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Open AccessArticle

Effects of Light and Daytime on the Regulation of Chitosan-Induced Stomatal Responses and Defence in Tomato Plants

1
Department of Plant Biology, University of Szeged, H-6726 Szeged, Közép fasor 52., Hungary
2
Doctoral School of Biology, University of Szeged, H-6726 Szeged, Közép fasor 52., Hungary
*
Author to whom correspondence should be addressed.
Plants 2020, 9(1), 59; https://doi.org/10.3390/plants9010059
Received: 15 November 2019 / Revised: 24 December 2019 / Accepted: 30 December 2019 / Published: 2 January 2020
(This article belongs to the Collection Feature Papers in Plant Physiology and Metabolism)
Closure of stomata upon pathogenesis is among the earliest plant immune responses. However, our knowledge is very limited about the dependency of plant defence responses to chitosan (CHT) on external factors (e.g., time of the day, presence, or absence of light) in intact plants. CHT induced stomatal closure before dark/light transition in leaves treated at 17:00 hrs and stomata were closed at 09:00 hrs in plants treated at dawn and in the morning. CHT was able to induce generation of reactive oxygen species (ROS) in guard cells in the first part of the light phase, but significant nitric oxide production was observable only at 15:00 hrs. The actual quantum yield of PSII electron transport (ΦPSII) decreased upon CHT treatments at 09:00 hrs in guard cells but it declined only at dawn in mesophyll cells after the treatment at 17:00 hrs. Expression of Pathogenesis-related 1 (PR1) and Ethylene Response Factor 1 were already increased at dawn in the CHT-treated leaves but PR1 expression was inhibited in the dark. CHT-induced systemic response was also observed in the distal leaves of CHT-treated ones. Our results suggest a delayed and daytime-dependent defence response of tomato plants after CHT treatment at night and under darkness. View Full-Text
Keywords: chitosan; chlorophyll a fluorescence; nitric oxide; reactive oxygen species; stomata chitosan; chlorophyll a fluorescence; nitric oxide; reactive oxygen species; stomata
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MDPI and ACS Style

Czékus, Z.; Poór, P.; Tari, I.; Ördög, A. Effects of Light and Daytime on the Regulation of Chitosan-Induced Stomatal Responses and Defence in Tomato Plants. Plants 2020, 9, 59.

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