Flowers initiation

Floral initiation is best studied at the microscopic level. The fact is, floral initiation often occurs and is unrecorded because abortion takes place or there is failure of the flower initials to develop to the macroscopic level where detection is easy with the unaided eye. There are many pieces of evidence that this is true. One was provided by Naylor (1941) with the photoperiodically sensitive cocklebur plant (Xanthium pennsylvanicum). He found that even when the plants were severely deficient in nitrogen or phosphorus or potassium they differentiated floral primordia after the leaves received an appropriate photoperiodic treatment. However, floral development did not occur. If dissection of stem apices had not been carried out, floral initiation would have gone undetected and the plants would have been recorded as vegetative. 

Regardless of how one views the phenomenon of floral initiation, it is clear that when a plant changes from the vegetative to the reproductive phase many 

Similar experiments to those done with gymnosperms involving applications of gibberellins to leaves and buds of woody angiosperms such as apple, pear. 

The search for a suitable system for the study of the biochemistry of flower initiation led Nitsch and Nitsch (1967 a, b) to employ tissue culture techniques for that purpose. Progress in the study of flower initiation at the biochemical 

CoussoN and Tran Than Van (1981) made the remarkable discovery that by using precisely defined physical and chemical conditions it is possible to cause 1x10 mm pieces of explant tissue from the basal part of the inflorescence of Nicotiana tabacum cv. Samsun—a short-day plant—to proceed directly to the production of flower buds. From 5 to 25 flower initials were obtained 

Biology and Chemistry of Jerusalem Artichoke Helianthus tuberosus L. 

FIGURE 10.4 Date of first flower (A) and the duration of flowering (B) for 190 Jerusalem artichoke clones grown at 30°57 N (after Kays and Kultur, 2005). 

---

Valde°s etal. (1987) concluded that plant height is a minor factor in flower initiation. In the Sierra Mazateca, most flowering stems are, in fact, very long, since the stems that elongate the most are most likely to receive direct sunlight. Plants grown in the University of Wisconsin... 

This phenomenon, which varies in intensity in different varieties, is characteristic of many other perennial fruit crops in which flower initials are laid down in the summer of the year before flowering. The sparse flower induction which accompanies a heavy crop was formerly attributed to depletion of the carbohydrate and nitrogenous reserves of the tree but, whilst alternate bearing may have developed as a means by which the tree could conserve its food reserves, the control mechanisms are clearly hormonal in nature. 

Apple cv. Emneth Early. Effect of fruit removal at different times on flower initiation in bourse buds... 

Off year treatments which have been tried in order to decrease flower initiation include -... 

Figure 1. Hormonal factors influencing flower initiation in bourse bud of apple. G = gibberel-lins, C = cytokinins, F = florigin P...

Meijer, W.J.M. and Mathijssen, E.W.J.M., The relations between flower initiation and sink strength of stems and tubers of Jerusalem artichoke Helianthus tuberosus L.), Neth. J. Agric. Sci., 39, 123-135, 1991. 

Ethylene promotes a large array of responses in seeds, plants, and fruits (Table I), some similar to and some dissimilar to effects of auxins. Those with actual or potential commercial application include (a) growth promotion of seedlings (rice), (b) inhibition of height growth, (c) root initiation, (d) chlorophyll destruction (citrus), (e) flower initiation (pineapple, bromeliads), (f) stimulation of fruit growth (figs). 

Pigment synthesis inhibition Flower initiation Flower inhibition Flower sex shifts Fruit growth stimulation Fruit degreening Fruit ripening Respiratory changes Storage product hydrolysis Latex secretion promotion... 

Figure 2. Different stages of growth in Ileracleum candicans field emergence (A) true-leaf initiation (B) vegetative growth (C) flowering initiation (D) blooming (E) pollination by insect (F) fruiting (G) final growth (FI) and harvested rhizome (I).

Nagao, A. (1983) Differences of flower initiation of Cryptomeria japonica under various alternating temperatures. J. Jap. For. Soc., 65 335-338 (in Japanese). 

Another possible reason why GA treatments do not induce flower initiation may be due to improper timing and/or supraoptimal doses. For example, exogenous GAs either promoted or inhibited flower formation (as measured by number of flower buds produced) in plants of the dwarf strain Kidachi of the SDP Pharbitis nil that were marginally induced by 1 inductive long night. Promotion of flowering was observed when the GA treatment occurred 11 to 17 h before the inductive dark period, while GA application immediately after the inductive dark period caused a reduction in the flowering response [9, 18]. 

Are Endogenous GA Levels Correlated with Flower Initiation ... 

Any attempt to rigorously define the role of a hormone in the regulation of a developmental process requires determination of the quantitative relationships between hormone levels and the process. To date, there are few studies in which changes in GA levels in relation to flower initiation have been carefully monitored. Part of the problem has been that most investigations rely on bioassays for quantitative analyses the reliability of this method of quantitation has been... 

---