Teores de pigmentos fotossintéticos, taxa de fotossíntese e estrutura de cloroplastos de plantas jovens de Mikania laevigata Schultz Bip. ex Baker cultivadas sob malhas coloridas

Abstract

O guaco (Mikania laevigata) é uma planta medicinal, usada para o tratamento de febre, reumatismo, gripe e doenças do trato respiratório. O entendimento do comportamento fisiológico dessa espécie e as suas respostas às condições do ambiente tornam-se necessários ao aperfeiçoamento dos métodos de cultivo. Nesse contexto, o presente trabalho teve como objetivo avaliar os efeitos do sombreamento com uso de malhas coloridas na concentração de pigmentos fotossintéticos, na taxa de fotossíntese e na ultra-estrutura de cloroplastos de plantas de Mikania laevigata. As plantas foram cultivadas por quatro meses sob malhas de 50% de sombreamento nas cores azul, vermelha e cinza e a pleno sol (0%). As plantas mantidas a pleno sol tiveram os menores teores de clorofila a e b e o menor teor de carotenóides, enquanto aquelas cultivadas sob malha azul tiveram a maior concentração de clorofilas a e b. A menor densidade de cloroplastos foi encontrada nas plantas cultivadas a pleno sol. Nos tratamentos com 50% de sombreamento, foram verificados cloroplastos mais alongados. Com relação à taxa de fotossíntese potencial, não foi observada nenhuma diferença significativa entre plantas crescidas sob as malhas vermelha, cinza e azul, fato que leva a acreditar que o espectro diferenciado transmitido pelas malhas coloridas não interferiu no aparelho fotossintético do guaco. Palavras-chave: Guaco, qualidade de luz, intensidade de luz, sombreamento DOI: 10.5433/1679 Abstract Guaco (Mikania laevigata) is a medicinal plant used to treat fever, rheumatism, flu and respiratory tract diseases. Understanding the physiology of this species and its responses to environmental conditions has become necessary to improving the cultivation methods. In this context, this work aimed to access the effects of shading by using colored nets in on photosynthetic pigment concentration, photosynthetic rate and ultrastructure of chloroplasts of Mikania laevigata. The plants were cultivated during four months under nets with 50% shading in blue, red and gray color nets and under full sunlight (0%). The plants grown under full sunlight had decreased contents of a and b chlorophyll, and of carotenoids, while those grown under blue nets shown higher concentrations of a and b chlorophyll. The lowest density of

Photosynthetic behavior, growth and essential oil production of Melissa officinalis L. cultivated under colored shade nets

“…Plants in full sunlight showed the highest value of specific leaf mass (SLM) ( The regrowth of the plants after the first cut was more pronounced in plants under blue net than the plants in full sunlight as the former treatment resulted in greater height at 120 DAT (Table 5). Similar result was observed in O. gratissimum (Martins et al, 2008) and M. laevigata (Souza et al, 2011) grown under blue net. As phytochrome and other photoreceptors absorb light in the blue region of the spectrum, which in turn causes differential responses in phototropism, growth and morphogenesis (Smith, 1982), the increased height in lemon balm plants may be due to higher blue/red ratio provided by the blue net.…”

“…Furthermore, we observed a significant increase of the values for leaf area (LA), leaf weight ratio (LWR) and plant height in plants subjected to blue net (168%, 12.5% and 116%, respectively) compared with plants grown under full sunlight (Table 4). The increase in LA caused by the blue net was similar to that observed in Artemisia vulgaris L. (Oliveira et al, 2009), Ocimum gratissimum L. (Martins et al, 2008) and M. laevigata (Souza et al, 2011). Increasing LA is a common strategy used by plants under lower levels of irradiance, as those produced by the blue net (lowest PPFD values, Table 2), to maximize the available area for capturing light energy.…”

“…The highest content of chlorophyll in leaves (increment of 42% in relation to full sunlight plants) was found in plants grown under blue net (Table 3). The total chlorophyll content was also significantly higher in plants of Mikania laevigata grown under the blue net (Souza et al, 2011). This difference is probably more the effect of light quality than quantity, since in the black and red nets this same response was not detected.…”

“…Increasing LA is a common strategy used by plants under lower levels of irradiance, as those produced by the blue net (lowest PPFD values, Table 2), to maximize the available area for capturing light energy. In addition, the increase of the photosynthetic surface can compensate the low photosynthesis rate per unit of LA, which is a characteristic of shade leaves (Souza et al, 2011;Meira et al, 2012).…”

Biophotonics: Acclimation of Pre-Sprouted Sugarcane Seedlings in Protected Environment

“…LEDs are suitable for light supplementation because of their versatility and ease to combine wavelengths (Maluta et al, 2013). Souza et al (2011) state that, in addition to the intensity, the quality of the radiation is determinant for the development of the plant cells. FIGURE 7.…”