There are no reports on the biomechanical significance of petiole trichomes, although the epidermis is the important structure involved in developing TS in growing non-lignified organs in herbaceous plants (Niklas and Paolillo 1997 Domínguez et al. Therefore, during water stress, which indicates a decrease in TS, the plant is not able to perform any movements (Esmon et al. Due to the existence of TS and the state of pre-stress, the amount of energy necessary for plant movement reactions can be lowered (Hejnowicz 1997 Spatz et al. TS is an important element that keeps the tissues, organs, and entire body at high level of potential energy (Niklas 1992 Hejnowicz 2011). In herbaceous plants, tissue stress (TS) is a result of the interactions between anatomical structures, mainly cell walls, and physiological processes related to the osmotic conditions of the cell. We conclude that trichomes can be involved in plant biomechanical system and serve as an additional reservoir of hydrostatic pressure that is necessary for maintaining petioles in the prestressed state. The application of the ‘tensile triangles method’ revealed that these trichomes had a biomechanically optimized shape in comparison to the adaxial side. Trichomes from the abaxial side of the petiole were larger at their base. The indentation test showed that non-isolated collenchyma is stiffer on the abaxial side of the petiole. However, strands of collenchyma with epidermis exhibited a significantly greater strength regardless of their position on the petiole. Isolated strands of collenchyma showed no correlation between strength values and position on the petiole.

Petioles without trichomes did not exhibit tropic response, and the dehydration of trichomes slowed and prevented complete leaf reorientation. The stiffness of the non-isolated tissue with intact epidermis was measured using the micro-indentation method. Isolated strands of collenchyma with intact epidermis or epidermis mechanically removed from the abaxial and adaxial sides of the petiole were subjected to breaking test. The experiment comprised four variants of the large non-glandular petiole trichomes: (1) intact, (2) mechanically removed, (3) dehydrated, and (4) intact but with longitudinally injured petioles. Time-lapse imaging was used to study the leaf reorientation of Cucurbita maxima ‘Bambino’ plants placed in horizontal position. The large, non-glandular trichomes on Cucurbita petioles occur across collenchyma strands. Trichomes are involved in petiole movement and likely function as a part of the plant biomechanical system serving as an additional reservoir of hydrostatic pressure.

Deltacad crack