Morphological and anatomical evaluation of adult and juvenile leaves of olive plants

Abstract

The olive tree (Olea europaea L.), like many other woody plants, has a long juvenile period in which the plant is not able to produce flowers. Knowledge of the moment when the plant is capable of flowering is important for breeding programs and also for determining the physiological basis for sexual reproductive behavior, but currently the only indicator of that moment is the actual flowering. In many species, the juvenile-to-adult phase shift includes changes in leaf structure known as heteroblasty, that is, varied form of successive leaves on the same plant. Some differences have been observed between juvenile and adult olive leaves, particularly in size and form, but to our knowledge, no complete systematic study has been carried out. In this research, we measured size, morphology and anatomy for juvenile and adult leaves of olive plants grown from seeds. Differences were found in most of the parameters studied, including leaf size, form, mesophyll thickness, layers of palisade parenchyma and quantity of peltate trichomes, which were generally significant but overlapping between the two leaf types. The most consistent and striking difference was the presence of an organized layer of subepidermal cells only in the abaxial mesophyll of adult leaves. This characteristic could be a simple and effective criterion of phase change in the olive tree.

From the juvenile to the adult vegetative phase in olive seedlings: the transition along the stem axis

“…1) increased linearly from the bottom to the top showing a transition along the axis and a stepwise loss of juvenile characters, and therefore, the juvenility with increasing distance of the leaves from the trunk base. Other researches carried out in olive and other species (Poethig, 1990;Moreno-Alías et al, 2009) found that juvenile leaves are smaller than adults; this study confirms these findings and adds that the transition tissue shows intermediate values for length, width and area of the leaves according to a linear trend. Also the significant differences obtained in rooting ability of cuttings in the Trial 2 measured as the percentage of rooted cuttings, the number and length of roots, the percentage of cuttings with callus, and the percentage of surviving cuttings (Table 1), confirm the upstream transition from juvenile-to-adult along the seedling axis, characterised by a lineal decrease of rooting ability in adulthood.…”

“…The transition from the juvenile-to-adult vegetative phase involves anatomical changes (Rapoport, 2008;Moreno-Alías et al, 2009) and changes in the biochemical composition of the leaves (Fernández-Lorenzo et al, 1999) and some authors also note differences in stomatal conductance and net photosynthesis (Sismilich et al, 2003;Kubien et al, 2007). In Trial 3, there is an upstream increase of stomatal conductance although statistically not significant, and no clear pattern for net photosynthesis (highest value in transition zone and lowest at the bottom) has been found.…”

“…In olive, it is known that the mesophyll thickness, the layers of palisade parenchyma and the quantity of the peltate trichomes differ between the two phases (Moreno-Alías et al, 2009). The peltate trichomes reduce the diffusion of water vapour (Proietti & Palliotti, 1997) and protect the photosynthetic activity by preventing UVB-induced stomatal closure (Grammatikopoulos et al, 1994).…”

Stemflow production and intrastorm rainfall intensity variation: an experimental analysis using laboratory rainfall simulation

“…Branches were steeply inclined toward the central stem, with inclinations of lower branches typically ~50° increasing to ~75°–80° for branches supporting the uppermost parts of the canopy. Lanceolate leaf sizes were in the range 8 mm × 40 mm to 10 mm × 50 mm, which are typical for olives (Moreno‐Alías et al ., ). In comparison, for three Italian cultivars, D'Imperio et al .…”

Intracanopy plasticity under strong wind conditions in the wild olive tree (Olea europaea L.): a conserved response between closely related taxa?

“…Phenotypic expression was characterized by randomly sampling 12-15 shoots per tree and exposure (Table 1). The lower parts of the crown were not sampled to avoid the possible ontogenetic effect in the phenotypic expression of this heteroblastic species (Moreno-Alías et al 2009). Sampling was performed at the end of spring (May-June), to ensure total elongation of leaves and internodes.…”