Pre-Acclimation to Elevated Temperature Stabilizes the Activity of Photosystem I in Wheat Plants Exposed to an Episode of Severe Heat Stress.

Andrej Filaček,Mária Barboričová,Lorenzo Ferroni,Xinghong Yang,Kristína Gašparovič,Marek Živčák,Marián Brestič,Marco Landi

doi:10.3390/plants11050616

Abstract

The importance of high temperature as an environmental factor is growing in proportion to deepening global climate change. The study aims to evaluate the effects of long-term acclimation of plants to elevated temperature on the tolerance of their photosynthetic apparatus to heat stress. Three wheat (Triticum sp. L.) genotypes differing in leaf and photosynthetic traits were analyzed: Thesee, Roter Samtiger Kolbenweizen, and ANK 32A. The pot experiment was established in natural conditions outdoors (non-acclimated variant), from which a part of the plants was placed in foil tunnel with elevated temperature for 14 days (high temperature-acclimated variant). A severe heat stress screening experiment was induced by an exposition of the plans in a growth chamber with artificial light and air temperature up to 45 °C for ~12 h before the measurements. The measurements of leaf photosynthetic CO2 assimilation, stomatal conductance, and rapid kinetics of chlorophyll a fluorescence was performed. The results confirmed that a high temperature drastically reduced the photosynthetic assimilation rate caused by the non-stomatal (biochemical) limitation of photosynthetic processes. On the other hand, the chlorophyll fluorescence indicated only a moderate level of decrease of quantum efficiency of photosystem (PS) II (Fv/Fm parameter), indicating mostly reversible heat stress effects. The heat stress led to a decrease in the number of active PS II reaction centers (RC/ABS) and overall activity o PSII (PIabs) in all genotypes, whereas the PS I (parameter ψREo) was negatively influenced by heat stress in the non-acclimated variant only. Our results showed that the genotypes differ in acclimation capacity to heat stress, and rapid noninvasive techniques may help screen the stress effects and identify more tolerant crop genotypes. The acclimation was demonstrated more at the PS I level, which may be associated with the upregulation of alternative photosynthetic electron transport pathways with clearly protective functions.

Highlights

Heat stress is one of the main abiotic stresses that negatively affects agricultural areas around the world due to the induction of a wide range of adverse physiological, biochemical, morphological anatomical, and genetic reactions of plants [1]
We addressed two major issues with respect to an episode of acute heat stress: (a) the differential effect of wheat genotypes according to their sensitivity to heat and type” (Thesee, Roter Samtiger, ANK 32A)
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Summary

Introduction

Heat stress is one of the main abiotic stresses that negatively affects agricultural areas around the world due to the induction of a wide range of adverse physiological, biochemical, morphological anatomical, and genetic reactions of plants [1]. A plant is considered under heat stress if exposed to temperatures above a certain limit for a period sufficiently long enough to induce irreversible changes [5]. Plants are exposed to a wide range of temperatures in natural conditions, whether during the day, between days, or seasons. This temperature variability directly affects the performance because the speed of all biochemical processes increases until the optimal temperature is reached [6]. Along with the direct effect of high temperature, further injuries are due to the production of toxic compounds and reactive oxygen species, as well as to reduced ion fluxes and starvation symptoms, resulting in overall growth inhibition [5]. The collapse of the cell structures and the consequent cell death are outcomes of a severe heat stress [10]

Methods

Results

Conclusion