Growth and rheological changes of collenchyma cells: The fusicoccin effect

Abstract

Fusicoccin enhanced the growth of collocytes from Apium Gravtolens petioles and modified the rheological parameters tested. But these changes do not sufficiently explain the variations of the cell wall extension. Such effects are discussed. Key words: Cell wall -Fusicoccin -Growth -pH Effect -Rheology -Wall extension.Fusicoccin (FC), a diterpene glucoside, promoted the elongation of various organs within minutes of application (12,13,26). Such action was similar to the effect of low pH and auxin on cell growth. FC has been reported to increase the proton concentration in the cell wall. The similar action of FC, low pH, and auxin on growth (3,4,24) may explain the primary action of auxin; the hypothesis presented (7, 23) is discussed in references {16, 27,29).Collenchyma is a choice material for testing cell wall extension and rheology during growth processes (8, 9). The rheology (including rheological parameters and the effect low pH on extension rate) of isolated collocyte bundles has been shown to change during growth and differentiation of the tissues. In order to test only the interactions between growth and the rheology of the collocyte walls, we decided to use FC. This substance can stimulate growth, while biphasic auxin responses suggest that the auxin action may consist of at least two stages (16,17,28). It has also been shown that the FC effect is not reduced by some inhibitors, e.g., abscisic acid (19,21). Changes of extensibility and induced growth have been also reported for isolated collocyte bundles incubated 4 hr in a solution containing auxin (20). But collenchyma can undergo passive growth, like the epidermis (25), being extended by the other tissues of the organs. Thus, the growth behavior of collocytes isolated from the petiole or naturally associated with it could be different. Collocyte walls prepared from intact collenchyma bundles, inside the petiole itself, were used in this study. Materials and methodsPlants of Apium Graveolens were cultivated in a greenhouse (under controlled temperature and humidity). High-and low-growing petioles (see 9) were detached from the shoot and washed in a beaker with distilled water. After alcohol sterilization, the basal part of the petiole (9) was cut, the initial length of the collocyte