The Effect Of The Light And Gibberellin Acid On The Ray Floret Cell Growth Of Gerbera Hybrida

Flower growth and pigmentation are two key factors mainly responsible for thecommercial characteristics of ornamental flowers, and both of them are regulated byenvironmental and developmental signals, among which GAs and light are the mostimportant factors. As one of the popular five cut-flowers in the world, Gerbera hybridahas been an ideal experimental material for the study on complex inflorescencedevelopment. Based on in vitro culture system, the effects of light and GA₃ on thedevelopment of infloreseences and ray floret (rf) were investigated by comparing the rfpetal size, the epidermis cell size and numbers. The major results are as follows:1. An agrose-blotting method was established. It can be used to effectively analyze theshape and size of plant epidermal cells.2. Gerbera seedlings were grown under standard greenhouse conditions andinflorescences developmental process was divided into six stages as described asMeng and Wang (2004). The inflorescences of P1 to P6 were harvested and the rayfloret petals were detached for the measurement of petal length and width. It wasfound that both the length and the width of rf petals increased from P1 to P6, andthe growth rate was different from P1 to P6: faster elongation of the petal wasobserved from P1 to P2 and radial expansion mostly increased from P2 to P3..Furthermore, both the number and the size of adaxial epidermal cells enlarged withthe growth of rf petal. The increase rate of cell size is higher than the increase ofcell numbers. Therefore, the growth of rf petals was mainly the result of elongationand expansion of epidermal cells.3. For in vitro culture, P1.5 inflorescences and ray florets were first incubated indarkness for 2.5 d, then exposed to light condition with or without 50μmol/L GA₃.The petal growth and cell elongation and expansion were measured. It was foundthat white light (WL) treatment could promote the elongation of rf petals and morestronger promotion was observed on petal width increasing. The cell numbers inpetal were kept stable after culture in vitro. The data demonstrated that it was cellsize instead of cell number did the contribution to enlargement of the rf petal during petal development.4. The inflorescences and rfs of P1.5 were cultured in vitro under the condition ofDark, WL, Dark+GA₃ and WL+GA₃, respectively. The results showed that the rfpetals were longer after GA₃ application in the dark, implying that GA₃ couldpromote elongation. Cultured under WL+GA₃, it found that GA₃ inhibit radiallyexpansion, The cell number in petal width kept unchanged, and that epidermal cellnumber in length increased a little at a rate far less than that of the petal elongation,suggesting that GA₃ strongly promoted the elongation of epidermal cells, whichaccelerated the petal elongation.5. The inflorescences and rfs of P1.5 were cultured in vitro under blue light (BL), redlight (RL) and far-red light (FRL), respectively. It was found that the cultured rfpetals under BL were wider but shorter than those under the other two lightconditions. In addition, the epidermal cells of the top, the widest-part and the basalpart of the rf petals under BL appeared shorter and wider, which showed that BLpromoted the epidermal cell to be wider, which was resulted in the expansion of rfpetals radially. BL, like WL, played a dominant role in the enhancement ofexpansion of rf petals.6. Among three parts, the basal part of the rf petal showed faster growth both inelongation and in wideness. Similar results were found in culture system in vitro.When petals were divided in three parts ofâ… ,â…¡,â…¢in culture system, the basal partofâ…¢showed most fast growth and the cell of this part was more sensitive to lightand GA3. If partâ…¢was further divided toâ…¢-1 andâ…¢-2, same sensitivity to lightand GA₃ was also found in basal part ofâ…¢-2.