CARBOHYDRATE STATUS OF TULIP BULBS DURING COLD-INDUCED FLOWER STALK ELONGATION AND FLOWERING

The effect of a cold treatment on the carbohydrate status of the scale s and flower stalk of Tulipa gesneriana L. cv Apeldoorn bulbs during g rowth after planting was studied and compared with bulbs not given col d treatment. Bulbs were stored dry for 12 weeks at 5 degrees C (precoo led) or 17 degrees C (noncooled). Only the 5 degrees C treatment led t o rapid flower stalk elongation and flowering following planting at hi gher temperatures. Precooling enhanced mobilization of starch, fructan s, and sucrose in the scales. The cold-stimulated starch breakdown was initially accompanied by increased alpha-amylase activity per scale. In noncooled bulbs, alpha-amylase activity slightly decreased or remai ned more or less constant. Cold-induced flower stalk elongation was pa rtially accompanied by a decrease in the sucrose content and an increa se in the glucose content and invertase activity per g dry weight. The starch content in internodes initially decreased and subsequently inc reased; alpha-amylase activity per g dry weight of the lowermost inter node showed a peak pattern during starch breakdown and increased there after. The internodes of noncooled bulbs, on the contrary, accumulated sucrose. Their glucose content and invertase activity per g dry weigh t remained low. Starch breakdown was not found and alpha-amylase activ ity per g dry weight of the lowermost internode remained at a tow leve l. Precooling of tulip bulbs thus favors reserve mobilization in the s cales and flower stalk and glucose accumulation in the elongating inte rnodes.