Metabolism of tulip bulbs as related to thermoperiodicity

Abstract

There are little published data on the physiolo-gical research of the growth of tulip bulbs throughout the yearly life cycle. In this report, the nitrogen and carbohydrate metabolism and the overall picture of activity of auxins and inhibitors throughout the life cycle are dealt with, especially, those relating to the so-called thermoperiodicity.
BLAAUW, by microscopic observations of the meristem during and immediately after each temperature treatment, distinguished between the direct and indirect temperature effect and identified each optimal temperature with a definite morphological stage.
Each developmental stage has its own optimal temperature; organ initiation needs the highest temperature, stem elongation and unfolding of the flower a lower one, and preparation for elongation, a stage which has no morphological significance, occurs best at the lowest temperature.
1. Fresh weight versus dry weight. Fresh weight of bulbs increases with the progress of the current season's shoot growth. Maximum weight is attained about June 15 in the sandy soil field and about June 25 in the paddy field and thereafter it decreases gradually. Dry weight of bulbs increases in parallel with the increase of the fresh weight and the maximum weight is gained 10 days earlier than the case of the fresh weight.
In practice bulbs are lifted from the ground after they have attained the maximum fresh weight.
Chilling stimulates the decrease of the dry weight but in the chilled bulbs fresh weight decreases less than that of those kept in the room temperature.
Progress of the growth processes of bulbs grown in the sandy soil field proceeds 10 days earlier than that of the bulbs grown in the paddy field.
2. Nitrogenous constituents: Nitrogen content per bulb increases with the increase of the fresh weight and maximum gain is attained later than that of the fresh weight. The percentage of nitrogen content to fresh weight increases also with the progress of the growth process.
Soluble and insoluble nitrogens show similar trends, the former reaching the first peak later than the latter.
In contrast to the bulbs kept in the room temperature, in chilled bulbs the percentage of insoluble nitrogen content to fresh weight decreases and of soluble nitroge increases. In chilled bulbs insoluble nitrogen is accelerated to change into soluble form.
Nitrogen content per bulb and percent content on a fresh weight basis of bulbs grown in the sandy soil field are higher than those of bulbs grown in the paddy field.
3. Carbohydrates: Carbohydrates content per bulb and percent content on a fresh weight basis increases/or decreases with the increase/or decrease of the fresh weight of the bulbs.
Carbohydrates content per bulb decreases gradually. Percent content of fresh weight basis of bulbs grown in the paddy field decreases gradually, whereas that of the bulbs grown in the sandy soil field rather abruptly.
Preceding to the fresh weight, total sugar content (percent of the fresh weight) reaches the maximum and then decreases rather abruptly up to May (bulbs grown in the sandy soil field. about May 25) or June (bulbs grown in the paddy field: about June 15) and then remain constant till the middle of October, whence increases again gradually.
Polysaccharides, having reached the maximum, decrease gradually. Polysaccharides of bulbs grown in the sandy soil field decreased rapidly than those of the bulbs grown in the paddy field. In chilled bulbs, polysaccharides abruptly decreased and total sugars increased abruptly. Polysaccharides are forced to change into sugars by chilling.
Starch is the main polysaccharide and most of sugars is non-reducing.
Starch accumulates initially in the outermost bulb scale, and having reached to the maximum, it decreases. Then it accumulates and decreases successively in the inner bulb scales.
In chilled bulbs, starch in the scale decreases abruptly.