Lighting Direction Affects Leaf Morphology, Stomatal Characteristics, and Physiology of Head Lettuce (Lactuca sativa L.).

Mengzhao Wang,Byoung Ryong Jeong,Hao Wei

doi:10.3390/ijms22063157

Mengzhao Wang, Byoung Ryong Jeong + Show 1 more

Open Access

https://doi.org/10.3390/ijms22063157

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Abstract

Plants are exposed to numerous biotic and abiotic stresses, and light is one of the most important factors that influences the plant morphology. This study was carried out to examine how the lighting direction affected the plant morphology by investigating the growth parameters, epidermal cell elongation, stomatal properties, and physiological changes. Seedlings of two head lettuce (Lactuca sativa L.) cultivars, Caesar Green and Polla, were subjected to a 12 h photoperiod with a 300 μmol·m−2·s−1 photosynthetic photon flux density (PPFD) provided by light emitting diodes (LEDs) from three directions: the top, side, and bottom, relative to the plants. Compared with the top and side lighting, the bottom lighting increased the leaf angle and canopy by stimulating the epidermal cell elongation in leaf midrib, reduced the leaf number and root biomass, and induced large stomata with a low density, which is associated with reduced stomatal conductance and carbohydrate contents. However, the proline content and quantum yield exhibited no significant differences with the different lighting directions in both cultivars, which implies that the plants were under normal physiological conditions. In a conclusion, the lighting direction had a profound effect on the morphological characteristics of lettuce, where the plants adapted to the changing lighting environments.

Highlights

Plants are continuously bombarded by biotic and abiotic signals from their environment
This study provides a great framework on studying leaf morphogenesis, since owing to the phototropism, the leaves exhibit different morphologies in response to lighting direction and a series of changes occur during this process, such as the change of cell elongation in leaves and the expression of plant growth regulators, genes, and proteins resulting from different lighting directions, which adds another dimension in studying leaf morphogenesis in addition to light intensity, quality, and photoperiod
The leaf angle of lettuce plants was considerably increased when the light was supplied from the bottom

Summary

Introduction

Plants are continuously bombarded by biotic and abiotic signals from their environment. Plants are stationary and cannot move away from sources of stresses, nor can they seek out a location with optimal environmental conditions [1]. Instead, they must change their developmental patterns to adapt to the environment for survival and reproduction. Light is one of the most important environmental cues that a plant’s developmental patterns are based on, and plants are sensitive to this crucial external signal [3,4]. The higher plants have evolved an elegant ability that controls the plant form according to the ambient light conditions, which is generally termed photomorphogenesis [5]

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