Abstract
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.
Highlights
Environmental conditions, such as light, humidity, and temperature can crucially influence plant immunity and infection [1,2]
Stomata started to open at dawn and reached the maxima of stomatal pore size around 12 h started to close during the afternoon
It can be concluded that CHT has a daytime- and light-dependent effects on intact tomato plants because it caused stomatal closure before dark/light transition only in leaves treated at 17:00 hrs but not in night-treated ones
Summary
Environmental conditions, such as light, humidity, and temperature can crucially influence plant immunity and infection [1,2]. Light-induced signalling, the regulation by circadian clock or the photosynthetic activity can influence physiological, biochemical, and molecular responses of plants [3,4,5]. Closure of stomata in response to pathogens is one of the earliest event among plant immune responses [8,9]. Pattern recognition receptors (PRR) are able to recognize a wide variety of plant pathogens by detecting microbial- or pathogen-associated molecular patterns (MAMPs or PAMPs) and induce rapid stomatal closure as a part of pattern-triggered immunity (PTI) [10,11]
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