Analyses of OJIP transients in leaves of two epiphytic orchids under drought stress

Jadson Bonini Zampirollo,Diolina Moura Silva,Priscila Conceição Souza Braga,Antelmo Ralph Falqueto,João Paulo Rodrigues Martins,Clodoaldo Leites Pinheiro,Vinícius Fonseca Dos Santos

doi:10.1590/2447-536x.v27i4.2334

Jadson Bonini Zampirollo, Diolina Moura Silva + Show 5 more

Open Access

https://doi.org/10.1590/2447-536x.v27i4.2334

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Abstract

Abstract The tolerance to low water availability is a decisive factor for growth and survival of orchids in their natural environment. The objective of this study was to characterize the photochemical traits of two epiphytic orchids (Cattleya warneri and Miltonia spectabilis) under water deficit (WD). Chlorophyll a fluorescence signals were recorded from young and fully expanded leaves of 5 plants/species after dark-adaption for 60 minutes, between 6-9 a.m. after 0, 30, 60, and 90 days of WD, using a Handy-PEA fluorometer (Hansatech, UK). Increases of O-J and J-I phases and L and K-bands and decreases of I-P phase were observed after 30 days of WD, especially in C. warneri. Decreases in the capacity to photochemically reduce quinone A (QA) and the kinetic properties required for redox reactions of the plastoquinone pool, the loss of energetic connectivity between units of PSII, inactivation of the oxygen evolution complex, and decrease of the overall rate of reducing the electron acceptor pool of photosystem I were observed in M. spectabilis, a more tolerant species. The greater ability of this species to maintain higher relative water content (RWC) in photosynthetic tissues allows greater photochemical activity.

Highlights

Among abiotic factors, low precipitation is among the environmental factors with the greatest negative effect on the survival of epiphytic plants
The relative water content (RWC) values decreased in both orchid species, from 92.7% and 93.3% to 45.8% and 54.4% after 90 days of water suppression in C. warneri and M. spectabilis, respectively, representing reductions of about 50.5% and 41.6% compared to water deficit (WD)-0 (Figure 1)
Reductions of RWC occurred from WD30 in C. warneri and only from WD-60 in M. spectabilis, which maintained higher values from WD starting at 30 days (WD-30) to WD-90

Summary

Introduction

Low precipitation is among the environmental factors with the greatest negative effect on the survival of epiphytic plants. Rainfall can be highly variable in space and time, affecting plant-water relationships (Grzesiak et al, 2019; Guevara-Perez et al, 2019). The low growth of plants in environments with low precipitation is probably due to physiological stress factors, such as low photosynthetic rate of chlorotic leaves. Previous studies have often found diminished fitness of plants growing under low precipitation in relation to well-watered plants. Among the main physiological disturbances caused by water deficit are lower cell turgidity, variations of stomatal opening and chloroplast structure, and decreased transpiration and CO2 assimilation rate (Lang et al, 2018).

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