Quantificação do amido na madeira de seringueira [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell-Arg.]
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Data
2018-12-18
Autores
Cherelli, Sabrina Galetti. [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O amido é o principal carboidrato de reserva das plantas, composto por dois tipos de α-glucanas, amilose e amilopectina, e tem um importante papel no metabolismo das árvores, incluindo sua importância para estudos de resposta das plantas à diferentes situações durante seu ciclo fenológico e como uma ferramenta complementar para predição do desempenho de sistemas de sangria nas seringueiras, assim como a associação de seu acúmulo com o crescimento e com a rebrota. Este constituinte é encontrado em grande quantidade na madeira de H. brasiliensis. Contudo, a quantificação de amido em madeira ainda é considerada problemática por diversas razões que vão desde a escolha até a implementação de um método adequado, apesar da grande quantidade de estudos encontrados na literatura. Considerando a importância deste carboidrato nas plantas e a problemática envolvida na escolha de um método de quantificação adequado para madeira, quantificou-se o teor de amido em amostras provenientes da direção radial (sentido medula ‒ casca) em discos de H. brasiliensis por dois protocolos diferentes, buscando, entre as técnicas convencionais de hidrólise (ácida e enzimática), qual é a mais apropriada para esta espécie e sugerir um protocolo de quantificação de amido viável à empresas produtoras de seringueira, caso queiram utilizar a quantificação de amido num processo de controle de qualidade da espécie, e à laboratórios de pesquisa com madeiras. Também analisou-se a distribuição radial de amido em amostras de H. brasiliensis coletadas em duas estações do ano e dois locais de crescimento das árvores e adicionalmente estimou-se a longevidade do alburno desta espécie por meio de análises microscópicas. Para o estudo metodológico, analisou-se cinco amostras radiais de discos de quinze árvores por dois diferentes protocolos. No protocolo 1 utilizou-se ácido para a hidrólise do amido e o método antrona para quantificação de glicose e no protocolo 2 utilizou-se enzimas para a hidrólise do amido e peroxidase-glucose oxidade (PGO) e o-dianisidina para quantificação de glicose. Para analisar a distribuição radial do amido em diferentes estações do ano e diferentes locais de crescimento das árvores, utilizou-se o protocolo 2 (hidrólise enzimática) em cinco amostras radiais de discos de oito árvores em ambos locais de crescimento e estações seca e chuvosa. Para observação da distribuição radial do amido e estimativa da longevidade do alburno desta espécie, utilizou-se análise microscópica pela observação de grânulos de amido corados com lugol e a observação de tilos comuns para caracterização de cerne. Comparando o teor de amido entre os dois protocolos utilizados, observou-se que o teor de amido foi significantemente maior no protocolo 1. Ambos os protocolos apresentaram boa precisão, apresentando um baixo coeficiente de variação. O protocolo 1 apresentou-se mais vantajoso em termos de tempo, facilidade de execução e custo de análise, podendo ser utilizado a nível de comparação de resultados, pois se mostrou sensível o suficiente para detecção de diferenças entre as amostras radiais estudadas. A periculosidade do protocolo 1 é maior devido a instabilidade do ácido perclórico, que pode sofrer decomposição de forma explosiva, devendo ser manuseado com os equipamentos de segurança adequados. A acurácia dos valores obtidos pelos protocolos não pôde ser avaliada diretamente, uma vez que não se encontra um valor padrão exato de porcentagem de amido na madeira de seringueira em diferentes amostras radiais. Isso nos leva a sugerir à empresas produtoras de seringueira e à laboratórios de pesquisa com madeira o protocolo 1, quando o objetivo da análise for a comparação entre resultados, e o protocolo 2, quando o objetivo for uma quantificação de amido com maior exatidão, devido à maior seletividade do amido pelas enzimas. A distribuição de amido na seringueira é decrescente desde o alburno até o cerne, apresentando maiores quantidades no alburno, com declínio no alburno mais externo sugerindo seu consumo na atividade do câmbio vascular para o crescimento radial. Encontrou-se maior teor de amido na madeira coletada no inverno e em árvores que cresceram no local com solo do tipo Latossolo. A longevidade média do alburno foi de 20 anos, mostrando que as árvores de 25 anos amostradas possuem cerne formado com grande presença de amido, contradizendo relatos encontrados na literatura sobre a depleção ou ausência de amido no processo de morte das células parenquimáticas e consequente formação de cerne. Portanto, pode-se afirmar que, para H. brasiliensis não deve-se utilizar a ausência de amido para caracterização de cerne.
Starch is the principal carbohydrate reserve in plants, represented by two types of α-glucans, amylose and amylopectin and has a significant role in tree metabolism including its importance for studies of plant response to different situations during its phenological cycle and as a complementary tool to predict the performance of tapping systems in rubberwood, as well as the association of its accumulation to rebudding and growth. This constituent is found in great content in the wood of H. brasiliensis. However, the starch analysis is still problematic despite of the large amount of studies found in the literature. Considering these key factors, the starch content was quantified in samples from the radial direction (pith – bark) of H. brasiliensis disks by two different protocols, seeking, among the existing conventional hydrolysis techniques (acid and enzymatic), which is the most appropriate for that species and to suggest a protocol for starch quantification that can be viable to the rubberwood producing companies in a quality control process of the species and to research laboratories that works with wood characterization. It was also analyzed the radial distribution of starch content of H. brasiliensis samples collected in two different seasons of the year and two different growth site and additionally, it was estimated the sapwood longevity of this species by microscopic analyzes. For the methodological study, we analyzed five radial samples from disks of fifteen trees by two different protocols. The protocol 1 used acid to hydrolyze the starch and anthone method for glucose assay and protocol 2 used enzymes to hydrolyze the starch and peroxidase-glucose oxidade (PGO) and o-dianisidine for glucose assay. To analyze the radial distribution of starch content in different seasons and different growth sites it was used the protocol 2 (enzymatic hydrolysis) in five radial samples from disks of eight trees in both growth site in the dry season and rainy season. To observe the radial distribution and estimate the sapwood longevity of this species it was used microscopic analysis by the observation of starch grains stained with lugol and the observation of common tylosis to characterize heartwood. Comparing the starch content between the two protocols, the starch content was significantly higher in protocol 1. Both protocols showed precision, presenting a low co-efficient of variation between the measurements. Protocol 1 was more advantageous in terms of time, ease of execution and cost of analysis, and could be used in the comparison of results, since it was sensitive enough to detect differences between the radial samples studied. The hazard of protocol 1 is higher due to instability of perchloric acid, which may be explosively decomposed and need to be handled with appropriate safety equipment. The precision of the values obtained by the protocols could not be directly evaluated, since it is not possible to find an exact standard value of starch percentage in the rubberwood different radial samples. This leads us to suggest to the companies producing rubber trees and the research laboratories with wood protocol 1, when the aim of the analysis is the comparison between results, and protocol 2, when the aim is a quantification of starch with greater precision due to the greater selectivity of starch by enzymes. The starch distribution in rubberwood is decreasing from the sapwood to heartwood, being the highest percentages found in the sapwood with a decline in the outermost sapwood suggesting its consumption by the vascular cambium activity for radial growth. The largest starch content was found in the winter samples and in the trees that grew in Latosol. The sapwood longevity was in average 20 years, showing that the 25-years-old trees sampled has heartwood with starch content, contradicting the literature about the starch depletion or absence in the process of parenchyma cells death and consequent heartwood formation. Therefore it can be assert that we should not use the absence of starch to characterize the heartwood in H. brasiliensis.
Starch is the principal carbohydrate reserve in plants, represented by two types of α-glucans, amylose and amylopectin and has a significant role in tree metabolism including its importance for studies of plant response to different situations during its phenological cycle and as a complementary tool to predict the performance of tapping systems in rubberwood, as well as the association of its accumulation to rebudding and growth. This constituent is found in great content in the wood of H. brasiliensis. However, the starch analysis is still problematic despite of the large amount of studies found in the literature. Considering these key factors, the starch content was quantified in samples from the radial direction (pith – bark) of H. brasiliensis disks by two different protocols, seeking, among the existing conventional hydrolysis techniques (acid and enzymatic), which is the most appropriate for that species and to suggest a protocol for starch quantification that can be viable to the rubberwood producing companies in a quality control process of the species and to research laboratories that works with wood characterization. It was also analyzed the radial distribution of starch content of H. brasiliensis samples collected in two different seasons of the year and two different growth site and additionally, it was estimated the sapwood longevity of this species by microscopic analyzes. For the methodological study, we analyzed five radial samples from disks of fifteen trees by two different protocols. The protocol 1 used acid to hydrolyze the starch and anthone method for glucose assay and protocol 2 used enzymes to hydrolyze the starch and peroxidase-glucose oxidade (PGO) and o-dianisidine for glucose assay. To analyze the radial distribution of starch content in different seasons and different growth sites it was used the protocol 2 (enzymatic hydrolysis) in five radial samples from disks of eight trees in both growth site in the dry season and rainy season. To observe the radial distribution and estimate the sapwood longevity of this species it was used microscopic analysis by the observation of starch grains stained with lugol and the observation of common tylosis to characterize heartwood. Comparing the starch content between the two protocols, the starch content was significantly higher in protocol 1. Both protocols showed precision, presenting a low co-efficient of variation between the measurements. Protocol 1 was more advantageous in terms of time, ease of execution and cost of analysis, and could be used in the comparison of results, since it was sensitive enough to detect differences between the radial samples studied. The hazard of protocol 1 is higher due to instability of perchloric acid, which may be explosively decomposed and need to be handled with appropriate safety equipment. The precision of the values obtained by the protocols could not be directly evaluated, since it is not possible to find an exact standard value of starch percentage in the rubberwood different radial samples. This leads us to suggest to the companies producing rubber trees and the research laboratories with wood protocol 1, when the aim of the analysis is the comparison between results, and protocol 2, when the aim is a quantification of starch with greater precision due to the greater selectivity of starch by enzymes. The starch distribution in rubberwood is decreasing from the sapwood to heartwood, being the highest percentages found in the sapwood with a decline in the outermost sapwood suggesting its consumption by the vascular cambium activity for radial growth. The largest starch content was found in the winter samples and in the trees that grew in Latosol. The sapwood longevity was in average 20 years, showing that the 25-years-old trees sampled has heartwood with starch content, contradicting the literature about the starch depletion or absence in the process of parenchyma cells death and consequent heartwood formation. Therefore it can be assert that we should not use the absence of starch to characterize the heartwood in H. brasiliensis.
Descrição
Palavras-chave
Hevea brasiliensis, distribuição radial de amido, hidrólise ácida, hidrólise enzimática, longevidade do alburno, starch radial distribution, acid hydrolysis, enzymatic hydrolysis, sapwood longevity