The Effect of Photoperiod on Necrosis Development, Photosynthetic Efficiency and 'Green Islands' Formation in Brassica juncea Infected with Alternaria brassicicola.

Violetta Katarzyna Macioszek,Magdalena Gapińska,Mirosław Sobczak,Jakub Oliwa,Iwona Ciereszko,Sylwia Michlewska,Andrzej Kiejstut Kononowicz,Andrzej Skoczowski

doi:10.3390/ijms22168435

Abstract

The main goal of growing plants under various photoperiods is to optimize photosynthesis for using the effect of day length that often acts on plants in combination with biotic and/or abiotic stresses. In this study, Brassica juncea plants were grown under four different day-length regimes, namely., 8 h day/16 h night, 12 h day/12 h night, 16 h day/8 h night, and continuous light, and were infected with a necrotrophic fungus Alternaria brassicicola. The development of necroses on B. juncea leaves was strongly influenced by leaf position and day length. The largest necroses were formed on plants grown under a 16 h day/8 h night photoperiod at 72 h post-inoculation (hpi). The implemented day-length regimes had a great impact on leaf morphology in response to A. brassicicola infection. They also influenced the chlorophyll and carotenoid contents and photosynthesis efficiency. Both the 1st (the oldest) and 3rd infected leaves showed significantly higher minimal fluorescence (F0) compared to the control leaves. Significantly lower values of other investigated chlorophyll a fluorescence parameters, e.g., maximum quantum yield of photosystem II (Fv/Fm) and non-photochemical quenching (NPQ), were observed in both infected leaves compared to the control, especially at 72 hpi. The oldest infected leaf, of approximately 30% of the B. juncea plants, grown under long-day and continuous light conditions showed a ‘green island’ phenotype in the form of a green ring surrounding an area of necrosis at 48 hpi. This phenomenon was also reflected in changes in the chloroplast’s ultrastructure and accelerated senescence (yellowing) in the form of expanding chlorosis. Further research should investigate the mechanism and physiological aspects of ‘green islands’ formation in this pathosystem.

Highlights

Modulation of light quality and quantity to optimize growing conditions of plants and to investigate their influence on photosynthetic efficiency with the addition of biotic and/or abiotic stresses has become a modern approach to plant science [1,2,3]
Various traits have been investigated in several plant species grown under continuous light (CL), which can have a contrasting impact on the circadian clock, photosynthesis and productivity
The plants were inoculated with A. brassicicola conidial suspension days thereafter, on the of the growing period and were incubated for up to three days thereafter, simultaneously

Summary

Introduction

Modulation of light quality and quantity (photoperiod) to optimize growing conditions of plants and to investigate their influence on photosynthetic efficiency with the addition of biotic and/or abiotic stresses has become a modern approach to plant science [1,2,3]. The effect of photoperiod on plant growth depends on many factors, such as light quality and intensity, plant species and/or cultivar, and growing conditions (soil, watering, and temperature) [6,7,8]. The application of an additional biotic or abiotic stress to plants grown under a prolonged day results in the expression of physiological and genetic responses, e.g., activation of defense pathways [3,7,12]. Manipulating day length can be used as a new tool of modern agriculture, especially in controlled-environment plant factories [14]

Methods

Results

Discussion

Conclusion