Espectros de luz e seus efeitos na germinação de sementes e crescimento de plântulas de alface

Abstract

The vegetable production Brazil's market is in constant development, and lettuce highlights as the most consumed leafy vegetable worldwide. Simultaneously, new technologies have arisen as interesting alternatives for application into production systems, including plant growth under covered environments and with controlled light conditions. Light-emitting diodes (LEDs) have shown increasingly promising for plant growth based mainly on their properties of lower heat emission, durability, and spectral control, which allows the adjustment of wavelengths to plant photoreceptors. Plant photoreceptors (chlorophyll a and b) absorb wavelengths in red (650-675 nm) and blue (440 nm) light ranges, a crucial factor for species whose germination is called positive photoblastic such as lettuce, as it needs light to trigger mechanisms of root protrusion. Phytochrome is the protein that controls germination through the photoreaction process, and after acquiring its active form, it reaches sufficient concentrations to initiate the germination process by stimulating the synthesis of phytohormones, especially the gibberellin. Several studies have assessed the influence of controlled light spectrum for enhancing plant growth, but research about the impacts of using LED light continuously on germination and early development of seedlings is still scarce. The exposure of plants to artificial light for inappropriate periods may induce a phenomenon known as photooxidative stress, usually caused by an excess of photons superior to the absorption capacity of plant photosynthetic apparatus. A feasible approach for measuring this damage is through checking the behavior of enzymes belonging to the plant antioxidant system, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and ascorbate peroxidation (APX). Thereby, upon the enzymatic activity comprehension, adaptations at the light supply and adjustments in wavelengths could maximize plant growth and reduce photooxidative stress damages on plant cells. Thus, scientific research that aims to study the effect of light on germination and seedling development for commercially crops like lettuce is increasingly required.