Influência de diferentes condições luminosas sobre as características morfoanatômicas e fisiológicas de Psidium cattleianum Sabine (Myrtaceae)

Abstract

The family Myrtaceae presents great importance to the human population, mainly due to its fruits, which are much appreciated. This is the case of Psidium cattleianum Sabine, popularly known as araçá- de- coroa, a species native to Brazil and which presents great economic potential, since it is already used, on a regional scale, both in food and in folk medicine, highlighting the need for studies on this species. Therefore, the present work aimed to evaluate the qualitative and quantitative anatomy, as well as the variations in the gas exchange and the photosynthetic rate in leaves of this species, in specimens grown under full sun and permanent shading conditions at the Federal University of Lavras, MG (UFLA). For this purpose, completely expanded leaves of 4º or 5º node were collected and used to prepare histological slides containing transverse and paraderm ic sections for anatomical analysis. Then , these were observed under a light microscope to obtain the qualitative data and then the ImageJ software was used to carry out the measurements and counts of the quantitative data. The data related to plant physiology was obtained in the field through the use of IRGA. After the measurements, tables were made, which were then submitted to tests of normality, homoscedasticity and data independence at 95% significance. The variables approved in these tests were compared by the Student's t- test, while the non - approved ones were compared by the non - parametric Mann - Whitney test, both for p <0.05. It was possible to notice that the leaves of the studied species are hypoestomatic, presenting paracytic stomata. The epidermis, both abaxial and adaxial, are unisseri ate and just below the adaxial epidermis, it was possible to perceive a hypodermic tissue, also unisseria te. The mesophyll presents a dorsiventral organization, possessing stratified palisade parenchyma, with 2 to 5 cellular strata and the spongy parenchyma is also stratified, with 7 to 9 cellular strata. The vascular bundles present a bicolateral structure. As for the venation , it was possible to notice that the general pattern of the nerves is pinned- camptodromous- broquidodromous, and the tertiary and quaternary veins form a reticulated structure. The last marginal nerve is fimbriated and the smaller caliber nerves are present more compactly in the leaves of the sun environment in relation to the leaves of shade environment. Regarding the quantitative anatomical variables, it was possible to observe differences between the leaves of sun and shade environments for the thickness of the cuticle, epidermis, hypodermis and mesophyll, as well as changes in the number of stomata / mm². It was also possible to perceive differences in length, width and consequently in the leaf area. Regarding the physiological evaluations, it was possible to perceive statistical differences between the leaves of sun and shade environments for the photosynthetic rate, transpiration rate and stomatal conductance. In this way, it was possible to infer that the different light conditions affected the morphoanatomic characteristics of the leaves and, consequently, their functioning, guaranteeing better use of the conditions to which they are submitted.