CAN GENETIC VARIATIONS IN THE DEPLETION PROCESS OF STARCH STOCKS BE DRIVING CONTEMPORARY MICROEVOLUTION IN Toona ciliata VAR. australis?

Abstract

ABSTRACT:A simple method to establish a relationship between physiological responses of plants and thermal stresses is by quantifying the number of parenchyma cells with remaining starch stocks. The knowledge of the dynamic of starch depletion can be achieved by using statistical models such as thermal performance curves (TPC). The aim of this study was to quantify radial parenchyma cells with remaining starch stocks in order to evaluate changes in TPC regarding increases in temperature over seedlings of Toona ciliata (Australian Red cedar), in different heat induced treatments of matching both exposure time and temperature; besides of the assessment of variations in the TPC's and also to understand whether these changes are over genetic control. We used a protocol of heat induced treatment in the stems of the seedlings, anatomical cuts and staining with neutral red for the commercial clone BV1120, which was used as template to fit polynomial curves of TPC. After these mathematical fits and validation of these models with lignotubers of Eucalyptus urophylla, we defined a depletion time of 50% (TD50) from the starch stocks for each thermal treatment, so we could compare the performance for the others five commercial clones: BV1110, BV1121, BV1151, BV1210 and BV1321. The R 2 values were all above 85%. Results indicated that clone BV1110 had the highest value for remaining starch stocks at all heat induced treatments, in contrast to the clone BV1210, which had the lowest values for remaining starch stocks. The variation of the starch content indicates high values of broad-sense heritability, ranging from 97,43 to 98,48%, suggesting a possible contemporary microevolution process undergoing in Australian Red cedar. Thus, further selections can help improving the tolerance of Australian Red cedar to increasing temperatures on the environment. VARIAÇÕES GENÉTICAS DA DEPLEÇÃO DO AMIDO ESTÃO DIRECIONANDO UMA MICROEVOLUÇÃO CONTEMPORÂNEA EM Toona ciliata VAR. australis?RESUMO: Uma maneira de relacionar as respostas fisiológicas das plantas aos estresses térmicos é pela quantificação das células com amido remanescente, decorrente da sua despolimerização em açúcares simples que serão utilizados para reparar danos aos vasos embolizados do xilema. A compreensão da dinâmica dessa depleção poderá ser feita, por meio do uso de modelos estatísticos, que estabelecem curvas de performance térmica ou normas de reação térmicas (NRT). O presente estudo objetivou quantificar as células do parênquima radial que possuíam reservas de amido remanescentes, para avaliar as mudanças nas curvas das NRT, em resposta a aumentos de temperatura induzidos no caule de mudas de Toona ciliata (cedro australiano), sob diferentes escalas de tempo, além de avaliar as variações nas curvas das NRT de diferentes clones de Toona ciliata, bem como se essas variações são, predominantemente, genéticas e herdáveis. Foi utilizado um protocolo de indução de calor, no caule das mudas, cortes anatômicos e coloração com vermelho neutro, para o clone BV1120, que foi ut...