Pigmentos fotossintéticos e potencial hídrico foliar em plantas jovens de coqueiro sob estresses hídrico e salino

Abstract

Resumo: Em regiões semiáridas, a deficiência hídrica e a salinidade do solo são os principais fatores ambientais que influenciam a capacidade de estabelecimento dos vegetais. Assim, objetivou-se com este trabalho investigar, em plantas jovens de coqueiro, os mecanismos bioquímicos associados às ações isoladas e/ou simultâneas da deficiência hídrica e da salinidade do solo. O experimento, em ambiente protegido, foi conduzido em delineamento estatístico em blocos casualizados, no arranjo de parcelas subdivididas, sendo nas parcelas aleatorizados diferentes níveis de deficiência hídrica, mediante a imposição de distintos percentuais de reposição das perdas de água por evapotranspiração potencial da cultura (ETpc) (20; 40; 60; 80 e 100%), associadas às subparcelas, constituídas por quatros solos com crescentes níveis de condutividade elétrica (1,72; 6,25; 25,80 e 40,70 dS m -1 ), oriundos do Perímetro Irrigado Morada Nova. Em condições de deficiência hídrica e de salinidade do solo, as plantas jovens de coqueiro apresentam mudanças significativas nos pigmentos fotossintéticos, com reduções nos teores totais de clorofilas (a+b), esses são indicadores dos efeitos dos estresses isolados. Os teores de carotenóides refletem o antagonismo entre os agentes estressores, deficiência hídrica e salinidade do solo. O potencial hídrico foliar é efetivamente reduzido quando a deficiência hídrica e a salinidade atuam isoladamente, isso ocorre, provavelmente, devido ao ajuste osmótico realizado pela espécie, adaptando-a à sobrevivência em condições adversas. Plantas jovens de coqueiro são mais suscetíveis às limitações de água, em detrimento aos elevados níveis de salinidade do solo, sendo a deficiência hídrica e a salinidade fatores de estresses aditivos para a espécie. Palavras-chave:Carotenóide. Clorofila. Cocos nucifera L. Estado da água. Tolerância à salinização. Abstract:In semi-arid regions, water deficiency and soil salinity are the main environmental factors that can influence a plant's ability to become established. The aim of this study therefore, was to investigate the biochemical mechanisms associated with the isolated and/or simultaneous actions of water deficiency and soil salinity in young plants of the coconut. The experiment, in a protected environment, was carried out in a design of randomised blocks, with an arrangement of subdivided lots. Differing levels of water deficiency were randomised in the lots, imposing different percentages for the replacement of water lost through the potential evapotranspiration of the crop (ETpc) (20, 40, 60, 80 and 100%). The sub-lots comprised four soils at increasing levels of electrical conductivity (1.72, 6.25, 25.80 and 40.70 dS m -1 ), from the Morada Nova Irrigated Perimeter. Under conditions of water deficiency and soil salinity, young coconut plants display significant changes in photosynthetic pigments, with reductions in the total chlorophyll content (a + b), indicators of the effects of isolated stresses. Carotenoid content reflects the antagonism between the stress f...

Effects of saline water and potassium fertilization on photosynthetic pigments, growth and production of West Indian Cherry

“…The reduction in chlorophyll a content ( Figure 1A) in West Indian Cherry plants exposed to water salinity may have occurred due to the decrease in the synthesis of chlorophylls or due to the participation of the chlorophyllase enzyme, which degrades the molecules of this photosynthesizing pigment (Freire et al, 2013 Carlin et al (2012) mention that the reduction in chlorophyll biosynthesis can be a form of adaptation to the stress condition to which the crop was subjected, aiming at energy saving and lower light energy capture to avoid oxidative stress, possibly resulting from photooxidation of the pigments, which damage the plants by oxidizing membrane lipids, proteins and nucleic acids. In addition, the decrease in chlorophyll a content of the West Indian Cherry observed in this study in plants cultivated at the highest saline level (3.8 dS m -1 ) may be a strategy to conserve energy and absorb less light energy and consequently decrease flow of electrons to the electron transfer chain, thus avoiding eventual photooxidative stresses (Silva et al, 2016). During this process, the energy absorbed at the reaction centers (photosystem I and II) oxidize the water to oxygen to produce ATP and reduce NADP + to NADPH.…”

Gas Exchanges, Quantum Yield and Photosynthetic Pigments of West Indian Cherry Under Salt Stress and Potassium Fertilization

“…Reduction in the chlorophyll a content in plants exposed to water salinity is probably due to the increase of the enzyme chlorophyllase, which degrades the molecules of this photosynthesizing pigment, as observed by Freire et al (2013). On the other hand, the decrease in carotenoid content may be attributed, among other causes, to the fact that salt stress leads to a reduction in the production of photosynthetic pigments, inducing the degradation of β-carotene, causing a decrease in the content of carotenoids, which are integrated components of the thylakoids, acting in the absorption and transfer of light to chlorophyll (SILVA et al, 2016).…”

“…Moreover, these reductions can be considered as the acclimation of the plants to the salt stress imposed, in an attempt to conserve energy and, consequently, capture less light energy, and so reduce the flow of electrons to the electron transfer chain, thus avoiding any photo-oxidative stresses (SILVA et al, 2016). Tatagiba et al (2014) explain that the contents of chlorophyll and carotenoids decrease under high salt concentrations and that the significant reductions found in A, as observed in the present study, may also be attributed to the loss of these photosynthetic pigments because, according to Taiz and Zeiger (2013), these pigments are an integral part of the light-harvesting complex for the photosynthetic process.…”

Saline water and potassium fertilization in cultivation of grafted west indian cherry BRS 366 Jaburu

“…Chlorophyll is one of the main factors related to plant photosynthetic efficiency and, consequently, to growth and adaptability to different environments and adverse conditions caused by the various types of stress (AMARANTE et al, 2007). Therefore, increase in chlorophyll synthesis, due to irrigation with saline water (3.8 dS m -1 ), may be associated with the activation of a mechanism of protection of the photosynthetic apparatus, and is apparently a direct result of the development of chloroplasts, by the increase in the number of thylakoids or even increase in the number of chloroplasts (SILVA et al, 2016).…”