The epiphytic fern Elaphoglossum luridum (Fée) Christ. (Dryopteridaceae) from Central and South America: morphological and physiological responses to water stress

Abstract

Elaphoglossum luridum (Fée) Christ. (Dryopteridaceae) is an epiphytic fern of the Atlantic Forest (Brazil). Anatomical and physiological studies were conducted to understand how this plant responds to water stress. The E. luridum frond is coriaceus and succulent, presenting trichomes, relatively thick cuticle, and sinuous cell walls in both abaxial and adaxial epidermis. Three treatments were analyzed: control, water deficit, and abscisic acid (ABA). Physiological studies were conducted through analysis of relative water content (RWC), photosynthetic pigments, chlorophyll a fluorescence, and malate content. No changes in RWC were observed among treatments; however, significant decreases in chlorophyll a content and photosynthetic parameters, including optimal irradiance (I opt) and maximum electron transport rate (ETRmax), were determined by rapid light curves (RLC). No evidence of crassulacean acid metabolism (CAM) pathway was observed in E. luridum in response to either water deficit or exogenous application of ABA. On the other hand, malate content decreased in the E. luridum frond after ABA treatment, seeming to downregulate malate metabolism at night, possibly through tricarboxylic acid (TCA) cycle regulation.

Figure 1

Details of SEM and LM images of Elaphoglossum luridum epidermis. (a) SEM image of adaxial epidermis cells. (b) LM image of polocytic stomata and epidermal abaxial cells with sinuous anticlinal walls. (c) SEM image of the polocytic stomata on the abaxial surface. (d) SEM image of branched trichome on the abaxial epidermis.

Figure 2

Cross-sections of Elaphoglossum luridum frond in LM. (a) Mesophyll consists of parenchyma tending to palisade (pp), spongy parenchyma (sp), and uniseriate epidermis, on both sides of the frond. (b) Details of the abaxial tissues showing pits in the spongy mesophyll cell walls. (c) Details of the cuticle showing a light positive Sudan IV reaction. (d) Details of stomata on the abaxial surface. (e) Details of the vascular tissue. Ab: abaxial epidermis, ad: adaxial epidermis, ct: cuticle, en: endodermis, ep: epidermis, p: pit, pp: palisade parenchyma, sp: spongy parenchyma, and st: stomata.

Figure 3

Daily fluctuation (6:00h–18:00 h) in malate content of fronds of Elaphoglossum luridum under different treatments. The data are presented as mean ± SD. Lowercase letters indicate the groups differentiated by ANOVA followed by Tukey's test; P > 0.05 (n = 3).

Figure 4

Chlorophyll (Chl a, Chl b, and total Chl) and carotenoid (Car) contents in fronds of Elaphoglossum luridum under different treatments. The data are presented as mean ± SD. Lowercase letters indicate the groups differentiated by ANOVA followed by Tukey's test; P > 0.05 (n = 3).

Figure 5

Rapid light curve (RLC) plotted as ETR (P) versus irradiance (I) in fronds of Elaphoglossum luridum under different treatments. The data are presented as mean ± SD. Lowercase letters indicate the groups differentiated by ANOVA followed by Tukey's test; P > 0.05 (n = 3).