elongation and flowering following planting at higher temperatures. Precooling enhanced mobilization of starch, fructans, and sucrose in the scales. The cold-stimulated starch breakdown was initially accompanied by increased a-amylase activity per scale. In noncooled bulbs, a-amylase activity slightly decreased or remained more or less constant. Cold-induced flower stalk elongation was partially accompanied by a decrease in the sucrose content and an increase in the glucose content and invertase activity per g dry weight. The starch content in internodes initially decreased and subsequently increased; a-amylase activity per g dry weight of the lowermost internode showed a peak pattern during starch breakdown and increased thereafter. The internodes of noncooled bulbs, on the contrary, accumulated sucrose. Their glucose content and invertase activity per g dry weight remained low. Starch breakdown was not found and a-amylase activity per g dry weight of the lowermost internode remained at a low level. Precooling of tulip bulbs thus favors reserve mobilization in the scales and flower stalk and glucose accumulation in the elongating internodes.It is well known that temperature controls the flowering process in many bulbous crops (Rees, 1972;De Hertogh and Le Nard, 1993). In the flowering process of tulips three phases have been distinguished: (a) the initiation phase, during which cell division and differentiation of the apical bud occur, resulting in the formation of a11 flower parts; (b) the preparation phase, during which the flower parts grow slowly and during which the conditions required for optimal flowering are prepared; and (c) the elongation phase, during which rapid extension growth of the shoot and flowering take place.In a temperate climate, flower initiation, flowering preparation, and shoot elongation occur in summer, winter, and spring, respectively. When bulbs are forced to flower at an earlier time, the cold winter period can be replaced by a welldefined, low-temperature treatment given to bulbs that are stored in climate rooms (dry-stored) (Rees, 1972;De Hertogh and Le Nard, 1993). Tulipa gesneriana L. cv Apeldoom bulbs require a dry-storage period of 12 weeks after planting at 5OC for optimal shoot elongation and flowering. The shoots of noncooled bulbs (dry-stored at 17OC) elongate slowly and, if anthesis is achieved, severe flowering disorders occur (Lambrechts et al., 1992).Experiments with exogenously applied GAs, GA biosynthesis inhibitors, and auxins showed that both GAs -and auxins are involved in the elongation process of the tulip flower stalk (Saniewski, 1989;Saniewski and Kawa-Miszczak, 1992). However, the sites of hormone action and the resu...

Mechanisms of vegetative propagation in bulbs : a molecular approach

“…Together with the long juvenile phase, this makes the development of a new flower bulb cultivar a slow and time consuming process. Many efforts in understanding and improving the physiological nature of flowering and vegetative propagation in bulbous plants took place in the last decades (Beijer 1952;Aung and Hertogh 1979;Lambrechts et al 1994;Balk and de Boer 1999;Rietveld et al 2000); however, the majority of these studies focused on physiological factors and limited molecular and genomic studies have been performed. Although various reasons can be brought forward for this, the large genome sizes for bulbous plants (Tulip ~25000 Mbp; Lily ~36000 Mbp) and technical difficulties in isolating e.g.…”

Fructooligosaccharides changes during maturation in inflorescences and seeds of onion (Allium cepa L. ‘W202’)

“…The metabolism of fructans during flowering has rarely been investigated. While studies on fructans in tulip have been done (Lambrechts et al 1994;Vergauwen et al 2000), none have looked at onion or other edible Alliaceae flowers.…”

The hot, the cold and the tulip : the regulation of flowering time and dormancy release

“…In Arabidopsis flowering directly commences upon the switch from vegetative to reproductive development, whereas tulip flower buds become dormant after their initiation and still require a period of prolonged cold in order to bloom in spring (Lambrechts et al, 1994).…”

“…Together with the long juvenile phase, this makes the development of a new flower bulb cultivar a slow and time consuming process. Many efforts in understanding and improving the physiological nature of flowering and vegetative propagation in bulbous plants took place in the last decades (Beijer, 1952;Aung and Hertogh, 1979;Lambrechts et al, 1994;Balk and de Boer, 1999;Rietveld et al, 2000); however, the majority of these studies focused on physiological factors and limited molecular and genomic studies have been performed.…”

“…At that moment all organs such as the stem, leaves and flower are already present inside the bulb. A subsequent period of prolonged cold is required for fast stem elongation, as well as for internal preparation of the flower to bloom in spring (Lambrechts et al, 1994;Rietveld et al, 2000).…”