Morfologia e função ecológica de lenticelas em espécies arbóreas da Caatinga

Abstract

Lenticels are pore-like structures, commonly originated in the substomatic cavity through a more intense meristematic activity of the phelogen. Unlike cork cells, which are tightly arranged and have suberified walls, lenticels are made up of cells with a rounded shape and delicate walls, a characteristic that allows for the presence of large intercellular spaces, which are directly related to the known functions of these structures. Lenticels are present in a variety of organs and species of terrestrial plants, presenting distinct adaptations that help individuals to establish themselves in the face of changes in the environmental conditions experienced. Although lenticels were described two centuries ago, there are many gaps in knowledge involving these structures. This dissertation to clarify the importance of lenticels and understand how these structures occur in plant species from semiarid environments. The first chapter aims to carry out a literature review on lenticels in order to understand how different approaches and studies have been developed over time, also seeking to map specific fields of knowledge that still need to be filled. Specifically, we sought to: 1) Describe how lenticels occur in different phylogenetic groups of plants; 2) Describe in which plant structures the lenticels can be found; and 3) Describe the main functions, implications and structural adaptations given to lenticels. For this, we reviewed the specific literature through searches in scientific repositories, readings and cross-references. We found that lenticels are not exclusive to stems and roots, occurring in several organs, being present in species of monilophytes, gymnosperms and angiosperms. In addition to gas exchange, lenticels perform other functions, such as water absorption, also serving as transpiration points. These structures can respond to environmental stressors, showing adaptations to the environment. Although knowledge about lenticels has grown over the years, there are still gaps to be filled, especially in arid and semi-arid climates, since most studies published to date deal with plant species from wet and humid environments. In the second chapter, we aim to describe the morphology of the lenticels and stem of 14 woody species from the Caatinga, in order to search for possible morphological patterns and separate them into functional types. Specifically, we sought to: 1. Characterize the types of rhytidomas and pattern of occurrence of lenticels in the stem; 2. Describe the lenticel morphology and separate them into functional types according to their structural organization; 3. Describe the morphology of bark and wood in structural and functional terms. Individual samples were collected for each species and histological slides were prepared for anatomical description. Additionally, lenticels were analyzed using electron scanning microscopy and fresh material under stereomicroscope for descriptions of external morphology. We found a difference between the morphological characteristics of the lenticels, as well as the general morphology of the stem. We also observed two patterns of structural changes and construction of occlusion layers in the lenticels, which indicates at least two possible strategies adopted by species adapted to semi-arid conditions, suggesting that the lenticels of plant species can evolve distinct characteristics in response to drought. The presence of occlusion layers can favor species in seasonally dry tropical forests, reducing transpiration rates and also allowing gas exchange in the absence of leaves in deciduous and semi-deciduous species in the dry seasons.