Efeito da disponibilidade de água no xilema secundário e laticíferos em plantas jovens de seringueira [Hevea brasilienses (Willd. ex A. Juss) Müll. Arg.]
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Data
2020-01-31
Autores
Nery, Ícaro Renã Alves Moureira
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Universidade Estadual Paulista (Unesp)
Resumo
A anatomia dos tecidos vasculares secundários e das estruturas secretoras, tais como os laticíferos, varia em função de fatores ambientais e genéticos. Restrições na disponibilidade de água para as plantas podem acarretar alterações nas características anatômicas do xilema secundário e na estrutura e densidade dos laticíferos. Em um cenário de mudanças climáticas e diante de previsões de intensificação dos períodos de seca, entender o efeito da falta de água no xilema secundário e em laticíferos, torna-se importante para compreender os mecanismos de adaptação e sobrevivência das plantas frente a essas variações. Desta forma, tivemos como objetivo responder como diferentes tratamentos de disponibilidade de água poderiam afetar as características anatômicas do xilema secundário, e características estruturais, de densidade e proporção de laticíferos em Hevea brasiliensis, espécie nativa da Amazônia brasileira, importante econômica e culturalmente. Estudamos 24 plantas jovens de Hevea brasiliensis (clone GT1), seis por tratamento, com aproximadamente três meses e meio de idade. Estas cresceram por cerca de 10 meses sob influência de quatro diferentes tratamentos, onde foram aplicadas, diariamente, as seguintes lâminas d’água: T1 = 7,7 mm; T2 = 10,7 mm; T3 = 14,2 mm e T4 = 16,9 mm. Destas plantas, coletamos seções do caule a 5 cm de altura de seu colo. Processamos o caule de cada uma das plantas segundo técnicas usuais em anatomia vegetal, as quais possibilitaram estudar as diferenças nas características anatômicas do xilema secundário e de laticíferos em Hevea brasiliensis. Utilizamos análise de variância e teste Tukey com alfa de 5% para comparar as variáveis quantitativas entre os tratamentos. Em uma segunda abordagem dos dados, realizamos análise de correlação de Pearson, considerando apenas as variáveis significativas pelo teste Tukey. Das 23 características avaliadas, seis variaram com os tratamentos de disponibilidade de água, a saber: comprimento das fibras libriformes, proporção de fibras libriformes e gelatinosas, densidade e agrupamento de vasos e densidade de laticíferos. Com maior lâmina d’água observamos maior comprimento de fibras libriformes, as quais estavam presentes em menor proporção, maior proporção de fibras gelatinosas, menor densidade e agrupamento de vasos e maior densidade de laticíferos. A maior disponibilidade de água favoreceu o comprimento das fibras libriformes, pois as células inicias cambiais do câmbio vascular estavam em maior turgor hídrico. A maior proporção de fibras libriformes observada no xilema secundário das plantas de tratamentos de menor lâmina d’água forma um mecanismo de resistência contra a implosão de vasos, permitindo maior segurança da condução de água. A presença de fibras gelatinosas em H. brasiliensis é uma característica comum à espécie, e como estas desempenham função de armazenamento de água, sua maior proporção nos tratamentos de maior disponibilidade hídrica indica maiores reservas para suprimento de necessidades do vegetal relacionadas ao crescimento. A maior densidade e agrupamento de vasos, observados em tratamentos de menor disponibilidade de água, permite vias de transporte de água, mesmo em casos de falhas hidráulicas. A presença de parênquima com septos é uma característica nunca antes descrita para a espécie. A maior densidade de laticíferos com aumento do recurso hídrico pode indicar mecanismo de defesa da espécie contra herbivoria e também maior produção em látex. As características qualitativas também foram avaliadas, entretanto, não variaram, sendo idênticas estatisticamente, entre os tratamentos. As variações ou ajustes anatômicos observados são respostas das plantas em função das diferentes lâminas d’água aplicadas, refletindo as tendências ecológicas que ocorrem nos diferentes ambientes. Características anatômicas que não variaram significativamente entre os tratamentos são conservativas para as plantas jovens de H. brasiliensis.
The anatomy of the secondary plant tissues and secretory structures such as laticifers, may vary as a function of genetic and environmental factors. Water limitation to plants may result in anatomical changes in the secondary xylem and in the structure, density and proportion of laticifers. In a scenario of recent environmental changes, with the prediction of intensification of drought periods, to understand the effects of lack of water in the plant’s secondary xylem and laticifers becomes important because these changes represent the mechanisms of adaptation and adjustments adopted by the plants to keep themselves functional and alive. Thus, our objective was to investigate if different treatments of water availability would have effect on the anatomical characteristics of the secondary xylem and on the structural characteristics, density and proportion of laticifers of Hevea brasiliensis, an Amazonian native species that carries great economic and cultural value. We have studied 24 young plants of Hevea brasiliensis (GT1 clone), six plants by treatment, with approximately three and half months of age. The plants grew for approximately 10 months under the influence of four different treatments, where we daily applied the following water laminas: T1 = 7,7 mm; T2 = 10,7 mm; T3 = 14,2 mm and T4 = 16,9 mm. From these plants, we collected steam samples, respecting 5 cm from plant lap. We processed the material according to usual techniques in wood anatomy, which has allowed us to study the differences between the anatomical characteristics of the secondary xylem and laticifers in Hevea brasiliensis. A variance analysis followed by a Tukey test at 5% of probability was conducted as a mean to compare the anatomical characteristics of the plants between treatments. In a second data approach we performed a Pearson correlation test taking in consideration only the significant variables to the Tukey test. From the 23 evaluated variables, six of them has shown significant variation with the water availability treatments, they are: the length of libriform fibres, proportion of libriform and gelatinous fibres, vessel density and grouping and laticifer’s density. With the largest water lamina applied (16,9 mm) we observed greater length on libriform fibres, which were present, in the secondary xylem, in smaller proportion; greater proportion of gelatinous fibres; lower vessel density and grouping and greater laticifers’ density. The greater water availability has favored the length of the libriform fibres, because the cambial initial cells were in great water turgor. The higher proportion of libriform fibres, observed in the secondary xylem of plants of the treatments with smaller water lamina, seem to mold a mechanism of resistance against vessel’s implosion, allowing greater safety in water conduction. The presence of libriform fibres in Hevea brasiliensis is a common specie characteristic, their function is to store water, and its greater proportion in the treatments of higher water availability, indicates more water reservoirs which are used to supply plant’s necessities in peaks of growth. The greater vessel density and grouping observed on treatments of lower water availability grant viable waterways, even in cases of hydraulic fails. The presence of septate parenchyma is a characteristic never described before for Hevea brasiliensis. The greater laticifers’ density observed with the increase in water availability indicates a mechanism of defense used by this specie against herbivory and also higher latex yield. The qualitative characteristics have also been evaluated, however, they did not vary among the treatments. The observed anatomical variations or adjustments are the responses of our plants as a function of different water laminas, and they reflect the ecological tendencies that would normally occur in different environments. The anatomical characteristics that did not varied, under the optics of the statistical test, are conservative for the young plants of Hevea brasiliensis.
The anatomy of the secondary plant tissues and secretory structures such as laticifers, may vary as a function of genetic and environmental factors. Water limitation to plants may result in anatomical changes in the secondary xylem and in the structure, density and proportion of laticifers. In a scenario of recent environmental changes, with the prediction of intensification of drought periods, to understand the effects of lack of water in the plant’s secondary xylem and laticifers becomes important because these changes represent the mechanisms of adaptation and adjustments adopted by the plants to keep themselves functional and alive. Thus, our objective was to investigate if different treatments of water availability would have effect on the anatomical characteristics of the secondary xylem and on the structural characteristics, density and proportion of laticifers of Hevea brasiliensis, an Amazonian native species that carries great economic and cultural value. We have studied 24 young plants of Hevea brasiliensis (GT1 clone), six plants by treatment, with approximately three and half months of age. The plants grew for approximately 10 months under the influence of four different treatments, where we daily applied the following water laminas: T1 = 7,7 mm; T2 = 10,7 mm; T3 = 14,2 mm and T4 = 16,9 mm. From these plants, we collected steam samples, respecting 5 cm from plant lap. We processed the material according to usual techniques in wood anatomy, which has allowed us to study the differences between the anatomical characteristics of the secondary xylem and laticifers in Hevea brasiliensis. A variance analysis followed by a Tukey test at 5% of probability was conducted as a mean to compare the anatomical characteristics of the plants between treatments. In a second data approach we performed a Pearson correlation test taking in consideration only the significant variables to the Tukey test. From the 23 evaluated variables, six of them has shown significant variation with the water availability treatments, they are: the length of libriform fibres, proportion of libriform and gelatinous fibres, vessel density and grouping and laticifer’s density. With the largest water lamina applied (16,9 mm) we observed greater length on libriform fibres, which were present, in the secondary xylem, in smaller proportion; greater proportion of gelatinous fibres; lower vessel density and grouping and greater laticifers’ density. The greater water availability has favored the length of the libriform fibres, because the cambial initial cells were in great water turgor. The higher proportion of libriform fibres, observed in the secondary xylem of plants of the treatments with smaller water lamina, seem to mold a mechanism of resistance against vessel’s implosion, allowing greater safety in water conduction. The presence of libriform fibres in Hevea brasiliensis is a common specie characteristic, their function is to store water, and its greater proportion in the treatments of higher water availability, indicates more water reservoirs which are used to supply plant’s necessities in peaks of growth. The greater vessel density and grouping observed on treatments of lower water availability grant viable waterways, even in cases of hydraulic fails. The presence of septate parenchyma is a characteristic never described before for Hevea brasiliensis. The greater laticifers’ density observed with the increase in water availability indicates a mechanism of defense used by this specie against herbivory and also higher latex yield. The qualitative characteristics have also been evaluated, however, they did not vary among the treatments. The observed anatomical variations or adjustments are the responses of our plants as a function of different water laminas, and they reflect the ecological tendencies that would normally occur in different environments. The anatomical characteristics that did not varied, under the optics of the statistical test, are conservative for the young plants of Hevea brasiliensis.
Descrição
Palavras-chave
Anatomia da madeira de H. brasiliensis (seringueira), Adaptações anatômicas, Proporção celular, Parênquima septado, Densidade de laticíferos, Produção de látex, Hevea brasiliensis, Wood anatomy, Anatomical adaptations, Septate parenchyma, Cellular proportion