Floral apex

C. aff. montana, C. suhcrustulata, C. setosa, C. centronioides (Fig 9.2H) and eight to nine slightly asymmetrical petals with a retuse apex in C. macrantha (Fig 9.2C,F), as well as six to seven large petals in C. rhodopetala (Fig 9.2G). Petals are initiated in a rapid sequence on the sides of an invaginating floral apex. The further development of petals is often unidirectional from the abaxial to the adaxial side in all species examined (Fig 9.2C,F). 

Fig 11.7 A. celastrifolia, carpel initiation. The organ-free floral apex is marked with an asterisk in aU. Note that in all samples the carpellary cleft (if already present) is pointing towards the floral centre. (A) Three very similar carpels suggesting simultaneous initiation. (B) Four carpels initiated and very similar in size. (C)-(E). Five carpels formed in no defined sequence. (F) Six carpels formed apparently in anticlockwise sequence. (G) Six carpels formed in no discernlhle sequence (i.e. erratic). (H) Seven carpels formed, six are of similar developmental stage, one lags behind. Scale hars = 100 pm in all. 

Horseweed is a native annual plant that can grow to a height of over 2 m. When mature, several flowering stems appear at the apex, which branch frequently and create a multitude of tiny composite flowers. In each flower, there are numerous yellow disk florets in the center, which are surrounded by tiny white ray florets. There is no noticeable floral scent. The blooming period can occur any time from midsummer to fall, lasting about 3 wk. 

Abe, M., Kobayashi, Y., Yamamoto, S., Daimon, Y., Yamaguchi, A., Ikeda, Y., Ichinoik, H., Notaguchi, M., Goto, K., and Araki, T., FD, a bZIP protein mediating signals from the floral pathway intergrator FT at the shoot apex, Science, 309, 1052-1056, 2005. 

Under non-inductive conditions, the GAs in question should be limiting in the apex. Conversely, experimental reduction of endogenous GA levels should inhibit or prevent floral initiation under inductive conditions. 

The floral stimulus acts at the apex and therefore determination of the site of GA action is important in formulating logical hypotheses about the role of GAs in flower initiation. Although not examined in many species, the evidence indicates that GAs can affect flower initiation at different sites. Flower induction brought about by GAg treatments in Bryophyllum daigremontianum and Hyoscyamus niger is the result of GA action in the leaves, not the apex where the floral stimulus acts [21, 22]. The situation is quite different in the SDP Pharbitis nil and Impatiens balsamina, where it was determined that the apex is the site of GA action [ 16,25,27]. 

The dynamics of AA production and utilization as well as the metabolic drifts of nucleic acids, proteins and other cell constituents have been studied in the shoot apex and differentiating floral organs of a number of species under different photoperlodlc and vernalization treatments and based upon these findings the ascorbic acid - nucleic acid -protein metabolism concept of growth and development was advanced (Chinoy, 1962) and subsequently elaborated (Chinoy and Mansurl, 1966 Chinoy, 1969). A brief resume of this concept Is reproduced here. 

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