Structural and physiological profile of leaf galls induced on Calophyllum brasiliense (Calophyllaceae)

Abstract

Gall-inducing insects cause modifications in the host plant leading to the formation of galls in response to chemical and feeding stimuli. Common responses to gall formations include cellular hypertrophy, tissue hyperplasia, and metabolic changes, such as the production and dissipation of reactive oxygen species (ROS) to maintain essential metabolic activities. Although galls are reservoirs of photoassimilates, they can contain chlorophyllous tissues and perform photosynthesis, helping to prevent hypoxia and hypercarbia. Green galls can exhibit tissue alterations, potentially activating chlorophyllous tissue. This study evaluated the anatomical, physiological, and histochemical characteristics of green claviform galls on leaves of Calophyllum brasiliense via anatomical and histochemical techniques and chlorophyll fluorescence parameters measured with a Handy FluorCam PSI. Galls exhibit cell hyperplasia and tissue hypertrophy, especially in compact nutritive tissue, along with anatomical modifications such as a reduction in palisade parenchyma, stomatal loss, and an increase in isodiametric cells. They also present different metabolic compounds distributed in the tissues, such as starch, lipids, reducing sugars, proteins, terpenoids, lignin, phenolics, and alkaloids, indicating their structural and chemical complexity. Additionally, these galls have active chlorophyllous tissue, although at lower levels than leaves do, confirming their photosynthetic potential and indicating the environmental stress experienced by the host plant. Furthermore, they suggest a possible role of photosynthesis in dissipating excess energy and regulating gases within the gall.