Date Published: June 27, 2018
Publisher: Public Library of Science
Author(s): Graciele Santos Monteiro Reis, Alex-Alan Furtado de Almeida, Pedro Antônio Oliveira Mangabeira, Ivanildes Conceição dos Santos, Carlos Priminho Pirovani, Dário Ahnert, Raffaella Balestrini.
Theobroma cacao is cultivated in the shade, in a so-called ‘Cabruca’ system, in intercropped with Erithryna or other tree species of economic value, and in full sun as a monoculture in irrigated or chemically-irrigated systems. Since it is a species quite intolerant to wind, it is practically impossible to implant cacao crops under full exposure to the sun, or in areas of frequent winds, without the protection of windbreaks, using arboreal species around the area of culture in the form of box. Wind can cause mechanical stimuli in plants, affecting their growth and development. The objective of this work was to evaluate the photosynthetic changes in mature leaves and the molecular, biochemical and ultrastructural changes in young and mature leaves of the CCN 51 cloned genotype of T. cacao subjected to intermittent (IW) and constant (CW) wind, with velocities of 2.5, 3.5 and 4.5 m s-1, during 3, 6 and 12 h of exposure. It was verified that CW and IW, considering different exposure times, interfered directly in stomatal conductance (gs), transpiration (E) and water use efficiency (WUE), causing a reduction of the photosynthetic rate (A) in mature leaves. In addition, the pulvinus and blade of young and mature leaves, exposed to IW and CW with different exposure times (3 and 12 h), showed marked macroscopic and microscopic mechanical injuries resulting from the constant leaf movement. At both speeds, there was rupture of the cell nuclear membrane in pulvinus and the mesophyll tissues, mainly in the young leaves. On the other hand, in young and mature leaves exposed to CW and IW at different speeds and exposure times, there was lipid peroxidation, increased activity of guaiacol (GPX) and ascorbate (APX) peroxidases in most treatments; and altered expression of transcripts of psba and psbo genes related to the phothosynthetic apparatus and Cu-Zn-sod and per genes related to antioxidative enzymes at the rate of 4.5 m s-1. Younger leaves were more intolerant to mechanical stress caused by the wind, since presented greater macro and microscopic damages and, consequently, greater molecular, biochemical and ultrastructural changes. High wind speeds can seriously compromise the development of young leaves of T. cacao plants and affect their productivity.
Mechanical stimuli caused by various environmental factors such as wind, touch, rainfall and obstacles  may interfere with plant growth and development . Wind action on the plants can cause several mechanical damages, such as alterations in the cell walls , premature falling of leaves, breaking of branches and even uprooting of the entire plant, consequently generating a series of physiological effects and changes in response to water loss, hormonal changes and reduction in the rate of cellular stretching, among others [4–6]. Wind action may also promote decreases in plant vitality, with consequent reductions in productivity .
The young and mature leaves of the CCN 51 cloned plants of T. cacao presented differential responses when exposed to intermittent (IW) and constant (CW) wind. The young leaves were more intolerant to the mechanical stress caused by the wind, since they presented greater macro and microscopic damages and, consequently, greater molecular, biochemical and ultrastructural changes.