Adelin Barbacci

Another Brick in the Cell Wall: Biosynthesis Dependent Growth Model

Expansive growth of plant cell is conditioned by the cell wall ability to extend irreversibly. This process is possible if (i) a tensile stress is developed in the cell wall due to the coupling effect between turgor pressure and the modulation of its mechanical properties through enzymatic and physicochemical reactions and if (ii) new cell wall elements can be synthesized and assembled to the existing wall. In other words, expansive growth is the result of coupling effects between mechanical, thermal and chemical energy. To have a better understanding of this process, models must describe the interplay between physical or mechanical variable with biological events. In this paper we propose a general unified and theoretical framework to model growth in function of energy forms and their coupling. This framework is based on irreversible thermodynamics. It is then applied to model growth of the internodal cell of Chara corallina modulated by changes in pressure and temperature. The results describe accurately cell growth in term of length increment but also in term of cell pectate biosynthesis and incorporation to the expanding wall. Moreover, the classical growth model based on Lockharts equation such as the one proposed by Ortega, appears as a particular and restrictive case of the more general growth equation developed in this paper.

SHINY BEECH WOOD IS CONFIRMED AS AN INDICATOR OF TENSION WOOD

This study sought to develop a method to quantify tension wood areas in stem discs. It was suggested that the shiny appearance of beech (Fagus sylvatica L.) could provide an indication of tension wood. Each of 21 stem discs were digitised and the images analysed. Small areas of the discs were selected, and from these areas, anatomical sections were stained with astra-blue and safranine and the stained sections were compared with the wood disc images. The analysis showed that the shape of shiny areas and tension wood were similar; moreover, the measured ratios of shiny wood and tension wood were in good agreement. This confirms the assumption that in Fagus sylvatica shiny wood corresponds to tension wood.

Examining the contribution of cell wall polysaccharides to the mechanical properties of apple parenchyma tissue using exogenous enzymes

The impact of enzymatic degradation of cell walls on the viscoelasticity of apple cortex tissue reveals that methylated homogalacturonan, crystalline cellulose, and xyloglucan branching are key structures in determining cell wall mechanical properties.

Theoretical and experimental study of a mechanical model describing the trunk behaviour of mature beech trees (Fagus sylvatica L.) under the static loading of the crown

The effect of the self-weight increment, caused by annual growth, can be one of the principal processes affecting the development of growth stresses linked to the formation of reaction wood. This paper presents a preliminary study focusing on the relationship between the whole weight of the crown and the trunk displacement it creates. A mechanical beam model is proposed and tested theoretically, as well as experimentally, on three mature beech trees. Once the suitability of the model has been established, a simple sensitivity test in proposed that highlights the principal parameters involved in displacement.