Cell and tissue dynamics of olive endocarp sclerification vary according to water availability

Abstract

Endocarp developmental timing in drupe-type fruits, involving tissue expansion and sclerification processes, is increasingly used as marker for biological studies and crop management. In spite of its wide application, however, little is known regarding how these morphogenetic processes unfold or the factors that modify it. This study evaluates endocarp expansion and sclerification of olive (Olea europaea) fruits, used as an example of drupe-type fruits, from trees growing under different water regimes: full irrigated, deficit irrigated (moderate reduction of water availability) and rainfed (severe reduction of water availability). Fruits were sampled weekly until pit hardening, and fruit and endocarp areas were evaluated in histological preparations. An image analysis process was tested and adjusted to quantify sclerified area and distribution within the endocarp. Individual stone cells differentiated independently but distribution and timing indicated the overall coordination of endocarp tissue sclerification. Increase in sclerified area was initially gradual, accelerated abruptly the week prior to the end of endocarp expansion and then continued at an intermediate rate. These results suggest that the end of the expansion period is driven by sclerification and the morphogenetic signals involved act first on sclerification rather than endocarp size. Intensification of sclerification and the end of expansive growth occurred first with lowest water supply. Moderate and severe reductions in water availability proportionately decreased endocarp expansion and prolonged the sclerification, delaying the date of physically perceived hardening but not affecting the final degree of endocarp sclerification.

Understanding olive adaptation to abiotic stresses as a tool to increase crop performance

“…The effect of water availability on endocarp development was further investigated by Hammami et al (2013). Maximum mesocarp-to-endocarp ratio is an important feature for olive fruit quality for both table consumption and oil production.…”

Changes in the physiological response between leaves and fruits during a moderate water stress in table olive trees

“…This phenological stage is a dynamic period which can change in length with the water status of the tree (Hammani et al, 2013). In addition, in conditions of significant fruit load in the tree, vegetative growth is stopped (Rallo and Suarez, 1989) and water relations are clearly changed in comparison with low fruit load conditions (Martin-Vertedor et al, 2011).…”

A detailed description of morphological and anatomical characters of olive (Olea europaea) fruits in relation to phenological growth stages

“…Hammami et al () also showed that the fruits of trees under rainfed treatment delayed pit hardening at 12 weeks AFB, although other studies on the development of the pericarp of the olive locate the end of the endocarp sclerification between 4 and 6 weeks AFB (Lavee, ), between 7 and 9 weeks AFB (Rallo & Cuevas, ) and between 8 and 10 weeks AFB (Rapoport et al, ). This variability in the stage where the sclerification of the endocarp is reached and the lack of coincidence with what was observed in this work could be due to the different varieties of olive, to the crop growing conditions, such as water status (Hammami et al, ), to the frequency with which the samples were taken or the different ways of measuring the hardness or to the possible variation between the sclerification and the hardness.…”

“…In the olive fruit, this process occurs in the cells of the endocarp and is responsible for its hardening as in other drupes (Gómez del Campo & Rapoport, ; Roth, ). The sclerification of endocarp occurs gradually during the growth of the fruit, beginning a few days AFB and ending between 10 and 11 weeks AFB (Hammami, Costagli, & Rapoport, ; Rallo‐Morillo & Rapoport, ).…”

“…Each endocarp cell begins its sclerification following its own rhythm of deposition of secondary lignified wall, independent of the rest of endocarp cells, so that various degrees of sclerification can be found throughout the phases of tissue sclerification (Hammami et al, ).…”