Cutin synthesis in plants. I. Free fatty acid movement during cutin synthesis in injured Gasteria verrucosa leaves

The alterations of the amount of free fatty acids (fFA) in Gasteria leaves was followed after application of a wound at the tip of the leaves in three segments of the recovering leaves. The studies were done with the injured leaves left on the plant (in situ), or with leaves that were cut at the base and kept under standard conditions (detached). In both cases the fFA concentration at the front segment with the wound surface, the second area, directly adjacent to the wound region, and at the center segment of the leaves was determined in successive time intervals. Under in situ conditions fatty acids are transferred from the intact leaves to the wounded one, leading to vast oscillations of the fFA level in the center region. At the front and nearfront segments, recovery starts after a very steep decrease of fFA concentration due to wound respiration. Under detached conditions recovery starts with a decline of the fFA concentration in the entire leaf as a result of wound respiration. A sharp increase in protein synthesis occurs simultaneously in the front segment. Protein synthesis in the near-front and center region starts later, leading to a stimulation of FA synthesis in the center part, which was found to be the main site of FA production. The fatty acids are transferred via the near-front segment to the wound surface, where the initial fFA level is reached after four days. At the fifth day the fFA in the front segment start to polymerize, thus initiating the formation of a new cutin layer, while simultaneously FA production in the center region reaches its maximum level. Once the formation of the protective layer has started, both FA and protein synthesis return to anormal level. The FA production within the center part of the leaf, the transport through the near-wound segment and the FA consumption at the front part with the wound surface can be seen more clearly with detached leaves than under in situ conditions, where FA translocation from intact leaves interfere with the reactions occurring in the wounded leaf.